Ecological Studies, Vol. 211 Analysis and Synthesis
Edited by M.M. Caldwell, Washington, USA G. Heldmaier, Marburg, Germany R.B. Jackson, Durham, USA O.L. Lange, Wu¨rzburg, Germany H.A. Mooney, Stanford, USA E.-D. Schulze, Jena, Germany U. Sommer, Kiel, Germany
Ecological Studies Further volumes can be found at springer.com Volume 193 Biological Invasions (2007) W. Nentwig (Ed.) Volume 194 Clusia: A Woody Neotropical Genus of Remarkable Plasticity and Diversity (2007) U. Lu¨ttge (Ed.) Volume 195 The Ecology of Browsing and Grazing (2008) I.J. Gordon and H.H.T. Prins (Eds.) Volume 196 Western North American Juniperus Communites: A Dynamic Vegetation Type (2008) O. Van Auken (Ed.) Volume 197 Ecology of Baltic Coastal Waters (2008) U. Schiewer (Ed.) Volume 198 Gradients in a Tropical Mountain Ecosystem of Ecuador (2008) E. Beck, J. Bendix, I. Kottke, F. Makeschin, R. Mosandl (Eds.) Volume 199 Hydrological and Biological Responses to Forest Practices: The Alsea Watershed Study (2008) J.D. Stednick (Ed.) Volume 200 Arid Dune Ecosystems: The NizzanaSands in the Negev Desert (2008) S.-W. Breckle, A. Yair, and M. Veste (Eds.) Volume 201 The Everglades Experiments: Lessons for Ecosystem Restoration (2008) C. Richardson (Ed.) Volume 202 Ecosystem Organization of a Complex Landscape: Long-Term Research in the Bornho¨ved Lake District, Germany (2008) O. Fra¨nzle, L. Kappen, H.-P. Blume, and K. Dierssen (Eds.)
Volume 203 The Continental-Scale Greenhouse Gas Balance of Europe (2008) H. Dolman, R.Valentini, and A. Freibauer (Eds.) Volume 204 Biological Invasions in Marine Ecosystems: Ecological, Management, and Geographic Perspectives (2009) G. Rilov and J.A. Crooks (Eds.) Volume 205 Coral Bleaching: Patterns, Processes, Causes and Consequences M.J.H van Oppen and J.M. Lough (Eds.) Volume 206 Marine Hard Bottom Communities: Patterns, Dynamics, Diversity, and Change (2009) M. Wahl (Ed.) Volume 207 Old-Growth Forests: Function, Fate and Value (2009) C. Wirth, G. Gleixner, and M. Heimann (Eds.) Volume 208 Functioning and Management of European Beech Ecosystems (2009) R. Brumme and P.K. Khanna (Eds.) Volume 209 Permafrost Ecosystems: Siberian Larch Forests (2010) A. Osawa, O.A. Zyryanova, Y. Matsuura, T. Kajimoto, R.W. Wein (Eds.) Volume 210 Amazonian Floodplain Forests: Ecophysiology, Biodiversity and Sustainable Management (2010) W.J. Junk, M.T.F. Piedade, F. Wittmann, J. Scho¨ngart, P. Parolin (Eds.) Volume 211 Mangrove Dynamics and Management in North Brazil (2010) U. Saint-Paul and H. Schneider (Eds.)
Ulrich Saint-Paul
l
Horacio Schneider
Editors
Mangrove Dynamics and Management in North Brazil
Editors Prof. Dr. Ulrich Saint-Paul Leibniz Center for Tropical Marine Ecology Fahrenheitstr. 6 28359 Bremen, Germany
[email protected]
Prof. Dr. Horacio Schneider Universidade Federal do Para´ Instituto de Estudos Costeiros Campus de Braganc¸a Alameda Leandro Ribeiro s/n 68.600-000 Braganc¸a/PA, Brazil
[email protected]
ISSN 0070-8356 ISBN 978-3-642-13456-2 e-ISBN 978-3-642-13457-9 DOI 10.1007/978-3-642-13457-9 Springer Heidelberg Dordrecht London New York Library of Congress Control Number: 2010935789 # Springer-Verlag Berlin Heidelberg 2010 This work is subject to copyright. All rights are reserved, whether the whole or part of the material is concerned, specifically the rights of translation, reprinting, reuse of illustrations, recitation, broadcasting, reproduction on microfilm or in any other way, and storage in data banks. Duplication of this publication or parts thereof is permitted only under the provisions of the German Copyright Law of September 9, 1965, in its current version, and permission for use must always be obtained from Springer. Violations are liable to prosecution under the German Copyright Law. The use of general descriptive names, registered names, trademarks, etc. in this publication does not imply, even in the absence of a specific statement, that such names are exempt from the relevant protective laws and regulations and therefore free for general use. Cover illustration: Dawn in the Mangrove (Amanhecer no Mangue) by Benedito Luz, a local artist from Braganc¸a, Brazil Cover design: WMXDesign GmbH, Heidelberg, Germany Printed on acid-free paper Springer is part of Springer Science+Business Media (www.springer.com)
Foreword
Sheltered coastal marine and estuarine areas in the tropics are the sites of mangrove communities: highly productive systems that provide a variety of essential ecosystem services, including (1) processing of organic matter transported in run-off waters, (2) coastal protection against erosion, and (3) reproduction sites for a large array of marine and estuarine fauna. Scientific studies of mangrove ecosystems throughout the world have a long history, and as a result, we understand much of their ecology and physiology. Presently, those systems are heavily impacted by human activities that have surpassed their tolerance limit. The impact derives from the increasing size of coastal cities and expansion of port services, and the large amount of human and industrial waste dumped into the rivers that feed coastal ecosystems with fresh water. Furthermore, the impact of sea level rise has to be included in the analyses of stability and maintenance of mangrove ecosystems. The biotic productivity of mangroves provide food and other resources to the human populations that inhabit or make use of them. Intensity of human use is also increasing, approaching in some cases the limits of biological resources renewal. In order to develop sensible and effective management strategies leading to conservation of mangroves ecosystems services and maintain their productive capacity, it is necessary to integrate the local human populations depending on mangrove ecosystems for their subsistence. Integrative studies of tropical ecosystems are essential to achieve conceptual advances in the understanding of their structure and function and to prepare for the impact of global change on ecosystems services. However, they constitute a technical and organizational challenge. Projects of this type need to be planned at a large scale and to develop over several years in order to produce meaningful and reliable results. The study of coastal systems is particularly demanding within this context as they involve not only the complexities of natural systems but also a vast range of human interactions. Coastal regions are historically preferential sites for human occupation, and tend to be heavily populated, constituting the center of vigorous
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economic activities. As a result, coastal ecosystems are also strongly impacted, being in many cases irretrievably destroyed. The MADAM project was conceptualized as such an endeavor on one of the largest continuous mangrove areas in the world, the Amazonian ecoregion located in the tropical eastern South American coast, comprising an area of more than 23,000 km2 (Sullivan Sealy and Bustamante 1999). It became a success story regarding the scale of the coordination required, its multidisciplinary and transdisciplinary character, and the integration of natural and social sciences, which produced a functional picture of the mangrove ecosystems in the coast of Para´ State in Brazil. It has also been a model of how to develop international cooperative projects, in this case the cooperation of Brazil and Germany, leading to a productive and long-lasting investment in development of human resources. The MADAM project has produced a large body of scientific information, as shown in the syntheses included in this book, but the most important result has been the sizable number of students influenced and educated within the project in both countries. In addition, and no less important, there has been the educational impact of the project on the local populations in many places along the Caete´ River, where the project was centered for more than 10 years. Beyond the scientific results, this book also provides information, guidelines, and examples on how to organize and develop multidisciplinary, international projects that lead to sensible and reliable management approaches for coastal systems conservation and ecologically sound use. E. Medina
References Sullivan Sealy K, Bustamante G (1999) Setting geographic priorities for marine conservation in Latin America and the Caribbean. The Nature Conservancy, Arlington, VA
Contents
Part I
Introduction
1
The Need for a Holistic Approach in Mangrove Research and Management . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 U. Saint-Paul and H. Schneider
2
MADAM, Concept and Reality . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 U. Saint-Paul
Part II 3
4
Geography and Biogeochemistry
The Geography of the Braganc¸a Coastal Region . . . . . . . . . . . . . . . . . . . . . . G. Krause 3.1 Background and Scope . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.2 Spatial Boundaries . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.3 Principal Features of the Natural and Social System . . . . . . . . . . . . . . . . 3.3.1 The Marine Seascape and the Estuary . . . . . . . . . . . . . . . . . . . . . . . . . 3.3.2 The Coastline . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.3.3 The Intertidal Zone . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.3.4 The Rural Hinterland . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.3.5 The City of Braganc¸a . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.4 Co-Evolutionary Outcomes of the Natural and Social Dynamics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
19 19 20 22 22 23 25 27 28 29 31
Palaeoenvironmental Reconstruction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35 H. Behling, M. Cohen, R.J. Lara, and V. Vedel 4.1 Coastal Region of Northern Brazil . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35 4.2 Holocene Environmental Changes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37
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4.3 Model of Braganc¸a Mangrove Development . . . . . . . . . . . . . . . . . . . . . . . . . 40 4.4 Holocene Coastal Dynamics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43 5
The Biogeochemistry of the Caete´ Mangrove-Shelf System . . . . . . . . . . B.P. Koch, T. Dittmar, and R.J. Lara 5.1 Introduction and Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.2 Sediment Processes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.2.1 Fate and Decomposition of Leaf Litter in Mangrove Sediments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.2.2 Long-Term Decomposition of Organic Matter in Mangrove Sediments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.2.3 The Use of Chemical Biomarkers as Source Tracers in Mangrove Sediments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.3 The Outwelling of Detritus and Decomposition Products into Coastal Waters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.3.1 Quantifying the Export of Organic Matter from the Mangrove into the Estuary . . . . . . . . . . . . . . . . . . . . . . . . . . 5.3.2 Driving Forces Behind Nutrient and Organic Matter Dynamics in Mangrove Creeks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.3.3 Water Storage in the Mangrove Sediment and Effect on Creek Water Chemistry . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.3.4 Effect of Autotrophic Activity in the Creek . . . . . . . . . . . . . . . . . . . 5.3.5 Requirements for Sustainable Outwelling . . . . . . . . . . . . . . . . . . . . . 5.4 The Fate of Mangrove Outwelling on the Continental Shelf and Concluding Remarks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Part III 6
45 45 46 46 47 49 52 52 54 54 57 58 60 64
Floristic and Faunistic Studies in Mangroves
Mangrove Vegetation of the Caete´ Estuary . . . . . . . . . . . . . . . . . . . . . . . . . . . U. Mehlig, M.P.M. Menezes, A. Reise, D. Schories, and E. Medina 6.1 Floristics and Forest Structure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6.2 Litter Fall and Phenology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6.2.1 Litter Fall Rates . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6.2.2 Phenology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6.3 Dendrochronological Studies of R. mangle Trees . . . . . . . . . . . . . . . . . . . . 6.3.1 Periodicity of Growth Rings, Life Span and Growth Curves of R. mangle . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6.3.2 Diameter Increment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6.3.3 Mean Stand Age and Age Structure . . . . . . . . . . . . . . . . . . . . . . . . . . . 6.4 Soil-Vegetation Nutrient Relations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6.4.1 Mangrove Communities and Methods . . . . . . . . . . . . . . . . . . . . . . . . 6.4.2 Soil Physical–Chemical Properties and Flooding . . . . . . . . . . . . . 6.4.3 Forest Structure and Function . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
71 71 77 79 81 85 86 87 88 91 91 93 96
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6.4.4 Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 102 6.5 Concluding Remarks and Outlook . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 103 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 104 7
Mangrove Infauna and Sessile Epifauna . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . C.R. Beasley, M.E.B. Fernandes, E.A.G. Figueira, D.S. Sampaio, K.R. Melo, and R.S. Barros 7.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7.2 The Infauna of the Mangrove Forest at the Furo Grande Tidal Creek . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7.3 Comparison of the Benthic Fauna Among Sites with Differing Degrees of Degradation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7.4 Settlement of the Tidal Creek Epifauna in the Caete´ Mangrove Estuary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7.4.1 Fistulobalanus citerosum . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7.4.2 Crassostrea gasar . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7.4.3 Mytella falcata . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7.5 Differences in Settlement of Epibenthos Between Mangrove and Tidal Creek Habitats . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7.6 Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Part IV 8
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109 110 113 115 116 116 118 120 120 120
Dynamics in the Mangrove System
Drivers of Temporal Changes in Mangrove Vegetation Boundaries and Consequences for Land Use . . . . . . . . . . . . . . . . . . . . . . . . . R.J. Lara, M. Cohen, and C. Szlafsztein 8.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8.2 Influence of Inundation Frequency and Sediment Salinity on Wetland Structure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8.3 Changes in Current Vegetation Units: Boundaries, Ecotone Shifts and Consequences for Land Use . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8.3.1 Coastline Vegetation Changes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8.3.2 Ecotone Shifts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8.3.3 Consequences for Land Use . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . System Processes and Forest Development . . . . . . . . . . . . . . . . . . . . . . . . . . . U. Berger and M. Wolff 9.1 The Interlink Between the Modeling Approaches . . . . . . . . . . . . . . . . . 9.2 Trophic Pathways . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9.3 Forest Dynamics Under Different Natural Disturbance Regimes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9.4 Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
127 127 127 133 133 135 137 140 143 143 144 146 149 150
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Synoptic Analysis of Mangroves for Coastal Zone Management . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . G. Krause and M. Bock 10.1 Background and Scope . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10.2 Research Strategy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10.3 Change Dynamics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10.3.1 Regional Scale Analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10.3.2 Local Scale Analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10.4 Classification of Mangrove Patterns . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10.4.1 Aerial Survey Analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10.4.2 Classification of Mangrove Patterns on the Peninsula with IKONOS Data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10.5 Potential Contributions to Coastal Zone Management . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Part V 11
12
153 153 154 156 156 157 159 159 161 163 165
Ecology and Fishery of Fin-Fish in the Mangrove System
Distribution Pattern of Fish in a Mangrove Estuary . . . . . . . . . . . . . . . . M. Barletta and U. Saint-Paul 11.1 Seasonal Changes in Fish Density and Biomass in the Caete´ Estuary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11.1.1 The Main Channel . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11.1.2 The Mangrove Tidal Creeks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11.2 Fish Assemblage Patterns . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11.2.1 Seasonal Movements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11.2.2 Fish Shelter Strategies in Mangrove Forests and Tidal Channels . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Dynamics in Mangrove Fish Assemblages on a Macrotidal Coast . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . U. Krumme and U. Saint-Paul 12.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12.2 Environmental Setting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12.3 Nekton Sampling in Macrotidal Environments . . . . . . . . . . . . . . . . . . . 12.4 Trends in Species Richness, Biomass and Density along a Shoreline Gradient . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12.5 Composition of Transients . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12.6 Tidal Movements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12.7 Tidal and Diel Changes in the Intertidal Fish Assemblages . . . . . . 12.8 Tide-to-Tide, Weekly, Fortnightly and Monthly Variation in Abundance, Catch Weight, and Species Richness of Transients . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12.9 Patterns in Feeding . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
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171 172 178 180 180 185 186
189 189 189 190 192 194 194 197
199 202
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12.10 Spatial Patterns in the Intertidal Fish Fauna . . . . . . . . . . . . . . . . . . . . . 203 12.11 Implications for Future Research and Long-Term Monitoring . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 204 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 205 13
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15
An Evaluation of the Larval Fish Assemblage in a North Brazilian Mangrove Area . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A. Barletta-Bergan 13.1 Value of Mangroves and Estuaries as Nurseries . . . . . . . . . . . . . . . . . . 13.2 First Ichthyoplankton Survey . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13.3 A North Brazilian Larval Fish Community in Relation to Mangroves Worldwide . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Molecular Phylogenetic and Population Genetic Structuring of Macrodon sp., a Coastal and Estuarine Fish of the Western Atlantic Ocean . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . I. Sampaio, S. Santos, and H. Schneider 14.1 Phylogenetic Studies in Fish Populations . . . . . . . . . . . . . . . . . . . . . . . . . 14.2 Genetic Differentiation of Macrodon . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14.3 Consequences for the Taxonomy of Macrodon . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Fisheries and Management . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . V.J. Isaac, R.V.E. Santo, and U. Saint-Paul 15.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15.2 Methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15.3 Fisheries Structure and Situation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15.4 Recommendations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Part VI 16
209 209 209 210 217
221 221 223 228 230 233 233 234 235 246 247
Ecology and Fishery of Mangrove Crabs
The Brachyuran Crab Community of the Caete´ Estuary, North Brazil: Species Richness, Zonation and Abundance . . . . . . . . . . K. Diele, V. Koch, F.A. Abrunhosa, J. de Farias Lima, and D. de Jesus de Brito Simith 16.1 Background and Scope . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16.2 Species Richness and Zonation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16.3 Abundance and Biomass . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16.4 Biogeographic Comparison . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
251
251 251 259 260 261
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18
19
20
Contents
Feeding Ecology and Ecological Role of North Brazilian Mangrove Crabs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . V. Koch and I. Nordhaus 17.1 Feeding Guilds . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17.2 Feeding Periodicity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17.3 Food Intake . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17.4 Ecological Role . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Comparative Population Dynamics and Life Histories of North Brazilian Mangrove Crabs, Genera Uca and Ucides (Ocypodoidea) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . K. Diele and V. Koch 18.1 Individual Size, Population Size Structure and Sex Ratio . . . . . . . . 18.2 Growth and Mortality . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18.3 Reproduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18.4 Contrasting Life Histories: Large, Long-Lived and Litter Feeding Versus Small, Short-Lived and Deposit Feeding . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Artisanal Fishery of the Mangrove Crab Ucides cordatus (Ucididae) and First Steps Toward a Successful Co-Management in Braganc¸a, North Brazil . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . K. Diele, A.R.R. Arau´jo, M. Glaser, and U. Salzmann 19.1 Background and Scope . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19.2 Capture Areas, Capture Techniques and Effort . . . . . . . . . . . . . . . . . . . 19.3 Standing Stock and Fishery Yields . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19.4 Legislation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19.5 Marketing Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19.6 Significance of Community Participation in Research and Management . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Simulating Ucides cordatus Population Recovery on Fished Grounds . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . C. Piou, U. Berger, and K. Diele 20.1 The Individual-Based-Ucides Model . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20.2 Inferences with the Pattern-Oriented Modeling Approach . . . . . . . 20.3 Importance of Movements Induced by Density-Dependent Processes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
265 265 266 268 270 271
275 275 277 279 281 283
287 287 288 291 293 294 295 296
299 299 300 302 303
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Part VII 21
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Mangroves and People
Mangroves and People: A Social-Ecological System . . . . . . . . . . . . . . . . . M. Glaser, G. Krause, R.S. Oliveira, and M. Fontalvo-Herazo 21.1 The Social-Ecological System (SES) Concept . . . . . . . . . . . . . . . . . . . . 21.2 Mangrove Values and Livelihoods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21.2.1 Mangrove Dependence . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21.2.2 Economic Value and Poverty . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21.3 The Coevolution of Natural and Social System Drivers at the Local Level . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21.3.1 Ajuruteua: A Coastal Village . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21.3.2 Tamatateua: An Agricultural Village . . . . . . . . . . . . . . . . . . . . . 21.3.3 Social-Ecological Systems as Co-evolving Entities . . . . . . 21.4 Sustainability Visions and Indicators . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21.4.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21.4.2 Case Study: An Indicator System as an Integrative and Transdisciplinary Tool . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21.4.3 The Social Dimension . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21.5 Participatory Management of Coastal Ecosystems . . . . . . . . . . . . . . . 21.5.1 Outlook . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21.6 Scenarios for Mangrove-Based Social-Ecological Systems: Linking Futures Across Stakeholder Rationalities . . . . . . . . . . . . . . . . 21.6.1 Setting Up Social-Ecological Scenarios . . . . . . . . . . . . . . . . . . 21.6.2 Possible Futures of the Mangrove-Based SES . . . . . . . . . . . . 21.6.3 Inclusion of “the Social Dimension” as Central Element Towards Sustainability in SES . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21.7 Appropriate Knowledge for a Mangrove-Based Social-Ecological System: Outlook for Future Work . . . . . . . . . . . . . 21.7.1 Identify Undesirable Feedback Loops and Modes of Addressing Them . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21.7.2 Assign Adequate Values to Poverty Alleviation Functions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21.7.3 Develop Alternatives to Unsustainable Forms of Behavior Towards Nature . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21.7.4 Recognize, Evaluate and Link Knowledge Systems . . . . . . 21.7.5 Build an Effective Social Base . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21.7.6 Collectively Envision Desirable Futures . . . . . . . . . . . . . . . . . . 21.7.7 Achieve Relevance and Sustainability at Multiple Scales from the Local to the Global . . . . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
307 307 309 310 312 314 315 318 322 323 323 325 327 330 333 334 334 335 338 340 341 342 343 343 344 345 346 347
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Part VIII 22
23
The Mangrove Information System MAIS: Managing and Integrating Interdisciplinary Research Data . . . . . . . . . . . . . . . . . . . . U. Salzmann, G. Krause, B.P. Koch, and I. Puch Rojo 22.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22.2 Implementation of a GIS-Database . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22.3 Database Model and Data Management . . . . . . . . . . . . . . . . . . . . . . . . . . 22.4 MAIS: A Tool for Supporting Interdisciplinary Research? . . . . . . 22.4.1 Quality Control and Improved Analysis Tools . . . . . . . . . . . 22.4.2 Appropriate Support and Funding . . . . . . . . . . . . . . . . . . . . . . . . . 22.4.3 Intellectual Property Rights and Better Incentives for Data Sharing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22.5 Concluding Remarks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Coastal Zone Management Tool: A GIS-Based Vulnerability Assessment to Natural Hazards . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . C. Szlafsztein and H. Sterr 23.1 Coastal Zone-Dynamic and Vulnerable Environment . . . . . . . . . . . . 23.1.1 The Northeast Part of Coastal Zone of the State of Para´: The Study Area . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23.1.2 The Natural Hazards Impacts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23.1.3 GIS-Based Composite Vulnerability Index for the Coastal Zone . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23.2 General Concepts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23.2.1 Data Problems and Shortcomings in Northeast Para´ . . . . . 23.2.2 Design of Composite Vulnerability Index, Based on GIS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23.3 Socio-economic and Natural Vulnerability . . . . . . . . . . . . . . . . . . . . . . . 23.4 Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Part IX 24
Data Synthesis and Assessment Tools
355 355 356 357 360 361 361 362 362 363
365 365 367 369 370 371 371 372 374 380 383
Closing Remarks
Epilog . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 389 U. Saint-Paul and H. Schneider References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 392
Index
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 395
Contributors
Fernando Arau´jo Abrunhosa Universidade Federal do Para´, Instituto de Estudos Costeiros, Campus Universita´rio de Braganc¸a, Alameda Leandro Ribeiro s/n, 68600-000 Braganc¸a, PA, Brazil,
[email protected] Ana Rosa da Rocha Arau´jo Universidade Federal de Sergipe, Centro de Biolo´gicose da Saude - CCBS; Nu´cleode Engenhavia de Pesca - NEP. Av. Marechal Rondon, s/n Jardim Rosa Elze, 49100-000 Sa˜o Cristo´va˜o, SE, Brazil, anafriedaar
[email protected] Audrey Barletta-Bergan Burgstr. 8, 21682 Stade, Germany,
[email protected] Ma´rio Barletta UFPE, Departamento de Oceanografia, Laborato´rio de Ecologia e Gerenciamento de Ecossistemas Costeiros e Estuarinos, Cidade Universita´ria, 50740-550 Recife, PE, Brazil,
[email protected] Renata Souza de Barros Universidade Federal do Para´, Instituto de Estudos Costeiros, Campus de Braganc¸a, Alameda Leandro Ribeiro s/n, 68600-000 Braganc¸a, PA, Brazil Colin Robert Beasley Universidade Federal do Para´, Instituto de Estudos Costeiros, Campus de Braganc¸a, Alameda Leandro Ribeiro s/n, 68600-000 Braganc¸a, PA, Brazil,
[email protected] Hermann Behling Department of Palynology and Climate Dynamics, Albrechtvon-Haller-Institute for Plant Sciences, University of Go¨ttingen, Untere Karspu¨le 2, 37073 Go¨ttingen, Germany,
[email protected] Uta Berger TU Dresden, Institute of Forest Growth and Forest Computer Sciences, Postfach 1117, 01735 Tharandt, Germany,
[email protected]
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Contributors
Michael Bock German Aerospace Center, German Remote Sensing Data Center, Environment and Security, Mu¨nchner Str. 20, 82234 Oberpfaffenhofen-Wessling, Germany,
[email protected] Marcelo Cohen Faculty of Oceanography, Federal University of Para´, Rua Augusto Correˆa 1, Guama, 66075-110 Bele´m/PA, Brazil,
[email protected] Karen Diele Leibniz Center for Tropical Marine Ecology, Fahrenheitstr. 6, 28359 Bremen, Germany,
[email protected] Thorsten Dittmar Max Planck Research Group – Marine Geochemistry, Carl von Ossietzky University, ICBM, PO Box 2503, 26111 Oldenburg, Germany,
[email protected] Roberto Vilhena do Espı´rito Santo Universidade Federal do Para´, Centro de Ciencias Biolo´gicas, Laboratorio de Biologia Pesqueira e Manejo de Recursos Aquaticos, Avenidada Perimetral 2651, 66077-530 Bele´m, PA, Brazil,
[email protected] Marcus Emanuel Barroncas Fernandes Universidade Federal do Para´, Instituto de Estudos Costeiros, Campus de Braganc¸a, Alameda Leandro Ribeiro s/n, 68600000 Braganc¸a, PA, Brazil Elder Augusto Guimara˜es Figueira Universidade Federal do Para´, Instituto de Estudos Costeiros, Campus de Braganc¸a, Alameda Leandro Ribeiro s/n, 68600-000 Braganc¸a/PA, Brazil Martha L. Fontalvo-Herazo Leibniz Center for Tropical Marine Ecology, Fahrenheitstr. 6, 28359 Bremen, Germany Marion Glaser Leibniz Center for Tropical Marine Ecology, Fahrenheitstr. 6, 28359 Bremen, Germany,
[email protected] Victoria Isaac Universidade Federal do Para´, Centro de Ciencias Biolo´gicas, Laboratorio de Biologia Pesqueira e Manejo de Recursos Aquaticos, Avenida Perimetral 2651, 66077-530 Bele´m, PA, Brazil,
[email protected] Boris P. Koch University of Applied Sciences, An der Karlstadt 8, 27568 Bremerhaven, Germany,
[email protected]; Alfred Wegener Institute for Polar and Marine Research, Am Handelshafen 12, 27570 Bremerhaven, Germany Volker Koch Universidad Auto´noma de Baja California Sur, Depto. Biol. Marina, Carretera al Sur, km 5.5, Ap. Postal 19-B, La Paz, B.C.S, C. P.23080, Me´xico,
[email protected]
Contributors
xvii
Gesche Krause Leibniz Center for Tropical Marine Ecology, Fahrenheitstr. 6, 28359 Bremen, Germany,
[email protected] Uwe Krumme Leibniz Center for Tropical Marine Ecology, Fahrenheitstr. 6, 28359 Bremen, Germany,
[email protected] Rube´n J. Lara Leibniz Center for Tropical Marine Ecology, Fahrenheitstr. 6, 28359 Bremen, Germany,
[email protected] Joˆ de Farias Lima Embrapa Amapa´, Rodovia Juscelino Kubitschek, km5, n 2600, Caixa Postal 10, Macapa´, 68903-149 AP, Brazil,
[email protected] Ernesto Medina Instituto Venezolano de Investigaciones Cientı´ficas, Centro de Ecologı´a, 1020-A Caracas, Venezuela,
[email protected] Ulf Mehlig Universidade Federal do Para´, Campus Braganc¸a, Alameda Leandro Ribeiro s/n, 68600-000 Braganc¸a, PA, Brazil,
[email protected] Kely dos Reis Melo Universidade Federal do Para´, Instituto de Estudos Costeiros, Campus de Braganc¸a, Alameda Leandro Ribeiro s/n, 68600-000 Braganc¸a, PA, Brazil Moirah P.M. Menezes Universidade Federal do Para´, Campus Braganc¸a, Alameda Leandro Ribeiro s/n, 68600-000 Braganc¸a, PA, Brazil,
[email protected] Inga Nordhaus Leibniz Center for Tropical Marine Ecology, Fahrenheitstr. 6, 28359 Bremen, Germany,
[email protected] Rosete da Silva Oliveira Universidade Federal do Para´, Campus Braganc¸a, Alameda Leandro Ribeiro s/n, 68600-000 Braganc¸a, PA, Brazil, rosete_dasilvaoli
[email protected] Cyril Piou INRA, Poˆle d’Hydrobiologie, Ecologie Comportementale et Biologie des Populations de Poissons, Quartier Ibarron, 64310 Saint Pe´e sur Nivelle, France,
[email protected] Annegret Reise Instituto de Biologı´a Marina, Campus Isla Teja, Universidad Austral de Chile, Avenida Ines Haverbeck 11-13, Valdivia, Chile, anneken.
[email protected] Ingo Puch Rojo Leibniz Center for Tropical Marine Ecology, Fahrenheitstr. 6, 28359 Bremen, Germany, anneken.
[email protected]
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Contributors
Ulrich Saint-Paul Leibniz Center for Tropical Marine Ecology, Fahrenheitstr. 6, 28359 Bremen, Germany,
[email protected] Ulrich Salzmann Northumbria University, School of the Built and Natural Environment, Ellison Building, NE1 8ST Newcastle upon Tyne, UK, ulrich.salzmann@ northumbria.ac.uk Iracilda Sampaio Universidade Federal do Para´, Instituto de Estudos Costeiros, Campus de Braganc¸a, Alameda Leandro Ribeiro s/n, 68600-000 Braganc¸a, PA, Brazil,
[email protected] Simoˆni Santos Universidade Federal do Para´, Instituto de Estudos Costeiros, Campus de Braganc¸a, Alameda Leandro Ribeiro s/n, 68600-000 Braganc¸a, PA, Brazil Horacio Schneider Universidade Federal do Para´, Instituto de Estudos Costeiros, Campus de Braganc¸a, Alameda Leandro Ribeiro s/n, 68600-000 Braganc¸a, PA, Brazil,
[email protected] Dirk Schories Instituto de Biologı´a Marina, Campus Isla Teja, Universidad Austral de Chile, Avenida Ines Haverbeck 11-13, Valdivia, Chile, dirk.
[email protected] Darlan de Jesus de Brito Simith Universidade Federal do Para´, Instituto de Estudos Costeiros, Campus de Braganc¸a, Alameda Leandro Ribeiro s/n, 68600000 Braganc¸a, PA, Brazil,
[email protected] Horst Sterr Universita¨t Kiel, Geographisches Institut, Ludewig-Meyn-Str 14, 24098 Kiel, Germany,
[email protected] Claudio Szlafsztein University Federal of Para´, NUMA, Cidade Universita´ria, Augusto Correa 1, 66075-900 Bele´m, Para´, Brazil,
[email protected] Vinvent Vedel Leibniz Center for Tropical Marine Ecology, Fahrenheitstr. 6, 28359 Bremen, Germany Matthias Wolff Leibniz Center for Tropical Marine Ecology, Fahrenheitstr. 6, 28359 Bremen, Germany,
[email protected]
Part I Introduction
Chapter 1
The Need for a Holistic Approach in Mangrove Research and Management U. Saint-Paul and H. Schneider
The term mangrove is commonly used to identify trees and shrubs that have developed morphological adaptations, like aerial roots, salt excretion glands and vivipary of seeds, to the tidal environment. Mangroves comprise 27 genera and approximately 70 species worldwide, and mangrove forests provide vital ecological benefits such as nursery grounds and shelter for many species, coastal protection, and nutrient retention. Local coastal populations derive sustenance from the mangrove forests, i.e., catching fish and crabs for subsistence or commercial purposes, and collecting firewood and other resources from this unique environment. The most extensive mangrove areas are found in Asia and Africa, followed by North and Central America, South America and Oceania. According to trend analyses from available data, an average of 15 million ha of mangroves are estimated to exist worldwide as of 2005, down from 19 million ha in 1980. This 20% decrease in total mangrove coverage in the last 25 years clearly demonstrates the threat to this valuable ecosystem. The decrease in global mangrove coverage has induced scientists to expand serious investigations on the topic so that mangrove-related publications have increased significantly in the recent past. A check of the “Aquatic Sciences and Fisheries Abstract” (ASFA) database from 1980 to 2009 exhibits an increase from 90 to 245 mangrove-related publications per year. The publications primarily treat various aspects of the biology and structure of mangrove forests and their food webs including: flora and fauna, community structures, species distributions, biodiversity, and how mangrove species composition varies in response to gradients in physical factors, such as salinity and soil type. More recently, mangroves were considered more as a land–sea transition zone in a holistic perspective. They have become part of the concept of an integrated coastal zone management (ICZM), taking into consideration the local socio-economic conditions and the needs of the local communities. The present book deals with one of those holistic approaches. The MADAM (Mangrove Dynamics and Management) project was executed in a mangrove belt in North Brazil. It focused on disciplinary, interdisciplinary, and transdisciplinary research in support of developing ICZM tools based on sound scientific data, and U. Saint-Paul and H. Schneider (eds.), Mangrove Dynamics and Management in North Brazil, Ecological Studies 211, DOI 10.1007/978-3-642-13457-9_1, # Springer-Verlag Berlin Heidelberg 2010
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on the socio-economic, environmental and structural development of regions where unique and largely untouched mangrove areas exist. The integration of natural and social science was difficult because of the different scientific working concepts used. Natural science disciplines use working hypotheses that support the understanding of the mechanisms which sustain ecosystems and investigate how to maximize potential resources. Socio-economic and conservation sciences investigate important human–nature dynamics and identify the levels and regimes of ecosystem resource utilization which are consistent with sustainable and desirable futures for mangroves and the societies that depend on them. This is done taking into account climatic and societal change. Due to the wide scope of this multitasking approach, it is not surprising that problems were encountered because of the inclusion of very different disciplines familiar to the scientists involved, and not least because of the differing cultures and languages. Overcoming these imbalances and synchronizing the efforts at all levels proved to be a challenging but highly worthwhile process. MADAM has shown that such a simultaneous multipronged approach can achieve clear and important results. The following chapters of the book provide a sound database for a better understanding of the social and ecological conditions of a mangrove system. Their purpose is to improve the theoretical framework for further studies on mangrove dynamics and for the development of methods for sustainable multipurpose management. They also reveal the large gaps that still exist and the requirement for further studies for a better understanding of the system. The book is divided into nine parts. Part I provides an extensive overview on the integrated structure of the project and highlights its research concept based on bilateral partnership. Part II considers the geography of the study site, its palaeo-environmental reconstruction and the biogeochemical characteristics of the mangrove. Chapter 3 considers the geography of the mangrove covered peninsula close to the city of Braganc¸a. The region as a whole can still be considered as rather undisturbed by human activities. Chapter 4 presents palaeo-ecological studies on age and growth dynamics of mangrove forests over the past thousands of years. The studies have helped to understand long-term environmental change in the study area. The role of mangroves as an important linkage between terrestrial and marine environments in the tropics is well accepted (Chap. 5). Based on our studies, it is estimated that on a global scale mangroves account for over 10% of the terrestrially derived, refractory dissolved organic carbon (DOC) transported to the ocean. Another major contribution to coastal science was enabled by the analysis of leaf litter retention within the forest system. In Part III, two chapters consider floristic and faunistic studies in the mangrove. Chapter 6 deals with the forest as a plant community. Studies on the growth of mangrove trees through both ring-structure analysis and growth experiments have gained new and applicable results, aiding in the understanding of the history of mangrove forests in prehistoric times, and the factors that determine succession, colonization (gaps and microclimate), and stress-induced growth. This information
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has helped in important management decisions regarding future options for protection, reforestation, and impact assessment of present and future human exploitation of mangrove forests. Chapter 7 deals with benthic organisms. Notable results have been obtained on the, thus far, neglected role of mollusks in the estuarine waters of the Caete´ region. The diverse species composition of the wood-boring shipworms (Teredinidae) has been revealed by molecular genetics. Mussel and oyster distributions are described. Their role as a resource for coastal inhabitants requires continued research to ensure their sustainable use. Part IV gives an overview in three chapters on the dynamic processes in such a mangrove ecosystem. Chapter 8 deals with the main abiotic factors influencing large-scale features of the mangrove ecosystem. The use of remote sensing and GIS with high resolution and visualization combined with radiocarbon dating have provided further insights into short- and long-term changes. The net loss of mangroves cover in the study area of MADAM between 1986 and 2002 was about 3%. A shift of mangroves to more elevated levels was detected. The mapping and pollen core samples of the entire mangrove coast indicated a sea level rise with at least two intercepts. Mangrove forest dynamics were studied through a more rigorous application of the different kinds of modeling approaches (individual-bases modeling, modeling of trophic networks, and spatial point pattern analysis), including the interactions between species, environment, nutrient flows, and pattern structure (Chap. 9). Much progress has been achieved regarding the dynamics of the mangrove forest on the scale of individual trees, spatial partitioning between mangrove species, and on the change of forest distribution in postglacial times. Modern remote-sensing methodologies using high resolution satellite images (i.e., IKONOS images) have paved the way for a major breakthrough (digitization) in mapping, although some methodological problems remain to be resolved (Chap. 10). These results have relevance in view of climate change and the sea level rise (e.g., salinity changes, inundation, rain fall, competition). The five chapters of Part V give a broad overview on the fisheries ecology and management. Studies on the importance of mangrove habitats for fish stocks were an integral part of MADAM. The work has led to fairly complete accounting of fish and shrimp species of the littoral zone within the Braganc¸a area. The results have been published as a separate species catalogue, presenting the regional biodiversity of the fish. Some videos have been filmed about the fishery and distributed to local schools. Our studies have improved the knowledge of the distribution of fish in a tropical estuary, the composition of fish communities in mangrove habitats, and their trophic position, dynamics, abundance, and migratory nature, mainly for commercially important species. Data on growth, mortality, and recruitment have been generated, not only for the Braganc¸a area but also for the neighboring estuaries (Chap. 11). Studies using modern shallow-water hydro-acoustics have documented the movements of fish into their temporary feeding grounds in the intertidal zone and have revealed that their migration is closely linked to the tidal cycle, often covering several kilometers into the mangrove forest (Chap. 12). A particularly well-studied example is the four-eyed fish Anableps anableps, always swimming at the water
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surface (and thus easy to observe). Those species that do not spend their entire life in the brackish mangrove environment move to the open bay and the coastal-marine areas, using the mangrove as a nursery area. Many of them are of commercial importance, e.g., the shrimps Farfantepenaeus subtilis and Cynoscion spp. (Sciaenidae), and catfish (Ariidae). Thus, our studies underpinned the notion that the mangrove environment is an important habitat and food source for juveniles of exploited fish and shrimp stocks along the northern coast of Brazil. The studies on fish did not only concern adults but more importantly addressed larval and juvenile stages. The results showed that the network of intertidal creeks draining the mangrove area is an important nursery area for many fish and shrimps (Chap. 13). Molecular systematics (Chap. 14) entered into MADAM only at its end with support from the Millenium Project, supported by the Brazilian Research Council (CNPq). The subprojects carried out thus far under these auspices have contributed significantly to the initial characterization and identification of biodiversity at the species and population levels. Fisheries studies set the scene for further investigations supporting decision-making on fisheries management within the mangrove (Chap. 15). Furthermore, studies have also focused on total landings, fishing intensity, and extent of the fishing community (about 25% of the population depend on fishery) while also identifying the value of the fisheries and classifying the fishing fleet and gear. These are important outcomes, which shows the importance of this type of business for the region. The biology and fishery of crabs have been the focus of several MADAM studies which have impacted local and regional biodiversity conservation and fisheries management and are the topic of Part VI. A full description of the crab community of the Caete´ estuary is now available, including detailed drawings of the species (Chap. 16). Feeding habits, diet and food intake of the most important mangrove crab species were studied and their ecological role examined (Chap. 17). It was shown that one species, Ucides cordatus, significantly contributes to the retention and remineralization of organic matter in the mangrove ecosystem by consuming up to 81% of the leaf litter. This large crab and four smaller Uca species together accounted for 90% of all crab biomass in the mangrove forest. Their population structure, growth, mortality, and reproduction were studied and their life history strategies compared in relation to their differing diet (Chap. 18). U. cordatus is the only commercially exploited mangrove crab and is of great socio-economic importance (Chap. 19). A comprehensive fishery monitoring implemented by the MADAM project was conducted over 8 years, including fishermen and students to promote local capacity building. The results suggest that the U. cordatus population is not yet overexploited. An individual-based model was developed to study the replenishment of harvested areas by crabs from nonharvested areas (Chap. 20). The approach was based upon patterns of orientation and general behavioral ecology of U. cordatus in relation to habitat and fisheries activities. It greatly helped in understanding local crab distribution, competition for space, and overall population recruitment mechanisms. The understanding of important socio-economic relationships has been a fundamental aim of MADAM from its inception and is the topic of Part VII (Chap. 21).
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Three subprojects were initiated, focusing on (1) human–nature interactions in mangrove areas, (2) major issues in mangrove management and system understanding, and (3) research and public policies in mangrove management (transdisciplinary policy analysis and capacitation). Initially, a limited number of local people took part in the development of this process. However, their engagement and dedication stimulated a large number of volunteers who assumed many responsibilities and began to form a critical mass that led to substantial progress in the final phase of MADAM. The sustainability of this development is exemplified by the continued engagement following the death of the most important village leader, “the activist” among local participants. The first subproject involved the establishment of a local radio station for effective communication in areas where communication infrastructure is still lacking. An increased dissemination of information on new and traditional knowledge to nearby communities was already taking place, leading to multiple spin-off effects. Organized learning and educational structures for the arrangement of programs and informational approaches have been accomplished by the radio. The second subproject was concerned with the creation of regional networks for production and trading. This led to close relationships with neighborhood communities, i.e., Braganc¸a and other areas of tourism. In particular, local specialized products such as honey and rural handicrafts formed the basis for a small-scale trade economy and contributed to diversified income. The third subproject was dedicated to the reduction of uncontrolled waste output from municipalities. There was a wide gap between the formal rules and normal practise of waste-disposal in this region where the threats of pollution have never been taken seriously. This change in attitude was based on a growing environmental awareness among the local inhabitants as directly encouraged by the MADAMsupported projects in environmental training offered in schools and promoted in community meetings. MADAM has encouraged the development of a deeper sensitivity towards a better quality of life. The methodological approach included questionnaires, interviews, and expert and group discussions. From the latter, the results were disseminated into the target groups. The information gained by this work was analyzed critically, considering the environmental, economic and social sustainability of several resource uses (such as mangrove tree utilization, which is illegal, and mangrove crab collection). It has led to co-management and policy models (RESEX project) since 2006 with emphasis on poverty alleviation and minimum rights and duties for stakeholders in the area. The extractive reserves are conservation units used by traditional populations whose existence depends on extractive activities, subsistence agriculture, and the breeding of small animals. The reserves ensure the rational usage of natural resources. Also, dysfunctional local and federal regulatory barriers were identified and appropriate changes recommended. It is implicit that any progress in this area will have to consider human rights and justice appropriately. Data synthesis and assessment tools are presented in Part VIII. The research on past and current natural dynamics is highly relevant for the assessment of human–nature feedbacks, such as in the context of road construction across a tidal
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watershed (Chap. 22). Further, the results can enable the responsible management authorities to make important decisions on appropriate mangrove use by the local populations. A GIS-based vulnerability assessment revealed that the coastal zone has been severely impacted by storm floods and erosion processes in the last 25 years. The results of the study serve as a solid base to implement an ICZM program of the State of Para´. In addition, a Mangrove Information System (MAIS) has been developed to enable data syntheses and to ensure long-term data availability, quality, and exchange (Chap. 23). In conclusion, the overall aim of MADAM was to highlight the linkages between ecosystem health and livelihoods in the study area. The project has successfully assessed ecosystem services, evaluated threats, and has identified indirect and direct drivers of change. Management options were developed in response to identified threats as part of an approach aiming for sustainable social–ecological dynamics and development paths. An integrated coastal management framework will be adopted to guide the process of project implementation on the ground. Mangrove forests had been classified by many governments and industries alike as “wastelands” or useless swamps. This mistaken view has led to exploitation of mangrove forests as cheap and unprotected sources of land and water. MADAM has clearly shown that mangroves are of ecological and economic importance, an insight adopted by the local population. It was a Thai fisherman from the Andaman Coast who brought it to the point when saying: “If there are no mangroves, then the sea will have no meaning. It is like having a tree without roots, for the mangroves are the roots of the sea.”
Chapter 2
MADAM, Concept and Reality U. Saint-Paul
Because of the excellent cooperation between Germany and Brazil in the field of environmental research in the past, North Brazil was identified during a bilateral fact-finding mission by Ulrich Saint-Paul (Center for Tropical Marine Ecology, ZMT) and Juan L. B. Hoyos (Federal University of Para´, UFPa) in 1993 as a potential region for the development of the MADAM project (Fig. 1). Here, the world’s second largest continuous mangrove cover is located. After a first meeting in Bele´m, the Federal University of Para´ offered the university campus at Braganc¸a for the field work and many Brazilian scientists showed great interest in collaborating in such an integrated long-term program. Both sides agreed that the future MADAM project should combine both research and capacity building, that a field station in Braganc¸a and a contact office in Bele´m were needed and that a group of German scientists would stay for long periods in Brazil. In this way, continuous cross-linking between participants from both nations was facilitated. After a first joint field trip to the mangrove-covered Braganc¸a peninsula in 1993, the participants agreed that the area was appropriate to study social and environmental topics and that the university campus would serve as an excellent logistical base. The German coordination was based at the Center for Tropical Marine Ecology (ZMT). Because of its scale and the long-term perspective, MADAM became a flagship for the initial stage of ZMT and was a trendsetter for further projects, particularly in SE Asia. Due to the fact that all technical and scientific positions became permanent posts in 2005, MADAM contributed significantly to ZMT’s consolidation and was a prerequisite for it becoming a member of the Leibniz Association (WGL) in 2009. Initial partners on the Brazilian side were the Federal University of Para´ (UFPa) and the Emı´lio Goeldi Museum (MPEG). During the second phase of the project, the Goeldi Museum withdrew its participation for technical reasons. MADAM was financed by the German Ministry of Education and Research (BMBF), the State of Bremen, and the Brazilian National Council for Scientific and Technological Development (CNPq). The total budget amounted to more than 15 million Euros over 10 years in addition to very substantial contributions in kind by both sides.
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Fig. 1 The MADAM logo
The contractual basis for MADAM was a Memorandum of Understanding (MOU) between the ZMT and the UFPa/MPEG from 1995. The project was incorporated in the Special Agreement on Cooperation in the Field of Environmental Research and Technology between the Brazilian Institute of Environment and Renewable Natural Resources (IBAMA) – the Brazilian environmental authority – and the German Aerospace Research Establishment (DLR). Later, CNPq joined the agreement. MADAM was affiliated to Land–Ocean Interactions in the Coastal Zone (LOICZ), which was a core project of the International Geosphere-Biosphere Program (IGBP) and the International Human Dimensions Program on Global Environmental Change (IHDP) of the International Council of Scientific Unions (ICSU). In the light of the experience particularly with MADAM, the Bremen Criteria for International Partnership Projects in Marine Science were developed by the ZMT. Those criteria are now more or less obligatory for major German activities in tropical ecology and they are also widely recognized internationally. The Bremen Criteria expect partnership programs to provide: l
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An important contribution to a scientifically important theme of social and economic relevance A major contribution to strengthening scientific capacity in the host country, particularly by on-the-job training and other means of advanced and specialized training Joint planning and execution, fully utilizing existing competence in the host country Long-term financial commitment with contributions from the host country Incorporation of expertise available at various German institutes Full integration into the scientific structure of the host country and its universities Links to regional and global program – so both partners also fulfill parts of their international obligations via such partnership projects
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Unrestricted data exchange and joint publications, preferably in international journals.
These criteria serving as a code of conduct were first approved at the annual meeting of the Society for Tropical Ecology (gto¨) in Bremen 2001 and slightly modified in 2005. The Code serves as a directive for the preparation of project applications. Adherence to the Code should be mentioned in publications and considered to be a seal of quality. It is MADAM’s stated objective to contribute significantly to a sustainable resource management, based on research and continuous long-term survey. This requires: l
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Development and integration of scientific knowledge about the natural and anthropogenic processes operating in relation to the mangrove system. Development of models for describing the mangrove system under specific scenarios, in order to elaborate management behavior recommendations for ecologically sustainable utilization of the mangrove and its resources. Development of models to outline the linkages between ecosystem resources and services, and economy and society, in order to outline both ecologically, socially and economically sustainable ecosystem management solutions.
MADAM was planned for a 10-year period with a quality check at about 3-year intervals. The research was organized in three long-term compartments. In order to quantify the functions of mangroves, the first compartment consisted of a multi- and interdisciplinary collaboration of different scientific disciplines, while the integration of the research results for modeling the system were developed. The individual tasks were combined in seven subject-specific modules with a closely linked data and information exchange, guaranteeing an optimization of the data flow within the project and of the feedback of results for subsequent planning phases. While Modules 1–6 were directly derived from the ecological appreciation of the mangrove system, Module 7 dealt with higher objectives. Figure 2 shows the structure of MADAM during its first phase. The second phase initiated a shift from a mono-disciplinary approach to more overarching issues, like “Function, productivity and seasonality of mangrove-systems,” “Fisheries resources and management,” “Synoptic analysis of area structure”, and “Decision support systems.” The conceptual frame became broader with time. Mangroves were considered as an integral part of the coastal zone rather than as an ecosystem surviving in isolation. Consequently, MADAM concentrated during its third phase on two focal subjects, which are supplemented by activities of overall interest, such as communication and data bank management. Research topics were “Synoptic analysis of the surface structures on both a local and a regional level” and “Natural resource management and its linkages to natural, economic, and social systems with special emphasis on the mangrove crab Ucides cordatus, the mangrove’s outstanding resource.” The questions behind these are shown in Fig. 3, demonstrating the linkages between the different research groups.
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Module 7 Modelling and management strategies
Module 6 Module 3 Socio economic environment
Energy and material transports
Module 4 Potential resources
Module 5 Primary production
Module 1 The abiotic environment
Module 2 Biodiversity
Fig. 2 The structure of the seven modules of the MADAM project during its first phase
Up to 100 scientists and students at a time worked in MADAM. For the field work, two stations in Bele´m and Braganc¸a with laboratory facilities and office space were created. During the very beginning of the project, only limited space was offered by the Brazilian partners. The further development of the project lead to an increasing demand over time. As a consequence, MADAM started to construct its own facilities, especially in Braganc¸a. Off-road vehicles and rubber boats with outboard engines were bought. Since the beginning, there was concordance that German scientists, PhD students and technicians should live in the region to foster the cooperation and to learn Portuguese. This led to excellent cooperation between the project members. For both the German and Brazilian students, a local
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Fig. 3 Interdisciplinarity. Simplified picture of the interlinked questions formulated by the several sciences involved in the MADAM project. The integration of the usually distinguished approaches within one project illustrates the necessity of a combined system analysis to achieve the main goal of the project: understanding the mangrove dynamics and development of sustainable management strategies
contact person helped to manage conflicts and to clear uncertainties with regard to the thesis work. In compensation, about ten Brazilian students completed their thesis work in Germany and obtained their degree from Bremen University. The exchange of senior scientists was facilitated by a number of scholarships to support the visit to the partner institution for several weeks. With regard to financial support, MADAM had a good spin-off effect. During the beginning, funding was restricted to the BMBF, the state of Bremen and the CNPq. But later, a significant amount of additional funding was acquired. Especially, the CNPq support through the Millennium Edition will help to establish a Center of Excellence on Integrated Coastal Research in North Brazil. Partnership in training and education constituted an indispensable component of the project. This is why German and Brazilian students and young scientists jointly planned and carried out scientific projects, field work, data analysis, and publication of the results. In addition to “training on the job,” joint courses and excursions were planned and exceeded. German scientist still form an integrated part of the curriculum of the UFPq master courses in both Bele´m and Braganc¸a, while Brazilian academic teachers are recognized as supervisors for German students and young scientists. Another vital element of MADAM were the public relations. A group of Brazilian journalists published on a 2-month basis the well-illustrated journal “Folha do Mangue” (Mangrove Leave) with project-related information and with more general topics on environmental issues. The journal was distributed for free and especially demanded by school teachers. A particular radio program was a further tool of
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communication. School courses on environmental issues were offered and were greatly in demand. Mangroves are not isolated ecosystems, they are strongly linked to the region and its population not only on the ecological but also on social, cultural, and economic levels. Therefore, other activities in the field of scientific, technical, and financial assistance were considered for close cooperation. MADAM was strongly linked to the following programs and projects: l
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PRORENDA (Programa de Renda Familiar): The project is coordinated by the German Agency for Technical Cooperation (gtz). The purpose is to implement a sustainable increase of profits for smallholder enterprises in several regions of Para´. The project is implemented by the state government of Para´, represented by the Ministry of Planning and Agriculture, research institutes and many NGOs and trade unions. PRORENDA is designed as a pilot program and as an associated bilateral project within the planned PP-G7 subprogram “Rehabilitation of Degraded Soils.” This was an important link for all mangrove crabrelated activities. PP/G7 (Pilot Program): The destruction of the Amazonian rain forest has led to an international discussion concerning sustainable development and protection measures. The German government is participating through the International Pilot Program for Preserving the Tropical Rain Forest in Brazil, which started after the 1992 World Environmental Summit in Rio. The objective of this program is to sustainably preserve the rain forest from the continuing process of destruction while at the same time formulating appropriate use concepts together with local population groups. The Pilot Program created a positive spirit among the decision makers and increased the willingness to support research and development projects of tropical forest systems, to which mangroves belong. PD/A (Projetos Demonstrativos, Tipo A): The Project purpose is to support local communities in the Amazon and the Mata Atlaˆntica region in their research and development of innovative models for sustainable development and conservation of natural resources. It is financed by the Brazilian Ministry for the Environment (MMA). The PD/A “Water and mangroves: management and fisheries development of the Caete´ estuary” was linked to MADAM. ´ rga˜os para Assisteˆncia Social e Educacional): The FASE (Federac¸a˜o de O regional program Amazonia supports the sustainable use of natural resources by advising and training small-scale farmers in methods of locally appropriate farming techniques thus improving their income. Farmers will be organized to improve their influence on local policy and decision-making. FASE consultants from the German Development Service (DED) cooperated with MADAM.
The cross-linkages between the different groups is shown in Fig. 4. The mangrove crab is of major importance for the local population. This justified the focus on the sustainable management demand for this resource and the integration of different agencies.
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German/Brazilian Cooperation in the Bragança Region PD/A Technical & Financial Cooperation
Technical & Methodological Development
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Fig. 4 Technical, financial, and scientific cooperation linkages for Braganc¸a region for the sustainable management of the mangrove crab
MADAM was a convincing tool for the integration of scientists from two different countries and an excellent example of an international partnership project. And it helped to coordinate different programs when dealing with overarching issues, like sustainable resource management or problems related to Integrated Coastal Zone Management.
Part II Geography and Biogeochemistry
Chapter 3
The Geography of the Braganc¸a Coastal Region G. Krause
3.1
Background and Scope
Mangrove ecosystems are a dominant feature of the intertidal zone of tropical deltas, lagoons, and estuarine coastal systems (Twilley 1995). They cover an area of roughly 181,000 km2 in more than 100 countries worldwide (Spalding et al. 1997). Throughout human history, people have characterized mangrove ecosystems as smelly, impenetrable swamps that harbor dangerous animals such as snakes and crocodiles, as well as vector diseases such as malaria (Ro¨nnb€ack 2001). Even Charles Darwin expressed his lack of appreciation of these ecosystems: “The channel . . . was bordered on each side by mangroves, which sprang like a miniature forest out of the greasy mudbanks. The bright green colour of these bushes reminded me of the rank grass in a churchyard: both are nourished by putrid exhalations; the one speaks of death past, and the other too often of death to come. . ..” (Darwin 1842). However, in recent years, there has been an increasing awareness of the vital role of the goods and services provided by mangroves, e.g., as daily nutrition source for coastal populations and coastal protection system. The importance of the latter was stressed for instance by the disastrous 2004 Tsunami in Indonesia. The combination of different geomorphologic settings, each with a variety of ecological types, contributes to the diversity of mangrove ecosystems, and to their specific characteristics of structure and function, goods, and services (Twilley 1995; Duke et al. 2007). In the following sections, a geographic overview of the principal features of the mangrove ecosystem research area of the MADAM project is provided. The description moves from the marine “seascape” to the coastal region, and it relates mangroves toward the landscape of the rural hinterland. Each of the geographic subdivisions is presented with its particular natural as well as social features, emphasizing the coevolution of ecological and social system elements as a central concept. The successive chapters of this book elaborate on these features in greater detail. Implications of the dynamics of the natural as well as social system elements for the current situation of the MADAM research area and its future development are discussed.
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Spatial Boundaries
The key research area of the MADAM project, the Braganc¸a coastal region, is part of the 2,340 km2 large municipality of Braganc¸a, which is located on the Atlantic coast, approximately 300 km southeast of the Amazon delta and 200 km east of Bele´m, the capital of the Para´ State in North Brazil (Fig. 3.1). The mangrove peninsula of Braganc¸a (0 800 –1 070 S, 46 760 –46 520 W) is encompassed by the estuaries of the Caete´ and the Tapera-Ac¸u Rivers. Being part of the Atlantic mangrove province (Pernetta 1993), the research area is situated within the secondlargest continuous mangrove ecosystem in the world (Kjerfve et al. 1997). The area belongs to the Inner Humid Tropics (Schultz 2000), which is determined by the semiannual alternation of rainy and dry seasons. The dry season lasts from June through December, followed by a very wet period lasting from January to May. The annual rainfall ranges between 1,085 and 3,647 mm (Souza Filho 1995).
Fig. 3.1 The research area of the MADAM project in the State of Para´, North Brazil. The dark shaded areas in the lower figure represent the area of the socio-economic rural communities that derive their direct income from mangrove resources of the Braganc¸a coastal region (Krause et al. 2001)
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The average annual temperatures revolve around 25.2–27.4 C and the relative air humidity range is between 60 and 91% (Krause et al. 2001). Positioned between the crystalline Precambrian shields of the Guyana and Brazilian highlands, this region belongs to the Amazon lowlands and is assigned to the landscape group of the “Amazon Oriental” of North Brazil (Grabert 1991). The geologic base of the research area is formed by Precambrian cratonic block consisting of granites and migmatites (Behling et al. 2001; Souza Filho et al. 2006; Cohen et al. 2005). Tectonic shear movements of the large shields have caused a break-up of the Brazilian coastline, characterized by small peninsulas (Souza Filho and Paradella 2002; Cohen et al. 2004). The major environmental factors which shape this region are (1) the “tide-dominated allochthonous” processes (after the classification of Thom 1984) and (2) substantial meteorological and hydrographic modifications which occurred during the Pleistocene Ice Age (Behling et al. 2001). Today, the Braganc¸a coastal region consists of three morphologic units, which can be differentiated according to their shape, lithology, stratigraphy, and vegetation (Fig. 3.2). A coastal high plateau, whose height ranges between 50 and 60 m, forms the hinterland unit. It is predominantly composed of late Miocene and early Pleistocene sediments (Souza Filho and El-Robrini 1997; Behling et al. 2001). Towards the coast, the plateau dips progressively down to the coastal lowlands. This transition unit from the high plateau to the coastal lowland features a small fossil bluff of approximately 1 m elevation and is dominated by an agricultural landscape and secondary vegetation. The third unit is characterized by the emergence of mangroves and is dominated by the approximately 104 km2 large estuary of the Caete´ River. To the north, the influence of the Atlantic Ocean gradually increases in this zone. The estuary consists of numerous channels, which branch off
coastal high plateau Rio Caeté
mangroves coastal plain
estuary channels salina
tidal shoal sequence of marine regression basal sequence of former marine transgression unclassified sequence sequence of barreias group
Fig. 3.2 Block diagram from a NE perspective with the major geomorphologic features and principal deposition sequences (modified after Souza Filho 1995)
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into the mangrove peninsula (Krause et al. 2001; Krause and Soares 2004; Souza Filho and Paradella 2002). The 180 km2 large mangrove peninsula of Braganc¸a is the main feature of this coast. It is covered up to 90% with mangroves (Krause et al. 2001), with two mangrove species dominating: Rhizophora mangle (red mangrove) and Avicennia germinans (black mangrove). Laguncularia racemosa (white mangrove) is rare (Mehlig 2001). Due to its high elevation, the entire peninsula is only flooded during spring tides, while the network of creeks running through the mangrove is flooded regularly by the semidiurnal tide. The tidal range is 2–3 m at neap and 3–4 m at spring tides and can be classified as a macrotidal regime (Krause et al. 2001). The tide is asymmetric; flood and ebb tide last approximately 4 and 8 h, respectively. Turbidity is high (mean Secchi depth: 30 cm) and positively correlated with tidal height (Krumme 2004). In the adjacent 130 km2 social rural area, about 13,000 people live and derive their livelihood from this mangrove peninsula. Small-scale fisheries and small landholdings form the two dominant economic systems. More than 80% of the households gain their livelihood from the products of the mangrove estuary (Furtado 1990; Glaser 2003). The most important mangrove product is the leaf-litter-consuming large semi-terrestrial crab Ucides cordatus, which reaches a carapace width of approximately 9 cm (e.g. Diele 2000; Schories et al. 2003). The crabs are captured by professional crab collectors and are sold either alive on local or regional markets, or are processed as meat for regional and national consumption. Fish, shrimps, and other invertebrates, as well as mangrove timber are also used, the latter predominately for the construction of fish weirs (Barletta et al. 1998), fuel for domestic cooking, and to fire brickwork kilns (Berger et al. 1999). In the following, the term “Braganc¸a coastal region” is used to describe this socialecological system, combining the 180 km2 of mangrove ecosystem together with the adjacent 130 km2 rural area. Communities that are not directly dependent on the mangrove resources are excluded from this definition.
3.3
Principal Features of the Natural and Social System
The research area, the Braganc¸a coastal region, is dominated by a viable mangrove ecosystem supplying a variety of goods and services to the local rural residents. The principal features of this socialecological system are described in more detail in the following sections. The description moves from the marine seascape and related mangroves toward the landscape of the rural hinterland and the city of Braganc¸a.
3.3.1
The Marine Seascape and the Estuary
The seascape of the Braganc¸a coastal region is influenced by freshwater run-off and tidal mixing, as well as by the Amazon counter-current, which drives the outflow
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and direction of the estuarine plume on the continental shelf (Dittmar et al. 2005). The estuary of the Caete´ River represents a typical tidal allochthonous estuary. It is comparable to other mangrove areas in terms of its spatial properties described in the literature, e.g., Kjerfve and Lacerda (1990), Schaeffer Novelli et al. (1990), Spalding et al. (1997), and Bunt and Stieglitz (1999). In general, tidally induced mixing in relatively shallow coastal water prevents stratification within the estuary. Salinity concentrations in estuarine waters can fall below 5 and exceed 35‰. In one of the mangrove tidal channels, locally called furo, a total of 46 species of phytoplankton from at least 29 different genera were identified. The majority of these species belong to the Diatomeaceae class. However, due to high loads of organic material and strong tidal mixing, primary production in the estuarine water column is restricted (Schories, personal communication). The local fisheries sector is entirely artisanal with a large-scale and a small-scale sector. Over half the rural population in the Caete´ Bay is engaged in small-scale fisheries in the mangroves. Subsistence fishers, who only occasionally sell parts of their catch (Glaser and Grasso 1998), account for about half the mangrove fishers, and commercial fishers the other half (Fig. 3.3). One much-cited official statistic shows that 11.5% of the total number of 4,365 vessels in the State of Para´ were registered in the Braganc¸a region (IDESP 1989). Of the 502 fishing vessels registered there, 40% were equipped with mostly low-power engines, 32% were non-motorized canoes, and 26% were sailing canoes (Barletta et al. 1998). Thus, the regional fleet is almost entirely artisanal, owner-operated, and nonmotorized. According to IDESP (1989) and to Isaac and Ferreira (1998), Braganc¸a’s fishery has contributed significantly to the regional economy for a long time. The artisanal fishery contributes half the entire fish catch of the State of Para´ (IBAMA 2004); it also plays an important role in the supply of the local markets of the state capital of Bele´m, as well as of the neighboring state capitals, Sa˜o Luı´s and Fortaleza (Grasso 2000; Isaac et al. 2006). The landings from the large-scale artisanal fishery are destined exclusively for the export market. Only a small part of the lower quality fish captured by Braganc¸a´s large-scale fisheries sector is sold in the local markets. Although most of the fish landings in the city of Braganc¸a originate from the largescale sector, there are clear indications that, in terms of rural income generation and protein provision for local rural and urban households, small-scale mangrove fisheries play the predominant role in the Braganc¸a coastal region (Glaser and Grasso 1998; de Barros et al. 2000; Isaac et al. 2006).
3.3.2
The Coastline
The northern shoreline of the Braganc¸a peninsula is divided into four beaches, one of which contributes significantly in tourist income to the local economy. Cheniers can be found in the transition zone between the mangrove and the dune ridges/ beach complex. Patches of restinga and coastal grassland (campo de dunas) occur on the sand plains and on the dunes along the north coast of the peninsula (Behling et al. 2001). The common floral compositions of these locations include
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Fishery type
Small-scale
coastal commercial 4 to 10-day trips
estuarine commercial & subsistence 1 to 3-day trips
Final consumers
local, regional & national markets
local markets and subsistence consumption
Technology
motorised small boats (inboard & outboard)
sail or oar-powered canoes fixed traps & fences
Fishing locations
Main catch (species)
Gó (Macrodon ancylodon)
Bagre (Arius hertzbergii)
Uricica (Cathorops)
Amoré (Eleotiedae guavina sp)
Caica Pratiqueira (Mugil sp)
Fig. 3.3 The structure of fisheries in Braganc¸a, Para´, Brazil (modified after Glaser and Grasso 1998)
Cyperaceae, Poaceae, Humiria balsamifera, Byrsonima crassfolia, and Chrysobalanus (Mehlig 2001). The majority of the coastline along the Braganc¸a peninsula is subject to strong natural littoral transport (Cohen et al. 2004; Krause et al. 2004). Four years of fortnightly beach profile monitoring identified four spatial cells, each with a specific morphodynamic behavior and local human utilization pattern. One cell showed a stable coastline, all others are subject to strong erosion (Krause and Soares 2004). Tight linkages between the degree of erosion risk and livelihoods exist. Poorer families are either marginalized at the shorefront or pushed into the hinterland in response to tourism demand. Some residents have had to relocate as much as five times due to the rapid changes of the beach morphology. These developments have also impacted on the physical infrastructure such as roads, schools, and
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local sanitation, with health implications for the local population (Krause 2002; Krause and Glaser 2003; Szlafzstein 2003). Losses of weekend accommodation and tourist homes have also occurred by erosion leading to a decline in the associated tourism income (Krause and Soares 2004).
3.3.3
The Intertidal Zone
The mangrove vegetation is the most remarkable feature of the intertidal zone of the Braganc¸a coastal region. The distribution patterns of the mangrove vegetation and the height variation of the mangrove stands indicate that there is a strong correlation between the hydrological regime, the microclimatic conditions, the topography, and the soil salinity (Mehlig 2001). A distinguishable spatial pattern is detectable by the variation of the mangrove tree heights. Mangrove trees react to a wide range of environmental conditions by adapting structural properties like stem diameter, height, or leaf size. Tall mangroves measuring more than 25 m occur as well as dwarf forms of the same species no taller than 1 m (Menezes et al. 2003). The latter are found in the less frequently inundated, central parts of the peninsula, which apparently offer less favorable growth conditions (Reise 2003). However, a distinct zonation pattern according to mangrove species could not be identified, rather a mosaic-like distribution predominates in this system (Krause et al. 2004; Schwarz 2005; Berger et al. 2006). Through the efforts of the Brazilian government to facilitate access to the coastal resources, a modification of the mangrove pattern took place. A case in point is the construction of the PA-458 road during the 1970s between the city of Braganc¸a and the coastal village of Ajuruteua on the north shore of the peninsula. This blacktopped road created a modification of the local hydrological regime, which led to a reduction of water flows. This caused massive die-off of the original mangrove vegetation, especially in the center of the peninsula. Over 200 ha of mangrove were adversely affected, which resulted in vegetation-free areas with degraded soils with high salinity that are common to arid coastal landscapes. Upper salt marshes (locally called Salinas dos Rochas) are located in the center of the mangrove peninsula which are dominated by Cyperaceae (e.g., Eleocharis spp.) and Sporobolus virginiacus (Poaceae) (Mehlig 2001). They rarely become flooded by the tides, and apart from soil salinity they are influenced predominately by terrestrial factors. However, patches of small mangrove bushes of Avicennia and Laguncularia occur within the salt marsh. Presumably variations in the local conditions, particularly the high salt concentrations, may prevent a more successful and widespread establishment of mangroves (Medina et al. 2001). During the rainy season, the salt marshes become completely inundated for months. During periods of little precipitation, the Salinas dos Rochas soils dry out. Because of the high evapo-transpiration, the mineral salts create a hardpan in the upper part of the soil profile. The cracks in the soil surface indicate the presence of a
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G. Krause
high proportion of small grain-size fractions. This phenomenon also occurs on the degraded soils. Mangroves play a major role in the fisheries system of tropical coastal areas, as well as providing a range of commercial and subsistence nonfish products. The cutting of mangroves for local consumption as cooking fuel as well as for local businesses (bakeries and brickyards) is common in the MADAM research area. In places, pockets of rice cultivation in mangroves exist (Berger et al. 2006). The traditional selective cutting of Laguncularia for the construction of fishing weirs (Barletta et al. 1998) is regarded as having a rather minor impact. A more significant problem is the growing population pressure on the Braganc¸a coastal region. Fisheries, as well as agricultural villages, with their infrastructure requirements are undergoing rapid development (Glaser and da Silva 2004). Different types of mangrove fisheries can be distinguished by size and type of equipment used. Before the introduction of nylon netting material, the main fishing devices of the region were fish weirs (curral, furzaca), cast nets (tarrafa), long lines (espinhel), and harpoons (arpa˜o). Traditional devices are still in use, such as large intertidal fish weirs made out of wooden fences with a fixed catch chamber and the heart-shaped tidal trap (corac¸a˜o) used for subsistence fishery. However, the introduction of modified, more predatory techniques, such as the furzaca (the fixed catch chamber is substituted by a large conical net with an average mesh size of 30–35 mm), is a clear sign of economic overfishing in the region as a reaction to declining fish stocks. Net barriers (tapagem), which block mangrove creeks at ebb tide, are another common fishing method in the region (Barletta et al. 1998). The most economically important direct mangrove product of the Braganc¸a coastal region is the mangrove crab Ucides cordatus (Glaser and Diele 2004; Diele et al. 2005). Two types of crab fisheries can be distinguished (see also Chap. 19). Traditional crab collectors sell their catch as livestock for local and regional consumption. The crab fishers live in Braganc¸a or nearby villages such as Acarajo´ and Bacuriteua that are located west of the Caete´ River. They enter the mangrove forest via the paved road that crosses the mangrove peninsula and catch the crabs (Diele 2000). The more “predatory” crab collectors come from villages such as Treme and Caratateua located east of the Caete´ River. The crab processors, which are less concerned about the size and sex of the crabs, buy their catches. Despite these collectors also aiming for the largest males, they retain smaller specimens and females more frequently compared to traditional fishers (see also Chap. 19). The “predatory” crab collectors enter the mangrove forest with powerboats and work in large groups of up to 25 people (Glaser 1999; Diele 2000; Glaser and Diele 2004; Arau´jo 2006). The declining stocks adjacent to the villages of the predatory crab collector groups on the eastern levee of the Caete´ River initiated an exploitation of areas that were previously used only by the traditional fishers. Consequently, conflicts between the two types of user groups have emerged, as traditional fishers are concerned that their future yield is threatened. With their powerboats, the predatory crab collectors have now started to exploit coastal regions outside the Caete´ estuary (see also Chap. 19).
3 The Geography of the Braganc¸a Coastal Region
3.3.4
27
The Rural Hinterland
As elsewhere in the tropics, a high proportion of adolescents characterize the population of the Braganc¸a coastal region. The 1991 census revealed that, of the 84,750 people living within the municipality of Braganc¸a, more than 63% were less than 20 years old (IBGE 2000). Most rural households in the Braganc¸a coastal region have the multi-occupational structures typical of rural poor regions worldwide. They engage in simultaneous multiple occupations and also utilize sequential seasonal opportunities for income generation. More than 80% of rural households depend on the diverse products of the Caete´ mangrove estuary, and about 68% of the rural households derive monetary income from the mangrove ecosystem (Glaser et al. 1997; Berger et al. 1999). Over 41% of rural households of the region derive their income from farming. For them, agriculture forms an important complementary source of income. Subsistence slash-and-burn cultivation of mandioca, beans, tobacco, malva (a natural fiber), and rice is common. Households located close to the mangrove area engage more in the cultivation of cupuac¸u and bacuri and other tropical fruit, as potential agricultural land adjacent to the mangrove is limited by high soil salinities (Klose et al. 2005). These fruits are all in high demand on the Brazilian market. As a whole, it was found that income diversity in the rural socio-economic area of the mangrove ecosystem was relatively high. Based on the findings of a rural census carried out in 19961997 (Glaser et al. 1997) and a re-census in 2001 (Glaser 2003), only about 31% of households had only one source of income, while a large proportion of these households consisted of single, often old persons. Furthermore, the income of the respective household level depends on the natural resources of the mangrove area in the first place, but also on their spatial location with respect to access to the mangroves and the distance to the main market in the city of Braganc¸a. For instance, villages located closer to Braganc¸a have a higher occupational and income source diversity than those further away from this local urban center. Next, the area situated on the west bank of the Caete´ River is mainly engaged in the primary production sector. Here, access to the mangroves, which provide the major part of economic subsistence, is by bicycle, bus, or on foot (Krause et al. 2001). With the paving of the road to Ajuruteua, crab and wood exploitation has intensified (Glaser and Diele 2004). The rural population on the east side of the Caete´ River is less well-connected to the urban markets since the local roads are not paved. As a result, the local crab production and crab processing sectors are dependent on intermediaries and realize lower economic returns. This has provoked an extension of the spatial radius of the local crab fishery and caused conflicts with the crab fisher population of the western part of the estuary. The tropical rain forest of the eastern Amazon, including the hinterland of the Braganc¸a coastal region, has been subject to large-scale “slash-and-burn” and shifting cultivation. The secondary vegetation (locally called “capoeira”) plays an integral part in the traditional cropfallow cycle by maintaining the
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Fig. 3.4 Pasto com leira. A new innovative cultivation method that employs permanent agriculture techniques (Klose 2004)
productivity of the areas subject to this form of agriculture (Henkel 1987; Kohlhepp 1987). Typical slash-and-burn activities in the Braganc¸a coastal region depend on the amount of land and access to financial resources of the respective rural household. Preferably, the farmer allows the capoeira to grow for up to 10 years prior to the clearing of a patch of secondary vegetation at the end of the dry season. This is followed by the burning of the dried cut vegetation shortly before the onset of the rainy season. The ashes contain water-soluble mineral materials that percolate into the soil providing natural fertilizers to the cultivated crops. This cultivation method is time and land intensive, as recovery periods are long before the patch can be utilized again. In Tamatateua, a village adjacent to the mangrove peninsula, a new innovative cultivation method has emerged that employs permanent agriculture techniques (Klose 2004; Klose et al. 2005). These permanent fields, locally called pastos com leira, are prepared in the following way: After one year of fallow, the land is cleared of vegetation and loamy elevated rows are shaped (Fig. 3.4). Cattle fertilize the soil for two weeks before the rows are sown or planted. In the subsequent year, up to two harvest cycles of maniok are possible before a oneyear fallow period takes place. Compared to the traditional shifting cultivation, which is still used in the rural villages further away from the mangrove peninsula, this innovative method produces higher and more continuous harvest outputs (Klose 2004). One incentive to engage in this new line of production can be attributed to the recognition of the local dwellers that mangroves play a crucial role as an economic buffer in times of crisis. This has acted as an incentive for land-use change and innovation, as the mangroves sustain local livelihoods in case that the new agriculture method fails (Klose et al. 2005).
3.3.5
The City of Braganc¸a
At the time of the European conquest of the South American continent during the early part of the sixteenth century, tribes of the Tupinamba´s occupied the Braganc¸a coastal region. The Tupinamba´s were the largest tribe and belonged to the language
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family of the Tupı´ (Henshall and Momsen 1974; Dickenson 1982). Toward the end of the late sixteenth century, the town “Souza de Caete´” was founded on the eastern shores of the Caete´ River. Its name was later changed to “Vila que Era”. In 1753, the settlement moved to the west of the Caete´ River, and the name changed again, to Braganc¸a (Ver-o-Para´ 1998). Since then, a strong transformation processes has taken place, firstly one towards industrialization accompanying the Amazon rubber boom (Bradford and Oliver 1994), and second towards a post-industrialized society. Today, Braganc¸a plays a key role in the supply of fish and other foodstuffs for the entire coastal region and the adjacent hinterland. The layout of the city center exhibits a gridiron pattern with several suburbs along the radial routes. Tight functional linkages exist between the town and its hinterland. For the rural population, the city of Braganc¸a plays a major role as the export channel for their products, as a local market, and as the administrative center. For instance, in the urban and “near-urban” areas, households tend to be more specialized, presumably in an effort to capitalize on larger markets (Grasso 2000). The paved road to Bele´m, the BR316, is the most important access road to and from Braganc¸a, which has enhanced the fisheries sector by allowing marketing to a much larger area. In addition to that, the blacktop road (PA-253) from Braganc¸a to Ajuruteua has facilitated an emerging tourist development on the north coast of the mangrove peninsula as an important alternative source of income. The relative proximity of Bele´m creates high seasonal tourism peaks for the region (Krause and Soares 2004).
3.4
Co-Evolutionary Outcomes of the Natural and Social Dynamics
Strong interconnections between the well-being of mangrove ecosystems and human activities exist in the Braganc¸a coastal region. Such kinds of linkages have also been observed and described for other mangrove ecosystems, such as by Pernetta (1993), Ro¨nnb€ack (1999), and Dahdouh-Guebas et al. (2000). The income of the rural population in the region is based on the primary production sector and shows strong dependencies on the natural resources of the mangrove ecosystem (Glaser 2003). The town of Braganc¸a has a local central supply function for the surrounding countryside. Thus, the Braganc¸a coastal region can be described as a raw material-producing peripheral region with a high diversity of income sources especially within the rural population. Being embedded in one of the largest, well-preserved mangrove ecosystems on the globe, this region can be regarded as an excellent representative showcase of a socialecological mangrove system, which has been subject to strong transformation processes in fairly recent time periods. The linkages between natural and social dynamics found here can be viewed as exemplary for the entire mangrove belt of North Brazil ranging between the States of Para´ and Maranha˜o.
30
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The ecology of the mangrove ecosystem of Braganc¸a as a whole is still considered relatively undisturbed by human activities. However, there is evidence of considerable and increasing local anthropogenic interference, especially by the increasing fishery activities, expanding tourist industry, urbanization, and commercialization. For instance, excessive woodcutting in the hinterland to expand agriculture has accelerated soil erosion in the catchment area of the Caete´ River during the past few years. This has increased the sediment load in the river. The successive silting-up of its bed can be verified by remote sensing change detection analysis (see Chap. 10). It is additionally confirmed by interviews with local fishermen, who state that navigation in the Caete´ River is difficult and has caused a reduction in access to the river. This is, however, essential for local livelihood, as the river is the major route of transport to bring the catch to the market at Braganc¸a. Thus, the shift in remote land-use patterns inflicts long-term damage to regional economic activities, such as to both small-scale and commercial fisheries. In addition to the increase in sedimentation, the construction of roads has resulted in major changes to the natural mangrove vegetation. The roads have not only modified the local hydrodynamic regime (e.g., Goch et al. 2005) but have also facilitated improved access to the mangroves. Due to the first factor, large numbers of trees died, while the second caused a shift in the traditional type of woodcutting. Selective cutting prevailed in former times, but because of the better accessibility via the road, commercial clear-cutting of mangrove areas has increased (Glaser et al. 2003). Such deterioration of mangrove areas is well known from other parts of the tropics (Eusebio et al. 1986; Ellison and Farnsworth 1996; Pearce 1999; Thia-Eng et al. 2000). In rural locations, particularly the poorer households protect their incomes through a diversification of their occupational options. Taking advantage of their greater proximity to the surrounding natural resources, this group tends to use ecological resources and temporary/seasonal opportunities provided by the natural environment. This generates a higher number of occupations per household and greater seasonal differences in occupation and income source, and this leads to a greater dependency on the well-being of the mangrove ecosystem. In places with unfavorable local environmental conditions, such as at the fishing village of Ajuruteua, an almost entire dependence on the seasonal income fluxes by fish landings due to limited possible alternatives can be observed; these are described in more detail in Krause and Glaser 2003 and in Chap. 21. The populations of such villages are exposed to socio-economic risks to a greater extent than rural villages closer to Braganc¸a. The entire Braganc¸a coastal region is experiencing a substantial population growth. Because of the lack of alternative livelihoods, increasing pressure on the natural resources of the mangrove system is to be expected, especially through further intensification of the fishery efforts (Glaser and Diele 2004). Further destruction of the mangroves is expected to occur through uncontrolled settlements and the growing tourist recreation areas on the beaches. The main mechanisms, which control the allocation of the mangrove resources within this region, are decisions taken by outside entrepreneurs and local individuals
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with lack of knowledge of the local environmental conditions. Particularly, the identification of the latter is crucial for the development of sustainable management concepts for the Braganc¸a coastal region. Such management recommendations should start with the dissemination of knowledge about the important role which stakeholders play in their mangrove-dominated environment, followed by a promotion of community-based co-management schemes for specific mangrove resources, e.g., mangrove crabs. The generation of alternative livelihood options and improved vocational schools should be further central issues on the political agenda.
References Arau´jo AR (2006) Fishery statistics and commercialization of the mangrove crab, Ucides cordatus (L.), in Braganc¸a – Para´ – Brazil. PhD thesis, University of Bremen, Bremen Barletta M, Barletta-Bergan A, Saint-Paul U (1998) Description of the fisheries structure in the mangrove-dominated region of Braganc¸a (State of Para´ – North Brazil). Ecotropica 4:41–54 Behling H, Cohen MCL, Lara RJ (2001) Studies on Holocene mangrove ecosystem dynamics of the Braganc¸a peninsula in north-eastern Para´, Brazil. Palaeogeogr Paleoclimat Palaeoecol 167:225–242 Berger U, Glaser M, Koch B, Krause G, Lara R, Saint-Paul U, Schories D, Wolff M (1999) MADAM – the approach of an integrated project on mangrove dynamics and management. J Coastal Conserv 5:125–134 Berger U, Adams M, Grimm V, Hildenbrandt H (2006) Modelling secondary succession of neotropical mangroves: causes and consequences of growth reduction in pioneer species. Perspect Plant Ecol Evol Syst 7:243–252 Bradford B, Oliver C (1994) Wild Rubber: Industrial organisation and the microeconomics of extraction during the Amazon Rubber Boom (1860-1920). J Latin Am Stud 26:37–72 Bunt JS, Stieglitz T (1999) Indicators of mangrove zonality: the Normanby river, N.E. Australia. Mangr Salt Marshes 3:177–184 Cohen M, Souza Filho PWM, Lara R, Behling H, Angulo RJ (2004) A model of Holocene mangrove development and relative sea-level changes on the Braganc¸a Peninsula (northern Brazil). Wetlands Ecol Manag 13:433–443 Cohen MCL, Behling H, Lara RJ (2005) Amazonian mangrove dynamics during the last millennium: the relative sea-level and the Little Ice Age. Rev Paleobot Palynol 136:93–108 Dahdouh-Guebas F, Mathenge C, Kairo JG, Koedam N (2000) Utilization of mangrove wood products around Mida Creek (Kenya) amongst subsistence and commercial users. Econ Bot 54:513–527 Darwin C (1842) The structure and distribution of coral reefs. University of California Press, Tuscon (reprint) de Barros HM, Eskinazi-Lec¸a E, Paranagua´ MN (2000) The disappearing fish: an understanding of sustainability among estuarine communities of Braganc¸a, Pa. Aquat Ecosyst Health Manag 3:553–560 Dickenson JP (1982) Brazil. Longman, London Diele K (2000) Life history and population structure of the exploited mangrove crab Ucides cordatus cordatus (L.) (Decapoda: Brachyura) in the Caete´ estuary, North Brazil. PhD thesis, University of Bremen, Bremen. ZMT Contribution, vol 9 Diele K, Koch V, Saint-Paul U (2005) Population structure and catch composition of the exploited mangrove crab Ucides cordatus in the Caete´ estuary, North Brazil: indications for overfishing? Aquat Living Resour 18:169–178
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Dittmar T, Hertkorn N, Lara RJ, Kattner G (2005) Mangroves, a major source of dissolved organic carbon to the oceans. Global Biogeochem Cycles 20:GB1012 Duke NC, Meynecke JO, Dittmann S, Ellison AM, Anger K, Berger U, Cannicci S, Diele K, Ewel KC, Field CD, Koedam N, Lee SY, Marchand C, Nordhaus I, Dahdouh-Guebas F (2007) A world without mangroves? Science 317:41–42 Ellison AM, Farnsworth EJ (1996) Anthropogenic disturbance of Caribbean mangrove ecosystems: past impacts, present trends, and future predictions. Biotropica 28:549–565 Eusebio MA, Tesoro FO, Cabahug DM (1986) Environmental impact of timber harvesting on mangrove ecosystems in the Philippines. Mangroves of Asia and the Pacific: Status and Management. Natural Resources Management Center, Ministry of Natural Resources, Quezon City, Philippines, pp 337–354 Furtado LG (1990) Caracterı´sticas Gerais e Problemas da Pesca Amazoˆnica no Para´. Bol Mus Para Emı´lio Goeldi Se´r Antropol 6:41–93 Glaser M (1999) Social sustainability in the management of mangrove crabs (Ucides cordatus) in coastal Para´, North Brazil. Proceedings of the annual development studies conference. Institute for International Policy Analysis, University of Bath, Bath Glaser M (2003) Interrelations between mangrove ecosystems, local economy and social sustainability in Caete´ Estuary, North Brazil. Wetlands Ecol Manag 11:265–272 Glaser M, da Silva OR (2004) Prospects for the co-management of mangrove ecosystems on the North Brazilian coast. Whose rights, whose duties and whose priorities? Nat Resour Forum 28:224–233 Glaser M, Diele K (2004) Asymmetric outcomes: assessing the biological, economic and social sustainability of a mangrove crab fishery, Ucides cordatus (Ocypodidae), in North Brazil. Ecol Econ 49:361–373 Glaser M, Grasso M (1998) Fisheries of a mangrove estuary: dynamics and inter-relationships between economy and ecosystem in Caete´ Bay, northeastern Para´, Brazil. Bol Mus Para Emı´lio Goeldi, Se´r Zool 14:95–125 Glaser M, Furtado LG, Nascimento I, Santana G (1997) Economy, ecosystem and society: Mangroves and people in the Caete´ bay, North Brazil. Annual Conference Development Studies Association (DAS), University of East Anglia, Norwich Glaser M, Berger U, Macedo R (2003) Local vulnerability as an advantage: mangrove forest management in Para´ state, north Brazil, under conditions of illegality. Reg Environ Change 3:162–172 Goch YG, Krumme U, Saint-Paul U, Zuanon JAS (2005) Seasonal and diurnal changes in the fish fauna composition of a mangrove lake in the Caete´ estuary, north Brazil. Amazoniana 18:299–315 Grabert H (1991) Der Amazonas – Geschichte und Probleme eines Stromgebietes zwischen Pazifik und Atlantik. Springer, Berlin Grasso M (2000) Understanding, modeling and valuing the linkages between local communities and the mangroves of the Caete´ river bay (Pa-Brazil). PhD thesis, University of Maryland, College Park Henkel K (1987) Agrarr€aumliche Entwicklungen im o¨stlichen Para´ (Amazonien), unter besonderer Ber€ucksichtigung kleinb€auerlicher Landwirtschaft. T€ ubinger Geogr Stud 93:255–273 Henshall J, Momsen RP (1974) A geography of Brazilian development. Bell, London IBAMA (2004) Estatı´stica da Pesca 2003. Ministe´rio do Meio Ambiente, Instituto Brasileiro do Meio Ambiente e dos Recursos Naturais Renova´veis, Diretoria de Fauna e Recursos Pesqueiros, Centro de Pesquisa e Gesta˜o de Recursos Pesqueiros do Litoral Nordeste – CEPENE, Brası´lia IBGE (Instituto Brasileiro de Geografia e Estatı´stica) (2000) Sinopse Preliminar do Censo Demogra´fico. Brası´lia, CD-Rom IDESP (1989) A pesca no Para´: a so´cio-economia da fauna acompanhante do camara˜o na costa norte do Brasil e a comercializac¸a˜o da pesca artesanal em Bele´m, Vigia e Braganc¸a. SECIRM (report) Relato´rio de Pesquisa, pp. 16
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Isaac VJ, Ferreira WB (1998) Peixes do estua´rio do rio Caete´, Braganc¸a, PA. Para´ Pesca 3:12–13 Isaac VJ, do Espirito Santo RV, Da Silva B, Castro E, Sena AL (2006) Diagnostico da pesca no litoral do estado de Para. In: Isaac VJ, Martins AS, Haimovici M, Andriguetto JM (eds) A pesca marinha e estuarine do Brasil no inı´cio do se´culo XXI: Recursos, tecnologias, aspectos, so-cioeconoˆmicis e institucionais. Editora Federal Univ Para´, Bele´m, pp 1–40 Kjerfve B, Lacerda LD (1990) Mangroves of Brazil. In: Lacerda LD (ed) Conservation and sustainable utilization of mangrove forests in Latin America and Africa regions. Part I – Latin America. ITTO/ISMA Project PD 114/90: 245-271 Kjerfve B, Lacerda LD, Diop S (1997) Mangrove ecosystem studies in Latin America and Africa. UNESCO, Paris Klose F (2004) R€aumliche und sozioo¨konomische Dynamik in der Landwirtschaft am Beispiel von Tamatateua, Para´. University of Bonn, Bonn, Brasilien Klose F, Krause G, Glaser M, da Silva Oliveira R, Bock M, Hanatschek R (2005) Manguezais como uma zona economica de tampa˜o: dinamica especial e socioeconomica num estuario no Norte brasileiro. In: Glaser M, Cabral N, Lobato Ribeiro A (eds) Gente, ambiente e pesquisa: manejo transdisciplinar no manguezal. UFPA/NUMA, Bele´m, pp 87–103 Kohlhepp G (1987) Wirtschafts- und sozialr€aumliche Auswirkungen der Weltmarktintegration Ost-Amazoniens. Zur Bewertung der regionalen Entwicklungsplanung im Grande Caraja´sProgramm in Para´ und Maranha˜o. In: Kohlhepp G (ed) Brasilien. Beitr€age zur regionalen Struktur- und Entwicklungsforschung, Vol 93. T€ ubinger Geographische Studien, pp 213–254. T€ubinger Beitr€age zur Geographischen Lateinamerika-Forschung 1 Krause G (2002) Coastal morphology, mangrove Ecosystem and Society in Northern Brazil: elements determining option and resilience. PhD thesis, University of Stockholm, Stockholm Krause G, Glaser M (2003) Co-evolving geomorphological and socio-economic dynamics in a coastal fishing village of the Braganc¸a region (Para´, North Brazil). Ocean Coast Manag 46:859–874 Krause G, Soares C (2004) Analysis of beach morphodynamics on the Bragantinian mangrove peninsula (Para´, Northern Brazil) as prerequisite for coastal zone management recommendations. Geomorphology 60:225–239 Krause G, Schories D, Glaser M, Diele K (2001) Spatial patterns of mangrove ecosystems: the Bragantinian mangroves of North Brazil (Braganc¸a, Para´). Ecotropica 7:93–107 Krause G, Bock M, Weiers S, Braun G (2004) Mapping land-cover and mangrove structures with remote sensing techniques – a contribution to a synoptic GIS in support of coastal management in north Brazil. Environ Manag 34:429–440 Krumme U (2004) Patterns in the tidal migration of fish in a north Brazilian mangrove channel as revealed by a split-beam echosounder. Fish Res 70:1–15 Medina E, Giarrizzo T, Menezes MPM (2001) Mangal comunities of the “Salgado Paraense”: ecological heterogeneity along the Braganc¸a peninsula assessed through soil and leave analysis. Amazoniana 16:397–416 Mehlig U (2001) Aspects of tree primary production in an equatorial mangrove forest in Brazil. PhD thesis, University of Bremen, Bremen. ZMT Contribution, vol 14 Menezes MPM, Berger U, Worbes M (2003) Annual growth rings and long-term growth patterns of mangrove trees from the Braganc¸a peninsula, north Brazil. Wetlands Ecol Manag 11:233–242 Pearce F (1999) An unnatural disaster – Clearing India’s mangrove forests has left the coast defenceless. New Scientist 164:1–12 Pernetta J (1993) Mangrove forests, climate change and sea level rise – Hydrological influences on community structure and survival, with examples from the Indo-West Pacific. IUCN, Cambridge/Gland Reise A (2003) Estimates of biomass and productivity in fringe mangroves of North-Brazil. PhD thesis, University of Bremen, Bremen. ZMT Contribution, vol 16 Ro¨nnb€ack P (1999) The ecological basis for economic value of seafood production supported by mangrove ecosystems. Ecol Econ 29:235–252
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Ro¨nnb€ack P (2001) Mangroves and seafood production: The ecological economics of sustainability. PhD thesis, University of Stockholm, Stockholm Schaeffer Novelli Y, Cintron Molero G, Rothleder AR, Camargo TM (1990) Variability of mangrove ecosystems along the Brazilian coast. Estuaries 13:204–218 Schories D, Barletta Bergan A, Barletta M, Krumme U, Mehlig U, Rademaker V (2003) The keystone role of leaf-removing crabs in a mangrove forests of North Brazil. Wetlands Ecol Manag 11:243–255 Schultz J (2000) Konzept einer o¨kozonalen Gliederung der Erde. Geogr Rdsch 52:4–11 ¨ stuars an der Nordk€ Schwarz H (2005) Klassifikation von Mangroven des Caete´-A uste Brasiliens im Staat Para´ mit Hilfe eines objektorientierten Verfahrens auf der Basis von IKONOS-Daten. Dipl thesis, University of Trier, Trier Souza Filho PWM (1995) Planı´cie costeira Bragantina (NE do Para´): Influeˆncia das variac¸o˜es do nı´vel do mar na morfoestratigrafia costeira durante o Holoceno. MSc thesis, University of Para´, Bele´m Souza Filho PWM, El-Robrini M (1997) A influeˆncia da variac¸a˜o do nivel do mar na sedimentac¸a˜o da Planı´cie Costeira Bragantina durante o Holoceno. In: Costa M, Ange´lica R (eds) Contribuic¸o˜es a` Geologia da Amazoˆnia. FINEP, Bele´m, pp 307–358 Souza Filho PWM, Paradella WR (2002) Recognition of the main geobotanical features along the Braganc¸a mangrove coast (Brazilian Amazon Region) from Landsat TM and RADAESAT-1 data. Wetlands Ecol Manag 10:121–130 Souza Filho PWM, Cohen MCL, Lara RJ, Lessa GC, Koch B, Behling H (2006) Late Quaternary coastal evolution and facies model of the Braganc¸a macrotidal flat on the Amazon Mangrove coast, Northern Brazil. J Coast Res 39:306–310 Spalding MD, Blasco F, Field CD (1997) World mangrove atlas. ISME, Okinawa Szlafzstein C (2003) Vulnerability and response measures to natural hazard and sea level rise impacts: long-term coastal zone management, NE of the state of Para´, Brazil. PhD thesis, University of Bremen, Bremen. ZMT Contribution, vol 17 Thia-Eng C, Gorre I, Ross A, Bernad SR, Gervacio B, Ebarvia MC (2000) The Malacca straits. Mar Pollut Bull 41:160–178 Thom BG (1984) Coastal landforms and geomorphic processes. In: Snedacker S, Snedacker J (eds) The mangrove ecosystem: research methods. UNESCO, Paris, pp 3–17 Twilley RR (1995) Properties of mangrove ecosystems related to the energy signature of coastal environments. In: May CAS (ed) Maximum Power. University Press of Colorado, Niwot, CO, pp 43–62 Ver-o-Para´ (1998) Braganc¸a – 200 anos de Marujada (11). Bele´mt, pp. 58
Chapter 4
Palaeoenvironmental Reconstruction H. Behling, M. Cohen, R.J. Lara, and V. Vedel
4.1
Coastal Region of Northern Brazil
The structure of coastal habitats is strongly influenced by inundation frequency and topographic characteristics, which determine the configuration and dynamic of coastal vegetation including mangrove ecosystems in the tropics. Therefore, mangrove ecosystems and other wetlands are highly susceptible to relative sea-level (RSL) fluctuations (Gornitz 1991). The sediments deposited beneath mangrove vegetation provide useful indications of past sea-levels (Scholl 1964; Woodroffe 1981; van de Plassche 1986), since the development of mangroves is controlled by land–ocean interaction (Woodroffe 1982). One of the most significant agents of environmental transformation following climatic change is the RSL change. Several studies, developed along the eastern and southern Brazilian coast, have suggested RSL changes during the Holocene (Suguio et al. 1985; Martin et al. 1988; Tomazelli 1990; Angulo et al. 1999). In order to understand past environmental changes in Amazonia, such as the natural amplitude of Amazonian ecosystem dynamics, including coastal ecosystems such as mangroves, as well as Amazonian climate changes, palaeoecological and palaeoenvironmental studies are important. Several lacustrine and mangrove sediment deposits have been studied by pollen analysis. The aim of this paper is to compare and summarize recent published pollen records and to give an overview of natural environmental changes in the coastal Amazon Basin region, related to the impact of the Holocene sea-level changes. The study area is the Amazon coastal region which includes areas of mangrove, salt marshes, restinga (coastal herb and shrub vegetation), and coastal savanna vegetation (e.g., Bastos 1988; Santos and Rosa´rio 1988). The atmospheric circulation of the Amazon region is controlled by the position of the Intertropical Convergence Zone (ITCZ), shifting from 7 to 9N in July to from 10 to 20 S in January. Consequently, two main climate types are represented in Amazonia: a climate without a dry season at equatorial latitudes, and a climate with a marked dry season north and south of the equatorial latitudes. South America north of the equator is
U. Saint-Paul and H. Schneider (eds.), Mangrove Dynamics and Management in North Brazil, Ecological Studies 211, DOI 10.1007/978-3-642-13457-9_4, # Springer-Verlag Berlin Heidelberg 2010
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influenced by the northeasterly trade winds blowing from the Caribbean, whereas the region south of the equator is influenced by the Atlantic southeasterlies, which originate from the subtropical high pressure cell over the south Atlantic Ocean. The Amazon coastal region receives between 2,000 and more than 3,250 mm precipitation per year. The climate station of Bele´m documents a mean annual precipitation of 2,277 mm (Walter and Lieth 1967). The average annual temperature is 25.9 C. Measured maximum and minimum temperatures are 31.7 and 18.0 C, respectively. Several sites have been studied in the coastal region of Amazonia (Fig. 1): Marajo´ Island (Behling et al. 2004), Lagoa da Curuc¸a (Behling 1996, 2001), Lago Crispim (Behling and Costa 2001), Taperebal (Vedel et al. 2006), three records from the Braganc¸a Peninsula (Behling et al. 2001a), and Lago Aquiri (Behling and Costa 2001). Marajo´ Island is located in the Amazon delta in Para´ State, northern Brazil (Fig. 1). The coring sites Barra Velha (0 430 10.500 S, 48 290 32.400 W) and Praia do Pesqueiro (0 390 34.000 S, 48 290 00.300 W) are located in the coastal mangrove area of the eastern part of Marajo´ Island, next to Baia de Marajo´. The distance between the two sites is about 10 km. The distance to the modern coastline from the Barra Velha site is 200 m, and from Praia do Pesqueiro, 100 m. Lagoa da Curuc¸a (0 460 S, 47 510 W) is found in the coastal region of northeastern Pa´ra State, about 100 km northeast of the city of Bele´m in northern Brazil (Fig.3.1). The lake is circular shaped, covers an area of ca. 15 ha, and is mostly about 2 m deep. Lagoa da Curuc¸a is isolated from rivers and lies in a relatively plain landscape at 35 m elevation, covered with mostly secondary Amazon rainforest vegetation. The lake is about 15 km from the Atlantic Ocean, but mangrove vegetation grows along small rivers within about 1.5 km of the lake. Lago Crispim (0 460 S, 47 510 W) also lies in the coastal region of northeastern Para´, about 130 km northeast of Bele´m (Fig. 1). The lake is located near the village Crispim, at the west side of the Baia´ do Maruda, which is formed by the Rio Marapanim. The isolated lake is 1–2 m above sea-level and only 500 m from the modern shore of the bay. The more or less circular lake has a diameter of about
Fig. 1 The Amazon coastal region with the location of the sites on Marajo´ Island: (1) Barra Velha and (2) Praia do Pesqueiro, and then (3) Lagoa da Curuca, (4) Lago Crispim, and (5) Taperebal, three records from (6) the Braganc¸a Peninsula, and (7) Lago Aquirı´
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100 m and a water depth of about 1 m. The lake seems to be part of a former interdune valley or channel in a relatively flat coastal area. Modern vegetation near the lake includes coastal vegetation (mangrove, restinga) and, further inland, strongly disturbed Amazon rainforest and edaphic white sand vegetation. Taperebal (00 580 1800 S, 46 470 2400 W) is near Braganc¸a City, about 220 km east of Bele´m. The coring site is situated in a low-level area about 2–3 m above the modern RSL. The site is about 200 m from the higher-level upland of 1–3 m, which is not inundated by tides. The distance from the modern shoreline is about 12–15 km. The tidal range is about 4 m. Mangrove, dominated by Rhizophora and some Avicennia, characterizes the study area. Braganc¸a Peninsula is located between the mouth of the rivers Maiau´ and Caete´ in the coastal region of northeastern Para´. The area is near Braganc¸a City, lying 200 km east of Bele´m. The 30-km-long and up to 15-km-wide peninsula is mostly covered by mangroves. Pollen records are available from three different areas. The first site, “Bosque de Avicennia” (00 550 6500 S, 46 400 0900 W, 2.4 m a.s.l), is located on the relatively high central southern part of the peninsula. Only Avicennia trees form the mangrove forest. The second site, “Campo Salgado” (00 540 4600 S, 46 400 6300 W, 2.7 m a.s.l), is in Cyperaceae-dominated open salt marsh of the central part of the peninsula. The third site, “Furo do Chato” (00 520 2500 S, 46 390 00W, 1.9 m a.s.l), is in the northern part of the study area at a lower elevation than the two other sites. Here, Rhizophora trees dominate the mangrove, but Avicennia trees occur close to the site. Lago do Aquiri (3 100 S. 44 590 W, 10 m a.s.l.) is located 3 km north from the village Viana, about 120 km southwest of Sa˜o Luis, capital of Maranha˜o State, and 450 km southeast of Bele´m (Fig. 1). The lake lies in a soft rolling landscape with elevated areas between 20 and 40 m a.s.l. and flood plain areas between 3 and 10 m a.s.l.. To the west, the study area is influenced by the river systems of the Rio Mearim. The shortest distance between Lago do Aquiri and Rio Mearim is 20 km, but sometimes a connection forms during the rainy season, when huge areas of the western study area are flooded. During the wet season, the fresh water lake is about 11 km long by 1–3 km wide, while the water depth is 3 m. During the dry season, the lake contracts to a small basin 1–2 km in diameter. The present-day vegetation to the west of the lake is anthropogenic palm forest/savanna. The eastern part is covered with periodically inundated swamp savanna. Only small remnants of rainforest, probably now secondary forest, exist. Mangroves were not observed in the Lago do Aquiri region.
4.2
Holocene Environmental Changes
Mangrove development and dynamics which reflect sea-level fluctuations are evident in pollen records from the coastal region of northern Brazil. The establishment of mangrove vegetation on the eastern side of Marajo´ Island occurred at the Barra Velha site around 2,750 14Cy BP (radiocarbon years Before Present)
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(2,880 cal BP) and at the Praia do Pesqueiro site around 650 14C years BP (670 cal BP). The location and elevation of the two sites are important for the local timing of the formation of the mangrove ecosystems. Throughout the record at both sites mangrove swamps were almost entirely formed by Rhizophora, while the contribution of Avicennia and Laguncularia was rare. The occurrence of micro-foraminifers in the deposits indicates that, at least since the establishment of mangrove swamps, the sites were continuously inundated by the Atlantic Ocean. Vegetation, mostly of mangroves, replaced the existing coastal Amazon rainforest at the study area, reflecting a late Holocene sea-level rise. Restinga shrub vegetation, which occurred during the period under study on some higher places with sandy soils, became less frequent during the late Holocene. The largest area of mangrove at both sites suggests the highest sea-level probably during the last 200–250 years. In the Lagoa da Curuc¸a sediment core, Rhizophora pollen grains were already present during the Lateglacial/Holocene transition. These pollen grains were probably transported by wind over some distance into the lake. Mangrove apparently developed along the rivers near the lake between 7,250 and 5,600 14Cy BP. The subsequent retreat of mangroves from these rivers reflects lower RSL stands between ca. 5,600 and 3,100 14Cy BP. Mangrove was replaced by successional stages of palms, first Mauritia, than Arecaceae and Mauritiella, suggesting a somewhat lower groundwater table in the Lagoa da Curuc¸a area. Mangrove expanded again along the rivers near the lake after 3,130 14Cy BP, indicating the return of relatively high RSL. Based on the Lago do Crispim record, mangroves first developed along the river close to the core site between 7,550 and 6,620 14Cy BP. There is evidence that areas originally covered by dense, tall coastal Amazon rainforest were partly replaced by mangrove and some restinga vegetation during the early Holocene. Decreasing Rhizophora pollen abundances document a retreat of mangroves, reflecting sealevel regression starting at around 7,000 14Cy BP. The marked reduction of mangroves near the lake indicates a lower RSL between around 6,620 and 3,630 14 Cy BP. During this period, a local Mauritia/Mauritiella palm swamp formed. That palm trees are sensitive to the local ground table changes is well known (Henderson 1995). Marked coastal environmental changes occurred at around 3,630 14Cy BP driven by sea-level transgression. Mangroves expanded again close to the site. The local palm swamp was replaced by a Cyperaceae swamp. Rainforest and restinga vegetation adjacent to the swamp were replaced by salt marshes as sea-level rose. The Atlantic Ocean was close to the core site, but the site, which is only 1–2 m above modern sea-level, was apparently never affected by marine incursions during the Holocene. Reduced mangrove vegetation since ca. 1,840 14Cy BP, may be due to a slightly lower RSL or to human impact. A 450-cm mangrove sediment core from Taperebal revealed that, during the early Holocene, a patchy vegetation of coastal Amazon rain forest, restinga, salt marsh and some mangrove, which was mostly Avicennia-dominated, covered the study area. The first mangrove started to develop earlier than in the other studied sites in northern Brazil. The occurrence of an early Avicennia-dominated mangrove phase at least before 6,500 14Cy BP has not been reported so far from the other sites
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in northern Brazil. The occurrence of marine micro-foraminifera in the deposits indicates that the study site was occasionally inundated by the Atlantic Ocean. During the mid-Holocene, the local vegetation was dominated by mangrove. Rhizophora trees expanded markedly and continuously, while Avicennia trees became less frequent. The area of Amazon rainforest and restinga decreased during this period. Recorded vegetation changes reflect a higher RSL since about 6,500 14 Cy BP and an increase in the RSL until around 5,950 14Cy BP. The deposition of mangrove sediments during the last decades and the pollen assemblages from them show that Rhizophora trees dominated the mangrove forests suggesting a high RSL. The Lago Aquiri record, far inland from the modern ocean, shows the formation of mangrove between 7,450 and 6,700 14Cy BP. Due to a sedimentary gap, only the last century is recorded. For this period, pollen data indicate the present-day environment, seasonally inundated swamp savanna and secondary forests on somewhat higher elevated areas. Mangroves were not found. Sea-level changes also play an important role in the development and dynamic of mangrove ecosystems on the Braganc¸a Peninsula (Fig. 1). The radiocarbon dates indicate that the development of mangroves started at the three sites at different times: Campo Salgado at around 5,120 14Cy BP, Bosque de Avicennia at 2,170 14 Cy BP and Furo do Chato at 1,440 14Cy BP. The development of mangrove during the early Holocene, as documented from the other sites, has so far not been recorded on the peninsula. The presence of mangrove at Campo Salgado, the highest elevated site on the peninsula, which is today a salt marsh, suggests relatively high sea-levels since the mid-Holocene. The highest amount of non-mangrove shrub and tree pollen in the basal samples suggests that mangroves here also replaced an earlier coastal forest ecosystem prior to 5,120 14Cy BP. Compared with other sites from northern Brazil, it is suggested that the RSL during the mid-Holocene was close to current level or slightly higher than today. The uninterrupted presence of mangrove pollen from 5,100 until 1,000 14Cy BP in the “Campo Salgado” area (Behling et al. 2001a) and the current mangrove development zone (1–2.4 m amsl) suggest that the RSL was apparently not significantly modified during this time interval, or otherwise another vegetation type would have occurred at this site (Cohen et al. 2005b). Between 5,100 and 1,000 14Cy BP, the RSL of the Braganc¸a coastline was probably never higher than 0.6 m above or lower 1 m below the present level. The current 168 km2 of mangrove area on the Braganc¸a Peninsula began to develop in the middle of the peninsula about 5,100 14Cy BP and disappeared from the plains as aggradations continued and/or a RSL fall occurred. It was replaced by herbaceous vegetation at about 400 14Cy BP, being presently dominated by Cyperaceae and Poaceae (Behling et al. 2001a; Cohen et al. 2005b) Thus, considering the last 1,000 years, two periods characterized by low inundation frequency were identified. The first event extended over a period of 380 years and took place between 1130 and 1510 AD. The second began about 1560 AD and probably finished at the end of the nineteenth century (Cohen et al. 2005a). Poor pollen preservation between 750 and 420 14Cy BP indicate that mangrove deposits were exposed and the area of the Campo Salgado site was relatively dry.
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The frequency of inundation must have been lower in response to lower sea-levels. Pollen assemblages indicate that an open Poaceae-dominated salt marsh with Avicennia shrubs developed after 420 14Cy BP. The change from a Poaceaedominated to a Cyperaceae-dominated modern salt marsh during the last 200 14 Cy BP, may be related to a lower RSL. The high Avicennia pollen concentrations in the sediments from Bosque de Avicennia during the last 180 14Cy BP also suggest a regression of sea-level. Studies by Cohen and Lara (2003), show that there has been a recent RSL rise on the Braganc¸a Peninsula during the last three decades.
4.3
Model of Braganc¸a Mangrove Development
Available pollen data from records of the Braganc¸a Peninsula allow one to establish a model of mangrove development and dynamics for this peninsula. This model includes four phases (Fig. 2) Phase 1: This stage occurred when the pre-existing valleys were flooded by a rapidly rising postglacial sea-level. The stabilization of the sea-level around 5,100 14Cy BP
Fig. 2 Model showing the mangrove development and dynamics of the Braganc¸a Peninsula
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probably resulted in the initiation of Holocene mangrove forests, as represented by the mangrove sediments at base of the “Campo Salgado” core. These sediments overlap basal sand that includes marine shell fragments. Assuming that the present Braganc¸a mangroves developed between 1 and 2.4 m amsl during the Holocene, the RSL during the mid-Holocene was most likely close to the modern level, with mangrove forests restricted to the “Campo Salgado” area, and to landward channels, which probably developed mangrove fringes on the Barreiras Group. The Amazon coastal forest was probably restricted to the highest part of the “Campo Salgado” area. Phase 2: Palynological data indicate the presence of mangroves at the “Bosque de Avicennia” site during the last 2,170 14Cy BP (Behling et al. 2001a). Since 2,170 14 Cy BP, mud sediments with mangrove pollen (unit B) have accumulated on the marine sand layer which rests 4 m below msl. Two hypotheses are proposed to interpret these findings. Firstly, the mud with mangrove pollen was deposited only in the mangrove area. This would imply that sea-level lay at least 5 m below the current msl at 2,170 14Cy BP, and that the whole sequence was deposited by vertical accretion. Alternatively, the mud with mangrove pollen was deposited mainly in the lower part of the tidal plain and in the tidal channel by lateral accretion, which would not imply a RSL rise during this phase. The second hypothesis is supported by the elevated sedimentation rates (1.16 cm/ year) found between 2,170 and 1,830 14Cy BP in the “Bosque de Avicennia” compared to “Campo Salgado” (0.011–0.1 cm/y). Therefore, probably, the mangrove vegetation at this time was topographically restricted to higher zones. Palynological data suggest the uninterrupted presence of mangroves from 5,100 until 1,000 14Cy BP in the “Campo Salgado” area (Behling et al. 2001a). Regarding the current mangrove development zone (1–2.4 m amsl), the RSL was apparently not significantly modified during this time interval, or otherwise another vegetation type would have occurred at this site. Thus, during Phase 2, it is unlikely that mangroves has occurred in the middle of “Bosque de Avicennia” areas, due to the topographical difference of approximately 6 m at 2,100 14Cy BP between the “Campo Salgado” and the “Bosque de Avicennia” area. (Note: this age is from the bottom of the Bosque de Avicennia core, see Fig. 2, Phase 2). Phase 3: From 1,800 until 420 14Cy BP, the mud progressively filled the estuaries and the mangrove forests expanded. The change in sedimentation rate in “Bosque de Avicennia” from 1.16 to 0.1 cm/y suggests a transition in mangrove sediment deposition from lateral to vertical accretion. Accordingly, between 1,800 and 1,400 14Cy BP, a low RSL was most likely a major factor in the development of mangrove forests in the “Furo do Chato” (0.1 m amsl). A relatively low sedimentation rate (0.18 cm/y) and topographic position suggest aggradation instead of lateral accretion in this area. During that time, and considering the topographic mangrove development zone and the mangrove presence in “Campo Salgado,” the RSL was probably not lower than 1 m below the current level. Phase 4: In the “Campo Salgado” site, pollen assemblages indicate that at 420 14 Cy BP a transition occurred from Avicennia-dominated mangrove forest to herbaceous vegetation mainly comprised of Poaceae. The site vegetation changed again to Cyperaceae after 200 14Cy BP (Phase 5), under continuously low
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inundation frequency. In the last 400 14Cy BP, based on the habitat salinity zone, this vegetation change suggests a gradual RSL fall or an aggradation of mangrove sediments that gradually eliminated the mangroves in this area. The 5-m-long core of the Amazon coastal forest area lies 3 m amsl (Fig. 2), and the absence of mud layers suggests an uninterrupted presence of forest vegetation during the last 5,100 14 Cy BP (Fig. 2). Therefore, the tidal floods were never high enough for mangrove development in this area.
4.4
Holocene Coastal Dynamics
During the Last Glacial Maximum (around 18,000 14Cy BP), the Atlantic sea-level was around 120 m lower than today (e.g., Shackleton and Opdyke 1973). During the Lateglacial/early Holocene sea-level rise, huge areas of the exposed coastal shelf were inundated by the Atlantic Ocean. The exposed area along the north Brazilian coast was a belt mostly about 150–200 km wide. Nothing is known about these former ecosystems, but this zone could have been partly covered by Amazon rainforest, savanna, mangrove and other coastal vegetation types. The compared and summarized pollen record from the Amazon coastal region document remarkable vegetational and environmental changes, related to the Atlantic sea-level rise during the Holocene. The coastline shifted inland during the Lateglacial/early Holocene sea-level rise. Ancient low elevated coastal ecosystems were destroyed and new ecosystems, such as mangroves, developed on intertidal, now higher elevated areas, replacing the former Amazon rainforest. The first occurrence of mangrove pollen in the sediment deposits reflects the early Holocene sea-level rise close to the modern sea-level. Mangrove developed near Lagoa da Curuc¸a between at 7,250 and 5,600 14Cy BP, at Lago do Aquiri between 7,450 and 6,700 14Cy BP and near Lago Crispim between 7,550 and 6,620 14 Cy BP. The occurrence of some Rhizophora pollen grains in the Lagoa da Curuc¸a record, already at the beginning of the Holocene (at 9,430 14Cy BP or earlier), is probably related to wind-transported pollen over somewhat longer distances. From the Taperebal record we know that, during the early development of mangroves, there may in some places have been an early Avicennia-dominated mangrove phase at least before 6,500 14Cy BP. Evidence of a mangrove environment in the Aquiri region, about 120 km inland from the modern coastline, suggests a significant early Holocene transgression near the Rio Mearim (Behling and Costa 1997). In the coastal region is found a retreat of the mangroves, reflecting a lower RSL: in Aquiri since 6,700 14Cy BP, in Lago Crispim between 6,620 and 3,630 14Cy BP and in Lagoa da Curuc¸a between about 5,600 and 3,950 14Cy BP. The interpolated age of 5,600 14Cy BP for the Lagoa Curuc¸a record could be older, due to the poor radiocarbon dating of this core. We know from the Amazon Basin that, during this mid-Holocene sea-level transgression, in lowland Amazonia shallower water levels are recorded than occur today, between 5,970 and 3,120 14Cy BP in Rio Curua´ and
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between 7,700 and 4,070 14Cy BP in Lago Calado (Behling and Costa 2000; Behling et al. 2001b). The second major period of mangrove formation at the modern coastline occurred during the late Holocene, at the Lagoa da Curuc¸a record since around 3,950 14Cy BP and at the Lago Crispim record since 3,620 14Cy BP reflecting the highest Holocene sea-level stands. The formation of the sedimentary deposits from the Braganc¸a mangroves can be described by a combination of models which include both lateral accretion and aggradation following the topographic zone of mangrove development correlated to the RSL. Between 5,100 and 1,000 14Cy BP. The RSL of the Braganc¸a coastline was probably never higher than 0.6 m above or lower 1 m below the present level. The first development of mangroves on the Braganc¸a Peninsula is found in the Campo Salgado area at around 5,100 14Cy BP. It is suggested that the radiocarbon date form the Campo Salgado core base is too old in comparison with events at the Lago do Crispim and Lagoa da Curuc¸a. The beginning of the mangrove development at the Campo Salgado site is probably not older than 4,000 14Cy BP. The formation of mangroves at the Bosque de Avicennia site started at around 2,170 14Cy BP and at the Furo do Chato since around 1,440 14 Cy BP. The changes in the coastal region are also found in the Amazon Basin. In the eastern Amazon Basin, a marked increase of va´rzea/igapo´ forests is documented in the Rio Curua´ record since 3,120 14Cy BP and especially since 2,470 14Cy BP. In central Amazonia, a marked increase of seasonally inundated forest is found since 4,070 14Cy BP and especially since 2,080 14Cy BP (Behling and Costa 2000; Behling et al. 2001b). The development and the modern extension of mangrove forests in the Amazon coastal region and the large extended areas of modern seasonally inundated va´rzea/ igapo´ forests in the lower Amazon Basin are consequently relatively young in age. However, the Atlantic sea-level rise was probably the major factor in palaeoenvironmental changes, but high water stands might also be due to greater annual rainfall during the late Holocene in western, central and eastern Amazonia.
References Angulo RJ, Giannini PCF, Suguio K, Pessenda LCR (1999) Relative sea-level changes in the last 5,500 years in southern Brazil Laguna–Imbituba region, Santa Catarina State based on vermetid 14C ages. Mar Geol 159:323–339 Bastos M (1988) Levantamento florı´stico em restinga arenosa litoranea na Ilha de MaiandeuaPara`. Bol Mus Para Emı´lio Goeldi Se´r Bot 4:159–173 Behling H (1996) First report on new evidence for the occurrence of Podocarpus and possible human presence at the mouth of the Amazon during the Late-glacial. Veget Hist Archaeobot 5:241–246
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Behling H (2001) Late quaternary environmental changes in the Lagoa da Curuca region (eastern Amazonia) and evidence of Podocarpus in the Amazon lowland. Veget Hist Archaeobot 10:175–183 Behling H, da Costa ML (1997) Studies on Holocene tropical vegetation, mangrove and coast environments in the state of Maranha˜o, NE Brazil. Quat S Am Antarctic Pen 10:93–118 Behling H, Costa ML (2000) Holocene environmental changes from the Rio Curua´ record in the Caxiuana˜ region, eastern Amazon Basin. Quat Res 53:369–377 Behling H, da Costa ML (2001) Holocene vegetation and coastal environmental changes from Lago Crispim in northeastern Para´ State, northern Brazil. Rev Palaeobot Palynol 114:145–155 Behling H, Cohen MCL, Lara RJ (2001a) Studies on Holocene mangrove ecosystem dynamics of the Braganc¸a Peninsula in north-eastern Para´, Brazil. Palaeogeogr Palaeoclimatol Palaeoecol 167:225–242 Behling H, Keim G, Irion G, Junk W, Nunes de Mello J (2001b) Holocene environmental changes inferred from Lago Calado in the Central Amazon Basin (Brazil). Palaeogeogr Palaeoclimatol Palaeoecol 173:87–101 Behling H, Cohen MCL, Lara RL (2004) Late Holocene mangrove dynamics of Marajo´ Island in Amazonia, northern Brazil. Veget Hist Archaeobot 13:73–80 Cohen MCL, Lara RJ (2003) Temporal changes of mangrove vegetation boundaries in Amazoˆnia: application of GIS and remote sensing techniques. Wetl Ecol Manag 11:223–231 Cohen MCL, Behling H, Lara RJ (2005a) Amazonian mangrove dynamics during the last millennium: the relative sea-level and the Little Ice Age. Rev Palaeobot Palynol 136:93–108 Cohen MCL, Souza Filho PW, Lara RL, Behling H, Angulo R (2005b) A model of Holocene mangrove development and relative sea-level changes on the Braganc¸a Peninsula (northern Brazil). Wetl Ecol Manag 13:433–443 Gornitz V (1991) Global coastal hazards from future sea level Rise. Palaeogeogr Palaeoclimatol Palaeoecol 89:379–398 Henderson A (1995) The palms of the Amazon. Oxford University Press, New York Martin L, Suguio K, Flexor JM, Azevedo AEG (1988) Mapa geolo´gico do quaterna´rio costeiro dos estados do Parana´ e Santa Catarina. DNPM Se´r Geol 28, Sec¸a˜o Geologia Ba´sica 18, Brasilia Santos JVM, Rosa´rio CS (1988) Levantamento da vegetac¸a˜o fixadora das dunas de AlgododoalPA. Bol Mus Para Emı´lio Goeldi Se´r Bot 4:133–154 Scholl DW (1964) Recent sedimentary record in mangrove swamps and rise in sea level over the Southwestern Coast of Florida, Part 1. Mar Geol 1:344–366 Shackleton NJ, Opdyke ND (1973) Oxygen isotope and paleomagnetic stratigraphy of equatorial Pacific core V28-238: oxygen isotope temperatures and ice volumes on a 105 and 106 year scale. Quat Res 3:39–55 Suguio K, Martin L, Bittencourt ACSP, Dominguez JML, Flexor JM, Azevedo AEG (1985) Flutuac¸o˜es do Nı´vel do Mar durante o Quaterna´rio Superior ao longo do Litoral Brasileiro e suas Implicac¸o˜es na Sedimentac¸a˜o Costeira. Rev Bras Geocieˆncias 15:273–286 Tomazelli LJ (1990) Contribuic¸a˜o ao estudo dos sistemas deposicionais holoceˆnicos do Nordeste da Provı´ncia Costeira do Rio Grande do Sul, com eˆnfase no sistema eo´lico, PhD thesis, University of Rio Grande do Sul, Porto Alegre Van de Plassche O (1986) Sea level research: a manual for the collection and evaluation of data. Geobooks, Norwich Vedel V, Behling H, Cohen MCL, Lara R (2006) Holocene mangrove dynamics and sea-level changes in northern Brazil, inferences from the Taperebal core in northeastern Para´ State. Veget Hist Archaeobot 15:115–123 Walter H, Lieth H (1967) Klimadiagramm-Weltatlas. Fischer, Jena Woodroffe CD (1981) Mangrove swamp stratigraphy and Holocene transgression, Grand Cayman Island, West Indies. Mar Geol 41:271–294 Woodroffe CD (1982) Geomorphology and development of mangrove swamps, Grand Cayman Island, West Indies. Bull Mar Sci 32:381–398
Chapter 5
The Biogeochemistry of the Caete´ Mangrove-Shelf System B. P. Koch, T. Dittmar, and R. J. Lara
5.1
Introduction and Overview
Major parts of the world’s tropical coastlines are fringed by mangroves. Mangroves are highly productive ecosystems, and outwelling of litter is well documented, whereas the exchange of dissolved or suspended nutrients and organic matter (OM) with adjacent environments has received less attention in the past. Recent studies on the role of tidal forests demonstrated the important linkage and interactions between terrestrial and marine environments in the tropics. Latest estimates on global mangrove net primary production (218 Tg organic carbon year1) and annual export rates of mangrove-derived organic material to the ocean (46 Tg total organic carbon year1) demonstrate the large influence of mangroves on coastal and marine nutrient cycles (Bouillon et al. 2008). The quantification and characterization of nutrient and OM exchange between mangrove and adjacent ecosystems are described in this chapter. The published results of these biogeochemical studies have mainly resulted from the project MADAM. A central study was the interdisciplinary monitoring of a tidal creek throughout 36 tidal cycles in the course of one year. Fluxes of dissolved organic matter (DOM) were determined by measuring dissolved organic carbon (DOC) and dissolved organic nitrogen (DON). Their particulate counterparts (POC, PON) and inorganic nutrients (N, P, Si compounds) were monitored in a tidal creek that connects a clearly defined area of mangroves with the estuary. The driving forces behind these material fluxes were analyzed. Additionally, the material exchange between mangrove and estuary was estimated on the more extended spatial scale of the whole estuarine mangrove fringe. Aimed at identifying the source and bioavailability of DOM and particulate organic matter (POM) in this coastal environments, lipid biomarkers, lignin-derived phenols and stable carbon isotopes were used as tracers for mangrove-derived OM and its diagenetic state (Dittmar et al. 2001; Koch et al. 2003; Dittmar et al. 2006). The application of ultrahigh resolution mass spectrometry yielded new insights into the molecular composition and diagenetic alteration of mangrove-derived DOM (Koch et al. 2005b).
U. Saint-Paul and H. Schneider (eds.), Mangrove Dynamics and Management in North Brazil, Ecological Studies 211, DOI 10.1007/978-3-642-13457-9_5, # Springer-Verlag Berlin Heidelberg 2010
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The principal pathway for nutrient and OM transport from the mangrove to the estuary was porewater flow from the upper sediment horizon to the tidal creek and subsequently to the estuary. The porewater flow was driven by tidal forces. Nutrient- and organic matter-rich porewater, incorporated into the creek mainly during low tide, flowed back to the mangrove forest during flood and was not transported to the estuary until the following ebb. During these transport processes, aquatic phototrophic organisms and photochemical processes altered the organic matter in the water body and led to considerably decreased ammonium and slightly increased DOC concentrations during daytime.
5.2 5.2.1
Sediment Processes Fate and Decomposition of Leaf Litter in Mangrove Sediments
Despite the frequent flooding and draining of the mangroves on the Braganc¸a peninsula, a significant fraction of litter fall remained in the forest and was not flushed into tidal creeks. The herbivorous crab Ucides cordatus played a major role in the retention of litter in the mangrove system (Schories et al. 2003; Chap. 16). The combined export of floating debris, suspended and dissolved matter accounted for approximately half of the total litter fall (Dittmar and Lara 2001b; Schories et al. 2003). The driving forces behind the export of organic matter and its fate in the coastal ocean are illustrated in the following sections. First we discuss the fate and dynamics of litter fall that remains in the mangrove system. Sedimentary organic matter at Furo do Meio was depleted in carbon compared to fresh litter fall as shown by the low molar carbon to nitrogen ratio (C/N) of 18 compared to 50–70 for leaf litter (Dittmar and Lara 2001b; Mehlig 2001; Koch 2002) and C/N of around 100 for mangrove bark, roots and pneumatophores (Koch 2002). This rapid initial release of carbon and selective enrichment of nitrogen during early degradation of leaf litter can be attributed to leaching or respiration. With increasing sediment depth, the C/N-ratio remained almost stable indicating that the organic matter degradation in the sub-surface sediment was characterized by reduced mineralization rates and similar reactivities for carbon and nitrogen. Assuming that the observed low C/N ratio in the sediment is exclusively obtained by depletion of carbon from leaf litter, a rapid initial loss of about 75% of carbon from the litter due to mineralization or leaching are necessary if other sources or sinks of carbon and nitrogen are not considered (Fig. 5.1). The generally low C/N ratios suggest that woody tissue which was characterized by very high C/N ratios did not substantially contribute to the sedimentary organic matter in general. However, decaying roots did cause pronounced local maxima of C/N ratios and organic carbon concentrations in the sediment (Dittmar and Lara 2001b) consistent with the low N-content in this material. Due to methodological challenges, so far only few studies
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Fig. 5.1 Typical surface sediment profile for total organic carbon content and stable organic carbon isotope ratio in the mixed mangrove forest at Furo do Meio (Dittmar and Lara 2001c)
have reported on the contribution of root biomass to the pool of organic carbon in mangrove sediments. The latest studies estimated a global average mangrove root production of about 44 mol C m2 year1 (Kristensen et al. 2008). Numerous studies have proven a rapid material loss during early diagenesis of mangrove leaf litter due to passive leaching or microbial decomposition, with halflives of decomposition in the order of weeks (e.g., Steinke and Ward 1987; Angsupanich et al. 1989; Sessegolo and Lana 1991; Wafar et al. 1997; Twilley et al. 1997; Kristensen et al. 2008). For the Furo do Meio, Schories et al. (2003) reported that, during an initial phase of mangrove leaf litter decomposition at the sediment surface and under exclusion of litter consuming crabs, the major part of the dry mass was lost within 3 weeks, reaching asymptotically about 20% of the initial value. This rapid initial decomposition was probably accelerated by the highly abundant active grazing macrofauna (Robertson et al. 1992; Schories et al. 2003). Assuming that nitrogen is preferentially retained in the sediment, the estimate of a selective carbon loss of about 75% appears realistic.
5.2.2
Long-Term Decomposition of Organic Matter in Mangrove Sediments
The age and long-term decomposition rate of sedimentary organic carbon were estimated using a simple mass balance approach. The sediment from the surface
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down to 1.5 m depth was considered for estimating decomposition rates. This sediment depth corresponded approximately to that part of the sediment that is directly affected by recent litter fall, indicated by vertical profiles of stable carbon isotope ratios (d13C; Fig. 5.1), lignin (Dittmar and Lara 2001c) and lipid biomarkers patterns (Koch et al. 2003). On average, an organic carbon content of 1.5 0.13 mmol C g1 was measured in this upper portion of the mangrove sediment with an average specific dry weight of the sediment of 2 g cm3 (Schwendenmann 1998; Koch et al. 2005a). Consequently, the sedimentary organic carbon pool in the Furo do Meio area, still affected by recent litter fall, is 4.5 kmol C m2. To calculate decomposition rates, the following assumptions were made: (1) The sedimentary OC pool is in a balanced steady state with the sum of all fluxes, sources and sinks being zero; (2) the annual litter fall (125 mmol C m2 day1; Mehlig 2001; Chap. 4) is representative on a long-term basis; (3) about 20% of the leaf litter fall is directly exported from the mangrove area (Schories et al. 2003); and (4) after a rapid initial depletion of about 75% of litter OC during early diagenesis, the loss of OC from the sediment is constant according to a first-order kinetic. Based on these assumptions, a rate constant for long-term degradation of organic carbon in the sediment, including mineralization and leaching, was estimated to be 0.21% per year (Dittmar and Lara 2001c; Fig. 5.2). The half-life of OC in the sediment would be about 330 years. This results in an average age of OC in the sediment from the surface to 1.5 m depth of 480 years. A similar approach using leaf litter biomarkers and their degradation constants in the interval from 0 to 1.5 m sediment depth resulted in an estimated average sediment age of 530 years (Koch et al. 2005a). Given that this organic carbon age is representative of a mixed pool of older and fresh material, and that several simplifications were assumed, possible uncertainties
Fig. 5.2 Decomposition of organic carbon (OC) derived by litter fall in the mangrove sediment. Half-lives (T½) for OC mineralization: OC is depleted from leaf tissue to 75% within weeks (T1½) followed by a slow mineralization in the sediment (T2½). After Dittmar and Lara (2001c)
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should be taken into consideration when interpreting these results. The comparison with data from a recent study on Holocene mangrove ecosystem dynamics at Furo do Meio (Behling et al. 2001) allows the validation of the assumptions in the diagenetic model (Chap. 3). In this study, Behling et al. (2001) carried out radiocarbon dating, pollen and stratigraphic analyses for a sediment core taken from Furo do Meio at a location with low bioturbation. Based on radiocarbon dating, the sedimentation rates were determined to be 0.1 cm year1 for the upper part (0.88–0 m) and 0.18 cm year1 for the lower part of a sediment core (1.80–0.88 m). The age of OC at each depth was extrapolated on the basis of these rates (Behling et al. 2001). Together with the corresponding OC concentrations, an average age of 680 years for organic carbon in the 1.5–0 m sediment depth interval can be determined, exceeding the value estimated by the simple balance approach of the present study by 150–200 years. This deviation could be attributed to inherent methodological uncertainties of the field studies. The assumption with the most assessable uncertainty is probably the estimate of the initial fast OC loss of 75%. Allowing a variation of this parameter from 70 to 85%, estimates for long-term OC degradation in the sediment ranged between 0.25 and 0.13% per year and the average age between 400 and 770 years. This general consistence of the different approaches, radiocarbon dating and the simple balance model for total organic carbon and lipid biomarkers, supported the reliability of the assumptions and simplifications made above.
5.2.3
The Use of Chemical Biomarkers as Source Tracers in Mangrove Sediments
5.2.3.1
Lignin
Long-term in situ decomposition rates of lignin in sulfate-reducing sediments were estimated by Dittmar and Lara (2001c). The assessed half-life of lignin derived from mangrove leaf litter is about 150 years whereas the mineralization of associated sedimentary OC is characterized by half-lives of more than 300 years. Hence, lignin is continuously depleted from sedimentary organic matter. Its use as a qualitative tracer of vascular plant organic matter in the mangrove environment is therefore confined to time periods of at most several hundred years, whereas quantitative estimates should only be carried out on shorter time scales. Although POM and DOM have a common source (mangrove leaf litter), their compositional patterns were different due to the different pathways of release, degradation and transport to the creek. An appropriate endmember determination and information about extent and type of diagenetic alterations are therefore basic requirements for the use of lignin as a tracer for vascular plant organic matter. On this basis, the lignin phenol composition of mangrove-derived DOC was differentiated from terrestrially and marine-derived OM (Dittmar et al. 2001).
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Fig. 5.3 Quantitative source estimation of dissolved organic carbon (DOC) calculated from the lignin phenol distribution in the Caete´ Estuary. Mangrove, terrestrial (river) and marine DOC sources can be distinguished between low tide (LT) and high tide (HT). The values shown are annual average values of DOC concentrations (mM) for low and high tide, split between the three sources (Dittmar and Lara 2001c)
Using a three-source mixing model based on the lignin phenol composition of the three endmembers, the contribution of each organic matter source in different parts of the estuary and at different tidal levels were quantified (Fig. 5.3).
5.2.3.2
Lipid Biomarkers
Pentacyclic triterpenols and sterols were shown to be well-suited tracers for primary sources of mangrove organic matter (Killops and Frewin 1994) and therefore suitable for chemotaxonomic fingerprinting (Koch et al. 2003). In addition to the lignin–phenol distribution which is suitable to distinguish between vegetation forms, lipid biomarkers can yield species-specific information (Fig. 5.4).
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Fig. 5.4 Chemotaxonomic markers. Pentacyclic triterpenols are suitable chemical substances to distinguish between organic matter derived by different mangrove species. After an initial rapid (weeks to months) and selective degradation (Koch et al. 2005a) of the original marker substances, a characteristic mangrove biomarker pattern is preserved in the mangrove sediments on geological time scales
Especially, germanicol and taraxerol, two pentacyclic triterpenols, were used as chemotaxonomic markers for leaves of R. mangle in northern Brazil (Koch et al. 2003) and other areas (e.g., Killops and Frewin 1994). As with most other organic tracers, lipid biomarkers are subject to selective degradation (Zonneveld et al., 2010). The triterpenoid markers in the sediment of the study area degraded two times faster than the bulk of the OC in the sediment (Koch 2002) which was comparable to the preservation potential of the lignin phenols. Batch experiments revealed that microbial degradation is highly selective (Koch et al. 2005a). The relative contribution of triterpenoids in leaves changed strongly after their deposition in the surface sediment. As for the bulk OC (Fig. 5.2) and the C/N ratios, after the initial rapid microbial decay in the first few months in the surface sediments, the marker pattern remained stable in deeper sediment layers and was applicable as a chemotaxonomical proxy in sediment cores. In conclusion, the sediment lipid marker composition was controlled by two key features: (1) leaf litter input from R. mangle contributed the largest proportion of markers, and the influence of leaf litter from A. germinans and L. racemosa is negligible in terms of the biomarker distribution in the sediment; and (2) selective microbial degradation led to a shift in the relative distribution of different triterpenol and sterol biomarkers (Fig. 5.4). Taraxerol is especially well preserved in sediments so that its application as a mangrove biomarker in combination with other triterpenoids is favorable and especially useful when macroscopic indicators like pollen grains are not preserved (Versteegh et al. 2004; Koch et al. 2005a; Scourse et al. 2005). Taking advantage of the stability of the typical biomarker pattern in the research area, the reconstruction of the mangrove paleoenvironment becomes an additional application for this proxy. The mangrove marker signatures can persist on time scales of thousands (Koch et al. 2003) or even millions of years (Koch 2002; Versteegh et al. 2004) and can be useful indicators for ancient tropical coastlines.
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5.3
5.3.1
B.P. Koch et al.
The Outwelling of Detritus and Decomposition Products into Coastal Waters Quantifying the Export of Organic Matter from the Mangrove into the Estuary
About four decades ago, Odum (1968) proposed a groundbreaking hypothesis in coastal ecology according to which the outwelling of litter from coastal wetlands is a major source of energy that supports much of the secondary production of estuaries and nearshore waters. Because of the regular tidal flooding and draining in most mangroves, the material exchange between the forests and coastal waters can be very efficient (e.g., Dittmar and Lara 2001b). Many of the most productive mangrove areas in the world lose a significant fraction of their net primary production to coastal waters (Robertson et al. 1992; Jennerjahn and Ittekkot 2002; Bouillon et al. 2008). Large differences occur between mangroves with respect to litter production and export rates, and some mangroves largely retain detritus within their sediments (Woodroffe 1992), which is then buried or mineralized. On a global average, however, numerous studies indicate that mangroves are a significant netsource of detritus to adjacent coastal water, and the global export rate of mangrove litter has been estimated to be 19 mol C m2 year1 which is approximately half the total litter production (Jennerjahn and Ittekkot 2002). The enormous flux of mangrove detritus to the coastal ocean can have recognizable effects on aquatic food webs in some areas (e.g., Odum and Heald 1975; Alongi et al. 1989; Alongi 1990), but the litter outwelling hypothesis has been challenged in other areas (Lee 1995). While there are clear patterns of high particulate detritus export in most mangrove forests, the utilization of this organic matter in marine food webs seems inconsistent. The influence of mangrove leaves on sediment processes is mostly restricted to the direct vicinity of the forests where large amounts of litter can accumulate (Jennerjahn and Ittekkot 2002). A few kilometers offshore, however, mangrove litter usually contributes an insignificant fraction to the organic matter accumulating in sediments. Two major processes can explain the lack of a significant offshore impact of litter outwelling. Firstly, the distribution of exported mangrove litter largely depends on the local geomorphology and hydrodynamics. Many mangrove forests fringe semi-enclosed bays and estuaries. Water currents within these settings can efficiently trap suspended particles (Jay and Musiak 1994) and cause enhanced sedimentation rates in direct vicinity of the mangrove environment. Lithogenic input from rivers can provide mineral ballast for the production of fast-sinking aggregates. Large-scale boundary currents can also diminish the dispersion of terrigenous suspended particles off the continental margins (Jennerjahn and Ittekkot 2002). Secondly, on the time-scale of outwelling, a significant fraction of litter is lost to the DOC pool. Within the first weeks of litter degradation in the water column or submersed sediments, >75% of organic carbon can be lost (Dittmar and
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Lara 2001c; Schories et al. 2003), most of it to the dissolved pool (Wafar et al. 1997; Benner et al. 1990). Mangrove-derived DOC is also released into the water column through the tidal pumping of DOC-rich porewaters, which can significantly add to the total organic carbon export. Quantitative estimates from mangrove forests around the world almost consistently indicate that a significant fraction of the net carbon fixation through primary production is indeed exported to coastal waters as DOC (e.g., Boto and Wellington 1988; Dittmar et al. 2006). Decomposition and leaching products of leaf litter are the likely sources of the exported mangrove DOC (Dittmar et al. 2001), but the contribution of root exudates or decomposing below-ground biomass is part of only a few studies (e.g., Kristensen et al. 2008; Tamooh et al. 2008). The total export rate of organic carbon from mangroves might significantly exceed the estimates for litter export from Jennerjahn and Ittekkot (2002) of 19 mol C m2 year1 if the export of DOC is taken into account. A Florida mangrove area (Twilley 1985) exported 3.1–3.7 mol C m2 year1, and a mangrove tidal creek in Australia (Ayukai et al. 1998) exported 1.8 mol C m2 year1. These export rates are based on small-scale studies performed within or in direct vicinity of the mangroves. Dittmar et al. (2006) performed a study on a continental-shelf scale indicating a significantly higher outwelling rate for DOC (12 mol C m2 year1) compared to previous small-scale studies in the same region in Northern Brazil (4 mol C m2 year1; Dittmar et al. 2001) or elsewhere in the world. The reason behind this discrepancy is probably the gradual release of DOC from floating and suspended detritus in the water column which adds to the total DOC fluxes and which was not accounted for in previous studies. The semi-enclosed system at Furo do Meio facilitated the study of exchange processes between mangrove and estuary. The tidal creek drains a clearly-defined area of mangroves (2.2 km2). The creek connects the mangrove with the estuary areas and consists of well-defined pathways for water and material exchange. The topography and the embankment of a road impede surface- and groundwater inflow from neighboring areas. Major flooding of the mangrove only occurs during spring tides. An annual monitoring campaign was carried out to quantify the material exchange between the mangrove and estuary. Sampling was performed between spring and neap tides (every 3 weeks; July 1996 to August 1997) over 1 year (total of 36 tidal cycles). Each campaign consisted of 24-h sampling in the creek. From the well-developed mangrove forest, approx. 13 mol C m2 year1 of floating debris were exported through tidal creeks over the course of an annual sampling campaign (Schories et al. 2003). In addition to floating debris, suspended solids were exported at a rate of 3 mol POC m2 year1 (Dittmar and Lara 2001a; Dittmar and Lara 2001b). Stable carbon isotope and lignin analyses indicated leaf litter as the primary source of the exported POC (Dittmar et al. 2001). The combined export of debris and POC accounted for approx. 40% of the total litter fall in this mangrove forest. Mangrove-derived DOC was exported at a rate of 4 mol C m2 year1 (Dittmar and Lara 2001a). The combined export rate for all organic matter fractions (debris, POC, and DOC) was 20 mol C m2 year1. A major fraction (12 mol C m2 year1) of this organic matter was ultimately
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transported across the shelf in the form of DOC, probably after extensive photochemical and microbial reworking (Dittmar et al. 2006). The release of DOC from mangrove compartments causes pronounced tidal signatures. For example, DOC concentrations in a tidal creek in northern Brazil that drained a well-developed mangrove area showed a pronounced tidal pattern (Dittmar and Lara 2001b). During ebb, DOC-rich porewater seeped out of the mangrove sediments and the concentrations sharply increased. The molecular lignin signature of this DOM showed that degradation products of mangrove detritus (mainly R. mangle and A. germinans litter) are the main source of DOC (Dittmar et al. 2001).
5.3.2
Driving Forces Behind Nutrient and Organic Matter Dynamics in Mangrove Creeks
Because of the well-defined flow pattern in the tidal creek Furo do Meio, the driving forces behind outwelling could be studied in a simplified way. In summary, important variables that predominantly control the magnitude of organic matter outwelling and the partition between debris, POC and DOC outwelling are net primary production, the abundance of litter-collecting fauna, microbial decay and tidal range. In the mangrove forest of Braganc¸a, the leaf-removing crab Ucides cordatus played a key role in leaf-litter turnover, significantly impacting its export and decomposition (Schories et al. 2003, Chap. 16). Microbial activity was not examined in the sediments of the study area but it has been previously demonstrated that bacterial abundance can be 1011 cells per gram dry surface sediment in tropical Australia, with an estimated production of 49 mol C m2 year1 (1.6 g C m2 day1, Gillan and Hogg 1984; Alongi 1988). The main vehicle for DOC and nutrient outwelling was tidally induced porewater flow from the upper sediment horizon (Dittmar and Lara 2001b) which is largely controlled by the tidal range. In the following section, we discuss the main driving forces of organic matter export in more detail.
5.3.3
Water Storage in the Mangrove Sediment and Effect on Creek Water Chemistry
The semi-enclosed catchment area at Furo do Meio implied that exclusively local processes within this sector could cause the strong increases of nutrient and DOC concentrations during low tide. Creek- and rainwater were the only water sources of this mangrove swamp. The characteristic tidal signature of all parameters could therefore not be attributed to simple mixing processes of different water bodies. After inundation or rainfall, water could, however, be stored in the mangrove
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sediment and released again during ebb. During storage, its composition was highly influenced by biogeochemical processes in the sediment. Based on the time series of physicochemical parameters and nutrient concentrations, the water reservoirs in the mangrove sediment were characterized and the driving forces behind nutrient-rich porewater outflow were identified (Lara and Dittmar 1999; Dittmar and Lara 2001b). After rainfall, the salinity decrease during ebb was even higher than during rainfall itself, even when rainfall occurred at low tide. This indicated that most rain was stored within the mangrove forest and was then successively released. Within days, this reservoir ran dry, as evident from a gradual decrease of the rainwater effect during the following ebbs. Several days after a rainfall event, salinity no longer exhibited any tidal pattern. Superimposed on the declining trend at ebb during the rainy season, a second small salinity increase generally occurred shortly before low tide. This was observed at both neap and spring tides and indicated the existence of a second type of sediment water, characterized by low mobility and higher salinity. At the beginning of ebb, when the hydrostatic gradient between creek water level and sediment water table was still low, highly mobile, lowsalinity water flowed into the tidal creek. Only at the end of ebb (high hydrostatic gradient), was there an input of the less mobile water. The salinity decrease, occurring generally at the onset of flood, was caused by water flowing back from the lower part of the creek, where it is wider and deeper and thus proportionally less influenced by high-salinity sediment water. Unlike the highly mobile water, lowmobility water did not show a rapid response on rainwater input, exhibiting a higher salinity during the rainy season and therefore reflecting an average concentration of the whole porewater reservoir over a period of several weeks. Ammonium increased mainly during low-mobility water input (shortly before low tide), whereas silicate, phosphate, DOC and, mostly, also nitrate increased simultaneously to porewater input in general. This indicated different compositional patterns of the two types of sediment water. During the dry season, evapotranspiration in the mangrove led to elevated salinities in the upper porewater horizon (Schwendenmann 1998). Accordingly, salinity increased during ebb in the tidal creek. During this period of the year, the sediment water reservoir was replenished only fortnightly with creek water during inundation at spring tide. The salinity increase at ebb was observed consistently at every tidal cycle. It can therefore be assumed that the sediment water reservoir did not run dry in the course of about 2 weeks. Small salinity increases, which occurred consistently during the dry season at spring tide inundation, were caused by the washout of high-salinity layers formed on surface sediments by evapotranspiration. No increase of nutrient concentration in the creek was associated with this dissolution process. Actual evapotranspiration, on the other hand, had no direct effect on creek water composition, since salinity exhibited no day/night differences. The hydrostatic gradient between creek water and sediment water led to an outflow of nutrient- and organic matter-rich water into the creek and to characteristic tidal signatures of nutrient and DOC concentrations. Thus, the longer the water level in the creek was below the sediment water table, the larger should be the nutrient input and the concentration increase during ebb. Creek water levels of
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4.5 m and 2.5 m corresponded to the water tables of two different groundwaterlayers in the sediment. The upper layer (0 – 2 m depth) is characterized by dense silt-clay sediments with a high proportion of macropores down to 1.5 m (crab holes). The deeper layer (>2 m depth) is dominated by sandy loam. The tidal impulse is transmitted into this layer, but not upward into the upper layer, which acted as an aquiclude (Schwendenmann 1998). Periods with tidal heights below 4.5 m and 2.5 m were calculated for each 24-h sampling campaign at the Furo do Meio. These times were correlated with low-tide night concentrations, in order to minimize the effects of varying dilution with estuarine water at high tide and uptake by primary producers during the day (Fig. 5.5). Phosphate and DOC concentrations presented a highly significant, positive correlation with tides higher than 4.5 m, supporting the assumption of a direct proportionality between nutrient and organic matter input and the hydraulic
Fig. 5.5 Daily cycles of inorganic and organic nutrients (Dittmar and Lara 2001b). Nutrient concentrations are controlled by the tidal water level and porewater input, and the daily lightinduced cycles of respiration and degradation. These parameters also determine pH (H3Oþ), dissolved oxygen (O2) and total suspended solids (TSS) concentration
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gradient. A positive correlation between nutrient and organic matter concentration and heights lower than 2.5 m, on the other hand, was not found, indicating that the deeper groundwater layer did not provide nutrients or organic matter to the tidal creek. The two types of sediment water whose outflow during ebb led to the increases of nutrient concentrations can therefore not be associated to spatially divided groundwater layers. The pores in the upper sediment horizon can be pooled into two clearly separated groups, namely micropores between sediment particles and macropores produced by burrowing crabs, which explains the existence of two porewater types. Interconnected crab holes serve as short-term water reservoirs, such as tree interception for rainwater. Isolated crab holes or sediment micropores, on the other hand, represent a substantial water reservoir with low flow rates. The mobile water is aerated, as evident from reddish coatings on macropores, whereas water in micropores is sulfate reducing. This may explain the higher ammonium content in the latter, as product of anaerobic ammonification (Smith et al. 1991). No correlation was found between tidal height and silicate, DIN or DON. This indicated that their concentrations in porewater changed throughout the year, unlike phosphate and DOC, or that there are other sources or sinks, such as uptake by aquatic organisms or aquatic nitrogen fixation in the creek.
5.3.4
Effect of Autotrophic Activity in the Creek
A decrease of oxygen and an increase of H3O+ concentrations was observed at night during most sampling campaigns in the tidal creek Furo do Meio (Fig. 5.5). These day–night differences reflected aquatic photosynthetic activity and associated uptake of carbonate species, which also resulted in increased POC concentrations during the day. Excluding POC peaks induced by strong rainfalls through erosion of forest sediments, POC was on average 50 20 mM higher during day than at night. Disregarding days of rainfall, total suspended solids (TSS) did not exhibit any day–night difference. Therefore, the elevated daytime POC values can be attributed to aquatic photosynthetic activity and considered as an active POC pool (35% of total POC). Photosynthesis also produced a measurable increase of DOC during the day (25 14 mM), which is an evidence for a labile DOC pool (8% of total DOC), consisting probably of phytoplankton exudates. Moran et al. (1991) estimated an algae-derived DOC proportion of 30% for a mangrove creek in the Bahamas, the remainder being refractory and derived from vascular plants. Also, in an Indian mangrove system, Balasubramanian and Venugopalan (1984) found a considerable contribution of phytoplankton-derived material to the POC and DOC pools. In contrast, Boto and Wellington (1988) concluded that DOC in an Australian mangrove creek was not linked with aquatic primary production, since there was no day–night variation in its concentration. Silicate, phosphate, nitrate and nitrite uptake by phytoplankton had no marked effect on their concentrations in the tidal creek. Phytoplankton covered their nitrogen requirements preferentially with ammonium, which invariably led to lower DIN
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concentrations during the day. In contrast, nutrient concentrations in an Australian mangrove creek did not exhibit any consistent day–night differences (Boto and Wellington 1988). The elevated daytime concentrations of PON in Furo do Meio (6 3 mM) can be only partly explained by an uptake of DIN (2.5 1.5 mM) or DON (0.3 1.4 mM) by organisms in the water body of the creek (Fig. 5.5). Atmospheric nitrogen may represent an additional source for PON formation. Blooms of blue-green algae (Cyanophyceae) were observed in the creek (Werner 1999) with >30 106 cells L1 at low tide. This represented more than half the total phytoplankton cell number. Thus, since nitrogen fixation can be light dependent (Potts 1979), the activity of blue-green algae may account for the daytime deficit of the nitrogen balance. Nitrogen fixation was identified as an important primary nitrogen source in different mangrove ecosystems by several authors (e.g., Potts 1984; Boto and Robertson 1990; Mann and Steinke 1992; Morell and Corredor 1993; Paling and McComb 1994). Based on the average day–night differences of PON, DIN and DON, the direct contribution of net N2-fixation to the creek’s nitrogen pool could be roughly estimated to be about 4 3.5 mM (15% of total PON). Average daytime DIN and DON concentrations correlated inversely (Fig. 5.5) with the corresponding oxygen values. This indicated that phytoplanktonic activity principally produced the annual oscillations of these nutrients. Uptake of DIN was already evident from day–night differences (Fig. 5.5). The release of organic nitrogenous compounds has been often reported to occur during active phytoplankton growth (e.g., Bjørnson 1998; Bronk and Glibert 1991). However, such a phenomenon was not obvious in this investigation, since DON varied only slightly between day and night. Aquatic primary production had no marked effect on silicate and phosphate, nor on either an annual or a diel basis. Unlike phosphate, the annual trend of silicate concentrations could not be associated either with tidally controlled porewater flow. The input of silicate from the estuary during flood was negligible during the whole year and did not cause variations of 24-h average values in the creek (Dittmar and Lara 2001b). The regular sinusoidal annual oscillation of silicate was neither directly related to any trends of physicochemical parameters in the sediment (Schwendenmann 1998) and water-column, as indicated by pH and salinity, nor to seasonal trends in diatom abundance (Schories, personal communication). Hence, other processes in the forest that influence porewater concentrations in the upper sediment horizon, must be responsible for annual silicate fluctuations in the creek. Litter fall, nutrient uptake by trees or activity of the burrowing benthic community can cause seasonal changes of interstitial water composition (Smith et al. 1991; Mann and Steinke 1992; Alongi 1996).
5.3.5
Requirements for Sustainable Outwelling
The mangroves at the Caete´ Estuary are characterized by well-developed forests, with maximum tree heights of >20 m, and high primary production (Mehlig 2001).
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Assuming a sustainable state of this ecosystem, the nutrient balance of the mangrove must be equilibrated in the long term. The net export of nutrients through tidal creeks must therefore be compensated by additional sources to the mangrove forest. Principal fluxes of nutrients and organic matter in the mangrove and driving forces behind their dynamics are summarized in Fig. 5.6. Morell and Corredor (1993) concluded that nitrogen fixation and tidal exports from mangroves in Hinchinbrook Island (Australia) are closely balanced. Assuming a similar equilibrium for the north Brazilian mangrove that we studied, an average rate for nitrogen fixation of 2.3 mmol N m2 day1 can be estimated (Dittmar and Lara 2001b). This is at least fivefold the rates determined in mangroves in the Philippines, Florida (USA), Australia, or Puerto Rico (Potts 1984; Boto and Robertson 1990; Morell and Corredor 1993). A positive sedimentation balance in the long term and mineralization in the mangrove sediment presumably compensate for the export of dissolved silicate and phosphate. Retention of litter in the mangrove sediment by crabs (Chap. 16) and consequently high leaching and mineralization rates within the
Fig. 5.6 Summary of the main driving forces for the biogeochemical fluxes (k; mmol m2 day1) within the Rio Caete´ mangrove system (Dittmar and Lara, 2001b)
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forest, lead to high nutrient and organic matter concentrations in porewater (Benner and Hodson 1985; Boto and Wellington 1988; Smith et al. 1991; Schwendenmann 1998). Uptake by trees and benthic micro-organisms such as sorption onto the sediment matrix can considerably reduce nutrient concentrations in porewater which can be an effective sink for nutrients (Alongi 1996). However, this is not the case for the north Brazilian mangroves (Schwendenmann 1998). At the Caete´ Estuary, the supply of inorganic nutrients evidently exceeds the demand of the benthic community and mangrove trees. This excess of inorganic nutrients in the porewater, closely related to high nitrogen fixation and mineralization rates, is a prerequisite for outwelling and may explain the comparatively high export rates from the north Brazilian mangrove swamp. The vehicle for nutrient and DOM outwelling is tidally-induced porewater flow from the upper sediment horizon into the creek and subsequently to the estuary. Phytoplanktonic activity considerably affects nutrient and organic matter concentrations in the tidal creek and can lead to flux asymmetries (Dittmar and Lara 2001b). The flux direction, however, is physically determined by the hydraulic gradient between porewater and creek water (Fig. 5.6). Advective flow of nutrient-rich sediment water toward tidal creeks leads to considerable outwelling, whereas diffusive solute exchange between sediment and water column would be less effective. The hydrostatic gradient controls advective flow. Tidal range and flooding frequency therefore determine direction and quantity of nutrient and organic matter exchange between mangroves and ocean. All mangrove flux studies already cited were carried out in micro- and mesotidal regions with the exception of Braganc¸a (Dittmar and Lara 2001b), where macrotides enable strong outwelling. It can be concluded that outwelling probably occurs only in mangrove systems with excess of inorganic nutrients in porewater, provided by high nitrogen fixation and a positive sedimentation balance, and only in macrotidal regions where porewater can flow in considerable amounts to the tidal creeks and the ocean.
5.4
The Fate of Mangrove Outwelling on the Continental Shelf and Concluding Remarks
Hitherto, lipid biomarker and pollen analyses are probably the most suitable parameters to follow the deposition of particulate mangrove-derived organic matter export on the continental shelves and to assess the contribution of mangrove organic matter on geological time scales (Behling et al. 2001; Koch 2002; Versteegh et al. 2004). Molecular tracers for mangrove organic matter and pollen in sediment cores are suitable indicators for ancient mangrove coastlines (Koch et al., 2002). However, only little is known about the fate of mangrove-derived DOC in the ocean. The bulk of the leachable fraction from R. mangle leaves can be mineralized
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rapidly and assimilated into microbial biomass with a high efficiency of 30% (Benner and Hodson 1985). A significant fraction of mangrove-derived DOC, however, is relatively resistant to degradation. Photo-degradation and bioincubations experiments (Dittmar et al. 2006) indicate that a substantial fraction (50%) of the DOC in mangrove porewater is refractory on a time-scale of weeks to years. Thus, it may be distributed over larger distances on continental shelves and beyond, depending mainly on the local hydrodynamics at the sites of export. Slow mineralization of mangrove-DOC could fuel aquatic (secondary) production far away from the mangrove areas, giving a reason to revive the original outwelling hypothesis in a modified form. On the north Brazilian shelf, mixing diagrams indicate a strong brackish water source of DOC and inorganic nutrients such as phosphate (Fig. 5.7). Stable carbon isotope analyses (d13C) confirmed mangroves, including microbial secondary products, to be the prime source of this DOC (Dittmar et al. 2006), and revealed the presence of mangrove-derived DOC on the north Brazilian shelf at distances >100 km offshore (Fig. 5.8). Mixing diagrams from a mangrove-fringed
Fig. 5.7 Increase of dissolved organic carbon (DOC) concentration and phosphate by production and degradation of mangrove-derived organic matter in the brackish zone of the Caete´ estuary and the adjacent shelf region (Dittmar et al., unpublished)
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Fig. 5.8 Long-distance export of mangrove-derived dissolved organic carbon (DOC) as determined by stable carbon isotopes taking photo-degraded and marine dissolved organic matter as endmembers for a two-source mixing model (Dittmar et al. 2006)
creek in Tanzania show a strong source of DOC at high salinity (Bouillon et al. 2007), i.e., due to highly saline porewater intrusion in the creek water column at low tide. Mangrove-derived DOC in this porewater appeared to mix conservatively with low-DOC waters suggesting a refractory nature of mangrove DOC in this system. Refractory properties are a prerequisite for further dispersion on continental shelves. Recent molecular pattern analyses via proton nuclear magnetic resonance spectroscopy (1H-NMR; Dittmar et al. 2006) and liquid chromatography/mass spectrometry (LC/MS; Dittmar et al. 2007) concordantly show significant photodegradation of the mangrove-derived DOC on the north Brazilian shelf. Since macroscopic markers are not available for research on dissolved organic substances, further molecular chemical proxies urgently need to be developed to increase our understanding of the distribution of mangrove DOM on the shelf. Hitherto, the molecular composition of DOM (and POM) is largely unknown because it consists of several thousand different compounds forming a polydispersed mixture which is irresolvable by conventional analytical techniques. The application of Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR-MS; Marshall et al. 1998) allowed extensive new insights into the molecular composition of complex DOM (Kim et al. 2003; Stenson et al. 2003; Kujawinski et al. 2004; Koch et al. 2005b; Hertkorn et al. 2006; Koch et al. 2008). Based on the ultrahigh resolution power of FT-ICR-MS, several thousand compounds can be detected in each mass spectrum. From the exact masses in the spectra, elemental formulas can be calculated (Koch et al. 2007, and references therein) yielding extensive new molecular information on the complex nature of this material (Koch et al. 2005b). The molecular composition of mangrove-derived and marine DOM exhibited a high degree of order. Typical mass spacing patterns were observed and explained by the existence of chemically-related families. The comparison between marine DOM and mangrove porewater DOM in an element ratio plot revealed characteristic molecular differences (Fig. 5.9). However, there was also a conspicuous overlap in the molecular organic signature of mangrove porewater and marine water. Further recent studies indicated that photochemical
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Fig. 5.9 FT-ICR-MS. Molecular analysis of dissolved organic matter (DOM) using ultrahighresolution mass spectrometry. The samples were extracted from mangrove porewater, photodegraded mangrove porewater and marine DOM. Every dot in the element ratio plot represents a molecular formula with the composition CxHyOz. The z-axis corresponds to the peak magnitude of the ions in the mass spectrometer. Photo-degradation of mangrove porewater led to a decrease of molecules with high O/C ratios (decarboxylation) and low H/C ratios (dearomatization). Compared to the marine signature (blue circle) some formulas of the original porewater (black circle) remained undegraded suggesting their future application as source biomarkers for mangrove-derived DOM
processes can affect the composition of DOM already in the estuary (Koch et al. 2005b; Tremblay et al. 2007). After 2 weeks of sunlight photo-incubation, the remaining elemental signature was more similar to the marine pattern and a large fraction of mangrove-derived compounds was mineralized or chemically altered (Fig. 5.9). For the remainder, it can be hypothesized that photo- (and microbial) degradation of DOM leads to molecular features which are intrinsically refractory and inaccessible or energetically unattractive for further microbial utilization. The future challenge is to identify the structural features of the exported DOM to unravel the mechanisms which result in its persistency and which determine the turnover rates of organic carbon at the mangrove–ocean interface. It can be concluded that the application of new analytical techniques improved our understanding of the sources and fluxes of organic material in the Caete´ mangrove system and supported the results achieved with conventional methods. They allowed identifying organic substances which were more persistent and which particularly contribute to the outwelling of DOC in our mangrove system. Globally, mangroves probably contribute >10% of the terrestrially-derived, refractory DOC transported to the ocean (Dittmar et al. 2006), while they cover only <0.1% of the continents’ surface. Organic carbon export from mangrove areas to the ocean is more than an order of magnitude higher in proportion of their net-primary production than any major river (Fig. 5.8). Their rapid decline over the recent decades (Valiela et al. 2001) may have significantly impacted the flux of terrigenous DOC to the ocean.
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Valiela I, Bowen LJ, York JK (2001) Mangrove forests: one of the world´s threatened major tropical environments. BioScience 51:807–815 Versteegh GJM, Schefuß E, Dupont L, Marret F, Sinninghe Damste´ JS, Jansen JHF (2004) Taraxerol and Rhizophora pollen as proxies for tracking past mangrove ecosystems. Geochim Cosmochim Acta 68:411–422 Wafar S, Untawale AG, Wafar M (1997) Litter fall and energy flux in a mangrove ecosystem. Estuarine Coast Shelf Sci 44:111–124 Werner U (1999) R€aumliche Verteilung und Prim€arproduktion des Phytoplanktons in einem Gezeitenkanal einer Mangrove (Braganc¸a, Para´). Dipl thesis, University of Bremen, Bremen Woodroffe C (1992) Mangrove sediments and geomorphology. In: Robertson AI, Alongi DM (eds) Tropical mangrove ecosystems, coastal and Estuarine studies. American Geophysical Union Press, Washington, DC, pp 7–42 Zonneveld KAF, Versteegh GJM, Kasten S, Eglinton TI, Emeis KC, Huguet C, Koch BP, de Lange GJ, de Leeuw JW, Middelburg JJ, Mollenhauer G, Prahl F, Rethemeyer J, Wakeham S (2010) Selective preservation of organic matter in marine environments; processes and impact on the fossil record, Biogeosciences 7:483–511.
Part III Floristic and Faunistic Studies in Mangroves
Chapter 6
Mangrove Vegetation of the Caete´ Estuary U. Mehlig, M.P.M. Menezes, A. Reise, D. Schories, and E. Medina
6.1
Floristics and Forest Structure
M.P.M. Menezes and U. Mehlig Diameter, height and architecture of mangrove trees present high plasticity (Halle´ et al. 1978). Their growth form apparently corresponds to site-specific environmental conditions, e.g., temperature, nutrient availability, soil pore water salinity or inundation frequency (Tomlinson 1986; Suarez et al. 1998). Abiotic conditions like these may impose certain rather static limits on mangrove tree recruitment and on the structural development of mangrove stands. In addition, the consequences of physical disturbances on forest development within the highly dynamic coastal environment have to be considered. Depending on environmental settings, predation and competition may further influence stand development. Studying spatiotemporal vegetation patterns is thus a direct key to understanding the responses of mangrove forest to environmental conditions and changes. In this description of the mangrove vegetation of the Caete´ Estuary and its structural and floristic properties, we concentrate on the western bank of the Caete´ river and on Ajuruteua Peninsula, both belonging to Braganc¸a district, Para´, north Brazil. Ajuruteua Peninsula is formed by extensive mud flats which are cut by tidal channels leading to the Caete´ river estuary in the east and to the Taperac¸u Bay in the west. Seawards, Ajuruteua peninsula is bordered by sandy beaches; sandy deposits exist at several places within in the mud flat area (Chap. 3). The mud flats, partly elevated above the mean high water level, have accreted around former barrier islands over the last 5,000 years (Cohen et al. 2005; Souza-Filho et al. 2009). Today, they are almost completely covered by mangrove forests. The forests are formed by the four mangrove tree species, Rhizophora mangle (Rhizophoraceae), Avicennia germinans, Avicennia schaueriana (both Acanthaceae-Avicennioideae), and Laguncularia racemosa (Combretaceae). R. mangle is the prevailing mangrove tree species in the Caete´ estuary. This is consistent with its dominance in estuaries with distinctly marine influence in Amazonia (Almeida 1996) and along the entire
U. Saint-Paul and H. Schneider (eds.), Mangrove Dynamics and Management in North Brazil, Ecological Studies 211, DOI 10.1007/978-3-642-13457-9_6, # Springer-Verlag Berlin Heidelberg 2010
71
72
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coast of Brazil (Prance et al. 1975; Lacerda et al. 2002). A. germinans, also abundant along the Brazilian north coast, is omnipresent in the Caete´ estuary. Contrastingly, the congeneric A. schaueriana has been recorded only in small numbers, mostly near sandy beaches (Amaral et al. 2001; Santos 2005). In agreement with general findings from other places along the Brazilian coastline, L. racemosa occurs often at forest edges, in large forest gaps, and other open areas (Berger et al. 2006). Several small, almost monospecific L. racemosa stands have been encountered on Ajuruteua peninsula (Harun 2004); they may represent intermediate successional stages. Among the plant species associated with mangrove trees, only a few occur under high salinity conditions. Most of them are halophytic herbs or subshrubs, e.g. Sesuvium portulacastrum (Aizoaceae), Blutaparon sp. (Amaranthaceae) and Batis maritima (Bataceae). They frequently grow at channel borders, among dwarf mangrove trees or in hypersaline, open areas but normally do not thrive in the shade of closed mangrove canopies. A few shrubs and vines (namely Muellera frutescens, Fabaceae-Faboideae; Rhabdadenia biflora, Apocynaceae; Stigmaphyllon bannisteroides, Malpighiaceae, and Crenea maritima, Lythraceae) have been observed in distinctly saline mangrove forest on the Ajuruteua Peninsula. Conocarpus erectus (Combretaceae) bushes colonize the ecotone between mangroves and marshes of salt-tolerant grasses like Sporobolus virginicus (Poaceae) on sandy, less frequently inundated soils (Medina et al. 2001). Other woody mangrove associates, as well as herbs like Crinum americanum (Amaryllidaceae) and the fern Acrostichum aureum (Pteridaceae), seem to be unable to survive without significant freshwater influence but have been found under brackish conditions (Menezes et al. 2003; Matni et al. 2006). For the Ajuruteua Peninsula, a number of studies of mangrove forest structure are available (Th€ ullen 1997; Reise 1999, 2003; Th€ullen and Berger 2000; Mehlig 2001; Menezes et al. 2003; Menezes 2006; Pereira 2005; Matni et al. 2006; Abreu et al. 2006; Seixas et al. 2006). Figure 6.1 shows the location of the respective study sites. Table 6.1 summarizes important structural parameters for each site. Based on these studies, we discern the following principal types of mangrove forest on the Ajuruteua Peninsula: l
Tall, R. mangle-dominated mixed forest (TRM in Table 6.1) with A. germinans as the second most important tree species. This is the prevalent mangrove forest type within the area; it occurs throughout the Caete´ estuary. At TRM forest sites where respective data are available, inundation frequency exceeds 140 days year1 and average soil porewater salinities at 0.5 m depth reach about 50 (Lara and Cohen 2006, and unpublished data). Average tree heights range between 11 and 14 m; single trees reach heights of 30 m and more. L. racemosa occurs within TRM throughout the estuary but is never a major constituent of the forest. Where fresh water influence is significant, a distinct TRM subtype can be distinguished by the presence of undergrowth of A. aureum and C. americanum (site 1 in Fig. 6.1, Table 6.1; maximum pore water salinity: 36; Mehlig 2001).
6 Mangrove Vegetation of the Caete´ Estuary
73
Fig. 6.1 Mangrove vegetation study sites in the Caete´ estuary. 1–12 forest structure (Table 6.1), 1, 3–7, 10–11 litter fall (Table 6.2); 1, 4, 7, 11, 13: phenology
l
Tall, A. germinans-dominated mixed forest (TAM in Table 6.1), partly intermingled with smaller R. mangle trees and occasionally L. racemosa. This forest type forms bands along tidal channels and probably corresponds to a successional stage during slow migration of mud banks (Salzmann and Mehlig, unpublished). An interesting exception is the upper Furo da Salinas site (3b in Table 6.1), where TAM apparently grows on sediments deposited by the Furo da Salinas tidal channel after its interruption by the road Braganc¸a–Ajuruteua in the early 1980s. Inundation frequency at site 3b is comparatively low (60 days
Acarajo´
Lower Furo da Salinas
Lower Furo da Salinas
Upper Furo da Salinas
Upper Furo da Salinas
Furo da Salinas
Salinas dos Roques*
Salinas dos Roques/Lagoon
Furo do Meio
Furo Branco
1
2a
2b
3a
3b
4
5a
6
7
8
Site
TAM, TRM
TRM
LA
LA, DA
TRM
TAM
TRM
TRM
TAM
TRM
Type R. mangle A. germinans L. racemosa R. mangle A. germinans L. racemosa R. mangle A. germinans L. racemosa R. mangle A. germinans L. racemosa R. mangle A. germinans L. racemosa R. mangle A. germinans L. racemosa R. mangle A. germinans L. racemosa R. mangle A. germinans L. racemosa R. mangle A. germinans L. racemosa R. mangle A. germinans
Species
Mean diam. (cm) 19.6 16.3 22.6 18.1 7.9 5.4 7.6 3.8 16.7 11.5 – 22.5 6.8 – 25.5 3.5 14.3 5.0 8.9 8.0 7.0 1.0 6.2 6.7 – 12.3 9.2 25.5 20.2 10.4 – 0.5 – – 4.2 – 25.8 11.3 49.0 47.1 – 8.3 5.9 15.3 11.9
Mean height (m) 12.7 8.0 16.2 8.6 5.4 3.0 9.8 4.2 13.5 6.1 – 17.9 4.7 – 9.0 8.5 9.7 3.0 7.5 3.0 5.6 1.0 6.6 6.7 – 8.6 4.5 15.3 2.1 8.0 – 0.4 – – 2.9 – 12.4 4.2 12.8 8.1 – 7.6 4.2 10.1 6.6
Density, (ind.ha1) 420 100 90 122 811 0 289 0 22 800 1,293 120 170 2,850 – 400 13 4 – 192,070 – – 96,270 – 280 80 – 194 292
Basal area (m2 ha1) 12.7 4.0 0.4 0.6 26.1 0 12.5 1.1 4.5 14.3 14.8 0.5 0.3 16.7 – 7.7 1.3 <0.1 – 0.6 – – 0.7 – 14.6 15.1 – 4.3 19.6 Pereira (2005)
Menezes et al. (2003), Th€ ullen (1997)
Reise (1999)
Reise (1999)
Abreu et al. (2006)
Reise (1999)
Menezes (2006)
Pereira (2005)
Pereira (2005)
Menezes et al. (2003)
References
Table 6.1 Forest structure data from the Ajuruteua Penı´nsula. All studies apart of Seixas et al. (2006), site 11, and Reise (1999), site 5, used a minimum diameter at breast height (dbh) of 2.5 cm. Site numbers correspond to Fig. 6.1. Diameter of Rhizophora trees is by convention measured above the highest stilt root, not necessarily at breast height (1.3 m) as in the other species. Standard deviation is reported with mean values as far as given by the authors
74 U. Mehlig et al.
TAM
12
**
all plants measured minimum diameter at breast height 3.2 cm
*
TRM
11c Furo Grande north bank**
Furo Grande north arm
TAM
11b Furo Grande north bank**
TRM
TAM, TRM
Furo Grande south bank (north PA-458)
10
TRM
11a Furo Grande north bank**
Furo Grande south bank (south PA-458)
9
L. racemosa R. mangle A. germinans L. racemosa R. mangle A. germinans L. racemosa R. mangle A. germinans L. racemosa R. mangle A. germinans L. racemosa R. mangle A. germinans L. racemosa R. mangle A. germinans L. racemosa – 16.9 9.9 19.9 7.6 – 23.3 13.0 33.4 16.0 14.5 9.0 – – – – – – – – – 7.3 2.9 12.0 9.7 –
– 11.7 4.1 11.7 3.7 – 13.7 4.0 14.7 4.0 10.0 4.0 8.6 11.9 – 8.7 11.0 – 11.3 10.5 – 6.1 1.8 7.5 3.4 –
0 210 420 – 270 32 16 681 747 0 59 797 0 1,193 128 0 122 1,278 0
0 4.7 13.1 – 4.4 8.4 1.7 9.7 21.6 0 2.8 17.2 0 20.0 4.4 0 0.8 27.1 0 Pereira (2005)
Seixas et al. (2006)
Seixas et al. (2006)
Seixas et al. (2006)
Menezes (2006), Nordhaus (2004)
Menezes et al. (2003)
6 Mangrove Vegetation of the Caete´ Estuary 75
76
l
l
l
U. Mehlig et al.
year1; soil pore water salinity is up to >60; Menezes 2006) but will be much higher at TAM channel border sites. Average tree heights range from 7 to 12 m. Low A. germinans forest (LA in Table 6.1) is usually restricted to higher elevations with reduced inundation frequency (e.g., 7 days year1 at site 5; Reise 2003) and higher soil pore water salinity. L. racemosa is a minor constituent of LA. Trees present a stunted, rather bushy growth but still reach mean heights of 3 m. The plants form closed stands with very few canopy gaps. Sparse dwarf A. germinans stands on hypersaline mud flats (DA in Table 6.1) occur at the highest elevations still subject to tidal inundation. Small A. germinans bushes are associated with subshrubby or herbaceous halophytes (B. maritima, S. portulacastrum, Blutaparon sp.) in an open formation. Almost monospecific L. racemosa stands (LR) stands may represent successional stages on previously disturbed sites but are also found in transition zones between LA or DA and TRM, then sometimes associated with A. germinans.
The linkage between inundation frequency and soil porewater salinity was confirmed by Lara and Cohen (2006); the same authors observed an inverse relationship of salinity and tree height, which agrees with our findings that lowheight mangrove vegetation types (LA, DA) are restricted to higher elevations on the Ajuruteua peninsula. Towards the upper inundation limit, salt-resistant grassland (mainly S. virginicus) may invade the mangrove; the ecotone is characterized by dispersed mangrove trees or bushes (mostly A. germinans and L. racemosa) within a Sporobolus marsh. The differences in elevation between Sporobolus marsh and mud flats with halophytic herbs are very small, and both formations are sometimes observed next to each other. In which way soil type or hydrological regime favor one or the other type of vegetation has not yet been investigated. Transitional forest types exist, especially between LA, DA and LR. TRM and TAM do not differ strongly in terms of total density and total basal area, TAM sites show, however, a tendency towards higher tree densities and smaller mean diameters (Table 6.1). It is interesting in this context that the trees with the largest diameters in TRM are often isolated individuals of A. germinans scattered among the dominating R. mangle trees (e.g., Th€ ullen 1997); both facts are consistent with our interpretation of TAM as being (at least partly) a successional stage of forest development. It is usually not possible to realize comprehensive ground-based forest structure surveys in difficult mangrove terrain; therefore, sampling areas at study sites on the Ajuruteua peninsula have small extensions between 0.1 and 1 ha. Satellite images may show differences of structural and physical properties within the vegetation cover over a wide range of spatial scales (e.g., Souza-Filho and Paradella 2002; Cohen and Lara 2003). If recognized units of similar appearance (i.e., spectral signature) can be matched with characteristic types of vegetation known from terrestrial surveys of vegetation structure, corresponding satellite data can be used to map remote areas where terrestrial reconnaissance is impracticable. Using a compilation of data from the above sources in combination with additional groundtruth data, we were able to match true mangrove vegetation cover and the spectral
6 Mangrove Vegetation of the Caete´ Estuary
77
response of Ikonos satellite scenes. To demonstrate the relative importance of the different mangrove tree species on the Ajuruteua peninsula, Fig. 6.2 shows the extension of mangrove forests dominated by each of the three mangrove tree genera, Avicennia, Rhizophora and Laguncularia, for a 125-km2 portion of the Ajuruteua peninsula; the chosen area was covered by a single Ikonos image taken in September 2003 and comprising all terrestrial forest structure study sites with the exception of Acarajo´ (site 1). Rhizophora (TRM) is the dominating genus for 62% of this area, followed by Avicennia (TAM, LA: 33%). The area dominated by L. racemosa is much smaller (3%). It would be desirable to quantitatively match forest structure data from groundbased surveys to remote sensing data. We calculated the correlation between Rhizophora and Avicennia basal area in 10 10 m plots as a terrestrial measure of dominance (from Pereira 2005) and the corresponding species-specific canopy coverage from the classified Ikonos image along a 370-m transect georeferenced by hand-held GPS (Furo Branco, site 8). The correlation was significantly positive for both occurring species (p < 0.01; Pearson’s correlation coefficients 0.63/0.55 for Rhizophora/Avicennia, respectively) but R2 was low in both cases (<0.4) due to high scatter (calculations done with routine cor.test, GNU R 2.6.2, R Development Core Team 2007). Exactly georeferenced ground data from larger areas would be needed to describe the correspondence between ground-based and satellite data in a more reliable fashion.
6.2
Litter Fall and Phenology
U. Mehlig Litter fall is a convenient proxy for primary production of forests, as methodology to determine litter production is cheap and simple, and the available database permits comparisons across a wide range of forest types from different regions. In addition, litter fall data from different sites with contrasting ecological settings provide, together with climatic records and phenological observations, valuable insights into the ecology of the litter-producing plant species in their respective environments. Numerous litter fall studies have been published for mangrove forest all over the world (e.g., Saenger and Snedaker 1993). However, until recently, the only published record for north Brazil was from Maraca´ Island, Amapa´ state, north of the Amazon mouth (Fernandes 1997). This section summarizes the results from litter fall and phenology studies performed in mangroves of the Caete´ river estuary between 1996 and 2005. With the exception of site 13 (Fig. 6.1), all litterfall/phenology sites were also object of forest structure surveys (see Fig. 6.1 and Table 6.1). Site 13 is a fringe of A. schaueriana and L. racemosa shrubs at Ajuruteua Beach (Santos 2005; Silva 2005).
78
U. Mehlig et al.
Fig. 6.2 Dominance of mangrove trees on Ajuruteua peninsula. Rhizophora-dominated forest: dark green. Avicennia-dominated forest: olive green. Laguncularia-dominated forest: light green. Non-mangrove vegetation: blue/violet. Areas covered or shaded by clouds are marked by hatched
6 Mangrove Vegetation of the Caete´ Estuary
79
All but one litter fall/phenology studies (that of Reise 1999) provide data for a period of at least 1 year. Only at sites 7 (Furo do Meio; Mehlig 2001, 2006) and 11 (Furo Grande North Bank; Carvalho 2002; Nascimento 2005) does the observation period exceed 2 years. In most studies of litter fall dynamics on the Ajuruteua Peninsula, suspended litter traps with 1-m2 openings were used; in one case, smaller traps were employed (0.5 m2; Nascimento et al. 2006). Litter traps were distributed at random by all authors except Reise (2003), who positioned her litter traps nonrandomly directly below the canopy of specific trees. She expected therefore to overestimate the actual site litterfall rates due to the neglect of canopy gaps, and tried to derive a correction factor from gap fractions determined by wide-angle photographs of the canopy. However, corrected litterfall rates at one of her sites (9 in Fig. 6.1) turned out to be extremely low in comparison with the neighboring site 10 where traps were randomly distributed (Nordhaus 2004), and Reise discarded the correction factor as presumably too conservative. With the exceptions of Carvalho (2002) and Nascimento (2005) who collected litter samples monthly, material was removed from the traps at biweekly intervals. Litter samples were oven-dried to constant weight at temperatures between 70 and 104 C. All authors provide separate collection rates for leaf material of the three mangrove tree species R. mangle, A. germinans and L. racemosa; however, different types of reproductive litter, miscellanea and viable propagules (the latter not being strictly “litter”) are not always distinguished. In the following, “total litter” includes propagules for convenience. Tree phenology was investigated by observing a number of trees repeatedly with binoculars (Carvalho 2002; Rodrigues 2005) and by monitoring individually tagged twigs and leaves (Mehlig 2006, for R. mangle; Santos 2005, for A. schaueriana and A. germinans; Silva 2005, for L. racemosa; Virgulino 2005 for L. racemosa), providing different levels of detail. Further, periodical changes in apparent litter shedding rates are considered as a reflection of phenological cycles.
6.2.1
Litter Fall Rates
Total litter fall rates at the different sites range from 4.1 to 16.4 Mg ha1 year1 (Table 6.2). The very low litter fall rates of 0.9 and 2 Mg ha1 year1 at site 5a and 6 (Reise 1999) are from a short-time study. Moreover, the trees were affected < Fig. 6.2 (continued) line patterns. Derived from a single Ikonos scene (September 2003) by supervised classification with GRASS GIS procedures r.gensig/r.maxlik (GRASS Development Team 2007) and subsequent calculation of species dominance within a gliding window of 50 50 m (10 10 m grid resolution). The mangrove tree species with the largest coverage within the window was considered as “dominant”; grid points where total mangrove tree coverage was below 50% were considered as “nonmangrove”. Areas covered or shaded by clouds as well as water bodies and terrestrial forests were masked out manually before analysis
80
U. Mehlig et al.
Table 6.2 Caete´ estuary litter fall study sites: total annual litter production (including propagules), annual leaf litter production and annual production of mature propagules. Site numbers correspond to Fig. 6.1 and Table 6.1 Site
1 Acarajo´ 3a Upper Furo da Salinas 3b Upper Furo da Salinas 4 Furo da Salinas 5a Salinas dos Roques 5b Salinas dos Roques 6 Salinas dos Roques/ Lagoon 7 Furo do Meio 9 Furo Grande south bank (south PA-458) 10 Furo Grande south bank (north PA-458) 11 Furo Grande north bank
Total annual litter production (Mg ha1 year1) 12.8 a, b 11.9 b 13.5 10.4 a, b 5.9 7.2 11.7 0.9 4.1 2.0 13.1 15.4
a, b b a, b
b
Annual leaf litter production (Mg ha1 year1) 9.9 a, b 8.9 b 10.2 7.6 a, b 4.9 5.3 7.9 0.8 3.7 1.8 8.8 11.9
a, b b a, b
b
Annual propagule production (Mg ha1 year1) 1.1 a, b – b 0.2 c 0.2 a, b – c <0.01 c 0.4 – 0.04 – 2.3 0.5
a, b b a, b
b
Authors
Mehlig (2001, 2006) Reise (1999) Reise (2003) Menezes (2006) Reise (1999) Menezes (2006) Nascimento et al. (2006) Reise (1999) Reise (2003) Reise (1999) Mehlig (2001, 2006) Reise (2003)
16.4
11.1
1.9
Nordhaus (2004)
7.4
5.3
–
Carvalho (2002), Nascimento (2005)
Investigation period <1 year Non-random positioning of litter traps, litter fall rate without canopy area correction factor (see text) c Not given explicitly in cited reference, calculated from original data a
b
during Reise’s study by an attack of leaf-sceletonizing larvae of the moth Hyblaea puera, which massively defoliated the stand in question. The effect of H. puera larvae on A. germinans litter fall rates was further analyzed by Mehlig and Menezes (2005) and Fernandes et al. (2009). Low litter fall rates were recorded in general at poorly inundated sites with low to medium-height A. germinans forest (LA, DA) and high soil salinities (sites 3, 5). On the other hand, the fresh water-influenced mangrove at site 1 and well-inundated but more saline sites show comparable, high litter fall rates. Litter fall rates correspond well to tree heights at the respective study sites (linear regression: intercept 1.47, parameter estimate for height 1.03, p < 0.001, R2 ¼ 0.77; GNU R 2.5.1, R Development Core Team 2007); a clear relationship with other structural parameters like tree density and basal area (Table 6.1) was not detectable (step-wise regression, GNU R procedure “step”). Saenger and Snedaker (1993) found a similar relationship between litter fall and stand height; however, with a distinctly different slope (0.34) and intercept (6.0), most probably because litter fall rates in their dataset level off at greater tree heights not recorded in our study area. Saenger and Snedaker (1993) also analyse to what degree litter fall is linked to latitude and detect declining litter production with greater distance from the equator. An updated dataset of worldwide reports of litter fall rates (Mehlig 2001) documents,
6 Mangrove Vegetation of the Caete´ Estuary
81
however, that the variation in litter fall within the region between 20 N and 20 S is extremely high, probably due to differences in physical conditions not directly linked to factors which vary with latitude (i.e., mean air temperature). Our small dataset recorded at neighboring sites almost directly at the equator in the humid tropics demonstrates clearly the profound effect of inundation frequency and associated factors on litter fall even under climatically homogeneous (and favorable) conditions. For direct comparison, Table 6.3 lists litter fall rates from different studies conducted in North and South America; as in the Caete´ estuary, litter fall rates vary greatly between nearby sites. At all study sites in the Caete´ estuary, leaf material (including R. mangle stipules; Table 6.2) was the greatest fraction within total litter. Leaf litter accounted for 67–100% of total litter. Production of reproductive litter and propagules was continuous in R. mangle but the quantity of material changed with season (see Sect. 6.2.2 below). Mehlig (2006) found strong differences (40%) in annual R. mangle propagule production between two subsequent years at site 7, indicating that the supply of dispersal units in this species may vary substantially. Further, large differences in R. mangle propagule production were observed between different sites within the same year (Mehlig 2006). Nascimento et al. (2006) compared litter fall of the mangrove forest at site 4 with that of terrestrial forest of a neighboring area not inundated by the tides. The terrestrial forest produced significantly less litter (8.8 t ha1 year1) in spite of similar forest structure. The authors concluded that the effect of the dry season might be more severe for the terrestrial trees, as their habitat did not provide abundant fresh water reserves. However, the authors emphasize that contributions of certain parts of the terrestrial vegetation, especially of palm trees, could have been underestimated due to limitations of the litter trap sampling technique.
6.2.2
Phenology
Litter fall studies as well as direct observations of tree phenology showed unequivocally that the mangrove trees at the Ajuruteua peninsula exhibit seasonal patterns in the production of leaves and reproductive structures. The seasonal differences in rainfall regime (Fig. 6.3) and associated changes in salinity and light availability are likely triggers for initiation of phenophases. R. mangle produces leaves and reproductive organs throughout the year, but the amount of leaves produced declines with decreasing light availability due to cloudiness during the peak rainy season (Mehlig 2006). Leaf production also slows down towards the end of the dry season when soil porewater salinity reaches its maximum values. Leaf fall reaches its minimum before the onset of the rainy season (Fig. 6.4; Reise 2003; Nordhaus 2004; Nascimento 2005; Mehlig 2006; Nascimento et al. 2006). The seasonality signal is weaker in Acarajo´ mangroves (site 1; Mehlig 2001, 2006) with their elevated fresh water input, than it is at Furo do Meio (site 7; Mehlig 2006) and other sites exposed to higher salinities. R. mangle
82
U. Mehlig et al.
Table 6.3 Overview of total and leaf litter fall rates from studies in North and South America Site
Total annual litter Annual leaf litter Authors production production (Mg ha1 year1) (Mg ha1 year1)
157 460 W 21 250 N Nuupia Ponds, Hawaii, USA 64 450 W 32 170 N Hungry Bay, Bahamas, USA 82 310 W 27 410 N Cockroach Bay, Tampa Bay, Florida, USA 80 220 W 27 250 N Indian River Lagoon, Florida, USA 81 450 W 26 010 N Estero Bay, Fort Myers, Florida, USA (“mixed site”) Estero Bay, Fort Myers, Florida, USA (“monospecific site”) 81 340 W 25 010 N Rookery Bay, Naples, Florida, USA (“mixed site”) Rookery Bay, Naples, Florida, USA (“monospecific site”) 96 220 W 19 360 N Laguna de la Mancha, Veracruz, Mexico 91 470 W 18 380 N Estero Pargo, Laguna de Te´rminos, Campeche, Mexico (“fringe”) Estero Pargo, Laguna de Te´rminos, Campeche, Mexico (“basin”) 91 490 W 18 290 N Boca Chica, Laguna de Te´rminos, Campeche, Mexico 91 550 W 18 340 N Laguna de Puerto Rico, Laguna de Te´rminos, Campeche, Mexico (“fringe”) 91 580 W 18 310 N Laguna de Carlos, Laguna de Te´rminos, Campeche, Mexico (“overwash”) 92 060 W 18 340 N Laguna de Atasta, Laguna de Te´rminos, Campeche, Mexico (“riverine”) 92 110 W 18 320 N Laguna de Pom, Laguna de Te´rminos, Campeche, Mexico (“riverine”) 93 100 W 18 250 N Laguna de Mecoaca´n, Tabasco, Mexico
12.8
9.9
9.4
7.0
Cox and Allen (1999) Ellison (1997)
11.3
7.7
Dawes et al. (1999)
13.5
8.6
8.7
5.5
Parkinson et al. (1999) Twilley et al. (1986)
3.5
2.1
7.5
5.8
5.0
3.6
9.1
7.0
7.9
7.3
4.0
3.6
12.5
8.8
Day et al. (1987)
6.6
5.8
Barreiro-G€ uemes (1999)
10.5
8.2
11.2
9.6
16.5
10.7
6.1
5.1
Twilley et al. (1986)
Rico-Gray and Lot (1983) Day et al. (1996)
Lo´pez-Portillo and Ezcurra (1985)
(continued)
6 Mangrove Vegetation of the Caete´ Estuary
83
Table 6.3 (continued) Total annual litter Annual leaf litter Authors production production (Mg ha1 year1) (Mg ha1 year1)
Site
61 310 W
16 210 N Grand Cul-de-Sac Marin, 8.7 Guadeloupe
7.0
61 000 W
14 340 N Baie de Fort-de-France (site A1), Martinique Baie de Fort-de-France (site A2), Martinique Baie de Fort-de-France (site A3), Martinique Baie de Fort-de-France (site B1), Martinique Baie de Fort-de-France (site B1), Martinique 06 270 N Onverwagt, Guyana North Maraca´ Island, Amapa´, Brazil (site 1) North Maraca´ Island, Amapa´, Brazil (site 2) North Maraca´ Island, Amapa´, Brazil (site 3) North Maraca´ Island, Amapa´, Brazil (site 4) North Maraca´ Island, Amapa´, Brazil (site 5) North Maraca´ Island, Amapa´, Brazil (site 6) 02 250 S Guayas River Estuary, Ecuador (site M1) Guayas River Estuary, Ecuador (site M2) Guayas River Estuary, Ecuador (site M3) 11 300 S Rio Piaui, Sergipe, Brazil (site 1) Rio Piaui, Sergipe, Brazil (site 2) Rio Piaui, Sergipe, Brazil (site 3) 23 000 S Itacurussa´, Sepetiba Bay, Rio de Janeiro, Brazil 25 000 S Cananeia Lagoon, Santa Catarina, Brazil
4.8
3.6
8.2
5.7
15.0
8.1
8.6
5.7
19.0
12.7
17.7 11.7
10.8 7.0
16.4
5.4
4.7
3.5
9.9
6.6
2.6
1.8
7.7
5.1
10.6
7.5
6.4
5.2
8.8
7.3
8.7
7.4
4.1
4.1
6.3
5.2
8.7
6.1
Silva et al. (1998)
7.6
4.6
Schaeffer-Novelli et al. (1990)
57 370 W
79 400 W
37 370 W
44 000 W 48 000 W
Imbert and Portecop (1986) Imbert and Me´nard (1997)
Chale (1996) Fernandes (1997)
Twilley et al. (1997)
Landim and Maia (unpublished)
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Fig. 6.3 Long-term rainfall (right ordinate) and temperature regime (left ordinate) in the Braganc¸a region (Tracuateua weather station, 24-year averages, 1973–1997). Monthly rainfall above 100 mm (black area) in scale 1:10. Months where the rainfall curve falls below the temperature curve are considered as arid (Walter and Lieth 1967; figure from Mehlig 2001)
propagules are mainly released in the rainy season; development from flower to mature propagule takes less than 1 year (Mehlig 2006). A. germinans leaf fall shows a more distinct seasonality (Fig. 6.4). Leaf fall increases in the transition from rainy to dry seasons (April–June), reaching peak values in June–August within the dry season. During the rest of the year, leaf fall rates are distinctly lower (Mehlig 2001; Reise 1999, 2003; Nordhaus 2004; Menezes 2006; Nascimento 2005). The same pattern was observed at all study sites from Acarajo´ to Furo Grande. Observations of marked shoots at Ajuruteua beach (site 13; Santos 2005) showed enhanced leaf production between March and June in the first year of observation (2003) and rather scattered production peaks between February and July in the second year (2004). In both years, leaf production was next to zero in the dry season after August. A. schaueriana, at the same site, showed a slow increase in leaf production over the dry season; leaf production maxima were reached, however, between March and July. The amount of mature propagules of A. germinans collected during litter fall studies was low at all study sites; occurrence of propagules was restricted to the rainy season. A. germinans in the Caete´ estuary is flowering during the dry season (August–December; Mehlig 2001; Santos 2005); flowering of A. schaueriana at Ajuruteua beach was observed from April to October (Santos 2005). L. racemosa leaf fall patterns are less easily observed from available litter fall data due to the low frequency of L. racemosa trees at the study sites. Mehlig (2001) reported higher levels of leaf fall from the end of the rainy season towards the peak
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Fig. 6.4 Annual temporal patterns in mangrove tree leaf litter collections from the Ajuruteua Penı´nsula (sites 1, 3, 4 and 7; dashed gray lines: data from different sites/years). The black, uninterrupted line shows the general trend; it was obtained by local polynomial regression fitting (“LOESS” smoother, 2-months span) over all data points
rainy season at Furo do Meio (Fig. 6.4; site 7). Silva (2005) observed irregular leaf production peaks on tagged shoots at the Ajurutuea beach (site 13). Fruit production was confined to the peak rainy season at Furo do Meio, less severely so at Acarajo´ (site 1; Mehlig 2001). According to Silva (2005), fruiting of tagged shoots at Ajuruteua beach also takes place mainly during the rainy season but she reported sporadic observation of fruiting trees during the whole year.
6.3
Dendrochronological Studies of R. mangle Trees
M.P.M. Menezes Analyses of forest dynamics in mangroves are rare due to the lack of information on growth rates, age and mortality of trees. Dendrochronological methods may help to fill the gap by providing data on stand demography, specifically on individual tree
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age, tree life span and stand age. Dendrochronological analyses are possible if stems exhibit periodical modulations of cambial activity which become detectable as growth rings in cross-sections of the boles. If growth ring sequences can be matched reliably to known time intervals, age determination by counting of rings is straightforward, and growth rates can be calculated from ring width. An integrated approach of observing phenological events and the corresponding cambial activity is necessary for sound interpretation of growth ring data in tropical trees (Worbes 1995). The occurrence of growth rings suitable for dendrochronological analyses in the wood of mangrove trees has not so far been universally accepted. The conspicuous ring structures of Avicennia stems result from anomalous secondary growth producing repetitive sequences of xylem, phloem and conjunctive tissue (Gill 1971; Zamski 1979; Carlquist 1988). It has been shown that these rings cannot be used for dendrochronological investigations. The presence of growth rings was reported in other mangrove trees (Davis 1940, cited after Tomlinson 1986; Duke et al. 1981); however, their value for dendrochronological studies has been controversial (Ash 1983; Tomlinson 1986). On the other hand, more recent studies have demonstrated the successful application of dendrochronological methods in R. mangle from north Brazil (Menezes et al. 2003) and in Rhizophora mucronata from Kenya (Verheyden et al. 2004). This section summarizes the principal results of dendrochronological studies of mangrove forests in the Caete´ estuary (Menezes et al. 2003; Menezes 2006).
6.3.1
Periodicity of Growth Rings, Life Span and Growth Curves of R. mangle
R. mangle stem cross-sections from the Caete´ estuary reveal macroscopically visible, concentric growth rings that result from changes of vessel density. Phenology data (see previous section) are supporting the assumption of periodical changes in growth rates due to seasonal changes in rainfall regime and porewater salinity; in addition, preliminary data from diameter recordings made with permanent girth tapes indicate that stem diameter increment rates slow down during the dry season (Fig. 6.5). The supposed annual periodicity of R. mangle growth rings could be verified by correlating the 14C isotope content of selected growth rings with known 14 C time series; both can be matched due to a peak in 14C fallout originating from nuclear testing in the second half of the twentieth century (Worbes and Junk 1989). The oldest trees sampled for dendrochronological analysis of stem discs were 111 and 100 years old. Their diameters were among the largest recorded for R. mangle in the Caete´ estuary; we therefore estimate that the life expectancy of the species in this area will not significantly exceed 100 years. Rhizophora tree discs were taken from the cylindrical section of the stem above the highest stilt root, and tree age determined by counting of growth rings does not therefore cover the time before the plant has reached the height of wood disk extraction. The time needed by the tree to reach this height is, however, presumably small in comparison to the total tree age. A maximum similar age (106 years) to the
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Fig. 6.5 Stem diameter increment rates of Rhizophora mangle adult trees at Furo Grande (0 500 0200 S, 46 380 2700 W) and precipitation. Diameter increment recorded from permanent girth tape measures (type D1, UMS, Germany); given are average and standard deviation (n ¼ 3; U. Mehlig, unpublished). Precipitation data collected by an automatic rain gauge installed above canopy (data made available by Large-scale Biosphere-Atmosphere Experiment in Amazonia, LBA)
values obtained in the Caete´ estuary was reported by Verheyden et al. (2004) for R. mucronata near Mombasa, Kenya. Life spans of about 100 years are short compared to those of other tropical trees which can reach approximately 400 years (Worbes and Junk 1999). We consider changes of hydrological regime and substrate erosion as well as burying of aerial root systems by sediment deposition to be important hazards for R. mangle trees. Static instability of the living trees may make R. mangle susceptible to gales or rainstorms; uprooting may be among the primary causes of death of R. mangle in the Caete´ estuary (personal observations).
6.3.2
Diameter Increment
Diameter increment curves of R. mangle are approximately linear, documenting constant growth during the entire life span of the tree without any distinct age trend (Fig. 6.6). Annual mean growth rates vary between 2.5 and 4.9 mm, with an overall average growth rate of 2.9 mm year1. Comparison of individual growth rates reveals high variability within study sites. Interestingly, trees at the different study sites fall into quite distinct groups of slow-, medium-, and fast-growing trees (Fig. 6.6). Trees reaching higher rates were only found at well-inundated, moderately saline sites, while trees with medium and slow growth rates were found at all
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sites. The reason for this grouping could not be explained satisfactorily. Menezes (2006) used field data on the neighborhood of dendrochronologically examined trees in conjunction with field-of-neighborhood (FON; Berger and Hildenbrandt 2000) calculations to analyze the influence of competition on growth; she could show that differences in abiotic conditions and in neighborhood competition between trees on a small spatial scale are reasonable causes for within-site variation of tree growth. However, the influence of these factors should result in a rather continuous spectrum of growth rates (Menezes et al. 2003). Trees from the fastgrowing group may reach a diameter of 25 cm within 30 years, whereas trees from the slow-growing group take 50 years to reach the same diameter.
6.3.3
Mean Stand Age and Age Structure
Estimating the mean stand age of larger mangrove areas reliably is made complicated by the observed individual variation of growth rates (Fig. 6.6). We therefore present stand age estimates for the Ajuruteua Peninsula and corresponding age structure data in the form of three case-studies concentrating on the R. mangledominated, tall mixed forest sites 1, 7 and 10 (Fig. 6.1, Table 6.1). Growth rates from dendrochronological analysis in conjunction with diameter data from forest structure surveys along 400-m transects were used to derive estimates for the mean age of the respective stands. The mean age for R. mangle was calculated from mean diameter and group growth rates (see above) weighted by the fraction of trees belonging to the fast-, medium- and slow-growing group at the respective site (Menezes et al. 2003). Unfortunately, no dendrochronological data are available for A. germinans and L. racemosa. Chen and Twilley (1998) provide growth rates for these two species based on observations of tree diameters from mangrove stands of known age in the Caribbean; we tentatively use these rates to approximate the age of both A. germinans and L. racemosa at our study sites. Mean stand age was then obtained as weighted average of the occurring species at each site.
Fig. 6.6 Stem diameter increment of R. mangle and tree age. Fast-, medium- and slowly-growing trees were tentatively grouped (group 1: fast-growing trees, group 2 and group 3: medium-/ slowly-growing trees; Menezes 2006)
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The mean stand age for sites 1, 7 and 10 was estimated to be 56, 62 and 31 years. The corresponding mean age of the different species are displayed in Fig. 6.7. Interestingly, the mean and maximum age for A. germinans are distinctly higher than those of R. mangle at all three sites. The estimated values for maximum tree age were 223, 346 and 127 years in A. germinans, and 120, 114 and 83 years in R. mangle at sites 1, 7 and 10, respectively. It is possible, however, that the Avicennia growth rates of Chen and Twilley (1998) from the Caribbean are too low for our equatorial A. germinans and do thus overestimate tree age at a given stem diameter. Therefore, comparisons between the species have to be considered with care. Moreover, possible differences in growth rates between sites are necessarily ignored. The same is true for L. racemosa, where the maximum tree age estimate was much lower than for the other two species (67 years). Histograms of tree age class distributions for populations of the three species at sites 1, 7 and 10 are given in Fig. 6.8a. Given the small numbers of A. germinans and L. racemosa trees in the sample, results for these species should not be overrated. However, it is interesting to observe that A. germinans spread more or less equally over the entire range of age classes at the respective study site (with a slightly elevated percentage of younger trees at site 1). There is no compelling evidence for assuming that A. germinans had a more prominent role in these forests in the past, but the species at least maintained its status as the second most important constituent after R. mangle for the lifetime of the older trees. Given the higher age of A. germinans trees at least at sites 1 and 7, we assume that these outlive two or even three generations of R. mangle; the forest at sites 1 and 7 is possibly maintaining a stable species composition for several hundreds of years. Nevertheless, the age difference of the oldest A. germinans trees between the nearby sites 7 and 10 is striking. It is tempting to suggest that the stand at site 10 developed more recently. Age structure of the R. mangle population at site 10 supports this view (see below). The sporadical occurrence and low maximum age of L. racemosa agrees with the view that this species is a light-demanding “pioneer” tree (Ball 1980; Berger et al. 2006) that colonizes forest gaps but cannot otherwise outcompete the other two species.
Fig. 6.7 Mean age of mangrove tree species and mean stand age at sites 1 (Acarajo´), 7 (Fuo do Meio) and 10 (Furo Grande) in the Caete´ estuary
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Fig. 6.8 (a) Age class distribution of A. germinans, L. racemosa and R. mangle trees at Acarajo´, Furo do Meio e Furo Grande (sites 1, 7 and 10), Ajuruteua Penı´nsula. Class width: 5 years. (b) Smoothed density estimates for R. mangle age class distribution functions. Ticks below the curve indicate data points
Age class distributions for all three R. mangle populations are roughly bellshaped and skewed to the right (Fig. 6.8a; and smoothed density plots of distributions in Fig. 6.8b). The number of very young trees is low at all sites. At sites 1 and 7, 50% of the trees are about 50 years old or younger (32 years at site 10). Distinct cohorts do not emerge, indicating that younger plants continuously substitute dead trees. Future studies in additional riverine, fresh water-influenced environments are needed to investigate whether the heavier right tail of the age class distribution at
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site 1 can be attributed to a higher life expectancy of R. mangle in less saline environments. The age difference between A. germinans and R. mangle is much smaller at site 10 than at the other two sites; furthermore, the mode of the age class distribution of R. mangle at site 10 is shifted towards younger trees, corroborating the hypothesis that the stand in question is indeed not older than a single tree generation. Today, site 10 is not located in the immediate neighborhood of larger tidal channels, and there is no obvious evidence that the mud flat where the forest emerged was formed more recently. The event that favored the development of a new mangrove stand at site 10 remains obscure. The dendrochronological approach yields interesting new information about mangrove forest dynamics on a time scale not available with other methods like remote sensing. However, to obtain more complete results, it will be necessary to determine the age of mangrove tree taxa other than Rhizophora, and to extend our knowledge about stem growth rates to mangroves in other areas with contrasting physical environments.
6.4
Soil-Vegetation Nutrient Relations
A. Reise, D. Schories, and E. Medina Distribution and structural complexity of mangrove communities are related to the response of species to physicochemical gradients. Variations in forest structure, biomass, and productivity along the Braganc¸a estuarine gradient appear to be clearly associated with soil fertility, inundation frequency, salinity, and fresh water availability. There are only a few previous studies on soil–vegetation relationships within the Braganc¸a peninsula (see Cohen et al. 1999; Medina et al. 2001; Lara and Cohen 2006). In particular, data on canopy development and nutrient cycling are missing. Therefore, based on the results of Reise (2003), we discuss in detail three distinctive mangrove communities along the Braganc¸a peninsula, considering their structural properties, ecosystem functions related to primary productivity such as litter fall and fine root production, nutrient retranslocation during leaf senescence and nutrient return in litter fall. These analyses were correlated with the physico-chemical properties of the mangrove sediments, as well as with the inundation frequency of the sites.
6.4.1
Mangrove Communities and Methods
Mangroves of the Ajuruteua peninsula show a variety of community types caused by environmental settings differing in topography, tidal influence and fresh water
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run-off. The sites selected represent local extremes of fresh water availability and soil salinity. They correspond to the areas 3, 6, and 9 depicted in Fig. 6.1. Site 9 (Fig. 6.1) is situated adjacent to the Furo Grande creek, at the northern end of the peninsula. This mangrove area has an undulating surface and is sectioned by several small drainage channels. Site 6 is characterized by a shrub-like monospecific Avicennia community located at both sides of the road bordering large water ponds. During the rainy season, the water ponds become dominated by Eleocharis mutata and the Avicennia stands are flooded by rainwater. Both areas drain completely during the dry season. For the main area of dwarf Avicennia forest northwards of the road, satellite images from 1997 show an extension of about 3.2 km in the north–south direction and 1.9 km in the east–west direction. Site 3a is a mixed community of Rhizophora and Avicennia with few individuals of Laguncularia, situated at the transition zone between the upper basin and the fringe. It is located at the lower part of the mangrove fringe towards the Para´ tidal creek leading into the Caete´ river. Each study site was sampled in the rainy and dry season (May and December 2000, respectively). Sediment cores were collected with a stainless steel auger, 100 cm in length and 5.5 cm in diameter. Each core was sectioned from 0 to 50 cm into layers of 10 cm. Measurement of bulk density and specific soil conductance were carried out as described by Medina et al. (2001). To estimate fine root biomass, 30-cm-deep sediment cores were obtained with a stainless steel corer (5.5 cm diameter, six soil cores per site) within the rooting area of the tree species present. Each core was divided into 10-cm layers. Root extraction followed the procedure of Robertson and Dixon (1993). Root samples were oven-dried at 70 C to constant weight for biomass estimation. Fine root production was assessed using a root ingrowth’s core method (Cuevas and Medina 1988). The canopy interception index (CII) corresponds to a species’ leaf and twig area expressed in percent of total canopy area. The CII was determined for Avicennia and Rhizophora by taking vertical pictures from underneath the tree canopies. Negatives were scanned and digitally analyzed with Adobe Photoshop# version 6.0. The digital analysis allowed the differentiation between leaves and twigs as well as between species (Reise 2003). Litter was collected synchronously at all sites in fortnightly intervals following procedures described by Mehlig (2001). Litter traps were located under tree canopies. Community litter fall was calculated accounting for the proportion of canopy of each species (see Reise 2003 and Mehlig, section 6.2 in this chapter). Retranslocation efficiency (RE) for N and P was calculated on a dry weight basis as the percentage of element remaining in senescent leaves compared to mature leaves (Soto 1992; Lugo 1999). To calculate the nutrient return in litter fall the biomass of each litter component was multiplied by its respective average nutrient concentration. Soil and plant chemical analyses were carried out by the soil and plant tissue laboratory of the Empresa Brasileira de Pesquisa Agropecua´ria in Bele´m following procedures described in Paula and Duarte (1997).
6 Mangrove Vegetation of the Caete´ Estuary
6.4.2
Soil Physical–Chemical Properties and Flooding
6.4.2.1
Specific Soil Conductance, pH, and Bulk Density
93
Soil specific conductance (SSC) varied with soil depth, season and sites (Fig. 6.9). All sites showed a uniform seasonal pattern with a statistical significant increase during the dry season. During the rainy season, SSC increased consistently with depth at all sites (Fig. 6.9), a result from leaching of salt from the upper soil layers. Site 6 showed lower SSC values between 0 and 20 cm revealing the prolonged effect of fresh water flooding typical of this site. The rainy season depth salinity gradient was similar for sites 3a and 9 (52–75 mmhos g1), but was much steeper for site 6 (40–85 mmhos g1). During the dry season sites 3a and 9 had contrasting salinity–depth gradients, decreasing in site 9 indicating strong salination of the upper soil layers. Rainy versus dry season SSC values increased by nearly 50 mmhos g1 at site 9 but only around 18 mmhos g1 at site 3a. Average pH decreased consistently with increasing depth, particularly during the dry season (Fig. 6.10). Differences in bulk density were highly significant between sites but not between seasons (Table 6.4). Similarly, particle size distribution varied significantly among sites, clay being the dominant fraction at all sites (Table 6.4). Site 6 differed markedly from the other two sites because of its higher bulk density and percentage of sand.
6.4.2.2
Element Concentrations
Overall average values showed that C and N (measured only during the rainy season) were distinctly higher at site 9 (Table 6.5). Phosphorus differed significantly between sites, the largest difference detected between site 3a and 6. The elements K, Ca, and Mg showed slightly, but significantly, lower concentrations at site 6 compared to sites 3a and 9, whereas Na concentration did not differ among sites. The Na/K and Mg/Ca ratios at site 6 indicate higher salt stress for plant growth at this site.
6.4.2.3
Tidal Inundation Frequency
The inundation frequency during the observation period fell within the average measured previously (Cohen et al. 2000). Site 9 became inundated 17 days per month, equivalent to 201 days of flooding per year. Site 6 was inundated in average 7 days per year, since tidal waters reached the studied plots only during the equinoctial tides. Site 3a became flooded by tidal waters 26 days a year during the months of January–April and July–November, with an average of 3 days per
94 Fig. 6.9 Variation of soilspecific conductance with soil depth in wet and dry season at sites 3, 6 and 9
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6 Mangrove Vegetation of the Caete´ Estuary Fig. 6.10 Variation of soil pH with soil depth in wet and dry seasons
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Table 6.4 Mean bulk density (wet season, 0–50 cm), sand and clay concentrations (0–30 cm) (standard deviation) at the study sites
Sand (%) Clay** (%) Bulk density* (g d wt cm3) Site 3 0.66 (0.07) b 1.1 (1.2) 73.1 (4.4) a Site 6 0.95 (0.12) a 2.9 (1.7) 74.4 (1.3) a Site 9 0.55 (0.06) b 1.2 (1.1) 64.4 (7.1) b *Differences significant between sites (F ¼ 473.9, p < 0.001) but not between seasons (F ¼ 5.9, p < 0.1) **Differences significant between sites (F ¼11.63, p < 0.0001), but not between depths (F ¼ 2.18)
Site
Table 6.5 Average soil nutrient concentrations (mmol kg1 dry weight) at the study sites Site 3 Site 6 Site 9 F Prob.>F
C 1,473b 1,713b 2,028a 9.1 <0.001
N 125b 108c 141a 14.8 <0.001
P 2.5a 0.6c 1.0b 96.4 <0.001
K 28b 24c 30a 26.5 <0.001
Na 709a 689a 684a 0.5 n.s.
Ca 54a 32c 47b 60.6 <0.001
Mg 201a 131c 160b 64.2 <0.001
C/N 12b 16a 14ab 7.5 <0.001
N/P 60c 243a 132b 37.4 <0.001
Na/K 26b 29a 23c 15.7 <0.001
Mg/Ca 3.8b 4.3a 3.6b 18.3 <0.001
Five depths (0–50 cm), 12 collections per site and season (February and October, except C and N) One-way analysis of variance. Averages followed by the same letter are not statistically different (Tukey-Kramer HSD test, p ¼ 0.05)
month. The tidal inundation frequency, together with fresh water run-off and accumulation during the rainy season, correlate with the pattern of soil salinity–depth gradients described above.
6.4.3
Forest Structure and Function
Structural characteristics of Braganc¸a mangroves are summarized in Table 6.1. Here, we describe additional characteristics that may be associated to soil physicchemical properties, and tidal inundation frequency. In terms of large tree density (dbh 10 cm), site 9 is dominated by Avicennia and site 3a by Rhizophora, but the opposite is observed for the fraction of individuals below 10 cm dbh (Table 6.6). Site 3a also presented a higher density of trees 10 cm dbh. However, the basal area of Avicennia was much larger than that of Rhizophora at both sites. Site 6 is peculiar because of the high density of low stature Avicennia trees.
6.4.3.1
Canopy Size and Interception Index
Mean tree canopy size of Rhizophora was similar for site 9 with 31 m2 and site 3a with 29 m2 (Table 6.7). Canopy size differences between site 6 and sites 3a and 9 were highly significant. The largest individual canopy sizes for both species were measured at site 3a with about 86 m2.
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Table 6.6 Structural features of mangrove communities of the Braganc¸a peninsula: Mean tree density, and average values of height, dbh per tree and stand basal area Species % Individuals dbh 10 cm dbh 2.5–9.9 cm Tree dbh (m2) Basal 1 trees ha (sd) area (m2) height (m) Site 3 Rhizophora 31 367 (206) 117 (75) 9.4 (3.8) 13.4 (5.5) 7.9 (5.0) Avicennia 59 21 (172) 700 (690) 6.9 (2.9) 9.3 (9.1) 12.1 (10.5) Laguncularia 10 17 (41) 133 (197) 5.2 (1.1) 6.5 (2.1) 0.6 (0.7) Total stand 600 (89) 949 (734) 7.5 (3.4) 10.3 (8.0) 20.0 (7.2) Site 9 Rhizophora 48 150 (176) 100 (126) 9.1 (5.2) 11.9 (7.8) 3.9 (5.3) Avicennia 52 233 (137) 34 (52) 13.5 (5.8) 23.1 13.5 (8.5) (10.7) Total stand 383 (204) 133 (103) 11.7 (5.9) 17.7 (2.1) 17.4 (9.3) Site 6 Height Height 1.00 m 0.30–0.99 m Avicennia 100 22,100 37,500 (14,200) 1.0 (0.7) – 4.0 (0.4) (4,600)
Table 6.7 Structural features of mangrove communities of the Braganc¸a peninsula. Canopy interception index (CII) and leaf fraction (%) and mean canopy size per species. For CII, n indicates the number of evaluated pictures. For canopy size, n indicates the number of trees measured Site n Stand CII (%) Species Leaf fraction (%) n Mean canopy size (m2) Site 3 33 65.7 (16.5) Avicennia 11.4 18 19.0 (26.0) Rhizophora 39.1 18 28.8 (20.1) Site 6 15 43.2 (14.3) Avicennia 31.4 36 0.5 (0.3) Site 9 33 69.1 (9.6) Avicennia 22.3 16 28.9 (20.2) Rhizophora 36.5 15 31.1 (22.5)
The CII of Avicennia and Rhizophora estimated in May, June, and August 2001 by digital analysis of images were not statistically different within sites. All data per site were averaged and the variance analysis showed significant differences between sites 3a and 9 with site 6 (Table 6.7). Average leaf fraction of Avicennia was largest at site 6 with 31%, followed by site 9 with 22%, whereas in site 3a it only amounted to 11% (Table 6.7). Leaf area fraction of Rhizophora was higher than that of Avicennia reaching 37% at site 9 and 39% at site 3a.
6.4.3.2
Leaf Size
Average mature leaf size was similar for Rhizophora and Avicennia at sites 3a and 9 (Table 6.8). Leaves of Avicennia, however, were significantly smaller at site 6, an indication of stress affecting leaf expansion at this site. This fact was also reported
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by Medina et al. (2001) for the dwarf Avicennia mangroves in the central lagoons of the Braganc¸a peninsula.
6.4.3.3
Leaf Nutrient Composition and Retranslocation Efficiency of N and P
Average N and P concentrations of Rhizophora mature leaves were always significantly higher than those of senescent leaves, but there were no differences between sites (Table 6.9). RE values were lower at site 9 compared to site 3a for both N and P. For the latter, RE values were slightly lower than for N at both sites, an unusual result that may be interpreted as a lack of P limitation for plant growth, probably associated with slower rates of organic matter decomposition limiting mineral N supply to plant roots. Nitrogen/phosphorus ratios are identical for mature leaves of both sites, decreasing only slightly in senescent leaves. These ratios are also similar to those calculated from data reported by Medina et al. (2001). In Avicennia leaves, mean N and P concentrations of both mature and senescent leaves are higher than those of Rhizophora. In addition, site 6 showed consistently lower N and P concentrations (Table 6.9). Average values for N and P were similar Table 6.8 Mean values for size and shape (sd) of mature leaves of Avicennia and Rhizophora at the study sites
Species
Study Mature leaf area* site (cm2) Avicennia Site 3 52.9 (19.6) a,b Site 6 28.0 (9.0) b Site 9 62.2 (20.0) a Rhizophora Site 3 51.0 (18.6) a Site 9 59.2 (17.9) a *Tukey-Cramer HSD test, n ¼ 50, p < 0.01
Leaf shape (length/width) 2.7 (0.3) 2.3 (0.3) 2.4 (0.5) 2.5 (0.2) 2.6 (0.4)
Table 6.9 Average N and P concentrations, and retranslocation efficiency (RE) of Rhizophora and Avicennia leaves Site Element Mature leaf Senescing leaf RE (%) N/P M S M S Rhizophora Site 3 1.24 (0.99) a 0.66 (0.19) b 47 45 39 1.06 (0.14) a 0.71 (0.13) b 33 43 41 Site 9 N mol kg1 Site 3 27.8 (9.3) a 16.8 (1.4) b 40 24.5 (5.4) a 17.4 (1.8) b 29 Site 9 P mmol kg1 Avicennia Site 3 2.03 (0.16) a 1.27 (0.15) b 37 33 29 Site 6 1.49 (0.19) b 0.75 (0.09) c 50 37 30 1.88 (0.36) a 1.27 (0.38) b 32 35 37 Site 9 N mol kg1 Site 3 62.0 (12.8) b 44.6 (17.89) b 28 Site 6 40.0 (4.9) b 25.2 (4.79) c 37 53.6 (6.7) a 34.2 (5.87) b 36 Site 9 P mmol kg1 For each element in a row, and for each leaf type in column numbers followed by the same letter are not statistically different (Tukey’s HSD, p ¼ 0.05)
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for sites 3a and 9 and higher than for site 6. The RE values for N were about the same at sites 3a and 9 but lower that at site 6. For P, RE values were higher at sites 6 and 9 compared to site 3a. Nitrogen/phosphorus ratios were always lower than those of Rhizophora, and there was no consistent reduction from mature to senescent leaves.
6.4.3.4
Fine Root Production
Both live and dead fine root mass showed large variability between seasons and sampling depths; however, no overall patterns for its distribution by species, season, and/or depth could be detected. For Avicennia, total and living fine root biomass were higher at site 9, followed by sites 6 and 3a. Similarly, fine root biomass of Rhizophora was about twice as high at site 9 compared to site 3a (Fig. 6.11). In all cases, living fine root biomass constituted about 50% of total fine root biomass. Fine root growth rates of Rhizophora and Avicennia showed a high variability at all study sites, without consistent patterns regarding depth. Therefore, total fine root productivity was calculated for 0–30 cm depth. Rhizophora fine root growth rates were slightly higher at site 9 compared to site 3a, but only after 60 days (Fig 6.11a). From 90 to 120 days, production rate tended to reach similar levels, ranging from 0.4 to 0.6 g m2 day1. Fine root production of Avicennia showed higher rates in general, and varied more between the study sites (Fig 6.11b) than that of Rhizophora. Fine root production rates peaked at 90 days at sites 9 and 6 (1.5–1.7 g m2 day1), and were consistently lower at site 3a (0.2–0.3 g m2 day1). The ANOVA showed significant differences of fine root growth rates between sites indicating that it was significantly lower at site 3a compared to sites 6 and 9. Comparison of average root production rate per day with the average amount of living roots measured in soil cores allowed a crude calculation of fine root turnover time (Table 6.10). Avicennia had turnover times of 3–4 days at sites 6 and 9, and up to 9 days at site 3a. Turnover times of Rhizophora fine roots amount to 4–5 days. 6.4.3.5
Rates of Litter Fall
Rhizophora leaf litter showed similar annual means and periodicities at sites 3a and 9. Mean total litter production was equivalent for both sites reaching 2.2–2.5 g m2 day1, leaf fraction accounted for 68–74% of total litter fall (Table 6.11). For Avicennia total litter fall was 1.86 g m2 day1 at site 9, about 0.50 g m2 day1 higher than the average amounts shed at sites 3a and 9 (Table 6.11). Leaf litter accounted for 78% of total litter fall, and had a similar seasonal pattern at all sites. Litter fall at sites 3a and 9 was calculated considering their respective species’ canopy area. Mean litter yields reached 5.2 and 5.0 t ha1 year1 for sites 3a and 9,
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Fig. 6.11 Fine root production of Rhizophora (a) and Avicennia (b) at sites 3, 6 and 9
Table 6.10 Structural features of mangrove communities of the Braganc¸a peninsula: Fine root biomass, fine root productivity and living roots turnover time
Site 3 Rhizophora Avicennia Site 6 Avicennia Site 9 Rhizophora Avicennia
Total fine roots
Fine root Turnover Live fine production time, days roots mean (g m2) (g m2 day1)
4.3 5.7
2.6 2.7
0.7 0.3
3.7 9.0
8.6
4.0
1.6
2.5
8.9 9.7
4.3 6.4
0.75 1.8
5 3.6
6 Mangrove Vegetation of the Caete´ Estuary Table 6.11 Average stand litter fall Site Species Litter fall (g dw m2 day1) Site 3 Rhizophora 2.49 (0.67) Avicennia 1.15 (0.55) Total stand Site 6 Avicennia 1.13 (0.86) Site 9 Rhizophora 2.23 (0.77) Avicennia 1.86 (1.39) Total stand
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Canopy area (%) 48.0 17.8 100 42.6 26.5
Stand litter fall (t ha1 year1) 4.4 0.7 5.7 4.1 3.5 1.8 5.3
Leaves (%) 68 78 77 74 78
respectively (Table 6.11). These values are significantly higher than the litter yield estimated for site 6. The contribution of Rhizophora to stand litter production was about twice as high that of Avicennia at site 3a and 9, as expected from their higher fractional canopy area. Rates of litter fall estimated here are smaller than most reports for mangroves of the Braganc¸a peninsula and other sites in northern South America (see Tables 6.2 and 6.3). Differences may derive in part from methodological approach (see Mehlig, above). However, mangrove development at these sites indicate smaller large tree densities and canopy cover. In any case, values reported here allow a precise comparison between sites and species. Therefore, these values were used to calculate forest stands’ nutrient fluxes.
6.4.3.6
Nutrient Return in Litter Fall
Nitrogen and P concentration of Avicennia leaf tissue was higher at the sites 3a and 9 compared to the dwarf community at site 6, and also compared to the N and P concentration of all Rhizophora leaves (Table 6.12). Avicennia leaves at sites 6 and 9 were richer in K than Rhizophora leaves of site 3a. To calculate the element flux in litter fall the annual fall of every litter component at each site (as given by Reise 2003) was multiplied by their corresponding mean element concentration, and were added to obtain the contribution per species. Then, this contribution was multiplied by the canopy fraction of each species at each site, and finally these amounts were added to obtain element return per area per year at each study site. At all sites, the largest amount of element returned in litter fall corresponded to Na, followed by N, K and P (Table 6.13). Nitrogen flux was similar for sites 3a and 9 and higher than for site 6, whereas K flux was similar for sites 6 and 9. Flux of P was highest in site 3a and lowest in site 6. The pattern of nutrient fluxes departed markedly from litter fall rates between sites. Total litter fall at site 6 was 29 and 25% lower than at sites 3a and 9, respectively. These same reductions were observed for N flux, but not for the other elements measured. Phosphorus return was only 15% lower, Na was 21 and 11% lower, whereas K was only 7% lower than at site 9 and even 13% higher than
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Table 6.12 Average element concentration of Rhizophora and Avicennia leaf litter Site n N (mol kg1 sd) P K (mmol kg1 sd) Rhizophora Site 3 26 0.60 (0.16) a 20.4 (5.1) b 113 (54) a Site 9 26 0.58 (0.20) a 17.3 (3.2) a 133 (29) a Avicennia Site 3 26 0.73 (0.15) b 24.7 (2.9) c 129 (46) a Site 6 21 0.55 (0.14) a 20.0 (5.7) b 163 (81) b Site 9 27 0.79 (0.33) b 23.1 (5.7) c 171 (48) b
Table 6.13 Annual element flux per site
Site
N
P
Site 3 Site 6 Site 9
3,034 2,292 3,185
106 83 97
Na
813 (276) 833 (225) 806 (406) 792 (444) 875 (398)
K (mol ha1 year1) 571 649 697
Na 3,618 3,241 4,120
at site 3a. These numbers again showed contrasting environmental conditions at site 6 that may be causing the dwarfing of Avicennia communities in this site.
6.4.4
Conclusions
1. It was shown that mangrove structural diversity along the Ajuruteua peninsula is primarily influenced by local topography, tidal inundation frequency, soil salinity and bulk density. 2. Significant nutrient deficiencies in the soil are not among the main factors determining the unique dwarf and monospecific stand structure at site 6. Only a lower soil P concentration compared to sites 3a and 9 possibly contributes to the limited structural complexity. These mangroves also experience shortage of soil aeration during the months of fresh water flooding. A significantly higher bulk density compared to sites 3a and 9 contributes to the latter strain. However, smaller leaf size and concentrations of N and P, both in mature leaves and litter of Avicennia in this site, point to limitations in nutrient supply. A reasonable assumption is that large seasonal variations in salinity and fresh water flooding hinders effective decomposition of organic matter at this site. 3. A comparison of the large mangrove stands 3a and 9 showed a significantly higher soil salinity at site 9. This may be the reason for the dominance of Avicennia, particularly in the fraction of trees less than 10 cm dbh, as this species is known to have a higher salinity tolerance than Rhizophora. Conditions at site 9 may be suffering a long-term change, because, in spite of the dominance of large Rhizophora trees, they are less productive at this site compared to site 3a.
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4. In Rhizophora, retranslocation efficiency was smaller for both N and P, and similar to that of Avicennia, at site 9. In the latter species, RE was modest for N and quite low for P in site 6. An unusual finding is that RE for N was higher than for P. This requires further investigation as it indicates peculiar N–P relationships in these mangroves. 5. Fine root production was smaller for both species at site 3a, probably reflecting better soil nutritional conditions. 6. Nutrient fluxes of N were commensurate with rate of total litter fall. However, cycling of P and K proved to be more efficient at site 6.
6.5
Concluding Remarks and Outlook
The mangroves of the Caete´ estuary show remarkable structural variability corresponding to the broad range of inundation levels encountered at the macrotidal coastline of Para´. Four of the six neotropical-Atlantic mangrove tree species occur; it remains a challenging task to investigate the reason for the absence of Rhizophora racemosa and R. harrisonii around Braganc¸a, as both species are found in neighboring regions such as Marajo´ Bay and further southeast in Maranha˜o. A number of mangrove associates were identified but are mainly restricted to fresh water-influenced forest; this suggests floristic relationships to the flora of riverine va´rzea swamps that have not so far been analyzed. The well-developed, tall mangrove forest types, either dominated by R. mangle or A. germinans, are restricted to areas with regular tidal inundation and low to moderate salinities, while at sites with reduced inundation frequency or temporal accumulation of still water, dwarf forests or shrubby stands prevail. Litter production corresponds closely to the structural development of the forest along the inundation/salinity gradient; nutrient limitations are not primarily responsible for growth reduction or reduced productivity, but adaptation to site-specific differences in nutrient availability by changes in fine root production or efficiency of nutrient retranslocation was nevertheless detectable. Both litter production and development of reproductive organs show distinctive temporal patterns related to the seasonal change between wet and dry seasons, which causes marked differences in salinity regime. The dominance of A. germinans at hypersaline sites is conveniently explained by the high salinity tolerance of this species; interestingly, A. germinans is also capable of forming almost monospecific stands on emerging mud banks along tidal channels. The nature of the competition between A. germinans and R. mangle on well-inundated mud flats and its implications for a supposed successional dominance shift need to be further analyzed. With the successful applications of dendrochronological methods in R. mangle and the determination of long-term stem growth rates and maximum tree age within a range of mangrove stands, it is now possible to enhance models of mangrove forest dynamics which may help to investigate the interaction of species behind the observed distributional and structural patterns.
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References Abreu MMO, Mehlig U, Nascimento RESA, Menezes MPM (2006) Analysis of floristic composition and structure in a fragment of terra firme forest and an adjacent mangrove stand on Ajuruteua peninsula, Braganc¸a, Para´. Bol Mus Para Emı´lio Goeldi Se´r Cieˆnc Nat 2:27–34 Almeida SS (1996) Estrutura florı´stica em a´reas de manguezais paraenses: evideˆncias da influeˆncia do estua´rio amazoˆnico. Bol Mus Para Emilio Goeldi Se´r Cieˆnc Terra 8:93–100 Amaral DD, Santos JU, Bastos MN, Costa DC (2001) A vegetac¸a˜o da Ilha Canela, municı´pio de Braganc¸a – Para´, Brazil. Bol Mus Para Emı´lio Goeldi Se´r Bot 17:389–402 Ash J (1983) Note on paper ‘Growth rings and rainfall correlations in a mangrove tree of the genus Diospyros (Ebenaceae)’ by Duke NC, Birch WR, Williams WT’. Aust J Bot 31:19–22 Ball MC (1980) Patterns of secondary succession in a mangrove forest of southern Florida. Oecologia 45:226–235 Barreiro-G€uemes T (1999) Aporte de hojarasca y renovacio´n foliar del manglar en un sistema estuarino del Sureste de Me´xico. Rev Biol Trop 47:729–737 Berger U, Hildenbrandt H (2000) A new approach to spatially explicit modelling of forest dynamics: spacing, ageing and neighbourhood competition of mangrove trees. Ecol Modell 132:287–302 Berger U, Adams M, Grimm V, Hildenbrandt H (2006) Modelling secondary succession of neotropical mangroves: causes and consequences of growth reduction in pioneer species. Perspect Plant Ecol Evol Syst 7:243–252 Carlquist S (1988) Comparative wood anatomy. Springer, Berlin Carvalho ML (2002) Aspectos da produtividade prima´ria dos bosques de mangue do Furo Grande, Braganc¸a-Para´. MSc thesis, University of Para´, Braganc¸a Chale FMM (1996) Litter production in an Avicennia germinans (L.) Stearn forest in Guyana, South America. Hydrobiologia 330:47–53 Chen R, Twilley RR (1998) A gap dynamics model of mangrove forest development along the gradients of soil salinity and nutrient resources. J Ecol 86:37–51 Cohen MCL, Lara RJ (2003) Temporal changes of mangrove vegetation boundaries in Amazonia: application of GIS and remote sensing techniques. Wetl Ecol Manag 11:223–231 Cohen MCL, Lara RJ, Ramos JFF, Dittmar T (1999) Factors influencing the variability of Mg, Ca and K in waters of a mangrove creek in Braganc¸a, North Brazil. Mangr Salt Marshes 3:9–15 Cohen MCL, Lara RJ, Szlafsztein CF, Dittmar T (2000) Digital elevation model as a GIS tool for the analysis of mangrove coasts, Amazon Region, Brazil. Int J Environ Creat 3:31–41 Cohen MCL, Souza Filho PWM, Lara RJ, Behling H, Angulo RJ (2005) A model of Holocene mangrove development and relative sea-level changes on the Braganc¸a Peninsula (northern Brazil). Wetl Ecol Manag 13:433–443 Cox EF, Allen JA (1999) Stand structure and productivity of the introduced Rhizophora mangle in Hawaii. Estuaries 22:276–284 Cuevas E, Medina E (1988) Nutrient dynamics within Amazonian forests. Oecologia 76:222–235 Davis JH (1940) The ecology and geologic role of mangroves in Florida. Papers from the Tortugas Lab vol 32. Carnegie Inst Wash Publ 517:303–412 Dawes C, Siar K, Marlett D (1999) Mangrove structure, litter and macroalgal productivity in a northern-most forest of Florida. Mangr Salt Marshes 3:259–267 Day JW, Conner WH, Ley-Lou F, Day RH, Navarro AM (1987) The productivity and composition of mangrove forests, Laguna de Te´rminos, Mexico. Aquat Bot 27:267–284 Day JW Jr, Coronado-Molina C, Vera-Herrera FR, Twilley R, Rivera-Monroy VH, AlvarezGuillen H, Day R, Conner W (1996) A 7 year record of above-ground net primary production in a southeastern Mexican mangrove forest. Aquat Bot 55:39–60 Duke NC, Birch WR, Williams WT (1981) Growth rings and rainfall correlations in a mangrove tree of the genus Diospyros (Ebenaceae). Aust J Bot 29:135–142
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Chapter 7
Mangrove Infauna and Sessile Epifauna C.R. Beasley, M.E.B. Fernandes, E.A.G. Figueira, D.S. Sampaio, K.R. Melo, and R.S. Barros
7.1
Introduction
The benthos of the northern coast is Brazil’s most poorly known fauna (Lana et al. 1996). However, between 1995 and 2005, the MADAM project stimulated an increase in the number of studies of the benthos in the Caete´ mangrove estuary, Braganc¸a, northeastern Para´ state. As in other mangroves throughout the world (Alongi and Sasekumar 1992; Hogarth 1999; Kathiresan and Bingham 2001), the macrobenthic fauna of the Caete´ mangrove estuary is mainly composed of crustaceans (Koch and Wolff 2002), molluscs (Beasley et al. 2005) and annelids (Acheampong 2001). The mangrove infauna consists of species that spend most or all of the adult life within the substrate, boring into hard substrates or burrowing in soft sediments (Levinton 2001). The infauna has significant ecological importance in mangroves, facilitating aeration and bioturbation of the sediment, thus stimulating nutrient recycling (Mann 2000). The infauna also serve as prey items for other invertebrates (Fauchald and Jumars 1979; Lee 1998), fish (Zavala-Camin 1996), birds (Rodrigues 1993) and mammals (Fernandes 2000). Polychaete worms may form up to 80% of the diet of certain fish of economic importance (Nonato and Amaral 1979). The mangrove infauna of the Caete´ mangrove estuary has been described by Acheampong (2001), Figueira (2002) and Sampaio (2004); the latter two studies are described in more detail below. The infauna of mangrove associated Spartina marshes was investigated by Braga et al. (2009), who found that increasing macrofaunal diversity and abundance is associated with greater plant density. Shipworms (Bivalvia, Teredinidae), which are important for the decomposition of woody material in mangroves, were investigated by Santos et al. (2005) and Santos Filho et al. (2008) who showed that, although several species occur along the Para´ coast, one in particular Neoteredo reynei, predominates in terms of abundance. The mangrove epifauna consists of animals that may move over, or are attached to, hard or soft substrates (Levinton 2001). The sediment surface, roots, living and dead plant material such as logs, branches and leaves are habitat for the epifauna
U. Saint-Paul and H. Schneider (eds.), Mangrove Dynamics and Management in North Brazil, Ecological Studies 211, DOI 10.1007/978-3-642-13457-9_7, # Springer-Verlag Berlin Heidelberg 2010
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(Alongi and Sasekumar 1992). Ucides cordatus, a semiterrestrial herbivorous crab, is an important species both ecologically (Diele et al. 2005; Nordhaus et al. 2006; Wolff et al. 2000) and economically (Glaser 2003; Glaser and Diele 2004). The ecology of the Caete´ mangrove epibenthos (mainly decapod crustaceans) has been studied by Koch and Wolff (2002) who found that the faunal composition and abundance varied among the forest, large creek and small creek habitats. Herbivorous and detritivorous epibenthos dominate the epibenthic energy budget, and the high mangrove productivity is probably due to tight coupling of mangrove production with crab and microbial activities. Settlement of the sessile epibenthos was investigated by Marques-Silva et al. (2006) on both sides of ceramic and wooden panels at two different depths in two mangrove creeks during 1 year. Peak settlement of barnacles and oysters occurred in the wet and dry seasons, respectively, whereas mussels settle during the transition period between both seasons. Overall, settlement was greater on the underside of ceramic panels close to the creek bottom. Salinity, conductivity, temperature, dissolved oxygen and pH, grain size and sorting, as well as organic material content, have been strongly correlated with the distribution of the benthos (Herna´ndez-Alca´ntara and Solı´s-Weiss 1995; Cheng and Chang 1999; Dittmann 2000; Mann 2000; Skilleter and Warren 2000). Due to their sedentary habits and their close association with the sediment and porewater, the benthos, particularly the infauna, has been recognized as an important tool for monitoring the effects of pollution and environmental degradation (Amaral et al. 1998; Goerke and Weber 1998). The increasing pressure from urban development along the northeastern coast of Para´ state (Glaser 2003; Glaser and Diele 2004) may already be affecting the mangrove infaunal and epifaunal assemblages, resulting in both ecological and economic consequences for the region.
7.2
The Infauna of the Mangrove Forest at the Furo Grande Tidal Creek
Data collection was carried out in an undisturbed mangrove stand that is located at km 30 of the PA-458 highway (00 500 19.500 S, 46 380 14.900 W) between Braganc¸a and the village of Ajuruteua. At this site, vegetation is composed of Rhizophora mangle, Avicennia germinans, and Laguncularia racemosa. Sediments were sampled, using Rebelo’s (1986) methodology, along 12 transects, from September 2000 to August 2001. At each station, four replicates were obtained using a cylindrical collector and taken to the laboratory for processing. The collector was pushed into the sediment to a depth of 20 cm, providing replicates of 1.6 l with a surface of 80 cm2. From these samples, a total of 3,954 specimens were collected, of which 87.5% were identified to species level (Table 7.1). The infauna comprised five phyla: Nemertina, Mandibulata, Crustacea, Annelida, and Mollusca, with a total of 21 species. Polychaeta represented 84.4% of the individuals collected, of which 76.3% were identified as Notomastus lobatus. Crustaceans were the second most representative taxon at 5.2%, with Halmyrapseudes spaansi (Tanaidacea) common
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Table 7.1 Checklist of the mangrove infauna at the Furo Grande and Km 17 of the PA-458 highway, Braganc¸a, Para´, Brazil Phylum Arthropoda
Class Arachnida
Copepoda Mandibulata Chilopoda (adulto) Insecta
Order Acaridida Araneae Harpacticoida
Coleoptera
Coleoptera (imaturo) Diptera
Diptera (adulto) Diptera (imaturo) Hymenoptera Hymenoptera (imaturo) Hymenoptera
Family
Genus
Species
Corinnidae
Castianeira
Castianeira sp.
Paratrechina Dolichoderus
Paratrechina sp. Dolichoderus lutosus Solenopsis sp. Azteca sp. Pheidole sp.
Buprestidae Carabidae Chrysomelidae Lampyridae Staphylinidae Tenebrionidae
Tipulidae Tabanidae Dolichopidae Stratiomyidae
Formicidae
Formicidae
Solenopsis Azteca Pheidole
Crustacea
Isoptera (adulto) Ortoptera Hemiptera (imaturo) Homoptera (imaturo) Insecta (ovos). Larva na˜o identificada Malacostraca Decapoda
Site
Blatidae
Grapsidae
Ocypodidae
Apseudidae
Sesarma
Sesarma crassipes Sesarma curacaoense Sesarma sp. Uca Uca maracoani Uca mordax Uca rapax Uca sp. Uca thayeri Uca vocator Ucides Ucides cordatus Hexapanopeus Hexapanopeus smitti Halmyrapseudes Halmyrapseudes spaansi
(continued)
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Table 7.1 (continued) Phylum Annelida
Class Oligochaeta Polychaeta
Order
Family
Tubificida Scolecida
Tubificidae Capitellidae
Eunicida Phyllodocida
Paraonidae Arabellidae Nephtyidae
Genus
Species
Capitella Notomastus
Capitella sp. Notomastus daueri Notomastus lobatus Aedicira sp.
Aedicira Aglaophamus
Aglaophamus verrilli
Namalycastis
Namalycastis sp.1 Namalycastis sp.2
Sigambra Isolda
Sigambra grubii Isolda sp.
Mytella Cyclinella Melampus
Mytella falcata Cyclinella tenuis Melampus coffeus Ellobium pellucens Acteon candens Littoraria angulifera Morulla nodulosa
Site
Nereididae
Terebellida Nemertina Mollusca
Bivalvia Gastropoda
Syllidae Pilargiidae Ampharetidae
Mytiloida Mytilidae Veneroida Veneridae Archaeopulmonata Ellobidae
Ellobium Cephalaspidea Mesogastropoda
Acteonidae Littorinidae
Acteon Littorina
Neogastropoda
Muricidae
Morulla
at a frequency of 46.2%. Molluscs represented only 4.0% of the total faunal abundance. Seasonal variation in mean monthly density of the infauna was significant (ANOVA; F ¼ 3.48; gl ¼ 11; p < 0.01) (Fig. 7.1). Density was higher at the end of the dry season (November and December) and lowest immediately after the period of peak rainfall (Fig. 7.1). N. lobatus showed highest densities (655 ind. m2). Other studies of the benthic fauna of the Brazilian Amazon coast report lower values; 316 ind. m2 on sandy–muddy beaches (Lopes 1993) and 305 ind. m2 in a muddy mangrove area (Fernandes 2003). Overall diversity, at the Furo Grande, was 1.23 bits ind.1 (Evenness ¼ 0.34) with significant differences during months of the year (Kruskal-Wallis; H ¼ 27.7; df ¼ 11; p < 0.01). Similar diversity was recorded in other mangrove areas along the north Brazilian coast. In the state of Amapa´, for example, Fernandes (2003) found 1.04 bits ind.1, whereas in the state of Maranha˜o, values of 1.58 (Lopes 1993) and 0.90 bits ind.1 (Oliveira and Mochel 1999) were recorded. However, the diversity of the benthic fauna of the Amazon coastline is very low in comparison to other regions. Dittmann (2000), for example, found much greater diversity (H0 ¼ 2.54 bits ind.1) studying a benthic assemblage in Avicennia stands in
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800
1200
700 600
1000
500
800
400 600
300
400
Rainfall (mm)
Density (Ind.m2)
7 Mangrove Infauna and Sessile Epifauna
Density Rainfall
200
200
100
0
0 S O N D
J
F M A M
J
J
A
2000/2001
Fig. 7.1 Monthly variation in benthic faunal density (ind. m2) and rainfall (mm) between September 2000 and August 2001 at the Furo Grande mangrove forest, Ajuruteua Peninsula, Braganc¸a, Para´, Brazil
Australia. The influence of rainfall and consequently sediment salinity, may be a key factor in understanding seasonal variation in the structure of the benthic faunal assemblage of the mangrove forest.
7.3
Comparison of the Benthic Fauna Among Sites with Differing Degrees of Degradation
This study was undertaken in a mangrove stand located on the western side of the PA-458 highway, at km 17 (00 550 36.300 S, 046 420 12.900 W). Based on a phytographic profile, the area was divided into three sampling sites: (1) highly degraded, (2) semidegraded, and (3) an undisturbed mangrove stand. Sediment was collected at each site every 2 months between February and December 2002 (ntotal ¼ 60), using the same methodology described above. A total of 559 individuals were collected belonging to six different phyla: Nemertinea, Mandibulata, Crustacea, Annelida, Mollusca, and Cheliceriformes, 85% of which were identified to species level (Table 7.1). Thirty individuals belonging to 17 morpho-species were collected at site 1, 228 specimens (24 morphospecies) were collected at site 2, and 301 individuals (23 morphospecies) at site 3. The most abundant morphospecies were N. lobatus (Polychaeta), dipteran larvae, crabs (Uca rapax), gastropods (Melampus coffeus) and mites (Acarina). The vast majority (72.3%) of the specimens collected were polychaetes, most of which were N. lobatus, contributing to 46.15% of the total. The second most abundant group was the Mandibulata, with 11.3% of the total. Of these, larvae of the Tipulidae accounted for 1.8% of the invertebrates collected.
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At site 1, the most abundant taxa were N. lobatus and two species of ant (Dolichoderus lutosus and Paratrechina sp.), each taxon representing 13.3% of the individuals captured. At sites 2 and 3, 42.5 and 52.2% of the invertebrates collected, respectively, were N. lobatus. Polychaeta dominated at sites 2 and 3, with 69.3 and 78.1% of the specimens, respectively. A comparison of abundance values revealed significant differences among sites (ANOSIM ¼ 0.107; p < 0.01) and seasons (ANOSIM ¼ 0.092; p < 0.01). Overall density of the benthic macrofauna was 94, 713 and 941 ind. m2, respectively, at sites 1, 2, and 3. There was a significant difference in mean density among sites (Kruskal-Wallis, H ¼ 11.25; df ¼ 2; p < 0.01). Mean monthly density varied from 1 to 11 ind. m2 at site 1, and from 8 to 36 ind. m2 at site 2. At site 3, values varied from 19 to 48 ind. m2. N. lobatus showed highest overall densities at all three sites (site 1 ¼ 13 ind. m2; site 2 ¼ 303 ind. m2; site 3 ¼ 491 ind. m2). At site 1, however, the densities of both ant species D. lutosus e Paratrechina sp. were the same as that of N. lobatus. Diversity and evenness values for the study area as a whole were H0 ¼ 2.12 bits ind.1 and E ¼ 0.58, respectively. At each site, the values were H0 ¼ 2.64 bits ind.1 and E ¼ 0.93 (site 1), H0 ¼ 2.01 bits ind.1 and E ¼ 0.63 (site 2), and H0 ¼ 1.81 bits ind.1 and E ¼ 0.58 (site 3). Diversity values varied significantly among collecting stations (Kruskal-Wallis, H ¼ 49.3; df ¼ 14; p < 0.01) (Fig. 7.2). In other studies of the fauna of mangroves of the northern Brazilian coast, the class Polychaeta has consistently been the most abundant benthic faunal group (Koch 1999; Oliveira and Mochel 1999; Acheampong 2001; Fernandes 2003). In general, the density of benthic invertebrates is very low in mangroves in comparison with marine environments (Dittmann 2002). The density estimate of 941 ind. m2 recorded in the undisturbed mangrove at site 3 during the present study is thus by far the highest value recorded for the northern Brazilian coast. Even so, these values fall far short of those recorded in subtropical mangroves (Cheng and Chang 1999). Erse´us (2002) has suggested that the density of some taxonomic groups of benthic fauna may be affected in degraded areas. This was also seen in the present study, where macrofaunal density was greatly reduced at the degraded site, in comparison with undisturbed forest. The soil at site 1 is extremely dry, which Rodrigues (1999) attributes to the blocking of the Furo do Para´ channel as a result of the construction of the highway. Desiccation has caused the soil to become compacted, making it an inadequate substrate for burrowing of benthic organisms. This may account for the low faunal density at the degraded site. At site 1, the marine mangrove fauna has been largely substituted by terrestrial organisms, principally insects. A similar situation was recorded by Fernandes (2003) in a mangrove forest, where the majority of the benthic fauna was made up of terrestrial components. According to Snelgrove and Butman (1994), organic content of the sediment may not always be the primary determinant of the distribution of the benthic fauna and may be a result of species-specific patterns of colonization or reproduction, rather than the influence of local environmental factors such as salinity and nutrient status (Fernandes 2003). Finally, spatial delimitation of the fauna in the degraded
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Fig. 7.2 Changes in (a) abundance and (b) diversity of the benthic fauna at three sites with differing degrees of degradation (DG degraded area, SDG semidegraded, and UND undisturbed area) at a mangrove stand at Km 17 on the PA-458 highway, Ajuruteua Peninsula, Braganc¸a, Para´, Brazil. 1A–3E collecting stations
area may not be related to the availability of resources but rather to restrictions on mobility imposed by the dry and compacted sediment.
7.4
Settlement of the Tidal Creek Epifauna in the Caete´ Mangrove Estuary
In contrast to the mangrove forest, which is completely flooded only during spring tide, the tidal creeks, that typically vary in water depth between 5 m at high tide and 1 m at low tide (Cohen et al. 1999), are flooded twice daily (Dittmar and Lara 2001). Salinity varies between 8 in the wet season and 39 in the dry season (Cohen et al. 1999; Dittmar and Lara 2001) with consequences for the settlement of larvae of barnacles (Fistulobalanus citerosum), mangrove oysters (Crassostrea gasar) and estuarine mussels (Mytella falcata). In November 2000, recording began of the settlement of these three species in two creeks (Furo do Meio and Furo do Cafe´) of the Ajuruteua Peninsula. Twelve months of monitoring settlement on ceramic and
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wooden panels at two different tidal heights showed that, in both creeks, peak barnacle settlement occurred during the wet season whereas oysters settled during the dry season. By contrast, settlement of mussels was generally low during the entire year. Overall, settler density was usually greater on the underside of ceramic panels close to the creek bottom (Marques-Silva et al. 2006). To investigate interannual variation, additional data were recorded from wooden panels (because of high losses of ceramic panels) close to the bottom of both creeks from November 2001 to October 2005.
7.4.1
Fistulobalanus citerosum
Settlement was high during the wet season in 2000 and in 2004–2005 (Fig. 7.3a). Between 2001 and 2003, settlement was very low except for two minor peaks in settlement of F. citerosum at the Furo do Cafe´ (Fig. 7.3a). Peaks in settlement also occurred in dry seasons. In general, there was good agreement in the timing of settlement peaks in both creeks. Barnacles are especially dense on lower surfaces and in seaward parts of mangroves, which may indicate the importance of desiccation in controlling density (Ross and Underwood 1997). Avoidance of desiccation may explain the predominance of settlement in the wet season. Predators such as Thais may be important regulators of barnacle population density on mangrove roots (Koch and Wolff 1996). The vertical distribution of adult barnacles appears to be determined by mortality occurring in the first month after settling that may include predation, intraspecific competition, and covering by algae and sediment, for example (Satumanatpan et al. 1999). Larval supply and larval behavior are also important factors causing barnacles to settle differentially on diverse substrates and zones of the mangrove (Ross 2001; Ross and Underwood 1997; Satumanatpan and Keough 2001; Satumanatpan et al. 1999). Encrusting barnacles may significantly reduce mangrove root growth (Ellison and Farnsworth 1992), and therefore barnacle predators may positively influence mangrove root development (Ellison and Farnsworth 1992; Koch and Wolff 1996).
7.4.2
Crassostrea gasar
Brazilian mangrove oysters tolerate annual variation in salinity between 0 and 40 (Nascimento 1991). In contrast to barnacles, settlement of C. gasar was restricted to the dry season, with zero settlement during the wettest months (Fig. 7.3b). Identical results were found by Sandison (1966) in a study of C. gasar (¼Gryphaea gasar) in Lagos Harbor, Nigeria. Moreover, growth of newly-settled oysters was higher during the period of high salinity. Somewhat in contrast, adult oyster survival was highest between salinities of 0 and 15 but lowest between 18 and 30 (Sandison 1966). Similarly, settlement of mangrove oysters in Brazil is greatest in waters of
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Fig. 7.3 Monthly variation in the density of newly-settled (a) barnacles, (b) oysters and (c) mussels on wooden panels (20 20 cm) between November 2000 and October 2005 at the Furo do Meio and Furo do Cafe´ creeks, Ajuruteua Peninsula, Braganc¸a, Para´, Brazil
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higher salinity whereas adult survival and growth is greater in the brackish waters of upriver locations with mangrove vegetation (Nascimento 1991). Afinomi (1984) reported that C. gasar settled throughout most of the year on mangrove roots in creeks of the Niger Delta (salinity 6–24, temperature 24–30 C) allowing yearround commercial exploitation. Settlement of larvae of C. gasar in the Casamance mangrove estuary, Senegal, was higher at a coastal site between April and June when high salinity and intermediate water temperatures occurred. However, at a landward site in a tidal creek, settlement was lower but peak numbers occurred between September and October, when water temperature was highest and salinity lowest (Gilles 1992). Similarly, at two other sites in the same region, peak settlement of C. gasar occurred when salinity values are low (IDEE 2005). High current velocities in mangrove creeks (Sandison 1966) and predation by Thais (IDEE 2005) could contribute to newly settled oyster mortality. Thus, spatial and temporal differences in mangrove oyster settlement and survival may occur, having important consequences for the choice of locations for oyster culture. In West African countries, C. gasar is commercially exploited (Ajana 1980; IDEE 2005) and cultivated (Afinomi 1984, IDEE 2005). However, management strategies for spat collection and on-growing depend on site-specific characteristics such as, for example, temperature, salinity and predator activity (Gilles 1992). In Para´ State, Brazil, C. gasar has been successfully cultivated at neighboring Nova Olinda, municipality of Augusto Correˆa where, due to the depth of the channel, current velocity and tidal exposure appear to be lower than normally found in the region. In the Caete´ mangrove estuary, there was a trend towards decreasing numbers of oysters settling over time in both creeks (Fig. 7.3b). The only significant adult mangrove oyster populations appear to be restricted to rocky substrates at the bottom of tidal channels. Where the tide uncovers the oyster beds, exploitation by locals is high and the maximum size of these oysters is low. Overexploitation of oyster beds in north-eastern Para´ state may be causing a reduction in numbers of larvae. Some beds are permanently covered by water and may contain large oysters, which, despite the difficult access, are also exploited by locals who dive 3–4 m to harvest them.
7.4.3
Mytella falcata
Generally restricted to the wet months, newly-settled mussel (M. falcata) spat may not tolerate desiccation. Pereira and Grac¸a Lopes (1995) found no settlement of M. falcata in the intertidal zone whereas settlers were abundant in the subtidal area. In our study, settlement was lowest in the dry months with the exception of October and November 2003 when unusually high numbers were recorded (Fig. 7.3c). Mussel settlement appeared to be greater in the Furo do Cafe´. Abundant populations of adult mussels occur on the tidal flats of the lower reaches of estuaries and are subject to intense human exploitation (Santos 2005). The beds are visited from August or September when mussels are near market size, and are usually completely depleted (Santos 2005). Mussels are removed using spades, rakes and
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other hand-held tools and thus the sediment is severely disturbed by harvesting activities. Mussels of all sizes are taken and it takes almost a year for further colonization to occur with some beds taking longer. Growth of M. falcata is being studied by us using newly-settled juveniles captured on ropes placed in tidal creeks. Young mussels are between 2.4 and 5.6 mm after a week and are then transferred to plastic recipients for on-growing for differing periods of time (1–12 months). The results to date suggest that
Fig. 7.4 Differences in settlement of epibenthos on wooden panels (20 20 cm) in creek and mangrove habitats shown by monthly variation in the density of newly-settled barnacles, oysters and mussels, respectively, in the (a, c, e) Furo do Meio and (b, d, f) Furo do Cafe´ creeks, Ajuruteua Peninsula, Braganc¸a, Para´, Brazil
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M. falcata may reach market size (ca. 40 mm) in up to 4 months and that a maximum size of 50–55 mm may be obtained in 5–6 months. There is therefore potential for mussel culture in the region given the relatively high abundance of settling larvae and rapid growth of juveniles.
7.5
Differences in Settlement of Epibenthos Between Mangrove and Tidal Creek Habitats
A comparison of settlement on wooden panels in the Furo do Meio and Furo do Cafe´ creeks with that on panels in the adjacent mangrove was carried out from January to December 2004. Not surprisingly, the results (Fig. 7.4) show striking differences in numbers of settlers of barnacles (F. citerosum), oysters (C. gasar) and mussels (M. falcata) between both habitats with very low levels of settlement, or none at all, in the higher, less frequently flooded, mangrove forest. This agrees with Koch and Wolff’s (2002) observation that filter-feeders predominate in the lower creek habitat.
7.6
Conclusions
In the Caete´ mangrove estuary, polychaetes, especially N. lobatus, dominate the mangrove fauna, even in degraded mangrove stands. Diversity in degraded mangroves may be similar to or even greater than undisturbed stands due to the replacement of the marine fauna by a terrestrial fauna, mainly insects. A study of the diversity of the epibiont assemblage of mangrove roots along the northern coast of Brazil, which is subject to high seasonal inputs of freshwater, should be carried out for comparison with that of the Caribbean region which appears to be highly diverse (Ellison and Farnsworth 1992; Marquez and Jimenez 2002). Finally, most of the studies in the region are mere descriptions of macrofaunal assemblages, often in relation to spatial and temporal variation in biological and environmental factors. While there is a need for such descriptions due to a lack of knowledge of the fauna, greater emphasis on experimental ecological studies will allow a more thorough quantification of biological and environmental interactions of the benthic macrofauna of the Caete´ mangrove estuary.
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Kathiresan K, Bingham BL (2001) Biology of mangroves and mangrove ecosystems. Adv Mar Biol 40:81–251 Koch V (1999) Epibenthic production and energy flow in the Caete´ mangrove estuary, North Brazil. PhD thesis, University of Bremen, Bremen. ZMT Contribution vol 6 Koch V, Wolff M (1996) The mangrove snail Thais kiosquiformis Duclos: a case of life history adaptation to an extreme environment. J Shellfish Res 15:421–432 Koch V, Wolff M (2002) Energy budget and ecological role of mangrove epibenthos in the Caete´ estuary, North Brazil. Mar Ecol Prog Ser 228:119–130 Lana PC, Camargo MG, Brogim RA, Isaac VJ (1996) O bentos da costa brasileira: avaliac¸a˜o crı´tica e levantamento bibliogra´fico (1858–1996). FEMAR, Rio de Janeiro Lee SY (1998) Ecological role of grapsid crabs in mangrove ecosystems: a review. Mar Freshw Res 49:335–343 Levinton JS (2001) Benthic life habitats. In: Levinton JS (ed) Marine Biology. Oxford University Press, New York, pp 245–268 Lopes ATL (1993) Distribuic¸a˜o e densidade da macroendofauna bentoˆnica de substratos mo´veis do mesolitoral da Ilha do Cajual, Alcaˆntara, Maranha˜o. MSc thesis, University of Pernambuco, Recife Mann KH (2000) Estuarine benthic systems. In: Mann KH (ed) Ecology of coastal waters with implications for management. Blackwell, Oxford, pp 118–135 Marques-Silva NS, Beasley CR, Gomes CP, Gardunho DCL, Tagliaro CH, Schories D, Mehlig U (2006) Settlement dynamics of the encrusting epibenthic macrofauna in two creeks of the Caete´ mangrove estuary (North Brazil). Wetl Ecol Manag 14:67–78 Marquez B, Jimenez M (2002) Associate molluscs of immersed roots of the red mangrove Rhizophora mangle, in Golfo de Santa Fe, Estado Sucre, Venezuela. Rev Biol Trop 50:1101–1112 Nascimento IA (1991) Crassostrea rhizophorae (Guilding) and C. brasiliana (Lamarck) in South and Central America. In: Menzel W (ed) Estuarine and marine bivalve mollusk culture. CRC, Boston, MA, pp 125–134 Nonato EF, Amaral ACZ (1979) Annelida Polychaeta. Caracterı´sticas, glossa´rio e chaves para famı´lias e geˆneros da costa brasileira. Editora da Unicamp, Sa˜o Paulo, Brazil Nordhaus I, Wolff M, Diele K (2006) Litter processing and population food intake of the mangrove crab Ucides cordatus in a high intertidal forest in northern Brazil. Estuar Coast Shelf Sci 67:239–250 Oliveira VM, Mochel FR (1999) Macrofauna beˆntica de substratos mo´veis de um manguezal sob impacto das atividades humanas no sudoeste da Ilha de Sa˜o Luı´s, Maranha˜o, Brasil. Bol Lab Hidrobiol 12:75–93 Pereira OM, Grac¸a Lopes R (1995) Fixac¸a˜o de sementes de Mytella falcata (sururu) em coletores artificiais no Canal de Bertioga, Estua´rio de Santos, Estado de Sa˜o Paulo, Brasil. Bol Inst Pesca 22:165–173 Rebelo FC (1986) Metodologia para o estudo da endofauna de manguezais (macrobentos). In: Schaeffer-Novelli Y, Cintro´n G (eds) Guia para estudo de a´reas de manguezal, estrutura, func¸a˜o e flora. Caribbean Ecological Research, Sa˜o Paulo, pp 162–187 Rodrigues, AAF (1993) Migrac¸o˜es, abundaˆncia sazonal e alguns aspectos sobre a ecologia de aves limı´colas na Baı´a de Sa˜o Marcos, Maranha˜o – Brasil. MSc thesis, University of Para´, Bele´m Rodrigues KB (1999) Estudo topogra´fico da a´rea degradada e do bosque de Avicennia no manguezal de Braganc¸a, Para´. Monograph, University of Para´, Bele´m Ross PM (2001) Larval supply, settlement and survival of barnacles in a temperate mangrove forest. Mar Ecol Prog Ser 215:237–249 Ross PM, Underwood AJ (1997) The distribution and abundance of barnacles in a mangrove forest. Aust J Ecol 22:37–47 Sampaio D (2004) Comparac¸a˜o da fauna macrobentoˆnica em bosques de mangue com diferentes graus de degradac¸a˜o no municı´pio de Braganc¸a-Para´. MSc thesis, University of Para´, Bele´m Sandison EE (1966) The effect of salinity fluctuation on the life cycle of Gryphaea gasar ((Adanson) Dautenberg) in Lagos Harbour, Nigeria. J Anim Ecol 35:379–389
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Santos HSS (2005) Levantamento da densidade, biomassa e a´rea de bancos de mexilho˜es Mytella falcata (d’Orbigny, 1846), localizados em Nova Olinda, Augusto Correˆa, PA. MSc thesis, University of Para´, Bele´m Santos SML, Tagliaro CH, Beasley CR, Schneider H, Sampaio I, Santos Filho C, M€ uller ACP (2005) Molecular studies of Teredinidae (Mollusca: Bivalvia) from northern Brazil and taxonomic implications. Genet Mol Biol 28:175–179 Santos Filho C, Tagliaro CH, Beasley CR (2008) Seasonal abundance of the shipworm Neoteredo reynei (Bivalvia, Teredinidae) in mangrove driftwood from a northern Brazilian beach. Iheringia Ser Zool 98:17–23 Satumanatpan S, Keough MJ (2001) Roles of larval supply and behaviour in determining settlement of barnacles in a temperate mangrove forest. J Exp Mar Biol Ecol 260:133–153 Satumanatpan S, Keough MJ, Watson GF (1999) Role of settlement in determining the distribution and abundance of barnacles in a temperate mangrove forest. J Exp Mar Biol Ecol 241:45–66 Skilleter GA, Warren S (2000) Effects of habitat modification in mangrove on the structure of mollusc and crab assemblages. J Exp Mar Biol Ecol 224:107–129 Snelgrove PVR, Butman CA (1994) Animal-sediment relationships revisited: cause versus effect. Oceanogr Mar Biol 32:111–177 Wolff M, Koch V, Isaac V (2000) A trophic flow model of the Caete´ Mangrove Estuary (North Brazil) with considerations for the sustainable use of its resources. Estuar Coast Shelf Sci 50:789–803 Zavala-Camin LA (1996) Introduc¸a˜o aos estudos sobre a alimentac¸a˜o natural em peixes. Editora da Universidade Estadual do Maringa´ (EDUEM), Maringa´
Part IV Dynamics in the Mangrove System
Chapter 8
Drivers of Temporal Changes in Mangrove Vegetation Boundaries and Consequences for Land Use R.J. Lara, M. Cohen, and C. Szlafsztein
8.1
Introduction
Wetland structure is highly dependent on inundation dynamics, which is in turn basically determined by basin topography and hydrological (fluvial and tidal) regime. Thus, a deep knowledge of the relationships among these factors is necessary in order to evaluate the stability of wetlands. Models incorporating this information can be useful to describe and predict the distribution of inundationdependent physicochemical soil parameters and related shifts in vegetation structure, particularly in a highly dynamic, changing environment. A main target of such models is the recognition of geobotanical patterns and their relationship with basin type, as well as the connections among the characteristics and distribution of wetland vegetation units and the spatial patterns of inundation frequency and salt content of surface sediments along the estuarine salinity gradient. This involves the integrated analysis of basin properties such as topography, inundation frequency, properties of adjoining water bodies, sediment and vegetation features. The information so gained can be incorporated into the analysis of vegetation changes and derived modifications of land use, and applied to the development of corresponding management scenarios.
8.2
Influence of Inundation Frequency and Sediment Salinity on Wetland Structure
The mangrove forests and adjoining wetlands on the Braganc¸a Peninsula (166 km2) are distributed within a topographic difference of about 1.5 m, with a tidal range of 4 m. In the dry season, this slope embraces a salinity range from about 10 to 90, depending on the position along the estuarine salinity gradient and on the topographical elevation. The main vegetation units in the Braganc¸a Peninsula and their relationship with topography along a longitudinal transect are shown in Fig. 8.1. U. Saint-Paul and H. Schneider (eds.), Mangrove Dynamics and Management in North Brazil, Ecological Studies 211, DOI 10.1007/978-3-642-13457-9_8, # Springer-Verlag Berlin Heidelberg 2010
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Fig. 8.1 Topographic profile of the Braganc¸a peninsula related to mean sea level (M.S.L.) with vegetation units, porewater salinities at 10 cm depth (dry season) and mangrove vegetation height (from Cohen and Lara 2003)
This system includes different vegetation types ranging from low-salinity, high Rhizophora forests with understorey, to hypersaline environments with an Avicennia dwarf forest, to an elevated mudflat with succulent plants in the center of the peninsula. The latter, highest sector is flooded much less frequently (<28 days/ year) than the mangrove vegetated areas, only during the highest spring tides. These flats constitute a hypersaline habitat, at least during the dry season, with porewater salinities reaching 90 and 100 (Fig. 8.1, sector A). There, within a 20 cm topographical gradient, vegetation changes from a monospecific Avicennia stand with trees of about 10 m height to a “dwarf” forest and to a salt marsh with abundant Sesuvium and other halophytes (Chap. 4), reaching salinities 90 in the dry season. This ecotone has shown to react sensitively to changes in inundation frequency, presumably due to sea-level rise (Cohen and Lara 2003). This sector changes smoothly into a wide extension of mudflats with a topographical gradient of around 1:3,000 covered by mangroves, extending for 3–6 km down to the mid-tide mark and being dissected by creeks that are much deeper than those in the elevated flats. These mudflats are inundated only during normal spring tides (28–78 days/year), with porewater salinities between 90 and 50, and are covered mainly by Avicennia. At about mid-tide level, a slope break occurs and an area of relatively steep, frequently flooded (233 days/year) mudflats with porewater salinity around 36 and mixed mangrove forest leads down to Rhizophora-dominated sectors fringing the estuary. Similar patterns were identified by Santos et al. (1997) in the mangroves of Maranha˜o State (northern Brazil) with porewater salinities between 35 and 50 around the mean high tide level. Similar to Para´, small Avicennia germinans trees occur in a hypersaline zone with porewater salinities around 80, positioned between the mean high tide level and the mean spring tide level. This area is limited by hypersaline tropical salt marsh communities with porewater salinities between 90 and 100 and is also close to the mean spring tide level. Previous work (Cohen and Lara 2003) indicated an inverse relationship between vegetation and topographic heights in a transect along the longitudinal axis of the Braganc¸a Peninsula (Fig. 8.1) indicating a close correlation between hydrography and vegetation structure.
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Inundation frequency and porewater salinity are important driving forces influencing vegetation patterns, as discussed below. In several studies, an inverse relationship between vegetation height or aboveground biomass and substrate salinity has been reported (e.g., Cintro´n et al. 1978; Saintilan 1997). However, the strong dependence of porewater salinity on, e.g., rainfall or inundation frequency makes it difficult to compare data from different sources even in a limited area. Thus, there is a need for proxies for describing the average physiological status of vegetation as a function of potential stress factors. Slavich et al. (1999) developed a “salinity index” for assessing flood impact on the health of vegetation in a saline floodplain. This index reflects the impact of flooding history on the long-term average soil water salinity, is strongly dependent on the inundation dynamics, and may be used as a management tool within a GIS. Topographical analyses of fluvial environments based on digital elevation models (DEMs) have been limited almost exclusively to areas of significant topographic relief or have used finer-scale DEMs that were generated from field surveys limited to small areas of a couple of hectares. Townsend and Walsh (1998) used a vertical resolution of 1 m for modeling the inundation and potential wetness of about 40,000 ha of floodplain, integrating GIS and remote sensing information. Poiani and Johnson (1993) used a finer resolution of <1 m for a spatial simulation of hydrology and vegetation dynamics in prairie wetlands embracing an overall area of about 4 ha. Modeling or description of the structure of salt marshes and mangroves can require a much higher vertical resolution of, e.g., about 10 cm for large areas. As mentioned above, the mangrove forests and adjoining wetlands on the Braganc¸a Peninsula embrace a topographic gradient of 1.5 m. Thus, a highresolution DEM-based model is essential for understanding the current wetland structure and the reactions of their different vegetation units to changes in the environmental setting. Therefore, an empirical, multiple regression and GIS-based model was developed for the Braganc¸a Peninsula, using high-resolution topographical and tidal information, and field data of porewater and estuarine salinity and vegetation structure, which allowed a realistic appraisal of the distribution of porewater salinity and vegetation height. For this, it is assumed that, in the dry season, porewater salinity is basically determined by the combined effects of salt input and leaching during inundation and evaporation. This assumption would predict salt accumulation at topographically higher locations, while near waterways, porewater and surface water should have similar salinities. Due to the overall high silt-clay content of >70% (Schwendenmann 1998) of the surface sediments in this region, their characteristics and effect on salt cycling were assumed to be invariable for the whole peninsula. Thus, for the dry season, porewater salinity would be solely determined by the local inundation frequency and the salinity of the estuarine water flooding the site. However, since the catchment areas on each side of the Braganc¸a Peninsula have different runoff characteristics, salinity distribution in each estuary is also different. Thus, the salinity of water from each estuary flooding the wetlands at each side of the peninsula’s watershed is also different. Therefore, higher places, seldom inundated by brackish water can have higher salinities that
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fringe mangroves daily inundated by seawater. The measured porewater salinities extended from 12 in the “fluvial” forests of Acarajo´ to almost 100 in the salt marsh in the seldom-flooded, topographically highest center of the Braganc¸a Peninsula. Estuarine water salinities ranged from 30 to 35 in the Maiau Bay and from 17 to 35 in the Caete´ Bay (see Chap. 3 for a geographic description of the peninsula and its boundaries). The implemented model described above includes a non-linear function of calculated inundation frequencies, the measured water salinity distribution in the adjacent estuaries, and sediment porewater salinities determined in the dry season (Lara and Cohen 2006). Its main output was a synoptic distribution of sediment porewater salinity for the whole Braganc¸a Peninsula, derived from values predicted by the model equation. The adequacy of the calculated inundation frequencies and of the porewater salinities produced by the model as a proxy of the average vegetation condition, sensu Slavich et al. (1999), was examined by a comparison of their relationship to tree height. A dataset was created including all available tree height data and the corresponding site inundation frequencies. A non-linear function of the calculated inundation frequencies was a good predictor of tree height, which should tend to be asymptotical as inundation frequency reaches a maximum. The fit used produced a highly significant correlation (r ¼ 0.89, n ¼ 80, p < 0.001) and an asymptote value of 21 m (Fig. 8.2), which is a realistic average value for the highest trees found at the more frequently inundated sectors of the Braganc¸a Peninsula. The porewater salinity values predicted by the model were adequate proxies for an average, synoptical stress situation in the dry season on the Braganc¸a Peninsula,
Fig. 8.2 Relationship between vegetation height and calculated inundation frequency (from Lara and Cohen 2006)
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and showed a highly significant correlation with tree heights (Fig. 8.3). Nonetheless, a close examination of apparent data scatter revealed the existence of at least three groups with a clear assignment to different vegetation units. In Fig. 8.3, the circles correspond to values from a monospecific Avicennia forest growing in a topographically high sector of the peninsula. These trees appear to grow under salt stress and have significantly smaller diameters in breast height (dbh) than trees of similar height in sectors with lower salinities (Menezes et al. 2003). This data subset above the regression line for “average forest” seems to represent a system under physiologically sub-critical, though hydrologically stable, conditions. The group marked with empty squares – “small” forest – corresponds to a low-height, high-salinity, high-density Avicennia stand, growing at the boundary of a salt marsh with Sesuvium, whose substrate can even show a thin salt crust in the dry season. This forest has also been called “dwarf” in the past. Nonetheless, analysis of satellite images shows that not only is most of this dense forest low in height it is also young (2–25 years) and is rapidly invading the salt marsh, probably as a response to increasing inundation frequency due to relative sea-level rise (Lara et al. 2002; Cohen and Lara 2003). Thus, this data subset represents a mangrove
Fig. 8.3 Relationship between vegetation height and sediment porewater salinities calculated with the multiple regression model described in Lara and Cohen (2006)
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forest with a boundary under physiologically critical but hydrologically changing conditions, evolving towards a sub-critical or a “benign” situation. The low height of these trees is in part a result of growth under salt stress but is also caused by their young age. At this point, it must be considered to what extent the effect of porewater salinity can be separated from the influence of the inundation itself. Both variables can highly correlate; however, the inundation regime affects not only salinity but also the redox and pH conditions in the sediment and, through this, also influences nutrient availability and forest structure. In previously investigated high-resolution topographic gradients in the Braganc¸a Peninsula, leaf phosphorus, available phosphorus in sediments, and tree height showed a significant positive correlation with inundation frequency (Cordeiro et al. 2003). The main dataset, named “mixed” in Fig. 8.3, corresponds to tree heights between 7 and 20 m for salinities in the range of 30–70 and shows a strong inverse correlation between these parameters. In Central and South America, similar patterns have also been reported by, e.g., Soto and Jimenez (1982) for mangroves in Puerto Soley at the north Pacific coast of Costa Rica and by Santos et al. (1997) in northern Brazil. The overall low diversity of mangrove tree species in the neotropics make them particularly suitable for the investigation or testing of general tendencies of basic abiotic–biotic relationships as in the porewater salinity model. The dynamics of the “small” forest, and the fact that most height values are, albeit below, close to the general trend, offers the interpretation that in the near future this forest will evolve to an average situation characteristic of most of the Braganc¸a Peninsula. Thus, we pooled this data subset with that from the mixed forest for the calculation of the regression equation. Even at extreme salinities, not included in the dataset, the regression equation renders reasonable values. For example, for salinities of 90, 95 and 97, the predicted vegetation heights decrease from 2.25 m to 70 cm and 8 cm, which realistically represents the transition from the “small” Avicennia forest into the Sesuvium sector. At low salinities of 10 and 17, the predicted heights are about 27 and 25 m, respectively. This is roughly in the range of the mean height of the three highest trees (29.33 0.89) reported by Menezes et al. (2003) for a brackish sector of the Braganc¸a Peninsula. It is clear that the kind of relationship as expressed by this empirical model is very general and does not explicitly consider, e.g., the existence of strata, age structure or climax situations. However, it must be considered that the good fit obtained for the relationship between vegetation height and porewater salinity for the Braganc¸a mangroves was obtained with predicted and not with measured salinities, clearly indicating the robustness of this indicator. Further, isolines of predicted porewater salinities for the whole peninsula rendered a synoptic distribution with a good correspondence with measured field data, as well as realistically delimited geobotanical units such as the salt marshes in the center and north of the peninsula (see Chap. 4).
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8.3
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Changes in Current Vegetation Units: Boundaries, Ecotone Shifts and Consequences for Land Use
Mangroves, like other coastal wetlands, are considered highly susceptible to sealevel rise (Gornitz 1991; Boorman 2000). Their extent is governed by tidal exposure and depends on the balance between sea level and sediment accumulation (Chapman 1960). Thus, a relative sea-level rise can result in both a mangrove retreat near the shoreline and a landward migration as a result of the increase in inundation frequency (Hanson and Maul 1989). In this context, it is relevant to assess whether the boundaries of vegetation units are stable or how they have changed in recent times. In general terms, specific sectors of two main geobotanical units in the Braganc¸a region have shown evident changes in the last decades. These are the periphery of the mangrove forest along the coastline, and the ecotone shifts involving the limit between mangrove and salt marshes in the central part of the peninsula.
8.3.1
Coastline Vegetation Changes
The evolution of mangrove coverage along a coastline of 170 km length, including the Braganc¸a coastal plain and adjacent sectors, was analyzed by time series of satellite images covering 25 years (Cohen and Lara 2003). In general, there were net losses of vegetation coverage. Vegetation death was mainly caused by erosion and/or landward sand migration, as well as deposition on top of older mud sediments (Fig. 8.4a–c). During the 1972–1997 period, losses were registered along 42% of the coastline length. For the same time span, no changes were observed along 39% of the coastline, while coverage gains occurred along 19%. In 1972, the study area had mangrove vegetation coverage over an area of about 592 km2, which progressively declined to 585, 583 and 573 km2 in 1986, 1991 and 1997, respectively. Local tendencies of coverage gain or loss were consistent for almost the whole studied area during the investigated period. In the 1972–1997 period, the overall net loss of vegetation coverage was 19 km2, representing a total net loss of 3.19%, which is 0.76 km2/year. On average, about 0.13% of the coverage was lost per annum, but the trend seems to have intensified in the 1991–1997 period. Gross coverage loss increased from 0.22 to 0.30 to 0.32%/year during the three periods assessed from 1972 to 1997. The overall annual rate of gross coverage gain increased from 0.13%/year in 1972–1986 to 0.24%/year in 1986–1991, decreasing sharply to 0.046%/year in 1991–1997. This indicates that, during the last period, in addition to an increase in gross loss, vegetation expansion had also stopped, even in the areas with previous gross gains where abiotic conditions should be more favorable for vegetation growth. This is the case, for example, on the west coast of Boiuc¸ucanga Island (Fig. 8.4a), which had a gross coverage gain of 0.55 km2
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Fig. 8.4 Evolution of coastal vegetation (map) according to the analysis of RADAR and satellite images covering a 25-year period (1972–1997). Aerial photographs (a) (b), (c), and (d): damaged sectors of the inner and outer mangrove
between 1972 and 1986, presenting no gains but gross losses in the last two periods. At the mouth of the Furo do Chato tidal creek, gross gains decreased throughout the three investigated periods from 0.15 to 0.063 to 0 km2. At the present rates, mangrove vegetation on some islands may soon disappear. For example, Maiau Island (Fig. 8.4c) presented insignificant gross gains over the last 25 years, while the annual rate of net loss has increased. An extrapolation of these trends suggests that all the mangrove vegetation on this island may perish within the next 15 years, perhaps sooner. If the rate of net coverage loss – 3.2% in 25 years – persists, the mangroves in the studied region would disappear almost entirely in 750 years. However, this may be a very conservative estimate. Global mean sea level has risen approximately 1–2 mm/year over the last 100 years (Gornitz 1995; Nakada and Inoue 2005), and the sea level could rise by about 80 cm by the year 2100 (Titus and Narayanan 1995; Douglas et al. 2000). In the Braganc¸a coastal plain, mangrove forests occur within a topographical range of 1.0 m between their boundaries and the inner peninsula. Thus, in this scenario, the distribution of mangroves would be restricted in 100–200 years to narrow bands along the estuary, which would retreat landward, leaving only small, mangrovecovered islands with more elevated topography.
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Nevertheless, loss rates should be interpreted with caution, since the driving forces of this process may be multiple and interrelated. Sand deposition causing mangrove death may be caused not only by transgression but also by littoral drift currents generated by waves (Suguio et al. 1985). Furthermore, the Para´-AmazonOrinoco plain is characterized by chernier formation (Price 1955), which is induced by the dominant winds and currents and which could cause cyclical, increased sand migration. The coasts of Suriname have extensive, shore-oblique mudshoals separated by troughs, considered as giant mudwaves with a migration period of 30 years. The cheniers may grow between the mudflats (Augustinus 1980). Until now, there have been no investigations dealing with the periodicity of formation of such geoforms in our study region. It is possible that recurrent, large-scale oscillations of wind or current regimes generate modifications in local sediment dynamics, inducing periods of prevailing gains or losses in the mangrove coverage along the coastline. If this phenomenon is merely a periodic oscillation, there must be evidence for cycles of death and recolonization at the marginal zones of the ecosystem. The satellite images used in this work show the presence of several paleo-cheniers or beach ridges partially covered by vegetation on this and neighboring peninsulas (Szlafsztein, unpublished). Thus, it is unclear to what extent the observed vegetation losses represent a short-term oscillation around “steady state” conditions, or whether it is consequence of a long-term, more generalized phenomenon, such as sea-level rise. This issue is further addressed in the next section.
8.3.2
Ecotone Shifts
Even subtle increases in the soil salinity caused by changes in rainfall or tidal flooding regimes can produce significant ecotone shifts in coastal regions. Thus, ecotone surveillance can serve as a warning system of short- to mid-term changes in the environmental setting in the scale of a few years. Vegetation coverage changes in the mangroves along the coastline of north Brazil have been significant in the last decades. Further, there are evident signs of an active shift of the ecotone between mangrove forest and herbaceous vegetation in seldom-inundated wetlands in the central area of the Braganc¸a Peninsula, which is flooded only during the highest spring tides. In this sector, a mangrove forest dominated by A. germinans limits with a salt marsh that in the dry season reaches sediment porewater salinities about 90, a critical value for tree development. In the ecotone, the grass Sporobolus virginicus and the herb Sesuvium portulacastrum coexist with small A. germinans (black mangrove) trees (0.5–2 m). An invasion of the mangrove front into the marsh area is highly dynamic and can be clearly followed during the 1972–1997 interval. The open marsh area consisted of 8.8 km2 in 1972 and had shrunk to 5.6 km2 by 1997, i.e., decreased 37% in 25 years, replaced by a monospecific stand of Avicennia. Mangrove invasion closely followed topography, being more
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pronounced in the area with a lower slope. The present boundary between marsh and mangrove corresponds to an inundation frequency of 40 days/year, with Avicennia trees 1–5 m height. The former mangrove/marsh boundary in 1972 is now inundated for about 60 days/year and presents trees of 8–10 m height. Marsh areas were converted to percentages of the 1972 value, which was taken as 100%. Regression analysis indicated a linear, highly significant (r ¼ 0.98, n ¼ 7, p < 0.001) relationship between these percentages and time. A linear extrapolation indicates that the herbaceous vegetation would disappear about 2035, probably to be replaced by an Avicennia forest. The low tree heights in the ecotone may be mostly due to the fact that trees have established relatively recently. Nevertheless, at several sites along the mangrove expansion front, trees seem to be growing under higher salinity stress. Therefore, it is probable that salt leaching as a result of increasing inundation frequency is displacing the boundaries of high soil salinity sectors, expanding the substrate area where mangroves can grow. A similar effect caused by a sustained trend of increasing rainfall seems unlikely. The analysis of a 25-year rainfall dataset from a neighboring meteorological station (Tracateua) did not reveal such a pattern for the investigated period, but instead a clear inverse relationship to the intensity of El Nin˜o events (Lara, unpublished). Vetter and Botosso (1989) reported correlations between rainfall, El Nin˜o strength and growth ring thickness in trees of Central Amazonian trees. However, to our knowledge, this kind of dependence has hitherto not been investigated for mangrove forests. The assumption that an increase in inundation frequency is driving the ecotone shift in the higher sectors of the peninsula is further supported by the extrapolation of the advance of the topographical mangrove/marsh boundary, which corresponded to a height of 2.4 m above m.s.l. in 1972 and of 2.5 m in 1997. This topographical change in the vegetation boundaries indirectly suggests the magnitude of the relative sea level rise expected for the area which, assuming linearity, would correspond to a rate of increase of 0.4 cm/year. At this rate, the ecotone or limit between both habitats would be about 15 cm higher in 2035 than in 1997. Thus, since the highest point in this sector is about 2.60 m, most marsh plants would have disappeared by that time, having been substituted by mangroves. These extrapolations are compatible with predicted estimates of sea-level rise. According to Titus and Narayanan (1995), there is a 1:1 possibility that greenhouse gases will have produced a sea-level increase of at least 15 cm in the year 2050, 35 cm in 2100, and 80 cm in 2200. A projection of the first estimate would imply that, by 2035, sea level might have risen by about 10 cm compared to 1997. The IPCC (2007) midrange projection for sea level rise in this century is 20–43 cm. Thus, it seems realistic that the advance of mangrove forests towards higher locations continues. Further, considering that changes in the boundaries of the mangrove vegetation and the establishment of sand accumulation surfaces (beaches) have been observed in recent times, a significant influence on land use and coastal vulnerability could be expected.
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8.3.3
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Consequences for Land Use
Mangroves and marine beaches are important and sensible landscape units that are protected and conserved in Brazil by laws of diverse government levels, e.g., the National Coastal Zone Management Program (IBAMA 1992). The major differences among the different legislation bodies reside in the type of property and use allowed or recommended in each of them. The mangrove can or cannot be considered as private property; however, the marine beaches, many of which originate after the migration of mangrove boundaries, are defined by the Brazilian Constitution (art. 20 IV) (Brasil 1988) as part of the national and public heritage. Further, this Constitution declares the use of private property as subject to a social function, such as, e.g., the “protection and conservation of the environment”. On the other hand, according to the article 10 of the Federal Law N 7.661/88 (IBAMA 1992), the marine beaches are for the common use of the population, and therefore the only aspect that must be preserved is the free access to them (see discussion below on the consequences of the construction of the road Braganc¸a-Ajurutea). Mangroves are of fundamental importance for the economical subsistence of local populations, but the progressive change of mangrove into sand accumulation surfaces establishes less biologically rich environmental units. As a consequence, settled communities considering the extraction of mangrove ecosystem products observe a decrease in the quantity, type and quality of the fish and crustaceans captured and move to other regions. The migration of coastal areas communities is also originating in the increasing erosive processes (see also Chap. 3). The Federal Forestry Code (Brasil 1965) established the “permanent preservation” of all vegetation forms which contribute to dune fixation or mangrove establishment, which has been interpreted as a prohibition of the use of any components of mangrove flora. In 1988, the “National Plan for Coastal Management” (IBAMA 1992) elaborated criteria for rational resource utilization in the coastal zone, prioritizing the conservation and protection of wetlands (Leme Machado 1993). The Laws 6938/81 and 7661/88 (IBAMA 1992) declare as punishable criminal offenses all activities leading to the degradation of “ecological reservations”. Since sustainable management of wood extraction by definition should not degrade the ecosystem, then this regulation provides an opening for the transformation of current uncontrolled illegal mangrove wood extraction activities into controlled management. For landowners with mangrove encroachment problems on their land, this also represents a way to develop sustainable legal forms of utilizing mangrove timber resources. In 1999, the State of Para´ declared the extraction of mangrove bush plants or trees illegal in all its territory (ALEPA 2000). The Organic Law of the City of Braganc¸a establishes that the Municipality can define protection areas, and prohibit any kind of utilization which may endanger flora and fauna in the coastal region (Braganc¸a 1990). No such protection areas had hitherto been established in this region. In the context above, the study case described in Sect. 8.3.2 is of particular interest. The topographically higher herbaceous plain experiencing Avicennia
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invasion is part of a farm situated in the central part of the peninsula. This area has been used since at least 1870, and until recently as grassland for water buffaloes and other bovines, though these activities have today mostly been abandoned. According to the Federal Forestry Code (Brasil 1965), this farm constitutes an environmental setting that contributes to mangrove establishment and thus represents an area of “permanent preservation”. This prohibits tree extraction, at least without an approved management plan. Further, the alternatives for commercial use of this sector are very limited: crab density is very low in Avicennia forests and fishery is not possible due to the absence of deeper creeks. Thus, under the current interpretation of relevant legislation, the usable area of this private farm has fallen by about 40% in 25 years and will probably disappear in the next 35 years. Mangroves play a crucial role in coastal dynamics, particularly under conditions of sea-level rise, and clearly must be preserved. However, ecosystem protection, reduced to the function of strict or partial prohibition of resource use, could cause unsustainable outcomes such as the disintegration of the economic strategies of rural households and consequent migrations of coastal populations to already overloaded urban areas. The state of Para´ has had the highest urban growth in its history during the last decade (IBGE 2000). The development of different management scenarios and the evaluation of their ecological, economic and social consequences can be facilitated by Decision Support Systems (O’Callaghan 1996), as exemplified in Fig. 8.5 for this study case.
Decision maker: users, politicians, scientists
Definition of requested conditions (e.g. protection of mangrove areas, preservation of social & economic sustainability)
Definition of possible management actions (e.g. controlled wood utilization, restablishment of natural hydrological regime in degraded areas)
Comparison of achieved & requested situations (e.g. with similar mangrove areas in natural conditions)
Implementation of desired management actions (e.g. enacting licence for supervised wood extraction)
Evaluation of consequences (e.g. assessment of ecological impact on forest dynamic and on internal (mangrove communities) and external (trade with the city) social structures
Fig. 8.5 Example of a decision support scheme, applied to a specific situation combining mangrove protection and use
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Decision makers should include resource users, politicians and scientists who should jointly define the requested systems conditions, such as the protection of mangrove areas and the preservation of the social and economic sustainability of a low-income population. An explicit operational goal could be the definition of areas for forestry studies in the farmland and specific sectors of the central peninsula under controlled quantity, spacing and frequency of wood extraction. A selective wood extraction would have the same effect on the development of the mangrove forest as the natural self-thinning process (Berger and Hildenbrandt 2000). This occurs in all forest stands under development and is analyzed and described for mono-specific cohorts in detail (Londsdale and Watkinson 1982; Londsdale 1990; Quang 1994; Adler 1996; Guo and Rundel 1998). The implementation risk of each scenario must be assessed including consideration of the ecological impact on the forest development as well as the effect on the internal (“mangrove communities”) and the external (trade with the city) social and economic structure. The former can be accomplished by using simulation models (Baker 1992; Bart 1995; Twilley et al. 1999). It must also be considered that mangrove vulnerability is not the same everywhere. Severe ecosystem degradation can be expected in the case of wood extraction along the coastline, where trees and sediment are exposed to higher energy and thus to erosion. In less frequently inundated low-energy areas such as the central part of the peninsula, mangrove vegetation will be more negatively affected by disturbances of the hydrological regime. This happened after the construction of the road Braganc¸a–Ajurutea: in order to facilitate tourism development on the beaches in the North of the peninsula, a road was built in 1974 across the mangroves. This constrained tidal inundation in some topographically higher locations, leading to the death of an estimated 6 km2 of mainly Avicennia forest on the left side of the road (Fig. 8.4e, “degraded mangrove”), while the right side apparently did not suffer any obvious impact. During, or as a consequence, of this process, the local population actively extracted wood from the degraded area. Analysis of available satellite images shows a partial recolonization of this sector, reducing the degraded area progressively from 3.8 km2 in 1986 to 2.9 km2 in 1997. It is not clear whether this process responded to “normal” vegetation dynamics or was accelerated by the increase in inundation frequency postulated as the responsible driving force of the Avicennia invasion in the herbaceous plain. In conclusion, if a controlled wood extraction was allowed in some parts of the farmland, the natural structure development of the forest would probably not be disturbed. The regulation of this activity could reduce the common practice of illegal, uncontrolled wood extraction in the mangroves of the region. Besides, simple management actions such as the dam opening and bridge construction at adequate sites along the road, could probably significantly accelerate recolonization in degraded areas by increasing inundation frequency. Although accomplishment of such plans seems straightforward, a careful contrasting of the situations achieved with the initial aims is always necessary (Fig. 8.5). If necessary, the whole process must be reevaluated. This is in agreement with Meirelles (1993), who states that the Executive Plan of Brazilian municipalities is not static but dynamic, and has to be
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adapted, in a permanent management process, to new needs. It is probably at this level where the greater potential for the integration of changing ecological and socio-economic settings resides.
References Adler FR (1996) A model of self-thinning through local competition. Proc Natl Acad Sci USA 93:9980–9984 ALEPA (2000) Assemble´ia legislativa do Estado do Para´. Bases de leis. http://www.prodepa.gov. br-alepa Augustinus PGEF (1980) Actual development of the chenier coast of Suriname (South America). Sed Geol 26:91–113 Baker WL (1992) Effects of settlement and fire suppression on landscape structure. Ecology 73:1879–1887 Bart J (1995) Acceptance criteria for using individual-based models to make management decisions. Ecol Appl 5:411–420 Berger U, Hildenbrandt H (2000) A new approach to spatially explicit modelling of forest dynamics: spacing, ageing and neighbourhood competition of mangrove trees. Ecol Modell 132:287–302 Boorman LA (2000) The functional role of salt marshes in link land and sea. In: Sherwood B, Gardiner BG, Harris T (eds) British saltmarshes. Forrest Text, Linnean Society of London, Cardigan, pp 1–24 Braganc¸a (1990) Lei organica do Municipio de Braganc¸a. Camara Municipal de Braganc¸a. CEJUP, Bele´m Brasil (1965) Codigo Florestal Brasileiro. Lei 4.771 de 15 de setembro de 1965 Brasil (1988) Constituc¸oes do Brasil e do Para´. CEJUP, Bele´m Chapman VJ (1960) Salt marshes and Salt deserts of the world. Interscience Publishers, New York Cintro´n G, Lugo AE, Pool DJ, Morris G (1978) Mangroves of arid environments in Puerto Rico and adjacent islands. Biotropica 10:110–121 Cohen MCL, Lara RJ (2003) Temporal changes of mangroves vegetation boundaries in Amazonia: application of GIS and remote sensing techniques. Wetl Ecol Manag 11:223–231 Cordeiro C, Mendoza U, Lara RJ (2003) Mangrove zonation and phosphorus distribution in sediment along a inundation gradient in Braganc¸a, North Brazil. X COLACMAR, De´cimo Congreso Latinoamericano de Ciencias del Mar, San Jose´, Costa Rica, Resu´menes, p 146 Douglas BC, Kearney MS, Leatherman SP (eds) (2000) Sea level rise, history and consequences, vol 75, International Geophysics Series. Academic, New York Gornitz V (1991) Global coastal hazards from future sea-level Rise. Palaeogeogr Palaeoclimatol Palaeoecol 89:379–398 Gornitz V (1995) Sea-level RSC: a review of recent past and near future trends. Earth Surf Proc Land 20:7–20 Guo Q, Rundel PW (1998) Self-thinning in early postfire chaparral succession: mechanisms, implications, and a combined approach. Ecology 79:579–586 Hanson K, Maul G (1989) Analysis of the historical meteorological record at Key West, Florida (1851–1986) for evidence of trace gas induced climate change. In: Maul G (ed) Implication of climatic changes in the wider Caribbean region. UNEP/IOC Regional Task Team Report, pp 63–71 IBAMA (1992) Coletaˆnea de Legislac¸a˜o Federal do Meio Ambiente. Instituto Brasileiro do Meio Ambiente e dos Recursos Naturais Renova´veis, Brasilia IBGE (2000) Resultados preliminares do censo de populac¸a˜o 2000. Instituto Brasileiro de Geografia e Estadistica, Brasilia
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IPCC (2007) Climate AHANGE 2007: the physical basis – summary for policymakers. http:// www.ipcc.ch/SPM2feb07.pdf Lara RJ, Cohen MCL (2006) Sediment porewater salinity, inundation frequency and mangrove vegetation height in Braganc¸a, North Brazil: an ecohydrology-based empirical model. Wetl Ecol Manag 14:349–358 Lara RJ, Szlafsztein CF, Cohen MCL, Berger U, Glaser M (2002) Consequences of mangrove dynamics for private land use in Braganc¸a, North Brazil: a case study. J Coast Conserv 97:102 Leme Machado P (1993) Protec¸a˜o Legal: Manguezais e Dunas. Universidade Aberta do Nordeste (S.L.) 9:7 Londsdale WM (1990) The self-thinning rule: dead or alive? Ecology 71:1373–1388 Londsdale WM, Watkinson AR (1982) Light and self-thinning. New Phytol 90:431–435 Meirelles HL (1993) Direito municipal brasileiro. Malheiras, Sa˜o Paulo Menezes M, Berger U, Worbes M (2003) Annual growth rings and long-term growth patterns of mangrove trees from the Braganc¸a peninsula, North Brazil. Wetl Ecol Manag 11:233–242 Nakada M, Inoue H (2005) Rates and causes of recent global sea-level rise inferred from long tide gauge data records. Quat Sci Rev 24:1217–1222 O’Callaghan E (1996) Land use. The interaction of economics, ecology and hydrology. Chapman & Hall, London Poiani KA, Johnson WC (1993) A spatial simulation model of hydrology and vegetation dynamics in semi-permanent prairie wetlands. Ecol Appl 3:279–293 Price WA (1955) Environment and formation of the chenier plain. Quaternaria 2:75–86 Quang VC (1994) A tree survival equation and diameter growth model for loblolly pine based on the self-thinning rule. J Appl Ecol 31:693–698 Saintilan N (1997) Above- and below-ground biomasses of two species of mangrove on the Hawkesbury River estuary, New South Wales. Mar Freshw Res 48:147–152 Santos MCFV, Zieman JC, Cohen RRH (1997) Interpreting the upper mid-littoral zonation patterns of mangroves in Maranha˜o (Brazil) in response to microtopography and hydrology. In: Kjerfve B, Lacerda LD, Diop EH (eds) Mangroves ecosystem studies in Latin America and Africa. UNESCO, Paris, pp 127–144 Schwendenmann L (1998) Tidal and seasonal variations of soil and water properties in a Brazilian mangrove ecosystem. MSc thesis, University of Karlsruhe, Karlsruhe Slavich PG, Walker G, Jolly ID (1999) A flood history weighted index of average root-zone salinity for assessing flood impacts on health of vegetation on a saline floodplain. Agric Water Manag 39:135–151 Soto R, Jimenez JA (1982) Ana´lisis fisiono´mico estructural del manglar de Puerto Soley, La Cruz, Guanacaste, Costa Rica. Rev Biol Trop 30:161–168 Suguio K, Martin L, Dominguez BACSP, JML FJM, Azevedo AEG (1985) Flutuac¸o˜es do Nı´vel do Mar durante o Quaterna´rio Superior ao longo do Litoral Brasileiro e suas Implicac¸o˜es na Sedimentac¸a˜o Costeira. Rev Brasil Geoc 15:273–286 Titus, TG, Narayanan VK (1995) The probability of sea-level rise. United States Environmental Protection Agency, Office of Policy, Planning, and Evaluation (2122), EPA 230-R-95-008, Washington, DC Townsend PA, Walsh SJ (1998) Modeling floodplain inundating using an integrated GIS with radar and optical remote sensing. Geomorphology 21:295–312 Twilley RR, Rivera-Monroy VH, Chen R, Botero L (1999) Adapting an ecological mangrove model to simulate trajectories in restoration ecology. Mar Pollut Bull 37:404–419 Vetter RE, Botosso PC (1989) El Nin˜o may affect growth behaviour of Amazonian trees. GeoJournal 19:419–421
Chapter 9
System Processes and Forest Development U. Berger and M. Wolff
9.1
The Interlink Between the Modeling Approaches
A sustainable use of an ecosystem requires the understanding of ecological processes driving the dynamics of the system. Moreover, the effects of management scenarios on these processes have to be assessed prior to their application in particular environmental settings. A general methodology, which has been proven to be adequate for such a situation is referred to as rapid prototyping (Breckling et al. 2005). It is based on the assumption that the functioning of a complex system at a certain level of integration can be explained by the interactions of its elements at a lower integration level. Following this approach, three questions have to be answered: (1) what are the essential elements that form the mangrove system, (2) how are they interconnected, and (3) what are the factors determining their spatio-temporal behavior? During the MADAM project, a trophic model was developed to answer the first two questions. It provides accessible “views” of the whole system and insights into the underlying ecological mechanisms expressed by energy and matter flows. Section 9.2 shows (1) how this model can be used to identify those species and functional groups, which currently exert the largest effects on the system, and (2) what are the potential consequences of changing abundance of these species or groups. Model outcomes stress the importance of mangrove trees as primary producers, and the importance of the mangrove crab Ucides cordatus as the most prominent resource and herbivorous species feeding on the leaf litter. Both elements (the trees and the crabs) are thus directly linked to each other. For example, U. cordatus’ habitat preferences directly relate to the distribution of Rhizophora mangle trees through specific microhabitat conditions beneath the trees (Piou et al. 2007b). Such interactions cannot be fully captured by a trophic model. For this reason, further empirical studies have been conducted focusing on the spatial distribution, growth performance, and phenology of trees and crabs. Basing on these empirical studies, two spatially-explicit, individual-based models were developed: the mangrove model KIWI describing the tree community, and the IBU model describing the behavior and interactions among crabs. Since Chap. 20
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focuses exclusively on the ecology and fishery of mangrove crabs, the IBU model is presented in detail there (20.1), while the present chapter targets the dynamics of the forest and its expressions in spatio-temporal vegetation patterns. For this reason, this chapter is particularly linked with Chap. 6, which introduces the mangrove tree species of the Caete´ estuary and describes the main mangrove forest types found within this area. Species composition and structural development characterizing these forest types correspond to an array of site-specific environmental factors (e.g., inundation frequency and associated parameters), which may hamper or favor tree growth. In addition, seasonal changes in environmental conditions induce cyclic tree growth reflected in the phenology (Chap. 6.2), as well as in rhythmic alterations in wood anatomy observed in stems of the most important mangrove tree species of the Caete´ estuary as annual growth rings. These growth rings can be used for age determination, and for the evaluation of stem growth under different abiotic conditions and in the context of neighborhood competition (Chap. 6.3). All these empirical studies are particularly important for the parameterization of the KIWI model presented in the final section of this chapter, which should be considered in conjunction with the empirical studies rather than separately. Here, we will explain the main features of the model and set out its contribution to a comprehensive understanding of the ecological processes behind mangrove forest dynamics.
9.2
Trophic Pathways
The Ajuruteua peninsula is part of the Caete´ Estuary (CE), a mangrove-dominated shallow water system. Here, a leaf-eating crab (U. cordatus) is the most prominent resource. Further, mangrove products of local importance are fish species of the families Sciaenidae, Aridae, shrimps (Penaeus spp., Macrobrachium sp.), the boreworm Neoteredo spp., mussels (Mytella sp.) and swimming crabs (Callinectes sp.). Mangrove wood is used locally for house construction, fishing traps and as firewood for brickworks. Key questions are how this system compares to other mangrove systems, how it is trophically structured, how the biomass is distributed over the main system compartments, and how the energy of the system flows among these compartments and into the harvestable resources. Through the approach of trophic modeling, these questions were addressed, the trophic flow structure was analyzed, and the model below was constructed (Fig. 9.1). When we look at this steady state flow model and ask for specific characteristics of the Caete´ estuarine system as compared to other mangrove-fringed estuaries, we find several interesting features. First of all, a very high primary production can be recognized due to the very large mangrove cover of the system. Compared to the mangrove forest primary production, aquatic primary production is relatively low. A second important feature are the catches on a per unit area basis. The harvest of crabs and fishes exceeds 6.5 gm2 for the total model area (CE: peninsula and estuary), which is considerable and goes along with a high fisheries efficiency
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Fig. 9.1 Trophic model of the Caete´ estuary (Wolff 2006). Note that values refer to the total model area (mangrove peninsula and estuary)
(FE ¼ 0.58%, e.g., the fraction of the primary production ending up in the fishery resources), although mean transfer efficiency between trophic levels is regular (9.8%). The reason for this high FE is the mangrove crab U. cordatus, which is the principal resource of the system besides the mangrove trees themselves. As this crab is a primary consumer, the trophic level of the fishery (here calculated as the mean trophic level of the resources combined þ1) is relatively low (3.1) If the substantial mangrove tree harvest of CE was included in the calculations, the value would be even lower (Fishery Trophic Level ¼ 2.1). While in many other mangrove-fringed ecosystems, predatory fish like carangids, catfish, snappers and grunts, morays, and flatfish as well as an important amount of shrimps may dominate the catches, only relatively small quantities of these groups are produced and harvested in the Caete´, where shrimps are of minor importance, and pelagic top predators are also insignificant. If an increase in mangrove cover was simulated by using the model, a positive effect on the land crab and crab fishery as well as on wood borers and (indirectly) on predatory snails is predicted. Conversely, crabs negatively impact the mangroves, since crabs consume >80% of total litter fall including the seed (propagules) of the mangroves (Rademaker 1998; Nordhaus et al. 2006). The current crab fishery might thus be beneficial to the mangroves by reducing crab population density and enhancing the recruitment success of mangroves. A simulated increase of detritus would positively impact fiddler crabs in the CE, the main converter of the system’s detritus.
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A remarkable difference between the Caete´ system and many mangrove-fringed estuaries that are flushed by daily tides is that filter feeders (bivalves, encrusting epifauna) are almost absent, while these groups are often prominent epifaunal species attached to the roots of mangroves trees. This can largely be explained by the topography and tidal regime of the CE. The system is completely inundated only each fortnight (at spring and neap tides), a situation encrusting fauna cannot cope with. These conditions also explain the enormous abundance of land crabs. In the Caete´ system, most of the primary energy fixed by the mangrove forest fuels the “forest ground” benthos through litter fall, of which the land crab and the fiddler crabs are the most abundant organisms. When the forest is inundated each fortnight relatively little of the primary energy is left for entering the estuary. In many other mangrove-fringed estuaries, on the contrary, mangrove litter is exported every day with the tidal waters providing the material for a rich detritus-based aquatic food chain, within which shrimps very often play a central role. If we ask how – based on the food web structure – the Caete´ system may be ranked on an ecosystem maturity scale, our modeling exercise points to a little developed (growing) system, in which total production is much higher than respiration. Energy flow seems very much bottom-up controlled and the trophic structure is relatively loose. This also seems to be reflected in the low average transfer efficiency between trophic levels (9.8%). For management measures to be successful, the system characteristics described above must be considered. The land crab biomass should be sustained at the present levels by avoiding recruitment and growth overfishing through a control of total fishing effort and minimum landing size (see Chaps. 19.2 and 19.3 for further details). Further mangrove logging must be impeded as mangroves represent the crab’s principal habitat and food source. A potential for a catch increase of finfish and shrimps inside the estuary should not be expected, as overall aquatic resource biomass and production is, for natural reasons, comparatively low. Our trophic flow studies suggest that generalizations regarding fishery resources of mangrove systems and the relationship between coastal mangrove cover and potential catches of aquatic resources should be treated with much care, with adequate attention being given to different geomorphological and botanical ecosystems settings. For analyzing the latter aspects in more details, the KIWI model was developed for simulating mangrove forest dynamics under varying environmental conditions and management scenarios. The following section presents the main features of this model and presents the main simulation results.
9.3
Forest Dynamics Under Different Natural Disturbance Regimes
The purpose of the KIWI model is to analyze the relative importance of environmental settings like porewater salinity and nutrient availability, local neighbor
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competition among trees, and different kinds of canopy disturbance on forest dynamics. For this, the model describes an individual tree spatially explicitly in its physical environment. A tree is firstly described by its stem position within a Cartesian coordinate system, and its stem diameter in breast height (dbh). Trees compete for spatially distributed resources. The model describes this by the overlap of the size-dependent “Fields-Of-Neighborhood” (FON) of the neighboring trees (see e.g. Berger and Hildenbrandt 2000 for details). The FONs are derived from the so-called “zone-of-influence” approach, but describe a decreasing competition strength of a tree depending on the distance to its stem position by a scalar field superimposing the circular zone. The model itself was written in Cþþ. However, the implementation provides a direct control of the model kernel by an experimenter using a simple script language like VBScript or Phyton. The experimenter can chose the extension and shape of the forest stand, as well as species composition, initial forest composition, and management or environmental scenarios among others. The size of simulated stands is limited by computer power, but typically ranges from 100 to 10,000 m2. Usersupplied map layers describe abiotic conditions and environmental settings like topography, porewater salinity, and nutrient availability. They are linked to the forest stand by the coordinate system. The model is parameterized for Avicennia germinans, Laguncularia racemosa, and R. mangle (Berger and Hildenbrandt 2000), which are the most important mangrove species in the study region. The time step of a simulation is 1 year, within which new trees can establish, and existing trees grow or die according to their environmental conditions and life history. The model updates all trees synchronously. Population dynamics emerge from the trees’ performance, their interactions, and environmental settings at the their locations, and corresponding tree-to-tree interactions. The following patterns may, e.g., occur as emergent properties of the system: characteristic spatial distributions of individuals, species, or size classes, specific species successions, or size-class- or fitness-dependent frequency distributions of trees. For all living and dying trees, the stem diameter is registered at each time step. From this value, further variables are derived, for example tree height and tree biomass. These data provide analyses of the total biomass, importance values, complexity indices, or geostatistic indices among others at the stand level. The experimenter can chose the initial number of trees and the species composition according to the requirements of the particular experiment. A typical initial density is 300 specimens per 10,000 m2. Newly established trees have an initial stem diameter of 1 cm at breast height (1.27 m) due to the chosen growth function (Shugart 1984; Chen and Twilley 1998). Recruitment rates include seed mortality. Usually, these rates depend on the number of parent trees in a plot, but can be modified in order to simulate, e.g., the effect of currents or sinks on available dispersal units. The concrete location of the sapling is chosen randomly, but may be restricted in a particular range related to the distance from a parent tree. Nevertheless, trees can only establish where
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competition exerted by neighbor trees is below a given species-specific threshold mimicking shade-tolerance. The equation describing the growth for a single tree is adapted from the FORMAN model (Chen and Twilley 1998). It is valid under optimal conditions, but modified by correction factors considering salinity and nutrient availability. A third correction factor considers neighbor effects. It is measured as a neighbor’s FON exerted on the FON of the focal tree (see explanation above and Berger and Hildenbrandt 2000). The probability that a tree dies increases after a prolonged period of growth depression. This might be a result of salinity stress, nutrient limitation, and/or neighborhood competition. This situation appears when environmental conditions constantly deteriorate but also when a tree approaches its maximum stem diameter. In case environmental conditions meliorate, for example salinity decreases or neighbors die, a tree has a chance to “convalesce” and survive. The experimenter can introduce additional mortality due to tree cutting or the effect of hurricanes. So far, KIWI applications have mostly addressed theoretical issues of mangrove forest dynamics such as self-thinning (Berger et al. 2002), the development of sizedistributions (Berger and Hildenbrandt 2003), or the validity of the intermediate disturbance hypothesis (Piou et al. 2007a). Also, the model was applied to nonmangrove-specific research questions like asymmetric competition among plants (Bauer et al. 2004), and age-related declines in forest production (Berger et al. 2004). More applied modeling experiments focused on effects of tree harvest on biomass production of a mangrove plantation (Fontalvo-Herazo et al., in preparation). Berger et al. (2006) simulated forest succession after clear-cutting and rice cultivation under brackish water conditions at the Ajuruteua peninsula. The results revealed that a combination of nutrient heterogeneity and disturbance history may determine the growth potential of the species, but seed dispersal, biogenic changes in abiotic conditions and tree competition tune the succession trajectory. The study showed that the interconnection of these factors can create multiple succession trajectories in terms of species compositions, although the forests consists of only a few species and growth conditions are optimal. Using the so-called “PatternOriented-Modeling” strategy (Grimm and Railsback 2005), the authors compared empirical versus simulated recovery patterns such as species dominance or vertical forest structure in order to test the plausibility of different ecological processes being responsible for the observed succession phenomena. The study revealed that species-specific differences in nutrient-uptake efficiency (Lovelock and Feller 2003) combined with a temporal decrease in nutrient availability probably explain the gradual replacement of L. racemosa by A. germinans in the canopy (Fig. 9.2). These results corresponded with an empirical study carried out in a tropical wet forest (Denslow et al. 1998), which demonstrated that higher nutrient pools in surface soils affected growth rates of high light-demanding species (such as L. racemosa) more than the growth rates of shade-tolerant species (such as A. germinans). Despite the confirmation of nutrient importance, KIWI simulations also demonstrate the significance of tree-to-tree competition effects on forest structure. For example, Berger and Hildenbrandt (2000), Berger et al. (2006) support the
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Fig. 9.2 Mangrove succession after the abandonment of rice cultivation parcels at Ajuruteua peninsula simulated by the KIWI model. During the course of time, L. racemosa trees became increasingly reduced in their growth rates due to both a reduction in nutrient availability and neighbor competition. This leads to a dominance change in terms of basal area from L. racemosa to A. germinans in the plot. Inundation regime hinders R. mangle propagules to enter the plot resulting in late establishment of that species (see Berger et al. 2006 for details)
hypothesis (stated, e.g., by Stoll et al. 2002; Roderick and Barnes 2004) that the slope of the so-called self-thinning-line is not fixed but bounded above by the strength of neighbor competition and below by morphological constraints such as the stem diameter–crown diameter relationship. Also, Berger and Hildenbrandt (2003) show that self-thinning in mangrove stands is linked to a homogenization process forcing the symmetry of the stem diameter distribution.
9.4
Conclusion
Over the last several decades, public awareness has been raised concerning the ecological and economic importance of mangroves, their ecological status and vulnerability. Nevertheless, degradation and coastal destruction have been increasing in their intensity and extent. There is an urgent need to assess the risk of disturbance and environmental changes on the structure and function of mangrove forests. The application of two different modeling approaches (trophic modeling and individual-based modeling) provided a suitable framework for understanding the dynamics of the mangrove ecosystem and to forecast how mangrove dynamics might change under varying environmental conditions. Even concerning their different objectives and applications, both models discussed in this chapter contributed to the understanding of critical processes in mangrove wetlands by synthesizing the empirical knowledge about essential relationships and mechanisms; particularly those regulating productivity, energy flows, and forest structure. Both models benefited from the field data obtained, which are essential for a solid
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parameterization of the models for the particular study sites. On the other hand, the models stimulated field studies regarding processes that needed further studies. For example, based on the requirements of the KIWI model, the dendrochronological studies (Chap. 6) were conducted, since information on tree growth responses to porewater salinity and precipitation, as well as data on tree age, were not available at the beginning of the MADAM project. The trophic model, on the other hand, enabled to visualize and quantify the energy flow relationships between the mangrove forest and other functional groups of the system, revealing, e.g., the central role of the land crab for the energy cycling within the system, and stimulating further studies on the population dynamics and feeding ecology of this resource within the MADAM project. Resource management scenarios could also be evaluated in terms of their overall effect on the ecosystem, and the specific characteristics of the Braganc¸a peninsula system could be elucidated through a comparison with other mangrove-fringed estuaries. Hopefully, our studies will spur additional modeling and field investigations, which will enhance scientific knowledge about one of the most productive ecosystems in the world.
References Bauer S, Wyszomirski T, Berger U, Hildenbrandt H, Grimm V (2004) Asymmetric competition as natural outcome of neighbour interactions among plants: results from the field-of-neighbourhood modelling approach. Plant Ecol 170:135–145 Berger U, Hildenbrandt H (2000) A new approach to spatially explicit modelling of forest dynamics: spacing, ageing and neighbourhood competition of mangrove trees. Ecol Modell 132:287–302 Berger U, Hildenbrandt H (2003) The strength of competition among individual trees and the biomass-density trajectories of the cohort. Plant Ecol 167:89–96 Berger U, Hildenbrandt H, Grimm V (2002) Towards a standard for the individual-based modeling of plant populations: self-thinning and the field-of-neighborhood approach. Nat Resour Model 15:39–54 Berger U, Hildenbrandt H, Grimm V (2004) Age-related decline in forest production: modelling the effects of growth limitation, neighbourhood competition and self-thinning. J Ecol 92:846–853 Berger U, Adams M, Grimm V, Hildenbrandt H (2006) Modeling secondary succession of neotropical mangroves: causes and consequences of growth reduction in pioneer species. Perspect Plant Ecol Evol Syst 7:243–252 Breckling B, Muller F, Reuter H, Holker F, Franzle O (2005) Emergent properties in individualbased ecological models – introducing case studies in an ecosystem research context. Ecol Modell 186:376–388 Chen R, Twilley RR (1998) A gap dynamic model of mangrove forest development along gradients of soil salinity and nutrient resources. J Ecol 86:37–51 Denslow JS, Ellison AM, Sanford RE (1998) Treefall gap size effects on above- and below-ground processes in a tropical wet forest. J Ecol 86:597–609 Grimm V, Railsback SF (2005) Individual-based modelling and ecology. Princeton University Press, Princeton, New York Lovelock CE, Feller IC (2003) Photosynthetic performance and resource utilization of two mangrove species coexisting in a hypersaline scrub forest. Oecologia 134:455–462
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Nordhaus I, Wolff M, Diele K (2006) Litter processing and population food intake of the mangrove crab Ucides cordatus in a high intertidal forest in northern Brazil. Estuar Coast Shelf Sci 67:239–250 Piou C, Berger U, Hildenbrandt H, Feller CI (2007a) Testing the intermediate disturbance hypothesis in species-poor systems: a simulation experiment for mangrove forests. J Veg Sci 19:417–424 Piou C, Berger U, Hildenbrandt H, Grimm V, Diele K, D’Lima C (2007b) Simulating cryptic movements of a mangrove crab: recovery phenomena after small scale fishery. Ecol Modell 205:110–122 Rademaker V (1998) Ern€ahrungso¨kologie, Habitatsbeschreibung und Populationsstruktur der Mangrovenkrabbe Ucides cordatus (Linnaeus, 1763) im Caete´-Mangroven€astuar, Nordbrasilien. Dipl thesis, University of Bremen, Bremen Roderick ML, Barnes B (2004) Self-thinning of plant populations from a dynamic viewpoint. Funct Ecol 18:197–203 Shugart HH (1984) A theory of forest dynamics: the ecological implications of forest succession models. Springer, New York Stoll P, Weiner J, Muller-Landau H, Muller E, Hara T (2002) Size symmetry of competition alters biomass–density relationships. Proc R Soc Lond B 269:2191–2195 Wolff M (2006) Biomass flow structure and resource potential of two mangrove estuaries: insights from comperative modeling in Costa Rica and Brazil. Rev Biol Trop 54:69–86
Chapter 10
Synoptic Analysis of Mangroves for Coastal Zone Management G. Krause and M. Bock
10.1
Background and Scope
So far, little overarching research has been carried out that tries to combine different spatial scales in mangrove research. In most studies, either a high degree of detail on small spatial scale or rather superficial assessments of mangroves on larger spatial coverage was conducted. Thus, despite modern technology, detailed geo-spatial information on these complex ecosystems, which would support its sustainable management, is still lacking. The often high degree of canopy cover in mangroves limits the accuracy of global positioning system (GPS) data for the spatial definition of certain mangrove stands. Accuracy calculations are thus difficult to achieve. This is due to the inaccessibility of most of the mangrove areas in the first place. Research that tries to cover a larger area within the mangrove ecosystem is therefore often hampered by the lack of sufficient ground truth data in order to validate the detected features in the respective images. The use of the term “synoptic analysis” in this chapter refers to the combination of repeated spectral measurements via remote sensing, imaging and other spatial information sources to produce a uniform view over time. In the light of the observed lack of synthesized synoptic data analysis in mangrove research, the focus in this chapter is placed specifically on the question of what spatial data is necessary to arrive at suitable and relevant coastal management-related information of mangrove ecosystems. This is timely, since the massive global deforestation of mangroves continues, despite the increasing awareness of their importance (Duke et al. 2007). Lack of ecological knowledge among valuators is an important determinant of the undervaluation of mangroves, which is often argued to be a major driving force behind this problem (Hamilton et al. 1989; Barbier 1994; Ro¨nnb€ack 1999; Lal 2003). Furthermore, the significant differences in the structure and function of mangrove habitats, not only between continents and regions but also within individual mangrove systems, create problems with generalizations. These are reflected in a lack of consistent and successful sustainable management concepts.
U. Saint-Paul and H. Schneider (eds.), Mangrove Dynamics and Management in North Brazil, Ecological Studies 211, DOI 10.1007/978-3-642-13457-9_10, # Springer-Verlag Berlin Heidelberg 2010
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Consequently, on the global scale, pressures on mangrove ecosystems have increased dramatically (Spalding et al. 1997), causing widespread degradation and deforestation. Valiela et al. (2001) note that at least 35% of the world’s mangroves were lost in the last two decades with highest loss rates (3.6% per year) in the Americas. There are many drivers behind the loss of mangrove forests. The conversion into fish and shrimp aquaculture ponds (52%) and unsustainable forest uses (26%) are by far the main attributes of the last decades (Valiela et al. 2001). As a case in point, forecasts on the effects of selective cutting of mangroves on the ecosystem as a whole are as yet fragmentary. Suitable and transferable techniques for remote sensing and airborne-based classification to assess the dynamics of ecosystem change and of the mangrove forest structures were developed within the framework of the MADAM Project. Examples of this research are presented in this chapter, and their relevance for coastal zone management is discussed. A comprehensive description of the recapitulatory results below is given in Krause et al. (2004) and Bock et al. (2006).
10.2
Research Strategy
From a synoptical point of view, the relationship between spatial resolution and spatial coverage determines the type of output of research activities in ecology, here mangrove ecology. However, in the search for environmental patterns that are known to be difficult to formalize and to document empirically, the application of spatial information technology to ecological analysis has grown (Buttenfield 2001), but has not necessarily resulted in relevant map outputs for coastal zone management. Therefore, different methods must be applied on the different scales, which in turn generate different information and insights into mangrove ecosystems. Synthesizing data gathered at multiple spatial levels (e.g., plot/patch, habitat, landscape) and in different time intervals are impeded by uncertainty. This high uncertainty is related to difficulties of access for field surveys and the highly sensitive nature of GPS ground truth data collection that are necessary as reference values required for validating airborne imagery of all types. Our strategy for the remote sensing investigations in terms of resolution and coverage involved three spatial layers (plot scale, local scale, regional scale) each of which employed different remote sensing methods that were relevant to the ecological and social research aspects of the MADAM project (Fig. 10.1). In the following, examples of two major themes of remote sensing analysis of mangroves are presented, namely detection of change dynamics and mangrove forest patterns. They employ pixel- as well as object-based approaches on various spatial levels. Typical pixel-based approaches for image analysis try to classify an image by scanning the scene and classifying each single pixel. The spectral
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Fig. 10.1 Conceptual scheme of the research strategy for the socio-ecological system (SES) of the Braganc¸a coastal region of the MADAM project. The remote sensing research provided the basis for the further analysis of the research fields in question. Depending on the respective relationship between spatial coverage and resolution, different scales were addressed with various methods for the social and ecological research priorities, respectively. On each level, methods exist that combine both science fields, i.e., the development of indicators on the village/habitat level
information of each pixel itself and/or its texture results in a certain defined vicinity around it. In contrast, object-based approaches attempt to isolate particular objects of interest within the image after a preliminary segmentation. The subsequent classification divides the image into more or less homogenous regions of spatially connected pixels. Hence, e.g., individual mangrove tree crowns may be readily identified and extracted from high-resolution imagery (Fortin and Edwards 2001; Park et al. 2007). An innovative improvement of the latter is the Multi-Scale Segmentation (MSS) that has been introduced by Baatz and Sch€ape (2000) and which is implemented in the software package eCognition (Definiens 2004). The MSS technique offers the extraction of image objects at different spatial resolutions to construct a hierarchical network of image objects, in which each object knows its context, its neighborhood and its sub-objects. The MSS technique was applied to the interpretation of very high resolution (VHR) images in this study, since pixel-based approaches have difficulties in handling the spectral variability of VHR images, resulting in the so-called “salt and pepper appearance” of the classification (Blaschke 2000).
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Change Dynamics
10.3.1 Regional Scale Analysis Several studies have employed remote sensing techniques to determine the spatial composition and alteration of mangrove forest patterns over time (e.g., Cantera and Arnaud 1997; Souza-Filho and El-Robrini 1997; Bunt 1999; Mehlig 2001). To monitor such temporal alterations of mangroves, several types of change algorithms were tested in the frame of the MADAM project (Weiers et al. 2001, 2004; Kleinod et al. 2005; Bock et al. 2006). Figure 10.2 shows the results of a change method that compares two satellite scenes by an index of spectral information applying a fuzzy logic algorithm (Weiers
Fig. 10.2 Change detection analysis from two satellite images in the time period 1990–1999 (Landsat TM5 and TM7) of the Braganc¸a coastal region. The resulting image matrix provides an aggregated fuzzy membership value scaled between 0 and 1 for the class “changed between 1990 and 1999”. The red colored areas indicate an intense change in the landscape (0.9–1.0), yellow areas intermediate land cover change (0.8–0.9) and green areas moderate change (0.7–0.8) The gray shaded areas highlight landscape stability. This type of analysis reveals the most prominent spatial hot spots of change (Krause et al. 2004)
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et al. 2001). The red marked regions indicate a high probability, while the green regions indicate a lower probability of change from 1991 to 1999. The analysis reveals the effects of the coastal dynamics by exposing the highest change rates. For instance, a local hot spot of change is in the center of the mangrove peninsula, where, among others, the north–south road construction in the mid-1970s has produced a clear impact on the mangrove ecosystem. Other areas, like the development of a new island close to the main channel of the Caete´ Estuary, are less pronounced. The main drawback of this purely spectral-based method is that it only indicates hot spots of change and not the type of change. On the other hand, the respective algorithms are straightforward and very quick to compute. They provide the first identification of hot spots, which direct further detailed spatial assessments.
10.3.2 Local Scale Analysis Purely spectral-based change methods provide no direct information on the type and direction of change. For this task, information on the class membership of a spatially and temporally defined object is essential. Therefore, post-classification methods, that compare the classifications of different points in time, are commonly used to assess and quantify the direction and type of change. However, especially in the (sub)tropical regions, knowledge on the spatial distribution of different land use classes and availability of feasible maps are both low. Moreover, the high seasonal variability of land use schemes complicates the extraction of valuable ground truth data for satellite image classification. This becomes even more critical for extracting historical spatial information, such as from the CORONA spy satellite in the 1960s. To overcome this problem a selective post classification approach was developed (Bock et al. 2006), which limits the analysis to (1) the relevant spatial regions and (2) to the possible change classes. The results of the rapid index-based change detection above have identified two major hot spots of change: the direct coastal shore areas and a large hot spot area in the center of the mangrove peninsula. Following an accurate radiometric calibration of the input images (Richter 1996) and a preselection of specific change classes, the analysis can be narrowed down on the separation of these target classes. This type of analysis allows the quantification and the determination of type and direction of change over time. Figure 10.3 displays an example for a subset of the peninsula at the vicinity of the Caete´ Estuary. The quantified results of mangrove changes for the whole peninsula within different time periods from 1966 to 2004 are summarized in Table 10.1. The results stress the strong dynamics of change within the mangrove systems, with a total increase of mangrove area over this time period of about 3.14 km2. Taking into account the mean accuracy for the specified change classes in Table 10.1 of about 82%, the estimated average errors are about 0.56–1.12 km2
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Fig. 10.3 Example of the results of the selective post classification change analysis (Bock et al. 2006). The four maps indicate the costal changes within four time periods from 1966 to 2004 on Caete´ Estuary of the peninsula of Braganc¸a. The change statistics reveal that the colonization of new mangroves exceeded the loss of mangrove vegetation within this specific area
Table 10.1 Summarized changes of mangrove vegetation in different time periods Period analyzed Mangrove decrease (km2) Mangrove increase (km2) Totals 1966–1986 9.93 þ10.13 þ0.20 1986–1999 6.43 þ7.67 þ1.23 1999–2003 2.97 þ4.68 þ1.71 Totals1966–2003 19.34 þ22.48 þ3.14
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in the worst case. The main cause of error roots in the insufficient detection of clouds by a prior masking procedure, leading to spurious changes. However, as the example in Fig. 10.3 reveals, no information on the species involved in the increase of mangrove area can be provided.
10.4
Classification of Mangrove Patterns
Several studies have aimed to determine the types of mangrove structure patterns (Cantera and Arnaud 1997; Prost 1997; Spalding et al. 1997; Bunt 1999). In many cases, mangrove species are neither strongly large-scale zoned nor randomly scattered, but often occur in small discrete monospecific zones (Hogarth 1999; Bunt and Bunt 1999; Bunt and Stieglitz 1999). Conceptually, these landscapes may be characterized as a mosaic of habitat patches, which may change over time. However, little attention has been given to the interactions between these different patches encompassing the entire landscape perspective, which is mainly due to the difficulties with the scale resolution of the information needed for such an attempt. Studies, such as by Khan et al. (1990), Dale et al. (1996), Green et al. (1997), Gao (1998, 1999), Rasolofoharinoro et al. (1998), and Smith et al. (1998) have employed remote sensing techniques with high-resolution satellites (e.g., LANDSAT, SPOT) to determine the spatial composition of mangrove forest stands. Due to the heterogeneity of mangrove tree distributions, a detailed assessment of the mangrove structure according to species has so far not been satisfactorily achieved. This is caused by the difficulties in generating sufficient spatial resolution by the use of satellite imagery in resolutions of 20–30 m to detect likely structural patterns. New VHR satellite data of the sensor systems IKONOS and QUICKBIRD have been tested for their applicability in mangrove research. Wang et al. (2004a) have carried out a comparative analysis of both sensor systems, using the example of the Caribbean mangroves of Panama. The authors conclude that both sensors are well suited to classify mangrove species. In a further study, Wang et al. (2004b) compared pixel-based and object-based classifications and a combination of both methods for the discrimination of three mangrove species in an IKONOS image. The combined method has been shown to be most suitable for this task. Nevertheless the object-based approach was adopted in this study.
10.4.1 Aerial Survey Analysis The heterogeneity of mangrove species distribution in the study area has acted as a major obstacle for a detailed assessment of the mangrove structure according to species. Top-down approaches must tackle the difficulties in generating sufficient spatial resolution by the use of satellite imagery in order to detect
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mangrove forest patterns in more detail. In contrast, bottom-up approaches that deal with explicit data (e.g., mangrove structure plots of 30 30 m), and spatial patterns of mangrove individuals and/or mangrove species have to be quantified to a larger geographical dimension to assign these to a certain mangrove structure. There are three dominant mangrove species in the research area: Rhizophora mangle (red mangrove), Avicennia germinans (black mangrove), and Laguncularia racemosa (white mangrove) (Mehlig 2001; Krause et al. 2001). In a first investigation step, four aerial photograph transects of the peninsula were recorded by an amateur camera. The software eCognition 4.0 was utilized for the development of multiscale segmentation and object-oriented classification procedures, which were then applied to all transects (Krause et al. 2004). Generally, segmentation is a spatial aggregation or area classification technique (Franklin 2001), by which boundaries between spatially homogenous clusters are detected (Fortin and Edwards 2001). The occurrence of only three species and the distinct spectral differences, especially within the green visible spectrum, supported the identification of species on a local scale level. Figure 10.4 (a–d) gives an example of the segmentation process and classification. In addition, the result of the segmentation according to mangrove species has direct links to the validation of the KiWi model (Chap. 9), since real-world patterns
Fig. 10.4 Example of the segmentation processing steps of the aerial photograph image to outline objects of the Rhizophora and Avicennia canopy; (a) Shows a subset of an aerial photograph. The outlines in (b) represent “superobjects” as a result of a lower scale segmentation; (c and d) are two different representations of the classification on a higher resolution level. The dark green color in (d) is classified as “R. mangle”, the bright green as “A. germinans”, the orange as bare ground and the black as shadow. The distribution pattern of the classification is then transformed into digital target objects within the GIS (e), which form the baseline for validation of the simulation results of the KIWI mangrove model (f)
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can be used (Fig. 10.4 e, f). Thus, this supports the robustness of the model, allowing detection of temporal species-specific change and response behavior at the same time.
10.4.2 Classification of Mangrove Patterns on the Peninsula with IKONOS Data As the results of the aerial survey were promising, three IKONOS images (1–4 m resolution) were subsequently acquired to cover the whole peninsula of the Braganc¸a coastal region. Ground truth data was collected, which was supported by local crab fishermen. The collection of reference data turned to be very difficult, due to the heterogeneous composition of the mangrove species and uncertainty of GPS data recorded in teh dense mangrove forest. Subsequently, two object-oriented techniques were evaluated by their suitability for the separation of mangrove species and coastal land cover types: 1. Schwarz (2005) developed a sophisticated multi-scale object-oriented rule network for a subset of the peninsula and achieved an excellent separation of mangrove species (Table 10.2). The results were further validated by groundtruth data and by the MADAM scientists, indicating only minor confusions between Avicenna shrubs, single tree stands and grasslands, and some uncertain assignments of Laguncularia. The transfer of this approach to the whole mangrove peninsula of the MADAM project was found impossible due to the following: the processing with a 1-m resolution data failed due to memory limitations of the software eCognition 4.0, and the difficulties occurring whilst transferring the complex hierarchical structured rule network to the regional scale. 2. To comply with this issue, the rule network was reduced to four hierarchical levels as shown in Fig. 10.5, and the supervised nearest-neighbor classificator was replaced by a fuzzy membership approach with a reduced number of spectral and textural features for classification (Bock et al. 2006). Processing demands were further reduced by using 4-m spatial resolutions for all IKONOS image bands. The new rule network was kept as simple as possible to allow a rapid transfer to other datasets and/or regions. In this context, a decrease of class accuracies of 5–20% was observed but accepted (Table 10.2). The stark decline of the accuracy for the species L. racemosa is noticeable. This may be founded in (1) the bad performance of the threshold-based classifier that relies on only a few features compared to the “trained” classifier used by Schwarz (2005), (2) the fragmented occurrence of adult L. racemosa in very small patches, (3) the imprecise localization of ground truth data, and (4) the lower spatial resolution of 4 m. Figure 10.6 shows the fundamental mangrove species patterns and other landscape elements of the peninsula.
Table 10.2 Comparison of the accuracy assessment of selected classes for the two classification approaches applied Object-oriented classification of subset of Braganc¸a peninsula, based Object-oriented classification on the whole Braganc¸a peninsula, based on 1-m Ikonos image (Schwarz 2005) on 4-m Ikonos image and a simplified rule network (Bock et al. 2006) Class User’s Producer’s Kappa Class User’s Producer’s Kappa accuracy accuracy accuracy accuracy Small mangroves 58.62% 48.57% 0.5172 Small mangroves 58.62% 48.57% 0.5172 Avicennia germinans 69.49% 78.85% 0.6127 Avicennia germinans 97.17% 97.46 0.9703 Rhizophora mangle 78.43% 85.11% 0.6500 Rhizophora mangle 90.87 % 97.69% 0.9658 Laguncularia 11.76% 20.00% 0.0801 Laguncularia 96.04% 92.98 0.9152 racemosa racemosa Open spaces 95.83% 42.59% 0.9466 Open spaces 99.55% 98.82% 0.9466 Total K 0.5524 Total K 0.9292 Overall accuracy 66.53% Overall accuracy 94.52%
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Fig. 10.5 Multiple scales used to classify the mangroves and landscape elements on the Braganc¸a peninsula. On the landscape level, the scene content is simply divided into maritime and inland “superobjects” (SO). The habitat level represents major habitats, e.g., tall and dwarf mangroves, grasslands, beach and others. Mangrove species are separated on this class level. Spectral object primitives comprise vegetation, bare soil, water and shadow
10.5
Potential Contributions to Coastal Zone Management
The approaches presented in this chapter can be viewed as a purposeful attempt in the assessment and representation of mangrove structure and their dynamics. The fact that the selected mangrove ecosystem consists of just three major mangrove species has significantly benefited the implementation of the new methodologies. This approach may be feasible to other South and Central American mangrove ecosystems where only 3–6 species occur. No statement can be made to date whether this approach would work for Asian mangrove systems consisting of manifold mangrove species. Nonetheless, the results show that the methodology is feasible in addressing questions of fragmentation, habitat shape and patch size, and how these features are arranged across the mangrove landscape. In the light of rapid societal, governmental and policy changes and little financial resources, such integrative tools which support the planning process and are able to swiftly adjust to the changing spatial patterns of land-use, ecosystem and institutional settings are of major importance. Both, pixel- as well as object-based approaches on various spatial levels, provide a preliminary basis for the analysis of pattern networks and their dynamics within a given mangrove area. For instance, on the local level, the detection of species distribution is of high relevance for the deeper understanding of the goods and services provided by mangroves. For instance, Rhizophora trees act as mangrove crab refuge (Piou et al. 2007) and therefore as a natural buffer for the maintenance of the crab population above a certain sustainable population threshold. In combination with the MAIS/CIS (Mangrove Information System/Crab Information System) developed for the MADAM project (Chap. 22), an assessment of productivity
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Fig. 10.6 Vegetation on the Braganc¸a peninsula. Result of object-based classification of three IKONOS images recorded on 22 September 2003
in traditional crab collection areas with the respective mangrove structure is possible. Continuous and complex processes drive changes in mangrove coverage. The deeper understanding of the cause-and-consequences of change is a necessity in order to allow for reasonable predictions of likely development trajectories into the
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future, especially on the regional scale (see Chap. 21). The detection of change dynamics that endorse the historical perspective, as well as their range and speed, allows the elaboration of thresholds of concerns at which management measures are timely. However, more research is needed to validate the remote sensing approach developed here. The promising first results hold the potential to bridge some gaps of knowledge on these complex ecosystems, and to provide new management tools. The ongoing development of new sensor satellites may support a more straightforward assessment of mangrove ecosystems in the future, i.e., by means of mangrove structure patterns. New sensors such as TerraSAR-X (Resolution 1–16 m) and Rapid Eye (Resolution 6.5 m) may generate new possibilities for mangrove ecosystem research and management. Product examples relevant for mangrove management cover the aspects of change detection, infrastructure mapping, and flood extent mapping.
References Baatz M, Sch€ape A (2000) Multiresolution segmentation – an optimization approach for high quality multi-scale image segmentation. In: Strobl J, Blaschke T, Griesebner G (eds) Angewandte Geographische Informationsverarbeitung XII. Beitrage zum AGIT-Symposium Salzburg. Herbert Wichmann Verlag, Heidelberg, pp 12–23 Barbier EB (1994) Valuing environmental functions: tropical wetlands. Land Econ 70:155–173 Blaschke T (2000) Objektextraktion und regelbasierte Klassifikation von Fernerkundungsdaten: Neue Mo¨glichkeiten f€ ur GIS-Anwender und Planer. In: 5. Symposium “Computergest€ utzte Raumplanung” – CORP2000, pp 153–162 Bock M, Weiers S, Hanatschek R, Schwarz H, Klose F (2006) Schlussbericht Unterauftrag Fernerkundung. MADAM III, Mangrove Dynamics and Management, Bremen Bunt JS (1999) Overlap in mangrove species zonal patterns: some methods of analysis. Mangr Salt Marsh 3:155–164 Bunt JS, Bunt ED (1999) Complexity and variety of zonal pattern in the mangroves of the Hinchinbrook area, Northeastern Australia. Mangr Salt Marsh 3:165–176 Bunt JS, Stieglitz T (1999) Indicators of mangrove zonality: the Normanby River, N.E. Australia. Mangr Salt Marsh 3:177–184 Buttenfield BP (2001) Mapping ecological uncertainty. In: Hunsaker CT, Goodchild MF, Friedl MA, Case TJ (eds) Spatial uncertainty in ecology – Implications for remote sensing and GIS Applications. Springer, Berlin, pp 115–132 Cantera JR, Arnaud PM (1997) Structure et distribution des associations de mangrove de deux baies de la coˆte pacifique de Colombie. In: Kjerfve B, Lacerda LD, Diop EHS (eds) Mangrove ecosystem studies in Latin America and Africa. UNESCO, Paris, pp 71–97 Dale PER, Chandica AL, Evans M (1996) Using image subtraction and classification to evaluate change in subtropical intertidal wetlands. Int J Remote Sens 17:703–719 Definiens (eds) (2004) eCognition user guide 4, M€ unchen Duke NC, Meynecke JO, Dittmann S, Ellison AM, Anger K, Berger U, Cannicci S, Diele K, Ewel KC, Field CD, Koedam N, Lee SY, Marchand C, Nordhaus I, Smith TJ III, Dahoud-Guebas F (2007) A world without mangroves? Science 317:41–42 Fortin MJ, Edwards G (2001) Delineation and analysis of vegetation boundaries. In: Hunsaker CT, Goodchild MF, Friedl MA, Case TJ (eds) Spatial uncertainty in ecology. Springer, New York, pp 158–174
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Franklin SE (2001) Modelling forest net primary productivity with reduced uncertainty by remote sensing of cover type and leaf area index. In: Hunsaker CT, Goodchild MF, Friedl MA, Case TJ (eds) (2001) Spatial uncertainty in ecology. Springer, New York, pp 284–307 Gao J (1998) A hybrid method toward accurate mapping of mangroves in a marginal habitat from SPOT multispectral data. Int J Remote Sens 19:1887–1899 Gao J (1999) A comparative study on spatial and spectral resolutions of satellite data in mapping mangrove forests. Int J Remote Sens 20:2823–2833 Green EP, Mumby PJ, Edwards AJ, Clark CD, Ellis AC (1997) Estimating leaf area index of mangroves from satellite data. Aquat Bot 58:11–19 Hamilton L, Dixon J, Miller G (1989) Mangroves: an undervalued resource of the land and the sea. In: Borgese EM, Ginsburg N (eds) Ocean yearbook VIII. University of Chicago Press, Chicago, pp 254–288 Hogarth PJ (1999) The biology of mangroves. Oxford University Press, Oxford Khan FA, Choudhury AM, Jinnahtul Islam MD (1990) Timber volume inventory in the sunderbans using aerial photography and other remote sensing techniques. Mangr Ecosyst Occas Pap 9:3–21 Kleinod K, Wissen M, Bock M (2005) Detecting vegetation changes in a wetland area in Northern Germany using earth observation and geodata. J Nat Conserv 13:115–125 Krause G, Schories D, Glaser M, Diele K (2001) Spatial patterns of mangrove ecosystems: the bragantinian mangroves of northern Brazil (Braganc¸a, Para´). Ecotropica 7:93–107 Krause G, Bock M, Weiers S, Braun G (2004) Mapping land-cover and mangrove structures with remote sensing techniques - a contribution to a synoptic GIS in support of coastal management in North Brazil. Environ Manag 34:429–440 Lal P (2003) Economic valuation of mangroves and decision-making in the Pacific. Ocean Coast Manag 46:823–844 Mehlig U (2001) Aspects of mangrove tree primary production in an equatorial mangrove forest in Brazil. PhD thesis, University of Bremen, Bremen. ZMT Contribution vol 14 Park NW, Chi KH, Kwon BD (2007) Accounting for spatial patterns of multiple geological data sets in geological thematic mapping using GIS-based spatial analysis. Environ Geol 51:1147–1155 Piou C, Berger U, Hildenbrandt H, Grimm V, Diele K, D’Lima C (2007) Simulating cryptic movements of a mangrove crab: recovery phenomena after small-scale fishery. Ecol Modell 205:110–122 Prost MT (1997) La mangrove de front de mer en Guyane: ses transformations sous l’influence du syste´me de dispersion amazonien et sou suivi par te´le´de´tection. In: Kjerfve B, Lacerda LD, Diop ES (eds) Mangrove ecosystem studies in Latin America and Africa. UNESCO, Paris, pp 11–126 Rasolofoharinoro M, Blasco F, Bellan MF, Aizpuru M, Gauquelin T, Denis J (1998) A remote sensing based methodology for mangrove studies in Madagascar. Int J Remote Sens 19:1873–1886 Richter R (1996) A spatially adaptive fast atmospheric correion algorithm. Int J Remote Sens 17:1201–1214 Ro¨nnb€ack P (1999) The ecological basis for economic value of seafood production supported by mangrove ecosystems. Ecol Econ 29:235–252 ¨ stuars an der Nordk€ Schwarz H (2005) Klassifikation von Mangroven des Caete´-A uste Brasiliens im Staat Para´ mit Hilfe eines objektorientierten Verfahrens auf der Basis von IKONOS-Daten. Dipl Thesis, University of Trier, Trier Smith GM, Spencer T, Murray AL, French JR (1998) Assessing seasonal vegetation change in coastal wetlands with airborne remote sensing: an outline methodology. Mangr Salt Marsh 2:15–28 Souza-Filho PWM, El-Robrini M (1997) A influeˆncia da variac¸a˜o do nivel do mar na sedimentac¸a˜o da Planı´cie Costeira Bragantina durante o Holoceno. In: Costa M, Ange´lica R (eds) Contribuic¸o˜es a` Geologia da Amazoˆnia. FINEP, Bele´m, pp 307–358
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Spalding MD, Blasco F, Field CD (1997) World mangrove atlas. The International Society for Mangrove Ecosystems, Okinawa, Japan Valiela I, Bowen JL, York JK (2001) Mangrove forests: one of the world’s threatened major tropical environments. Bioscience 51:807–815 Wang L, Sousa WP, Gong P, Biging GS (2004a) Comparison of IKONOS and QUICKBIRD images for mapping mangrove species on the Caribbean coast of Panama. Remote Sens Environ 91:432–440 Wang L, Sousa WP, Gong P (2004b) Integration of object-based and pixel-based classification for mapping mangroves with IKONOS imagery. Int J Remote Sens 25:5655–5668 Weiers S, Wissen M, Bock M, Schade B (2001) Satellitenfernerkundung im Naturschutz – vom Pilotprojekt zur operationellen Anwendung. Photogrammetrie Fernerkundung Geoinformation 3:177–189 Weiers S, Bock M, Wissen M, Rossner G (2004) Mapping and indicator approaches for the assessment of habitats at different scales using remote sensing and GIS methods. Landsc Urban Plan 67:43–65
Part V Ecology and Fishery of Fin-Fish in the Mangrove System
Chapter 11
Distribution Pattern of Fish in a Mangrove Estuary M. Barletta and U. Saint-Paul
11.1
Seasonal Changes in Fish Density and Biomass in the Caete´ Estuary
In the Caete´ estuary, the salinity shows a seasonal trend. At the beginning of rainy season, the salinity values decreased in all areas. After this period, the rainfall decreased and salinity rose again. Independent from season, the upper estuary (Fig. 11.1) showed the lowest salinity values and the lower estuary the highest ones. Water temperature, except in the lower estuary, and dissolved oxygen showed the same seasonal trends as salinity (Barletta et al. 2000, 2003, 2005). The estuary supports a resident fish community that is functionally important as an intermediate trophic level for many consumers. The production and seasonal occurrence of fish appear to vary with salinity, hydrology and nutrient status in the estuary, all of which are controlled by both freshwater flow and tidal sea level rise. Many species are adapted to these salinity fluctuations and are resident within the estuarine habitats. Other species stay in the estuary only during a certain period of their lives and/or when the conditions are appropriate. Estuaries are frequently referred to as nursery areas for both fish and invertebrates (Beck et al. 2001). Ichthyoplankton can originate either from within the estuary or from adjacent marine and freshwater environments (Barletta-Bergan et al. 2002a). Juveniles use the estuary as a feeding ground and refuge. Marine species move to coastal shallow waters before reaching maturity, where they contribute to the coastal fisheries yield Barletta et al. (1998). The structure and seasonal dynamics of the fish larvae and juvenile fish communities clearly show the importance of the main channel (Barletta-Bergan et al. 2002a; Barletta et al. 2005) and of the mangrove forest of (Barletta-Bergan et al. 2002b; Barletta et al. 2003) the estuary as a fish nursery habitat. This estuary is not an exception; Embley Estuary (northern Australia) habitats have the same function when compared with the Caete´ River estuary (Barletta and Blaber 2007).
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Fig. 11.1 Caete´ Estuary, showing the upper, middle and lower estuary
11.1.1 The Main Channel The water salinity of the Caete´ Estuary follows a marked seasonal trend. In the early rainy season (January), salinity values decrease in all three areas (upper, middle and lower) with the lowest values (0–17) occurring in April (Fig. 11.1). From then on, rainfall decreases and salinities rise again. Independent from season, the upper estuary always shows the lowest salinity (0–10), whereas the lower estuary is associated with the highest values (17–35). Water temperature, except in the lower estuary, shows a similar seasonal trend (Barletta et al. 2005). The absolute mean density and biomass, estimated from all samples, is 0.25 ind. m2 and 0.9 g m2, respectively (Barletta et al. 2005). The upper estuary has the highest mean values of density (0.3 ind. m2) and biomass (1.2 g m2). The estuarine species S. rastrifer, C. spixii, S. microps, Aspredo aspredo, Aspredinichthys filamentosus and Aspredo sp. 1, out of 82 species present in the estuary, comprise c. 88% of the total density and 77% of the total biomass. This suggests that, in spite of a high number of species, the structure of the fish assemblage in this estuary is composed of only a few species. The importance of the most abundant species varies considerably in each of the three main areas of the estuary (Fig. 11.2 a, b). S. rastrifer occurs in all three areas, but species such as C. spixii, are captured in the highest numbers and greatest biomass principally in the middle and lower estuary. S. microps, A. aspredo, A. filamentosus and Aspredo sp. 1 have highest densities and biomasses in the upper estuary. These species, except S. microps, Aspredo sp.1 (density and biomass), S. rastrifer, A. aspredo and C. acoupa (density), show significant differences
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a Upper
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Fig. 11.2 Mean variation and range (þsd) in biomass (a) and in density (b) of the most dominant species per area in the Caete´ estuary (upper, middle and lower) and season (early dry, late dry, early rainy and late rainy season)
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b 1 0.8 0.6 0.4 0.2 0
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Fig. 11.2 (continued)
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between seasons. Interaction between season and area for these species, except for A. aspredo, Aspredo sp.1 (density and biomass), S. rastrifer, S. microps, and Aspredo sp.2 (biomass), can be detected, suggesting that the distribution of these species (in terms of density and biomass) in the three different areas of the Caete´ Estuary areas differ from each other, and that they are also influenced by the seasons. Therefore, the spatial and temporal distributions of these species (in terms of density and biomass) differ from each other. Factorial analysis ordination bi-plot diagrams of species scores, as well as regression statistics, permit an interpretation of the distribution of the species groups in the different areas of the Caete´ River estuary in relation to environmental variables (Fig. 11.3). Salinity and distance to the bay mouth (as co-variables of the estuarine gradient) are important in determining the first factorial axis, and seem
Fig. 11.3 Factorial analysis ordination biplots showing species centroids in relation to environmental variables (CW channel width, Distance to the bay mouth, Rain fall, salinity). SRAS S. ratrifer, CSPIX C. spixii, SMIC S. microps, AASP A. aspredo, AFIL A. filamentosus, AASP1 Aspredo sp. 1, ASP2 Aspredo sp. 2, PBLOC P. blochii, PNOD P. nodosus, RAMAZ R. amazonica, CACOUP C. acoupa, SSTEL S. stellifer, OMUCR O. mucronatus, CPLEUR C. agassizii, CPSITT C. psittacus, APHRY A. phrygiatus, CMICRO C. microlepdotus, AQUAD A. quadriscutis, LGROS L. grossidens, EIGEN E.virescens, ATIBIC A. tibicens, BBAGR B. bagre, ADUME A. dumerelli, LLANCE L. lanceolatus, LORIC Loricaria sp., GLUT G. luteus, PLAGIO Plagioscion sp., OPALO O. palometa, GBROC G. broussonneti, PHARROW P. harroweri, GOCEA G. oceanicus, CFABER C. faber, ALINEA A. lineatus, BVAIL B. vaillanti, MANCY M. ancylodon
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to define the main gradient structuring the fish species into ecological groups in the upper and lower estuary. Channel width was also a significant variable and highly correlates with salinity. The first factorial axis explained 40% of the total variability. The truncation of the species scores along the first axis suggests that these variables (principally the salinity ecocline) control the large-scale pattern of fish fauna structure in the Caete´ River estuary. The second factorial axis explains only 18% and best represents the seasons of the year (early and late rainy and early and late dry) in this region. Plots of species factorial analysis centroids and cluster analysis clarify distinct patterns in the structure of the fish assemblage in the main channel of the estuary, involving different species associations (Figs. 11.3 and 11.4). Furthermore, projection of these centroids onto environmental vectors reflected large-scale changes in the assemblage structure that coincide with abiotic environmental gradients. In other words, the seasonal variation of the environmental variables, principally salinity, structure the fish assemblages in the main channel of the estuary. Estuarine fish assemblages seem to undergo large seasonal fluctuations in biomass and density. The estuarine-dependent species are ordered along a large-scale spatial gradient during the early and, principally, the late dry season, when relatively stable hydrological conditions create a well-defined salinity gradient in the estuary (Fig. 11.3). On the other hand, during the late rainy season, freshwater runoff increases, salinity declines and the estuary becomes propitious for freshwater fish (Pimelodus blochii, Brachyplatystoma vaillanti, Hypostomus plecostomus and Loricaria sp.) and brackish-water fish species (Pseudauchnipterus nodosus) (Fig. 11.4, Group I). According to Barletta and Blaber (2007), these freshwater species (Siluriforms) characteristic of the upper Caete´ River estuary have no equivalent functional guilds in the Embley Estuary (northern Australia). Representatives of this order and the Characiforms, Gymotiforms and Perciforms were able to colonize Asian, African and South American waters before these continents were separated. Aside from two catfish families (Ariidae and Plotosidae) that became secondarily adapted to salt water, Ostariophysan fish have not been able to reach Madagascar, the West Indies, New Zealand and Australia. This suggests that those land masses have not been connected to any of the larger continents since the upper Jurassic (Briggs 1995). This also explains why, despite seemingly suitable habitats and hydrological conditions, there are no fresh water Ostariophysan fish species in the Embley Estuary. Not only salinity, but also turbidity, is indicated as an important factor associated with larval fish abundance (Cyrus and Blaber 1987a, b; Whitfield 1994a, b, c; Barletta-Bergan et al. 2002a). Melville-Smith et al. (1981) and Barletta-Bergan et al. (2002a) suggested that high abundance in most upstream sections of the estuary may reduce the chances of larvae being flushed out to less productive, inhospitable, offshore areas where they subsequently die. Additionally, increased organic matter and turbidity in the upper reaches of the estuary might also provide shelter from predation for larval fish assemblages (Barletta-Bergan et al. 2002a). The authors also concluded that the species number was greatest in the upper estuary, due to a combination of freshwater and marine species with estuarine ones. Young-of-the-year and adult fishes are captured more in the upper estuary.
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Distribution Pattern of Fish in a Mangrove Estuary E.virescens H. plecostomus Loricaria sp. S.microps A. aspredo A. filamentosus A. tibicens Aspredo sp.1 Aspredo sp.2 P. blochii A. dumereli C. acoupa B. vaillanti Plagioscion sp. P. nodosus S. stellifer R. amazonica C. pleurops A. phrygiatus C. psittacus S. rastrifer C. spixii M. ancylodon C. microlepdotus O. mucronatus A. quadricutis L. lanceolatus A. lineatus G. broussonneti L. grossidens G. oceanicus O. palometa C. crysurus P. harroweri B. bagre G. luteus C. faber
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BRAY-CURTIS SIMILARITY (RANKED) Fig. 11.4 Cluster dendrogram based on similarities of the most important species captured in the upper, middle and lower estuary of Caete´ Estuary. Samples were clustered by complete linkage of ranked Bray Curtis similarity index. Group I represents the freshwater species and marineestuarine species which show high density and biomass in the upper estuary independent from season. Group II is represented by two subgroups. The first sub-group (Group II, a) is represented by species, except P. nodosus, which occur in the middle and lower estuary. Most of these species in the late dry season and early rainy season are common in the upper estuary. Group II, b is formed by species which are more frequent in the lower estuary principally during late dry season
When the salinity values rise in the estuary, during the early and late dry season, these species move upstream toward the upper estuary for spawning and shelter for young-of-the-year. But, during the end of the rainy season, a strong reduction of salinity values in the entire system is observed, independent of turbidity, and most of the fishes move downstream to inshore areas (Barletta et al. 2005).
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11.1.2 The Mangrove Tidal Creeks As in the main channel of the estuary, the water salinity and temperature in tidal creeks of the Bragantine peninsula show a clear seasonal trend (Barletta et al. 2000, 2003). At the end of December, the rainy season begins, and salinity decreases from 35 to 28. Between March and May, the lowest salinity values (6–12) are recorded. Subsequently, rainfall decreases and salinity rises once more. Fishes which utilize the intertidal mangrove forest as a habitat (Fig. 11.5) do so in two different ways. The first is represented by the fish assemblage which remains in the intertidal area at low tide (Barletta et al. 2000). The second group comprises the fish species which avoid the intertidal area during low tide and make use of this habitat only when it is submerged (Barletta et al. 2003). Among the 14 species captured in this habitat during low tide, Myrophis punctatus is dominant, and occurs independently of area and salinity fluctuations across the entire system. However, samples taken from the boundary area between the coastal plain and sand plain show the lowest density and biomass values (Fig. 11.6 a, b). This suggests that this species is well adapted to use this habitat (Barletta et al. 2000). The family Gobiidae shows the highest specific diversity, indicating that the
Fig. 11.5 Mangrove Forest at Furo do Meio Intertidal Creeks. 1 Mangrove tidal creek at high tide (4–5 m), 2 low tide, 3 mangrove intertidal creek bordered by Rhizophora mangle, 4 Uca sp. (a) and Ucides cordatus (b) holes at the base of R. mangle
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Fig. 11.6 Mean densities (a) and biomass (b) of the three numerically dominant species, and number of species (a) per sampled area. These species are frequent in the mangrove forest even when this habitat has no tidal influence at low tide (see Fig. 11.5)
species of this family are also well adapted to this habitat. The fact that gobiids are territorial defenders (Lowe-McConnell 1987) may explain their low density and biomass. Furthermore, during the end of the dry season, G. smaragdus individuals are captured in the mangrove forest located on the upper estuary. At the end of rainy season, they did not occur in this area. This suggests that G. smaragdus undertake longitudinal movements in the mangrove forest in accordance with salinity variations in the estuary. The euryhaline fresh water Poecilia sp. is frequent in the mangrove forest but does not occur in areas close to the mouth of the estuary, suggesting that this area is a distribution limit for this species (Barletta et al. 2000).
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Of 49 fish species which make use of the intertidal mangrove forest during diurnal neap tides, C. agassizii, C. psittacus and A. clupeoides are the most important, both in number (70%) and weight (74%), of all catches independent of season (Barletta et al. 2003) (for tidal and diel dynamics, see also Chap. 10). Total fish densities do not differ significantly among creeks and seasons (Fig. 11.7 a). However, total fish biomass differs significantly among seasons. For C. agassizii and C. psittacus, densities and biomass differ significantly among seasons (Fig. 11.7 b). Density and biomass of C. agassizii, P. atherinoides, Pseudauchnipterus nodosus and S. naso show significant temporal differences. On the other hand, C. psittacus, A. clupeoides and Genyatremus luteus do not show any significant differences among seasons. Significant differences between creeks can be observed for A. clupeoides (density and biomass) and Rhinosardinia amazonica (biomass). The density and biomass curves (ABC plots) show that, during the early rainy season, the dominant species increase in number and weight (Fig. 11.8). At this time, the dominant species (C. agassizii) represent more than 70% of the total density and biomass. Therefore, a reduction in the diversity index is recorded, whereas the number of species and evenness show no significant changes. After April, rainfall decreases and the density and biomass curves show similar trends to those in the period before the rainy season. The significant increase in density and biomass of some species in the Furo do Meio creeks during the early rainy season suggests that these species are migrating into the mangrove tidal channels of the lower estuary because of an increased fresh water runoff in the estuary main channel. The tidal channels in the lower estuary serve as refuge areas for those species that seek shelter when the estuary is strongly influenced by fresh water. The main tidal channels and their tidal creeks are buffer areas for the intertidal fish community against a drastic reduction of salinity in the Caete´ estuary. The same tendency was observed in the main channel of Caete´ estuary by Barletta-Bergan et al. (2002a, b) and Barletta et al. (2005). This feature, which reflects the seasonal fish movement and migration among mangrove tidal channels, is explored in greater detail below.
11.2
Fish Assemblage Patterns
11.2.1 Seasonal Movements Rain in the Caete´ River basin falls mainly from January to June, which results in a high river discharge into Caete´ Estuary. During the peak of the rainy season (March and April), the Caete´ River is a completely flushed system. Even in the lower estuary, salinity of >20 was found only in coastal waters outside the estuary. At that time, a reduction in biomass occurs throughout the estuary (Barletta-Bergan et al. 2002a; Barletta et al. 2005), except in the Furo do Meio creeks (Barletta-Bergan et al. 2002b; Barletta et al 2003). However, the periods of high water discharge from the Caete´ estuary coincide with the peak period of dispersion of juvenile fishes
Fig. 11.7 Mean variation range (þSD) in density (a) and in biomass (b) of the dominant species per creek (1, 2 and 3) and season (dry and rainy) which use the mangrove forest at high tide
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Fig. 11.7 (continued)
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Fig. 11.8 Abundance biomass comparisons (ABC) plots (x-axis logged) for species density (solid line) and biomass (dotted line) per season
from nearby coastal waters (S. rastrifer, C. spixii, A. aspredo and S. microps) (Barletta et al. 2005) and from the Caete´ River (P. blochii and P. nodosus) into the estuary and tidal creeks of the mangrove forest (Barletta et al. 2000, 2003; Barletta-Bergan et al. 2002a, b). Males of C. agassizii carrying eggs, vitellinic larvae and juveniles in their mouths are caught in the Furo do Meio creeks from the end of December through April. This suggests that this species starts to spawn at the beginning of the rainy season. Juvenile C. psittacus and P. atherinoides are present during the same period. In addition, at the peak of the rainy season the total biomass and density of C. agassizii, C. psittacus and P. atherinoides increase in the Furo do Meio creeks. These species are considered as residents in the mangrove forest creeks and main tidal channels. During the dry season at high tide, shoals of filter-feeding C. edentulus and the carnivorous Strongylura timocu and Trichiurus lepturus inhabit the mangrove tidal creeks, where they can be considered as marine seasonal migrants. Juvenile Genyatremus luteus, C. acoupa and Micropogonias furnieri are caught during the entire sampling period. These are marine juvenile migrant species, marine coastal spawners that utilize the estuarine environment as a nursery area in the post-larval and juvenile stages. Young forms of Lutjanus jocu, Caranx spp., Tarpon atlanticus and Scomberomorus maculatus (marine species) are caught in the mangrove creeks during the peak of the dry season (salinity >30). Juvenile Pseudauchnipterus nodosus (fresh–brackish water species) are caught during the peak of the rainy season (salinity <10). Most of the species in the Furo do Meio are more abundant in the rainy season. On the other hand, most of the species in the main channel of the Caete´ River are less abundant during the peak of the rainy season (Barletta et al. 2005). This suggests that during the rainy season the fish assemblage in the main channel and the intertidal mangrove forest concentrates in coastal areas and in the mangrove tidal channels of the lower estuary (Fig. 11.9). Analyzing the movement pattern of
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Fig. 11.9 Fish species movements induced by seasonal fluctuation of salinity in the Caete´ Estuary at the end of dry (a) and end rainy season (b). This fish movement pattern induced by seasonal fluctuation of salinity ecocline could be generalized for other tropical and sub-tropical regions in the tropical (1, 2, 3, 4 and 5), subtropical (5 and 6) South America and tropical (7) Africa (c)
both fish assemblages in the Caete´ Estuary, it becomes clear that the seasonal changes of estuarine fish assemblages are determined by a combination of temporal fluctuations of abundance induced by rainfall, reproduction and recruitment of estuarine species, and by recruitment of marine and freshwater species. These findings are supported by data from Rio de la Plata Estuary in Uruguay and Argentina (Jaureguizar et al. 2004), southern African estuaries (Whitfield 2005), Gambia River estuary in West Africa (Simier et al. 2006), a marine embayment in Zanzibar (Luguendo et al. 2007), mangrove creeks in Tanzania (Mwandya et al. 2009), Rı´o Champoto´n in southeastern Mexico (Lopez-Lopez et al. 2009), and an estuary in the Gulf of Mexico in Florida (Bacheler et al. 2009). Seasonal changes in the catch rates of tropical and subtropical fish communities have also been reported in Australia (Blaber et al. 1989), Madagascar (Laroche et al. 1997), south Florida (Thayer et al. 1987), Guyana (Lowe-McConnell 1987), northern Brazil (Batista and Reˆgo 1996), and southeast Brazil (Giannini 1989). These changes have been ascribed mainly to reproductive patterns and increased recruitment. Blaber et al. (1990) suggested that this phenomenon, of fish concentrating around estuaries, together with the probability that during the rainy season freshwater species move to the lower estuary, may explain the correlation between fish abundance and rainfall. However, according to Barletta et al. (2008), Paranagua´ Estuary (south Brazil) seems to be an exception to this model, since the middle and
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lower estuary have stable salinity values even toward the late rainy season, and the most abundant estuarine species remain in these areas of the estuary during this period. This suggests that the combinations of geomorphology of the estuary and river flow basin drainage are also conditioning factors on the fish assemblages’ distribution in the ecocline of an estuarine ecosystem. In the Caete´ Estuary, as in other tropical and subtropical estuaries, seasonal fluctuation of salinity influences the seasonal movements of fish species. Together, these movements result in a succession of fish species composition in the estuarine ecosystem. When conditions are propitious, many marine and/or freshwater juvenile fishes, together with the resident species, enter this ecosystem to exploit this environment.
11.2.2 Fish Shelter Strategies in Mangrove Forests and Tidal Channels At high tide, most fish using the tidal creeks in the Furo do Meio avoid exposure to air by moving into the main tidal channel or directly into the main channel of the estuary during ebb tide (Barletta et al. 2003). The intertidal mangrove fish species which move into the mangrove forest during flood move back to the main tidal channel (lower estuary) (Barletta et al. 2003), or to the mouth of the mangrove tidal creeks of the Caete´ estuary (middle estuary) (Barletta et al. 2005) by ebb tide. This group is formed by estuarine species (C. agassizii, C. psittacus, A. clupeoides, P. atherinoides, A. anableps, G. luteus and Sciades herzbergii), and estuarinedependent species (C. acoupa, Chaetodipterus faber, Lutjanus jocu, Tarpon atlanticus, Caranx latus, C. bartholomei, C. crysos and M. furnieri). According to Wootton (1998), this endogenous tidal rhythm in locomotory activity and ability to find shelter of these intertidal mangrove fish species may be a component of adaptation to live in this habitat. During low tide in the mangrove forest of the north Brazilian coast, the shoreline remains sub-aerial and it changes suddenly from aquatic to virtually terrestrial (tidal range: >4 m) (Fig. 11.5). The fish species develop different strategies to overcome predation by terrestrial predators and by desiccation during low tide (Fig. 11.10). The first strategy (Fig. 11.10, Group 1 – G1) is to avoid tidal creeks during low tide. These fish (M. punctatus, Guavina guavina and Eleotris pisonis) wait for the next flood tide in crab holes of Uca spp. and Ucides cordatus close to the creeks (Fig. 11.5). The second group includes species of the family Gobiidae, which use their pelvic fins to attach to Rhizophora mangle roots or to the sediment (Fig. 11.10, G2). Species of this family are also able to breathe air, by a highly vascularized buccopharyngeal chamber. They are able to move into adjacent pools during low tide. The last strategy (Group 3) (Fig. 11.10, G3) is to stay in tidal creeks during low tide (Poecilia sp. and Kryptolebias sp.). These fish species are adapted to utilize the water surface layer which is well oxygenated due to its direct contact to the
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Fig. 11.10 Mangrove intertidal fish strategies at low tide. A1 and A2 represent the main channel; B1 and B2 represent the small creeks in the intertidal mangrove forest (see also Fig. 11.5). Crosssection 1 intertidal mangrove forest at high tide; cross-section 2 intertidal mangrove forest at low tide; cross-section 3 represents the three different ecological strategies developed by fish to reduce interspecific competition in the intertidal mangrove forest at low tide. The first strategy (Group 1 – G1) includes the fish species that stay in the crab hole until the next flood tide. Group 2 (G2) represents the fish species which stay buried or attached to the Rhizophora mangle roots. The third group (G3) represents the species which stay in the water stream
atmosphere (Lewis 1970). All these ecological strategies reflect the interactions among individuals of the same or different species (competition and predation) during ebb and low tide in a very limited, and limiting, habitat. These strategies can explain the high concentration (density and biomass) of M. punctatus and the high diversity of the Gobiidae species, and may help to reduce interspecific competition in the intertidal mangrove forest during low tide.
References Bacheler NM, Paramore LM, Buckel JA, Hightower JE (2009) Abiotic and biotic factors influence the habitat use of an estuarine fish. Mar Ecol Progr Ser 377:263–277 Barletta M, Blaber SJM (2007) Comparison of fish assemblages and guilds in tropical habitats of the Embley (Indo-West Pacific) and Caete´ (Western Atlantic) estuaries. Bull Mar Sci 80:647–680 Barletta M, Barletta-Bergan A, Saint-Paul U (1998) Description of the fishery structure in the mangrove dominated region of Braganc¸a (State of Para´ – North Brazil). Ecotropica 4:41–53
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Barletta M, Saint-Paul U, Barletta-Bergan A, Ekau W, Schories D (2000) Spatial and temporal distribution of Myrophis punctatus (Ophichthidae) and associated fish fauna in a Northern Brazilian intertidal mangrove forest. Hydrobiologia 426:65–74 Barletta M, Barletta-Bergan A, Saint-Paul U, Huboldt G (2003) Seasonal changes in density, biomass, and diversity of estuarine fishes in tidal mangrove creeks of the lower Caete´ Estuary (Northern Brazilian coast, East Amazon). Mar Ecol Progr Ser 256:217–228 Barletta M, Barletta-Bergan A, Saint-Paul U, Hubold G (2005) The role of salinity in structuring the fish assemblages in a tropical estuary. J Fish Biol 66:45–72 Barletta M, Amaral CS, Correa MFM, Guebert F, Dantas DV, Lorenzi L, Saint-Paul U (2008) Factors affecting seasonal variations in demersal fish assemblages at an ecocline in a tropicalsubtropical estuary. J Fish Biol 73:1314–1336 Barletta-Bergan A, Barletta M, Saint-Paul U (2002a) Structure and seasonal dynamics of larval fish in the Caete´ River in north Brazil. Estuar Coast Shelf Sci 54:193–206 Barletta-Bergan A, Barletta M, Saint-Paul U (2002b) Community structure and temporal variability of ichthyoplankton in North Brazilian mangrove creek. J Fish Biol 61(suppl A):33–51 Batista VS, Reˆgo FN (1996) Ana´lise de associac¸o˜es de peixes, em igarape´s do estua´rio do Rio Tibiri, Maranha˜o. Rev Bras Biol 56:163–176 Beck MW, Heck KL Jr, Able KW, Childers DL, Eggleston DB, Gillanders BM, Halpern B, Hays CG, Hoshino K, Minello TJ, Orth RJ, Sheridan PF, Weinstein MP (2001) The identification, conservation, and management of estuarine and marine nurseries for fish and invertebrates. Bioscience 51:633–641 Blaber SJM, Brewer DT, Salini JP (1989) Species composition and biomass of fishes in different habitats of a tropical northern Australia estuary: their occurrence in the adjoining sea and estuarine dependence. Estuar Coast Shelf Sci 29:509–531 Blaber SJM, Brewer DT, Salini JP, Kerr J (1990) Biomass, catch rates and abundances of demersal fishes, particularly predators of prawns, in a tropical bay in the Gulf of Carpentaria, Australia. Mar Biol 10:397–408 Briggs JC (1995) Global Biogeography. Elsevier, The Netherlands Cyrus DP, Blaber SJM (1987a) The influence of turbidity on juvenile marine fish in the estuaries of Natal, South Africa. Cont Shelf Res 7:1411–1416 Cyrus DP, Blaber SJM (1987b) The influence of turbidity on juvenile marine fish in the estuaries. Part 1. Field studies at St. Lucia on the southeastern coast of Africa. J Exp Mar Biol Ecol 109:53–70 Giannini R (1989) Distribuic¸a˜o temporal e espacial e aspectos bioecolo´gicos da famı´lia Sciaenidae na baı´a de Santos, SP, Brasil. MSc thesis, University of Sa˜o Paulo, Sa˜o Paulo Jaureguizar AJ, Menni R, Guerrero R, Lasta C (2004) Environmental factors structuring fish communities of Rio de la Plata Estuary. Fish Res 66:195–211 Laroche J, Baran E, Rasoanandrasana NB (1997) Temporal patterns in a fish assemblage of a semiarid mangrove zone in Madagascar. J Fish Biol 51:3–20 Lewis WM (1970) Morphological adaptation of ciprinodontids for inhabiting oxygen deficient waters. Copeia 1970:319–326 Lopez-Lopez E, Seden˜o-Dias JE, Romero FL, Trujillo-Jime´nez P (2009) Spatial and seasonal distribution patterns of fish assemblages in the Rı´o Champoto´n, southeastern Mexico. Rev Fish Biol Fish 19:127–142 Lowe-McConnell RH (1987) Ecological studies in tropical fish communities. Cambridge University Press, Cambridge Luguendo BR, Nagelkerken I, Jiddawi N, Mgaya YD, van der Velde G (2007) Fish community composition of a tropical nonestuarine embayment in Zanzibar, Tanzania. Fish Sci 73:1213–1223 Melville-Smith R, Baird D, Woolridge T (1981) The utilization of tidal currents by larvae of estuarine fish. S Afr J Zool 16:10–13
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¨ hman MC, Andersson MH, Mgaya YD (2009) Fish assemblages in Mwandya AW, Gullstro¨m M, O Tanzanian mangrove creek systems influenced by solar salt farm constructions. Estuar Coast Shelf Sci 82:193–200 Simier M, Laurent C, Ecoutin JM, Albaret JJ (2006) The Gambia River estuary: A reference point for estuarine fish assemblages studies in West Africa. Estuar Coast Shelf Sci 69:615–628 Thayer GW, Colby DR, Hettler WF (1987) Utilization of the red mangrove prop root habitat by fishes in south Florida. Mar Ecol Progr Ser 35:25–38 Whitfield AK (1994a) An estuary-association classification for the fishes of southern Africa. S Afr J Sci 90:411–417 Whitfield AK (1994b) A review of ichthyofaunal biodiversity in southern African estuarine systems. Ann Mus Rep Afr Cent Zool 275:149–163 Whitfield AK (1994c) Abundance of larval and 0+ juvenile marine fishes in the lower reaches of three southern African estuaries with differing freshwater inputs. Mar Ecol Progr Ser 105:257–267 Whitfield AK (2005) Fishes and freshwater in southern African estuaries. Aquat Living Res 18:275–289 Wootton RJ (1998) Ecology of teleost fishes, Fish and fisheries series 24. Kluwer, Dordrecht
Chapter 12
Dynamics in Mangrove Fish Assemblages on a Macrotidal Coast U. Krumme and U. Saint-Paul
12.1
Introduction
The world’s largest continuous mangrove forests thrive on coastal plains where large rivers meet the sea and where tidal ranges are large (see Spalding et al. 1997; Krumme 2009). These macrotidal estuarine mangroves seem to provide an outstanding nursery function for fishes due to the favorable strength and frequency of the inundation disturbance. Robertson and Blaber (1992) compared four mangrove estuaries in Australia and concluded that higher tidal ranges increase the nursery function of mangrove estuaries due to higher turbidity, lower visibility, fewer piscivores and hence less juvenile mortality caused by piscine predators. Macrotides likely facilitate transport of larvae (see also Chap. 13), foster regular tidal movements of juveniles from low-water resting sites to high-water feeding sites, and ontogenetic movements from juvenile to adult habitats. Juveniles riding the tides may reduce significant expenditure of energy for movement, thereby gaining capacity for faster growth. However, studies on fish use of macrotidal mangroves are rare. Understanding the temporal and spatial dynamics that macrotides impose on variations in fish assemblage structure is crucial to allow the definition of sampling strategies and long-term monitoring programs in these highly productive coastal areas. Our studies in north Brazil focused on three main issues related to the tidal pulse: (1) temporal and spatial patterns in the composition of the intertidal fish fauna in the mangrove, (2) patterns in the movements of fishes during tidal cycles, and (3) temporal patterns in feeding of abundant fish species.
12.2
Environmental Setting
In the study area in north Brazil, the coastal plain is dissected by dendritic systems of tidal creeks. The creeks connect the subtidal area of the open estuary with the intertidal mangrove. For the remainder of this chapter, the creek order is defined as U. Saint-Paul and H. Schneider (eds.), Mangrove Dynamics and Management in North Brazil, Ecological Studies 211, DOI 10.1007/978-3-642-13457-9_12, # Springer-Verlag Berlin Heidelberg 2010
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follows: intertidal creeks draining into a large subtidal channel (called Furo) are first-order creeks (20–30-m wide at the mouth and ramified further upstream), and second-order creeks (10–15-m wide at the mouth) are the intertidal creeks draining into a first-order creek. The Furos can be several kilometers long and about 50 m wide in the upper reaches and several hundred meters wide in the lower reaches. They are connected to the Caete´ Bay, but extensive sand banks at the lower reaches and in the bay prevent their complete drainage so that the Furos hold considerable amounts of water each low tide. In the Furos, maximum water depth at low tide is 3–5 m. The deepest sections of the open Caete´ Bay are found in the river main channel (up to 10 m). On a coast with semidiurnal tides, each tidal cycle is completed with a 25-min time delay in relation to the diel cycle. Due to the retardation from tide to tide, neap high tides in the study area occur at midday (ND) and midnight (NN), but a week later, spring high tides occur in the evening (SE) and in the morning hours (SM). In the study area, slack high tide at SE usually occurred after sunset (already darkness), SM after sunrise (already daylight). The intertidal creeks are flooded twice every day by the semidiurnal tide while the mangrove plateau is only flooded twice a month during the days of spring tides. In the Furos, the tidal range at neap and spring tides is 2–3 m and 3 to >4 m, respectively. The maximum tidal current speed at neap tides is usually <0.5 ms1 and can exceed 1.2 ms1 at spring tides. Seagrass meadows or coral reefs are absent from the coastal areas in north Brazil due to the combined effect of coastal estuarization, macrotides, low water transparency and the lack of extensive hard bottom. Therefore, the tidal movements of fish connect unvegetated subtidal areas (sand, mud) with intertidal areas which are sand, mud or vegetated with mangrove.
12.3
Nekton Sampling in Macrotidal Environments
Semidiurnal tides represent the highest frequency of regular water level change in nature (two high and low waters per day). Hence, a quasi-continuous sampling would be desirable to describe the natural processes. However, the number of quantitative samples that can be taken within a tidal cycle is limited for technical and financial reasons. In addition, in macrotidal mangrove areas, the structural complexity of the forest, strong currents and high litter content may hamper sampling with conventional fishing gear. What is needed is a fishing methodology of high, stable efficiency and sufficient validity that provides a large number of representative samples throughout tidal cycles. Only a few kinds of fishing gear can be considered. An excellent overview of the array of techniques that can be used to sample intertidal fish is given in Horn et al. (1999) and Kneib (1997). However, note that no one capture method is suitable for all conditions and all species. In the mangrove in north Brazil, several methods were tested to sample fish.
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Block and fyke nets: Setting a block or fyke net at the mouth of an intertidal creek at slack high tide is an inexpensive and effective fishing method since it is supposed to catch almost 100% of the nekton community upstream when it attempts to leave the creek at ebb tide (Krumme et al. 2004; Giarrizzo and Krumme 2007). However, block nets integrate information over the entire upstream area and during the tidal cycle (Kneib and Wagner 1994). To study patterns in fish movements over time, block nets can be set at different tidal stages or a fyke net can be emptied at fixed time intervals (Giarrizzo, Krumme, Wosniok, unpublished data). To study patterns in space, several block nets can be set simultaneously at different sites along an intertidal drainage system. Beach seine: Experience was gathered with a beach seine (Krumme et al. 2004) that, however, has low and variable catch efficiency similar to trawls (Rozas and Minello 1997; Wennhage et al. 1997). However, the comparability of beach seine catches is not seriously affected when only relative abundances of species and age groups are concerned (Ansell and Gibson 1990). Tidal fish weir: Large commercial tidal fish weirs provided insight into the composition of transients over sand banks in the Caete´ Bay (Schaub 2000). A modified tidal fish weir used in the upper reaches of a Furo revealed details about the tidal migrations of fishes (Krumme 2004), though weak neap tides did not exert a sufficiently strong directional force on the movements and species-specific avoidance became apparent. Lift nets: Rozas and Minello (1997) reviewed the efficiency of different gear types to quantitatively sample nektonic organisms in shallow estuarine habitats and recommended enclosure samplers, particularly a bottomless lift net (Rozas 1992). Further lift net designs suited for quantitative sampling are described in Kneib (1991, 1997), Connolly (1994) and Hindell and Jenkins (2005). Lift nets were tested, but the efficiency varied enormously with the tidal stage and did not allow for representative sampling at different tidal stages (Leal-Flo´rez 2001; Krumme and Saint-Paul 2003). Likewise, gill nets are inappropriate due to strong tidal currentrelated changes in catchability. Hydro-acoustics: Hydro-acoustics have four advantages over any other type of observational technique in water: 1. Non-selectivity: the echoes from virtually all swimbladders in range of the sonar are recorded; conventional fish sampling techniques are notorious for sample biases. 2. The ultra high-frequency sound waves have no effect on fish behavior. 3. No other method provides continuous coverage in water at high spatio-temporal resolution. 4. The method is non-intrusive. It does not cause mortality and animals are not removed while sampling. Modern split-beam systems provide estimates of the acoustic size of a target, its swimming speed, 3-D location in the water column, and direction of travel, and allow target tracking (Simmonds and MacLennan 2005). Unfortunately, however, fish species cannot be identified directly, due to high variability in backscattering
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properties of individual fish. Therefore, simultaneous fish captures are required to infer to the species composition insonified (Simmonds and MacLennan 2005). Although modern shallow-water sonar is costly, it represents an invaluable tool for an understanding of the spatio-temporal dynamics in aquatic environments and is applicable in a turbid mangrove environment (Krumme and Saint-Paul 2003; Krumme 2004; Krumme and Hanning 2005). Visual census: Underwater visual fish census was not feasible due to low water transparency (mean vertical Secchi depth 30 cm). However, the four-eyed fish Anableps anableps (Anablepidae) always swim on the water surface, thus providing a unique and inexpensive opportunity to study patterns in tidal migration with high temporal resolution on the species level by visually counting individual fish (Brenner and Krumme 2007, Krumme, unpublished data).
12.4
Trends in Species Richness, Biomass and Density along a Shoreline Gradient
In macrotidal estuaries, fish assemblage composition may be dynamic due to the tidal movements of fishes. Transient species enter and leave the intertidal zone whereas residents constantly live there (Gibson 1988). Despite the temporal variation caused by the tides, spatial differences can be studied by taking samples at different sites but at comparable tidal stages, i.e., at low or high water. In the Caete´ estuary, four estuarine habitats were sampled – subtidal Caete´ Bay, subtidal Furo, and intertidal mangrove creeks at high tide and low tide – using an otter trawl (Barletta et al. 2005), a beach seine and block nets (Krumme et al. 2004), and an ichthyotoxin (Barletta et al. 2000), respectively (see also Chap. 9). Catch weights and abundance from all estuarine habitats were always standardized to biomass (g m2) and density (individuals m2) and allow for a rough overall inter-habitat comparison. The estuarine fish species richness decreased along a vertical gradient of shore height from the subtidal Caete´ Bay to the high intertidal zone (Fig. 12.1) suggesting that the subtidal areas of the Caete´ Bay represent the species pool from which variable subsets of transient species are assorted each tide. The intertidal resident fish fauna had the lowest species richness (14 species) due to the extreme environmental changes characterizing the amphibious mangrove zone. The snake eel Myrophis punctatus (Ophichthidae) was the dominant resident accounting for almost 75% of the mean total biomass of resident mangrove fishes at low tide (Barletta et al. 2000). In contrast to species richness, biomass and density increased with shore height (Fig. 12.1). Biomass and density of residents and of the subtidal Furo at low tide was more than one order of magnitude higher than that of intertidal transients and subtidal bay fishes. The extreme environment of the high intertidal led to the dominance of a single resident species, i.e., M. punctatus, whereas the subtidal
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Fig. 12.1 Changes in overall mean fish species richness, biomass (g m2) and density (individuals m2) (þ1SD) along an estuarine shoreline gradient in the Caete´ Bay, north Brazil. From left to right: species pool in the Caete´ Bay main channel (Barletta et al. 2005), transients in intertidal mangrove creeks at high tide (Krumme et al. 2004), transients in subtidal section close to mangrove creeks at low tide (Krumme et al. 2004), intertidal residents in mangrove creeks at low tide (Barletta et al. 2000)
assemblage of the Furo was closely linked to the assemblage of intertidal transients (Krumme et al. 2004). In the intertidal zone, residents are usually more abundant than transients (e.g., in salt marshes; Kneib 1997). In contrast, Gibson (1988) suggested that transients of rocky and sandy shores of higher latitudes outnumber residents in both biomass and number. Apparently greater productivity and stability of the intertidal zone of tropical and subtropical low energy coasts are able to sustain relatively high standing stocks of resident fish. Due to the high biomass and density, intertidal residents may play an important role in the trophic flows of the mangrove. Their life is closely linked to the mangrove environment but we know little about their biology and ecology. At low tide, an unknown portion of transients rests in the subtidal sections of the Furos close to their high-water feeding sites. Due to the accumulation of transients in the subtidal sections of the Furos, low-tide biomass and density there were >20 and 10 times higher than in the adjacent mangrove creeks at high water, respectively (Fig. 12.1; Krumme et al. 2004). The other unknown portion of transients apparently commute several kilometers between the high-water feeding sites in the mangrove creeks and low-water resting sites in the subtidal sections of the Caete´ Bay (Schaub 2000, Krumme et al. 2004) which may lead to a high biological connectivity in the Caete´ mangrove system (Sheaves 2005). The tidal movements of fish between bay habitats and Furos may add a significant temporal variation to overall spatial differences in biomass and density estimates. Unfortunately, the sampling design of the Caete´ Bay study did not consider the influence of the tide, but the standard deviations of the mean biomass and density values in Barletta et al. (2005) suggest that there is in fact considerable tidal connectivity.
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Composition of Transients
Fishes of the intertidal zone can be distinguished into residents and transients (Gibson 1988). The remainder of this chapter focuses on transients, i.e., temporary visitors which move between the subtidal Furo and bay areas and the intertidal mangrove creeks. The composition of intertidal residents is described in Barletta et al. (2000) and the subtidal Caete´ main channel fish community is analyzed in Barletta et al. (2005) (see Chap. 11). The most abundant intertidal transient nekton species of wet season block net samples were the polychaete feeding sea catfish Cathorops sp. (Ariidae) (probably a new, as yet undescribed species), the banded puffer Colomesus psittacus (Tetraodontidae) which feeds basically on hard-shelled organisms such as barnacles and crabs, the Pemecou sea catfish Sciades herzbergii (Ariidae) which feeds on crabs and polychaetes, the cocosoda catfish Pseudauchenipterus nodosus (Auchenipteridae) feeding on insects, the shrimp Fenneropenaeus subtilis (Penaeidae), the phytoand zooplanktivorous anchovy Anchovia clupeoides (Engraulidae), iliophagous mullets Mugil spp. (Mugilidae), and the omnivorous four-eyed fish A. anableps (Krumme et al. 2004). Intertidal transients were mostly estuarine, benthophage species suggesting that most fish production is retained in the estuarine-nearshore system. Most intertidal fishes are either juveniles of larger species or adults of small species. Juvenile fish consistently accounted for more than 85% of the total catch. Although the nursery role of the mangrove creeks was not assessed according to the factors given by Beck et al. (2001), it is likely that the Furos are important nursery sites within the mangrove ecosystem and deserve high conservation status. Predation on fishes was likely low because piscivores such as large piscine predators or birds were almost absent and still of small size (piscine fish species). Stomach content analysis of potentially piscivorous transient fish species (Sciaenidae, Batrachoides surinamensis, Centropomus parallelus, Lutjanus jocu) showed that only 25% 18 of the piscivores had at least one prey item in their stomach (n ¼ 10 high tide samples with >10 potential piscivores; Krumme, unpublished data). Major prey items of piscivores were juvenile Mugilidae, Clupeidae, Engraulidae, Pristigasteridae and shrimps. Mortality due to predation may rather affect postlarval and early juvenile stages that were not sampled by the mesh sizes used (for larval fishes, see Chap. 13). However, the influence of piscivores on mortality of shallow-water fishes should not focus merely on the abundance of piscivores in shallow waters but rather on “whether or not predator-induced mortality is reduced in shallow estuarine habitats” relative to other habitats (Sheaves 2001).
12.6
Tidal Movements
Given the small size of most fishes and the dimensions of intertidal creeks (some first-order creeks penetrate >1 km into the forest), considerable distances have to be covered by the fishes during their tidal migrations. The extensive tidal foraging excursions are facilitated by the tides on several levels.
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First, higher velocities at flood than at ebb tide render the Furos flood-dominated systems with a net upstream longitudinal current. There is a mean net upstream drift of ca. 0.5 km in a neap and 1.5 km in a spring tide cycle (Krumme 2004). Hence, a surface particle in a Furo is physically displaced upstream little by little leading to retention. The successful retention in the Furo do Meio from one tide to the next was apparent for copepods (Krumme and Liang 2004), phytoplankton (Schories, unpublished data) and is suggested for fish, too (Krumme 2004). Second, each tide the fishes are riding the first flood rise to enter the intertidal mangrove creeks (Fig. 12.2). This was observed using both visual censuses of the movements of surface-swimming A. anableps (Brenner and Krumme 2007) and hydro-acoustic observation of the entire subsurface fish community (Krumme and Saint-Paul 2003; Krumme 2004) using a floating device (Krumme and Hanning 2005). Immigration with the first rise likely enables fish to take a “migratory lift” for early access to the productive mangrove zone. It may be part of a strategy of the fish, especially of the juvenile stages, to save transport energy and concurrently increase surplus power that can be converted in faster growth and hence increased survival. Moreover, first flood rise coincides with lowest Secchi disc readings and
Fig. 12.2 Schematic overview of short-term changes in transient fish assemblages and in abiotic processes in the mangrove channel Furo do Meio, Braganc¸a, north Brazil, during 24 h at spring tides (upper figure) and neap tides (lower figure). 15 min measurements of water level and surface current speeds are shown. Numberletter abbreviations characterize changes in variables at different tides and tidal stages (see Table 12.1)
Table 12.1 Tidal and diel changes in transient fish assemblages and in abiotic processes in a macrotidal mangrove creek (see Fig. 12.2) Variable Tidal stage 0 1 (a, b) 2 (a, b, c, d) 3 (a, b) Water level Same level at Flood tide (a, b) Mangrove Ebb tide all tides usually inundated; (c, d) inundation restricted to creeks Current speed Zero, stagnant At least 2 maxima Slack high tide period 1 maximum low tide period Water level change Negligible (a) Rapid first rise; Little Fall (b) weaker Maximum (a) Decrease, then increase; Secchi depth Mean: 0.3 m (a) Decrease, then increase; (b) decrease (b) increase Fish biomass High Low Fish movements Milling, resting Rapid upstream, Slower, milling, Gradual return riding the tide foraging during first rise immigration Stomach fullness Emptier Fuller Block net catches (a) High; (b) highest; (c) lowest; (d) low Species composition (a) Diverse; (b) most diverse; (c) poorest; (d) poor Vertical distribution (c) Close to the bottom; (d) throughout the water column Mangrove detritus (a) Massive litter export; (b) minor export
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highest seston transport during a tidal cycle. Increased turbidity reduces the visual range of predators and thus likely minimizes the risk of predation for first rise immigrating fish. The current velocities at neap tides are weak, but at spring tides the fishes achieve a quick longitudinal and vertical lift into the intertidal zone when water level rise can be more than 2 m in less than 1 h (Krumme and Saint-Paul 2003) (Fig. 12.2). Third, at spring ebb tides, large amounts of leaves and mangrove detritus are exported (Schories et al. 2003). The floating material may provide structure, shade and transport for larval and juvenile fishes and decapods (Daniel and Robertson 1990; Wehrtmann and Dittel 1990; Schwamborn and Bonecker 1996). Fourth, the temporal patterns in the movements of fishes during a tidal cycle are species and size group specific (Krumme et al. 2004). In the mangrove creeks A. anableps is virtually the first transient species that enters and the last that leaves the intertidal zone, thus maximizing the time spent in the mangrove habitat. Other species may enter later at flood tide according to their preference for greater water depths or different current speed phases and forage shorter periods in the creeks. Furthermore, differences between size groups in the timing of the intertidal migration were apparent in C. psittacus (Giarrizzo, Krumme, Wosniok, unpublished data) and A. anableps (Krumme, unpublished data). In both species, the smaller individuals entered earlier and left later than the larger individuals suggesting that the youngest stages particularly rely on the intertidal creek habitat. Smaller individuals may maximize the food intake in the intertidal area because they use relatively more energy for the basal metabolism and growth than larger individuals. They may also maximize the reduction of the risk of predation, or the smaller individuals stay longer because they are still less efficient foragers.
12.7
Tidal and Diel Changes in the Intertidal Fish Assemblages
Several fish assemblage parameters changed predictably in response to the level of high water and the combination of the factors tide and the time of high water. The higher the high-water level of a tidal cycle was in the mangrove creeks, the more fish and shrimp entered. The relationships were best described by power functions (Krumme et al. 2004). Figure 12.3 shows the interactive effect of the tide and time of high water on abundance, catch weight, and species richness of transients in second-order creeks. The three assemblage parameters increased from lowest values at ND to highest values at SE. At neap and spring tides nightly samples yielded higher values than daytime samples (NN > ND and SE > SM) (Krumme et al. 2004). Moreover, the interaction of the spring/neap tide cycle and the time of high tide led to specific and recurring assemblage structures. Characteristic fish assemblages enter the creeks at ND, NN, SM, and SE (Krumme et al. 2004). As the environmental conditions recur in accord with the interactive effect of the lunar and diel cycle,
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Fig. 12.3 Box plots of median (a) total abundance, (b) catch weight and (c) species richness of transient fish from intertidal second-order mangrove creeks blocked at neap tide-midday, neap tide-midnight, spring tide-morning and spring tide-evening; 25–75% quartile and minimum and maximum values are shown
specific fish assemblages recur, too. Thus, for a given site, each tide a specific subset of nektonic species and size groups from different subtidal habitats assembled to temporarily use the intertidal creeks. The assemblages altered in a characteristic pattern that not only involved species presence or absence but also proportional differences in the intertidal occurrence among dominant species (Krumme et al. 2004). Results from hydro-acoustic surveys (Krumme and Saint-Paul 2003; Krumme 2004) suggest that the pattern of low fish abundances at ND pervaded the entire intertidal zone. At neap tides, some species or major parts of a population apparently skip entering the intertidal creeks for several days at a time (e.g., Sciaenidae)
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while others may confine their visits rather to the daytime (e.g., C. psittacus) or nightly inundation (e.g., S. herzbergii). Consequently, the relative abundances among species from one of the four abovementioned dieltidal combinations reflect just one facet of the complex picture of short-term variations inherent in dynamic macrotidal systems.
12.8
Tide-to-Tide, Weekly, Fortnightly and Monthly Variation in Abundance, Catch Weight, and Species Richness of Transients
Understanding the temporal variation characterizing transient fish assemblages is crucial to sampling design, interpretation of ecological studies, and long-term monitoring studies (e.g., Thompson and Mapstone 2002). Given the dynamics in intertidal fish assemblage composition on macrotidal coasts, replicate samples on the short- to mid-term scale should be taken at dieltidal combinations that ensure low variation among the replicates. There are several possible time intervals for taking replicate samples. Figure 12.4 schematically shows the four time intervals considered here: tide-to-tide variation among successive tides (ND-NN, SE-SM), weekly variation (spring and neap tides, i.e., ND-SM and NN-SE), fortnightly variation (same tide, but different lunar phase, i.e., ND, NN, SM, SE), and monthly
Fig. 12.4 Four levels of possible short- to mid-term replicates on a macrotidal coast. Spring tides at full and new moon. Dashed line replicate taken at night, continuous line replicate taken at daylight
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variation (again ND, NN, SM, and SE, but same tide and same lunar phase). We use the results of two studies from the same Furo to analyze the temporal variation between successive samples of different time scales in three fish assemblage parameters (abundance, total catch weight, species richness). Barletta et al. (2003) blocked three first-order creeks at ND (waning moon) during 13 months and thus also covered seasonal changes. Creek 2 was 1.5 and 5 times larger than creeks 1 and 3, respectively. Krumme et al. (2004) blocked two second-order creeks at consecutive tides each week at neap (ND, NN) and spring tides (SE, SM) during two lunar cycles. For each time scale, the differences in abundance, total catch weight, and species richness between consecutive samples were calculated and the absolute values were used to calculate the mean difference and its standard deviation. Standard deviations of differences between consecutive samples in abundance, catch weight and species richness at the scales tide-to-tide, weeks, fortnights and months are presented in Fig. 12.5. The lowest variation between consecutive samples occurred on the fortnightly and monthly scale at spring tides (SM, SE) in abundance and weight (Fig. 12.5a, b). The lower fortnightly and monthly variation in abundance in spring tide samples may reflect the close relationship between highwater level and nekton assemblage parameters and the fact that the variation between high-water levels is lower at spring than at neap tides (Krumme, unpublished data). In abundance and weight, the tide-to-tide and weekly variation was relatively high. The tide-to-tide variation was slightly higher at spring than at neap tides whereas the weekly variation showed an opposite trend between samples at daylight (SM-ND) and nightly samples (SE-NN) in abundance and weight. The monthly variation at ND in abundance and weight of the large first-order creeks 1 and 2 was extremely high. Given that the monthly ND samples covered an annual cycle, the monthly variation contains significant seasonal variation. However, the variation between the small first-order creek 3 and the second-order creeks at NN was similar (Fig. 12.5a, b). This suggests that smaller creeks – due to the fact that larger fish schools are less likely to enter – may have lower variation in abundance and weight than large first-order creeks. If this is true, then we may momentary ignore the results of the first-orders creeks 1 and 2 and focus on the fortnightly and monthly variation of the smaller creeks. The similar order of magnitude of the variation at ND (except for creeks 1 and 2), NN, SM, and SE at the fortnightly and monthly time scale suggests that the lunar phase (full vs new and waxing vs waning moon) is of minor importance and that the relative importance of the fortnightly variation (springneap tide cycle) in monthly or seasonal samples is very high. In species richness, lower variation on the fortnightly time scale at NN and SE suggests that nightly samples vary less (Fig. 12.5c). The monthly variation in species richness was greater at spring than at neap tides, but note that assemblage parameters were on average >2 times higher at spring than at neap tides (Fig. 12.3) and that, consequently, variations at spring tides may also be proportionally larger. However, differences in the monthly variation may also provide evidence that smaller creeks – due to greater stochastic processes – have higher variations in species richness than larger first-order creeks.
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Fig. 12.5 Tide-to-tide, weekly, fortnightly and monthly variation in mean differences between consecutive samples of (a) abundance (numbers), (b) total catch weight (kg), and (c) species richness (numbers) of transient mangrove fishes in the Furo do Meio, north Brazil. Data sources: Barletta et al. (2003) (shaded area monthly variation at ND from first-order creeks: creeks 1, 2, 3) and Krumme et al. (2004) (second-order creeks). The sample size is indicated for each temporal category. Abbreviations of the temporal categories: see text
The results are not fully consistent. This may be due to different sample sizes and the fact that different creeks and creek orders were sampled with different mesh sizes and in different years. However, based on the experience gathered in the last years and our current understanding of the temporal variation in transient mangrove fish assemblages, we may derive the following recommendations for sampling design and long-term monitoring studies using block nets: (1) long-term sampling should be carried out at spring tides when sample sizes are larger, species richness
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is higher and variations in high-tide levels and between replicate samples are lower; (2) sampling should occur at slack high and/or slack low tide to sample when assemblage compositions are most stable and to reduce the bias from tidal movements; and (3) given the strong spring tide currents and the fact that spring tides yield large catches, sampling may be confined to second-order creeks close to the mouth of a first-order creeks (or to small first-order creeks) to ensure proper operation of the block net and to reduce taking of too much nektonic organisms and to avoid expensive catch analysis.
12.9
Patterns in Feeding
In the macrotidal mangrove, feeding was the most obvious motive for the fish to enter the intertidal zone. The fishes’ rhythm in feeding was closely related to the tidal cycle and the interaction of the tides and time of high water. Tidal cycle: All species so far studied left the creeks at ebb tide with filled stomachs (Pseudauchenipterus nodosus: Krumme et al. 2004; S. herzbergii: Krumme et al. 2008a; Cathorops sp.: Leal-Flo´rez 2001; Pterengraulis atherinoides: Krumme et al. 2005; A. clupeoides: Brenner 2002; Cetengraulis edentulus: Krumme et al. 2008b; A. anableps: Brenner and Krumme 2007; C. psittacus: Krumme et al. 2007). Results of Leal-Flo´rez (2001) showed that stomach fullness of fishes was lower at flood tide and higher at ebb tide, suggesting that the fishes enter the creeks to feed and return to the subtidal area with well-filled stomachs. This pattern was also observed in subtropical and temperate salt marsh creeks (e.g., Kneib 1997; Hampel and Cattrijsse 2004) and is likely a general short-term pattern in many transients (Krumme 2009). The fact that transients enter with relatively empty stomachs further suggests that the low-tide period is usually a resting period without intensive feeding. However, in the subtidal basins of the Furos, the plankton abundances were significantly higher during low tide than during high tide, both for phytoplankton (Schories, unpublished data) and zooplankton (Krumme and Liang 2004). Hence, foraging of planktivorous species and size groups in the Furos should be most efficient during the low-tide period. In fact, the phytoplanktivorous engraulid C. edentulus most likely fed continuously (Krumme 2004; Krumme et al. 2008b). Krumme and Liang (2004) supposed that the tidal pulse synchronizes the temporal patterns of several zooplankton-feeding species and their size groups as well as the trophic interplay between them. Tide and time of high water: Similar to the fish assemblage structure, the foraging success of the fish was significantly influenced by the interaction of tide (spring/neap tide cycle) and time of high water (light intensity). This is exemplified by A. anableps (Brenner and Krumme 2007). The four-eyed fish use the underwater eyes to graze on epiphytic algae and the above-water eyes to capture insects and Grapsidae on prop roots. The combination of high inundation and daylight (SM) provided best foraging conditions in the mangrove. The fish entered
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the creeks with the flood tide still at darkness between 0400 and 0500 hours and reached their foraging grounds in the upper reaches of the creeks at high tide at sunrise. The foraging conditions at ND ranked second despite significantly lower levels of inundation. Apparently, the four-eyed fish is a visual grazer and predator. However, the greater foraging success at daylight could also be related to a diurnal rhythm in activity of insects and Grapsidae. The stomach fullness at SE ranked third despite of high levels of inundation, but poor illumination. Poorest foraging conditions were encountered at NN when darkness and low inundation coincided. Diel cycle: The diel differences in stomach fullness are species-specific and can depend on the tide and on the activity patterns of the prey. For instance, C. psittacus may feed more successful at daytime irrespective of the tide (Krumme et al. 2007), similar to A. anableps, whereas P. nodosus fed most intense at SE (Krumme et al. 2004). Spring/neap tide cycle: Generally, spring tide stomachs were always fuller than neap tide stomachs. For instance, the stomach fullness of A. anableps and S. herzbergii was 60 and 380% higher at spring than at neap tides, respectively (Brenner and Krumme 2007; Krumme et al. 2008a). The changes in feeding related to the spring/neap tide cycle were closely reflected in the growth increment formation in otoliths of Tenualosa ilisha from Bangladesh waters (Rahman and Cowx 2006) where the tides are similar to those in north Brazil. The outstanding change between spring and neap tides in consumption of transients, and thus in mortality of their prey populations, has important implications not only for the growth periodicity of the fish but also for the energy flow of the system and for the modeling of food webs of macrotidal nearshore ecosystems (Krumme et al. 2008a). The plateau mangrove and the spring/neap tide cycle in north Brazil lead to significant changes in intertidal resource accessibility and result in one ecosystem with two alternating states. Mid tides: We may speculate that the foraging conditions at spring tides here assumed to be most appropriate for the fishes, might be surpassed by mid-tides before and/or after spring tides. At mid-tides, the mangrove is predominantly inundated either around daylight or darkness and the maximum tidal height is medium. Diurnal or nocturnal species could benefit more from this tidetime of day combination than from spring tide conditions that are more advantageous for crepuscular species. The foraging conditions at mid-tides deserve study.
12.10
Spatial Patterns in the Intertidal Fish Fauna
Our understanding on spatial patterns in mangrove fish assemblages is still scarce. The major focus of our research was on the influence of different temporal scales on the intertidal fish fauna. However, some interesting results emerged related to the effect of different spatial scales. On a small scale, no significant spatial differences between the fish assemblages of two neighboring second-order creeks, 50 m apart and similar in size, were
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detected (Krumme et al. 2004). However, on a larger scale of 0.5 km, the smallest of three first-order creeks had significantly lower fish densities (Barletta-Bergan et al. 2002; Barletta et al. 2003). The stomach analysis of fishes captured from intertidal creeks located in the upper and lower reaches of a Furo (1.2 km apart) showed that the stomach fullness of S. herzbergii did not differ between the creeks (Krumme et al. 2008a), but it differed significantly for A. anableps with fuller stomachs in the creek of the lower reaches (Brenner and Krumme 2007). Spatial differences can be species-specific and may depend on the longitudinal position and the drainage density along a drainage system (Kneib 1994). At a medium spatial scale of 4 km in the Curuc¸a estuary, ca. 150 km west of the Caete´ estuary, Giarrizzo and Krumme (2007) found significantly higher densities in two outer than in two inner first-order creeks and concluded that landscape features are more important than creek size per se. A remarkable spatial pattern emerged from the first large-scale comparison of the intertidal creek fish fauna from three estuaries (Curuc¸a, Caete´, and Sa˜o Luis Maranha˜o) which are part of the world’s longest contiguous mangrove coastline in north Brazil (Giarrizzo and Krumme 2008). The comparison showed that there was a decrease in biomass of Sciaenidae and Mugilidae and an increase of Tetraodontidae and Engraulidae toward the Amazon mouth. This suggests dissimilar trophic structures in the mangrove estuaries despite the homogeneity of the mangrove area (only two dominant tree species) and highlights that the results from the Caete´ estuary are not readily transferable throughout the mangrove belt, especially not to the mangrove areas in eastern Maranha˜o. Giarrizzo and Krumme (2008) recommended a classification of the mangrove estuaries to identify types of estuaries and coastal sectors. Prior to this, however, the spatial variability within single estuaries must be understood (e.g., role of landscape features, habitat use and spatio-temporal patterns) (Giarrizzo and Krumme 2007) to ensure that the between-estuary comparisons are actually based on comparable sites from within the estuaries (Giarrizzo and Krumme 2008)
12.11
Implications for Future Research and Long-Term Monitoring
Our understanding of the dynamics of fish assemblages of macrotidal mangrove areas is far from complete. Virtually nothing is known about the distances traveled with the tides, home range sizes, or ontogenetic movements of major species, information necessary to, e.g., define the dimensions of no-take areas (Giarrizzo and Krumme 2009). Markrecapture and ultrasonic telemetry are useful methods to study the movement dynamics of fishes. During the low-tide period, all transients are inevitably accumulated in the subtidal area. Site fidelity to subtidal resting sites or the inter- and intraspecific interactions during low tide have rarely been studied in mangrove settings.
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Previous studies identified the major temporal scales of variation in the macrotidal mangrove estuary (tidal cycle, time of high water, spring/neap tide cycle, season, years). However, the spatial dynamics of the nektonic assemblages are still an enigma (Giarrizzo and Krumme 2007, 2008). The identification of sampling sites that ensure comparability between nekton samples taken 100s of meters, kilometers, 10s and 100s of km apart is not an easy task, but essential to understand spatial patterns in, e.g., fish abundance, biodiversity, or nursery function. How can we understand different spatial creek arrangements within the system? How do complex creek networks influence fish distribution? Several spatial factors may play a role in adding variation to local fish assemblage compositions, e.g., creek size, creek order, topographical height, distance to low-tide resting sites, estuarine salinity zone. Well-designed, nested studies are needed to identify the contribution of real changes, short-term movements or sampling error to temporal and spatial variations in nektonic organisms from macrotidal mangrove areas. The Braganc¸a mangrove peninsula is an excellent area to study spatial patterns of habitat use by fish on small to medium scales (intra-estuarine habitat comparisons) because the road crossing the entire mangrove belt allows for relatively easy access to all salinity zones. Once comparable sites from within an estuary have been identified, robust comparisons between estuaries can be tackled (inter-estuarine and regional comparisons) along the longest contiguous mangrove coast of the world covering more than 30 estuaries and about 650 km of comparably undisturbed coast of the states of Para´ and Maranha˜o. The research in such a macrotidal ecosystem should strongly rely on multidisciplinary approaches since many abiotic, biotic and social cycles occur synchronized in response to the tidal pulse (e.g., the dynamics in nutrients, phyto- and zooplankton, fishes, and fishermen’s activities).
References Ansell AD, Gibson RN (1990) Patterns of feeding and movement of juvenile flatfish on an open sandy beach. In: Barnes M, Gibson RN (eds) Trophic Relationships in the Marine Environment. Aberdeen University Press, Aberdeen, pp 191–207 Barletta M, Saint-Paul U, Barletta-Bergan A, Ekau W, Schories D (2000) Spatial and temporal distribution of Myrophis punctatus (Ophichthidae) and associated fish fauna in a northern Brazilian intertidal mangrove forest. Hydrobiologia 426:65–74 Barletta M, Barletta-Bergan A, Saint-Paul U, Hubold G (2003) Seasonal changes in density, biomass, and diversity of estuarine fishes in tidal mangrove creeks of the lower Caete´ Estuary (northern Brazilian coast, east Amazon). Mar Ecol Prog Ser 256:217–228 Barletta M, Barletta Bergan A, Saint-Paul U, Hubold G (2005) The role of salinity in structuring the fish assemblages in a tropical estuary. J Fish Biol 66:45–72 Barletta-Bergan A, Barletta M, Saint-Paul U (2002) Community structure and temporal variability of ichthyoplankton in North Brazilian mangrove creeks. J Fish Biol 61:33–51 Beck MW, Heck KL J, Able KW, Childers DL, Eggleston DB, Gillanders BM, Halpern B, Hays CG, Hoshino K, Minello TJ, Orth RJ, Sheridan PF, Weinstein MP (2001) The identification, conservation, and management of estuarine and marine nurseries for fish and invertebrates. Bioscience 51:633–641
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Brenner M (2002) Nahrungso¨kologische Untersuchungen an Anableps anableps, Arius herzbergii ¨ stuars in Nord-Brasilien. Dipl und Anchovia clupeoides in den Gezeitenkan€alen des Caete´-A thesis, University of Bremen, Bremen Brenner M, Krumme U (2007) Tidal migration and patterns in feeding of the four-eyed fish Anableps anableps L. in a north Brazilian mangrove. J Fish Biol 70:406–427 Connolly RM (1994) Comparison of fish catches from a buoyant pop net and a beach seine net in a shallow seagrass habitat. Mar Ecol Prog Ser 109:305–309 Daniel PA, Robertson AI (1990) Epibenthos of mangrove waterways and open embayments: Community structure and the relationship between exported mangrove detritus and epifaunal standing stocks. Estuar Coast Shelf Sci 31:599–619 Giarrizzo T, Krumme U (2007) Spatial differences and seasonal cyclicity in the intertidal fish fauna from four mangrove creeks in a salinity zone of the Curuc¸a Estuary, North Brazil. Bull Mar Sci 80:739–754 Giarrizzo T, Krumme U (2008) Heterogeneity in intertidal fish fauna assemblages along the world’s longest mangrove area in northern Brazil. J Fish Biol 72:773–779 Giarrizzo T, Krumme U (2009) Temporal patterns in the occurrence of selected tropical fish to mangrove creeks: implication for the fisheries management in north Brazil. Braz Arch Biol Technol 52(3):679–688 Giarrizzo T, Krumme U, Wosniok W. Size-structured migration and feeding patterns in the banded puffer fish Colomesus psittacus (Tetraodontidae) from north Brazilian mangrove creeks. Mar Ecol Progr Ser, unpublished data Gibson RN (1988) Patterns of movement in intertidal fishes. In: Chelazzi G, Vanini M (eds) Behavioural adaptions to intertidal life, vol 151, NATO ASI Series Life Sciences. Plenum, London, pp 55–63 Hampel H, Cattrijsse A (2004) Temporal variation in feeding rhythms in a tidal marsh population of the common goby Pomatoschistus microps (Kroyer, 1838). Aquat Sci 66:315–326 Hindell JS, Jenkins GP (2005) Assessing patterns of fish zonation in temperate mangroves, with emphasis on evaluating sampling artifacts. Mar Ecol Prog Ser 290:193–205 Horn MH, Martin KLM, Chotkowski MA (1999) Intertidal fishes: Life in two worlds. Academic, San Diego Kneib RT (1991) Flume weir for quantitative collection of nekton from vegetated intertidal habitats. Mar Ecol Prog Ser 75:29–38 Kneib RT (1994) Spatial pattern, spatial scale, and feeding in fishes. In: Stouder DJ, Fresh KL, Feller RJ (eds) Theory and application in fish feeding ecology. The Belle W. Baruch Library in Marine Science, Number 18, University of South Carolina Press, Columbia, SC, pp 171–185 Kneib RT (1997) Early life stages of resident nekton in intertidal marshes. Estuaries 20:214–230 Kneib RT, Wagner SL (1994) Nekton use of vegetated marsh habitats at different stages of tidal inundation. Mar Ecol Prog Ser 106:227–238 Krumme U (2004) Patterns in the tidal migration of fish in a north Brazilian mangrove channel as revealed by a split-beam echosounder. Fish Res 70:1–15 Krumme U (2009) Diel and tidal movements by fish and decapods linking tropical coastal ecosystems. In: Nagelkerken I (ed) Ecological connectivity among tropical coastal ecosystems. Springer, Berlin, pp 271–324 Krumme U, Hanning A (2005) A floating device for stationary hydroacoustic sampling in shallow waters. Fish Res 73:377–381 Krumme U, Liang TH (2004) Tidal-induced changes in a copepod-dominated zooplankton community in a macrotidal mangrove channel in northern Brazil. Zool Stud 43:404–414 Krumme U, Saint-Paul U (2003) Observation of fish migration in macrotidal mangrove channel in Northern Brazil using 200-kHz split-beam sonar. Aquat Living Resour 16:175–184 Krumme U, Saint-Paul U, Rosenthal H (2004) Tidal and diel changes in the structure of a nekton assemblage in small intertidal mangrove creeks in northern Brazil. Aquat Living Resour 17:215–229
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Krumme U, Keuthen H, Barletta M, Saint-Paul U, Villwock W (2005) Contribution to the feeding ecology of predatory wingfin anchovy Pterengraulis atherinoides (L.) in north Brazilian mangrove creeks. J Appl Ichthyol 21:469–477 Krumme U, Keuthen H, Saint-Paul U, Villwock W (2007) Contribution to the feeding ecology of the banded puffer fish Colomesus psittacus (Tetraodontidae) in north Brazilian mangrove creeks. Braz J Biol 67:383–392 Krumme U, Brenner M, Saint-Paul U (2008a) Spring-neap cycle as a major driver of temporal variations in feeding of intertidal fishes: Evidence from the sea catfish Sciades herzbergii (Ariidae) of equatorial West Atlantic mangrove creeks. J Exp Mar Ecol Biol 367:91–99 Krumme U, Keuthen H, Barletta M, Saint-Paul U, Villwock W (2008b) Resuspended intertidal microphytobenthos as major diet component of planktivorous Atlantic anchoveta Cetengraulis edentulus (Engraulidae) from equatorial mangrove creeks. Ecotropica 14:121–128 Leal-Flo´rez J (2001) Feeding ecology of Uricica branca, Cathorops agassizii (Pisces:Ariidae), in an intertidal channel of the Caete´ estuary, northern Brazil. MSc thesis, University of Bremen, Bremen Rahman MJ, Cowx IG (2006) Lunar periodicity in growth increment formation in otoliths of hilsa shad (Tenualosa ilisha, Clupeidae) in Bangladesh waters. Fish Res 81:342–344 Robertson AI, Blaber SJM (1992) Plankton, epibenthos and fish communities. In: Robertson AI, Alongi DM (eds) Tropical mangrove ecosystems, Coastal and estuarine studies 41. American Geophysical Union, Washington, DC, pp 173–224 Rozas LP (1992) Bottomless lift net for quantitatively sampling nekton on intertidal marshes. Mar Ecol Prog Ser 89:287–292 Rozas LP, Minello TJ (1997) Estimating densities of small fishes and Decapod crustaceans in shallow estuarine habitats: a review of sampling design with focus on gear selection. Estuaries 20:199–213 ¨ stuar des Rio Caete´/Norbrasilien. Schaub CM (2000) Untersuchung der Großreusenfischerei im A Dipl thesis, University of Bremen, Bremen Schories D, Barletta-Bergan A, Krumme U, Rademaker V (2003) The keystone role of leafremoving crabs in mangrove forests of north Brazil. Wetl Ecol Manag 11:243–255 Schwamborn R, Bonecker ACT (1996) Seasonal changes in the transport and distribution of meroplankton into a Brazilian estuary with emphasis on the importance of floating mangrove leaves. Braz Arch Biol Technol 39:451–462 Sheaves M (2001) Are there really few piscivorous fishes in shallow estuarine habitats? Mar Ecol Prog Ser 222:279–290 Sheaves M (2005) Nature and consequences of biological connectivity in mangrove systems. Mar Ecol Prog Ser 302:293–305 Simmonds JE, MacLennan DN (2005) Fisheries Acoustics: Theory and Practice, Fish and Aquatic Resources Series 10. Blackwell, Oxford Spalding M, Blasco F, Field C (1997) World mangrove atlas. The International Society for Mangrove Ecosystems (ISME), Okinawa Thompson AA, Mapstone BD (2002) Intra- versus inter-annual variation in counts of reef fishes and interpretations of long-term monitoring studies. Mar Ecol Prog Ser 232:247–257 Wehrtmann SI, Dittel AI (1990) Utilization of floating mangrove leaves as a transport mechanism of estuarine organisms, with emphasis on decapod Crustacea. Mar Ecol Prog Ser 60:67–73 Wennhage H, Gibson RN, Robb L (1997) The use of drop traps to estimate the efficiency of two beam trawls commonly used for sampling juvenile flatfishes. J Fish Biol 51:441–445
Chapter 13
An Evaluation of the Larval Fish Assemblage in a North Brazilian Mangrove Area A. Barletta-Bergan
13.1
Value of Mangroves and Estuaries as Nurseries
Mangroves and estuaries share features such as shallow water, reduced wave action, high organic content in the sediment, high primary production, and the provision of protection from predators, which may all contribute to their role as nurseries (Manson et al. 2005). If predation rates are low, the survival of individuals and hence population abundance are high. Growth will also potentially be increased because less time is spent hiding from predators and more time can be spent on foraging and feeding (Heck et al. 2003). The value of mangroves as nursery habitats is measured in terms of juvenile density, survival, growth, and movement to adult habitats (Sheridan and Hays 2003). It is important to note that fishes only use mangroves for a proportion of the tidal cycle (Pittman and McAlpine 2003). The depth and duration of tidal inundation are likely to influence both the movement of animals into the mangroves and their ability to use the resources therein (Meager et al. 2003). Fishes may use estuarine habitats only occasionally, at certain life stages, or they reside permanently within them (Whitfield 1999). Thus, species can be categorized as marine stragglers, marine-estuarine species, or estuarine residents (Manson et al. 2005). These differences in life-history behavior may influence the nature of any interactions between species and their habitats (Manson et al. 2005).
13.2
First Ichthyoplankton Survey
This review identifies in a first large-scale survey of which species and at what abundance occur in a north Brazilian mangrove area and at what life stage these species are using mangroves as a nursery site. The present study may serve as a basis to relate the community structure and temporal variability in north Brazilian mangrove creeks to other estuaries worldwide. U. Saint-Paul and H. Schneider (eds.), Mangrove Dynamics and Management in North Brazil, Ecological Studies 211, DOI 10.1007/978-3-642-13457-9_13, # Springer-Verlag Berlin Heidelberg 2010
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For this purpose, the species composition and dynamics of fish larvae in three mangrove creeks located in north Brazil (Caete´ Estuary) were studied monthly from October 1996 to October 1997 using a trap net during diurnal ebb tides.
13.3
A North Brazilian Larval Fish Community in Relation to Mangroves Worldwide
The recognition that estuarine mangroves act as important nursery areas for certain teleosts by providing a rich food source and protection from predation has already been documented in many mangrove estuaries worldwide (Austin 1971; Odum and Heald 1972, 1975; Ya´n˜ez-Arancibia et al. 1980; Krishnamurthy and Jeyaseelan 1981; Haedrich 1983; Beckley 1984; Bell et al. 1984; Blaber et al. 1985, 1989; Janekarn and Boonruang 1986; Robertson and Duke 1987; Little et al. 1988; Blaber and Milton 1990; Tzeng and Wang 1992; Blaber 1997; Whitfield 1999). This is also reflected in the composition of the larval fish assemblage of a study in northern Brazil, with 25 families and 54 species being recorded (Barletta-Bergan et al. 2002) (Table 13.1). However, the annual means of species diversity were low in this study since only a few species dominated the community (Fig. 13.1), a situation found in many other estuarine fish populations (Austin 1971; Odum and Heald 1972; Allen and Horn 1975; Lasserre and Toffart 1977; Ya´n˜ez-Arancibia et al. 1980; Allen 1982; Bell et al. 1984). Low species diversity may be associated with increased fluctuations of abiotic conditions as demonstrated by various authors in different estuarine ecosystems in earlier years (Dahlberg and Odum 1970; Allen and Horn 1975; Moore 1978). Another feature documented by Barletta-Bergan et al. (2002) is the higher diversity among larvae of demersal than of pelagic fish in the ichthyoplankton assemblage in north Brazil. Janekarn and Kiørboe (1991) related such a difference to a more complex benthic environment as compared to a relatively more homogeneous pelagic environment in mangrove areas in Thailand. According to Barletta-Bergan et al. (2002), the most abundant larval species of north Brazilian mangals were species that spawn in mangroves or species which have the ability to complete their entire life cycle within the estuary, namely the eleotrid Guavina guavina (46.7%) and the engraulid Anchovia clupeoides (14.9%) (Table 13.1). The relative contribution of species that spawn exclusively in the sea was low in this mangrove area. The sciaenid Cynoscion acoupa was the only marine species that used the mangroves extensively as a nursery site. This habitat may not be preferred by many larvae of marine spawners as a result of the very high turbidities and seasonally varying salinities. McHugh (1967) described stenohaline species as adventitious invaders of the estuary. Other estuarine fish surveys do not confirm this, since a large portion of the catch consisted of marine species due to marine conditions in these estuaries (Wallace 1975; Tzeng and Wang 1992; Neira and Potter 1994; Harris and Cyrus 1995). Barletta-Bergan et al. (2002) reported that larval freshwater species did not occur at all in north Brazilian mangrove creeks, as
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Table 13.1 Numbers of species caught in trap nets in three mangrove creeks and relative contributions of these species to the adjusted numbers in the total catch in each creek Percent (>0.1%) Habitat Family Species Total catch/ 100 m3 No. % Creek 1 Creek 2 Creek 3 Eleotridae Guavina guavina 51,282 46.7 55.9 36.1 42.1 MS Engraulidae Anchovia clupeoides 16,359 14.9 17.7 10.9 19.4 E Sciaenidae Cynoscion acoupa 10,946 10.0 5.4 16.3 3.1 M Gobiidae Microgobius meeki 6,099 5.5 5.9 5.6 2.0 MS Sciaenidae Micropogonias furnieri 5,707 5.2 1.5 9.8 3.6 M Engraulidae Pterengraulis 3,922 3.6 3.9 2.8 6.2 E-F atherinoides Clupeidae Rhinosardinia 3,295 3.0 2.8 3.0 4.9 E amazonica Sciaenidae Stellifer stellifer 2,056 1.9 1.3 2.7 1.0 E-M Achiridae Achirus sp. 1,582 1.4 1.1 2.0 0.2 M Gobiidae Chriolepis sp. 1,528 1.4 0.3 2.8 1.4 MS Gobiidae Gobionellus stigmaticus 1,394 1.3 0.2 2.5 1.4 MS Sciaenidae Stellifer rastrifer 1,181 1.1 0.7 1.7 0.2 M Engraulidae Lycengraulis grossidens 961 0.9 0.9 0.9 0.4 M Tetraodontidae Colomesus psittacus 639 0.6 0.1 0.3 7.2 E-M Carangidae Oligoplites sp. 552 0.5 0.4 0.3 2.7 M Centropomidae Centropomus sp. 444 0.4 0.7 <0.1 0.2 M Haemulidae Genyatremus luteus 338 0.3 0.2 0.4 0.2 M Engraulidae Anchoa spinifer 275 0.2 0.4 0.1 <0.1 E-M Ephippidae Chaetodipterus faber 204 0.2 <0.1 0.4 <0.1 M Tetradontidae Sphoeroides testudineus 171 0.2 <0.1 0.1 1.0 E-M Gobiidae Coryphopterus sp. 160 0.1 <0.1 0.2 0.7 MS Poecilidae Sp. 1 148 0.1 <0.1 0.1 0.6 E-F Gerreidae Ulaema lefroyi 113 0.1 <0.1 0.1 0.3 E-M Gobiidae Gobionellus oceanicus 109 <0.1 <0.1 0.2 <0.1 MS <0.1 <0.1 <0.1 – E-M Sciaenidae Bairdiella sp. 978 Sciaenidae Stellifer sp. 701 <0.1 <0.1 0.1 – E-M Paralichthyidae Citharichthys sp. 60 <0.1 <0.1 <0.1 0.4 M Aspredinidae Aspredinichthys sp. 53 <0.1 – 0.1 <0.1 E-F Megalopidae Megalops atlanticus 38 <0.1 <0.1 <0.1 <0.1 M Poecilidae Gambusia sp. 31 <0.1 <0.1 <0.1 0.4 E-F Mugilidae Mugil sp. 22 <0.1 <0.1 <0.1 <0.1 M Sciaenidae Cynoscion 18 <0.1 <0.1 <0.1 – M microlepidotus Gobiidae Gobiosoma 15 <0.1 <0.1 <0.1 – MS hemigymnum Engraulidae Anchovia surinamensis 15 <0.1 <0.1 <0.1 – E-F Engraulidae Anchoviella 13 <0.1 <0.1 <0.1 – E-M brevirrostris 12 <0.1 – <0.1 0.2 M Lutjanidae Lutjanus jocu Syngnathidae Syngnathus rousseau 10 <0.1 – <0.1 <0.1 E-M Aridae Arius herzbergii 7 <0.1 <0.1 <0.1 – E-M Belonidae Strongylura timucu 5 <0.1 <0.1 <0.1 <0.1 M Engraulidae Cetengraulis edentulus 5 <0.1 <0.1 <0.1 – M Aridae Cathorops sp.1 4 <0.1 <0.1 <0.1 – E-M Hemiramphidae Hyporhamphus roberti 2 <0.1 <0.1 <0.1 – E-M (continued)
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Table 13.1 (continued) Family Species
Total catch/ Percent (>0.1%) Habitat 100 m3 No. % Creek 1 Creek 2 Creek 3 Engraulidae Stellifer brasiliensis 2 <0.1 <0.1 <0.1 – E-M Eleotridae Eleotris sp. 2 <0.1 – <0.1 – MS Ophichthidae Myrophis punctatus 2 <0.1 <0.1 – – E-M Engraulidae Anchoviella cayennensis 2 <0.1 – – <0.1 E-M Engraulidae Anchoviella elongata 1 <0.1 <0.1 <0.1 – E-M Syngnathidae Syngnathus caribbaeus 1 <0.1 – <0.1 – E-M Sciaenidae Isopisthus parvipinnis 1 <0.1 – <0.1 – M Anablepidae Anableps anableps 1 <0.1 – <0.1 – MS Carangidae Caranx sp. 0 <0.1 – <0.1 – M Cynoglossidae Symphurus sp. 0 <0.1 – <0.1 – M Sciaenidae Lonchurus lanceolatus 0 <0.1 – <0.1 – E Carangidae Selene vomer 0 <0.1 – <0.1 – M No. of larvae 109,954 56,698 47,243 6,013 No. of species 54 42 52 33 Creek length (m) 364 494 149 6,484 9,351 1,856 Creek drainage area (m2) Creek width (m) 20 22 14 Creek depth (m) 1.7 1.9 1.6 9,664 2,904 5,674 1,085 Volume filtered (m3) Data are based on catches between October 1996 and October 1997. The relative contributions were calculated from numbers in each sample after these had been adjusted to a constant volume of 100 m3. Dash indicates species not caught in that region. M marine, E-M estuarine-marine, E estuarine, MS mangroves, E-F estuarine-freshwater, F freshwater
no perennial freshwater streams fed the mangroves. The most important euryhaline freshwater component in the north Brazilian mangal were the small fishes of the Poecilidae (Barletta-Bergan et al. 2002) (Table 13.1). Adults of the ophichtid Myrophis punctatus were found in large numbers in the same system by Barletta et al. (2000) whereas only a few larval individuals were collected by Barletta-Bergan et al. (2002). The small numbers of larvae of M. punctatus in the system studied by Barletta-Bergan et al. (2002) could also indicate recruitment into the estuary at larger sizes. Seasonal cycles of community indices in the present study (Fig. 13.1) seem to be mainly related to variations of salinity (Barletta-Bergan et al. 2002) (Fig. 13.2), a common characteristic for all tropical estuaries (Albaret and Ecoutin 1990; Plumstead 1990). According to Taylor (1982), freshwater inflow is the key factor regulating both the structure and functioning of estuarine systems. Barletta-Bergan et al. (2002) registered highest species richness, diversity and evenness in the early rainy season in February, when salinity started to decrease (Figs. 13.1 and 13.2). The study in the Cayenne River Estuary (de Morais and de Morais 1994) also resulted in high species numbers in February, which can be attributed to the similar environmental conditions and the close proximity of both
An Evaluation of the Larval Fish Assemblage in a North Brazilian Mangrove Area
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regions. A subsequent sudden drop in the diversity indices from March to June in the Caete´ mangrove creeks coincided with the extremely low salinity and the absence of stenohaline species (Barletta-Bergan et al. 2002). At the beginning of the dry season in July, the species number increased again as a result of the influx of stenohaline species into the mangroves (Barletta-Bergan et al. 2002). According to Jones (1978), successive cohorts of fish larval species through time minimize competition between different species during the larval stages in the mangroves. In the tidal mangrove creeks of the Caete´ Estuary, the dominant species peaked in abundance in August and, to a lesser degree, in April (Barletta-Bergan et al. 2002) (Fig. 13.3). Tricklebank et al. (1992) confirms that overall seasonality patterns are often reflected in the abundance of dominant taxa. Moreover, peaks in abundance often depend on how “estuarine” a system is, i.e. the environmental conditions for that system (Harris and Cyrus 1997). In the study by Barletta-Bergan et al. (2002), the density peaks are mainly from estuarine spawners, which can be related to the eletroid G. guavina and the engraulid A. clupeoides (Fig. 13.3). The dominance of Gobioidei and Clupeiformes is typical of other estuaries throughout
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Fig. 13.2 Mean monthly variations of salinity and precipitation, temperature and current speed of surface samples in mangrove creeks of the Caete´ estuary. Precipitation values are averages of daily measurements. Open bars on the horizontal axis denote late dry season, striped bars early rainy season, black bars late rainy season and dotted bars early dry season
the world (Melville-Smith and Baird 1980; Jenkins 1986; Roper 1986; Whitfield 1989a; Janekarn and Kiørboe 1991; Neira et al. 1992; de Morais and de Morais 1994). The sciaenid C. acoupa was the only marine species of commercial interest (Barletta et al. 1998) that used the estuary extensively as a nursery ground. According to Mongkolprasit (1983), eleotrids spend their complete life cycle in the mangrove area. The constantly small size classes of G. guavina over the sampling period in the study by Barletta-Bergan et al. (2002) confirm continuous spawning in the mangroves and subsequent tidal removal (Fig. 13.4). G. guavina apparently returns to the mangrove system as a juvenile on flood tides and settles to a benthic lifestyle, burrowing into the mud (Barletta et al. 2000). This type of re-recruitment of G. guavina parallels that exhibited by the postflexion larvae of gobiids in an estuary in southern Africa (Whitfield 1989b). Barletta-Bergan et al. (2002) conclude that high densities of G. guavina in the mangroves in August indicates that spawning occurs predominantly during the dry season when salinities are high. Loneragan and Potter (1990) by contrast found a negative correlation between abundance of estuarine species and salinity. Tzeng and Wang (1992) stress, however, that the response of larval densities to environmental variables is species-specific. According to Barletta-Bergan et al. (2002), the temporal pattern of
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Fig. 13.3 Density of dominant species in each month in three mangrove creeks of the Caete´ estuary
Density (No. of larvae per 100 m3)
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13 An Evaluation of the Larval Fish Assemblage in a North Brazilian Mangrove Area 215
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Fig. 13.4 Size distribution of G. guavina (a) and A. clupeoides (b) for 12 months, sampled in three mangrove creeks of the Caete´ estuary (pooled data)
G. guavina may ensure that this species reproduces during a time when species competition is lowest. Ecological separation of the dominant species by recruitment timing was also observed by Tzeng and Wang (1992). Barletta-Bergan et al. (2002) found that the marine sciaenid C. acoupa by contrast occurred in relatively high densities in north Brazilian mangrove creeks in the rainy season with a peak in April (Fig. 13.3). Likewise, Cervigo´n (1985) cited maximal spawning intensities for C. acoupa in the period from January to April in the Laguna de Maracaibo in Venezuela. de Morais and de Morais (1994) found that the marine sciaenid Micropogonias furnieri seemed to be dependent on low salinity, as peaks were registered when precipitation and freshwater inputs were high during the rainy season. According to Janekarn and Boonruang (1986), nutrients
13
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from land are transported to the sea, causing high primary productivity after heavy rain in mangrove areas of Thailand. Increased nutrient concentrations and, thus, elevated phytoplankton biomass and abundance of Ucides cordatus larvae could have also stimulated spawning activity of C. acoupa in nearshore areas (Barletta-Bergan et al. 2002). The recruitment of predominantly old larvae (postflexion) and early juveniles of marine fish into estuarine nursery areas from offshore is a common feature for both subtropical and temperate estuaries worldwide (Day et al. 1981; Haedrich 1983; Claridge et al. 1986; Whitfield 1989a; Cyrus and Forbes 1994; Neira and Potter 1994). Barletta-Bergan et al. (2002) emphasized the importance of mangroves as nursery sites for certain marine species at the postflexion larval stage, since a large proportion of the larvae of C. acoupa collected were old larvae. The recognition of the importance of mangroves for certain species allows the hypothesis that reduction in mangrove habitat complexity would affect faunal communities within them and, ultimately, influence the biodiversity and abundance of the associated fauna (Manson et al. 2005). These changes might have the potential to cause cascading effects at higher trophic levels with possible consequences for catch of commercial fisheries (Manson et al. 2005). It may be difficult to separate the contribution of mangroves to biodiversity and fisheries from that of estuaries themselves (Loneragan et al. 2005). Mumby et al. (2004) has shown that the biomass of adults of several commercial species was higher where mangroves were adjacent to the adult habitats. Where there were no nursery habitats close to the adult habitats, many species were present in low densities only or even absent. A prerequisite for management may be to perform comparative sampling of faunal ichthyoplankton communities within and outside of affected and unaffected mangal estuaries to confirm that a loss of mangrove habitats would lead to a reduction of individuals that recruit to adult populations, resulting in a decrease of commercial fisheries.
References Albaret JJ, Ecoutin JM (1990) Influence des saisons e des variations climatiques sur les peuplements de poissons d’ une lagune tropicale en Afrique de l’ Ouest. Acta Oecol 11:557–583 Allen LG (1982) Seasonal abundance, composition and productivity of the littoral fish assemblage in upper Newport Bay, California. Fish Bull US 80:769–790 Allen LG, Horn MH (1975) Abundance, diversity and seasonality of fishes in Colorado Lagoon, Alamitos Bay, California. Estuar Coast Mar Sci 3:371–380 Austin HM (1971) A survey of the ichthyofauna of the mangroves of western Puerto Rico during December, 1967 – August, 1968. Caribb J Sci 11:27–39 Barletta M, Barletta-Bergan A, Saint-Paul U (1998) Description of the fisheries structure in the mangrove-dominated region of Braganc¸a (State of Para´, North Brazil). Ecotropica 4:41–53 Barletta M, Saint-Paul U, Barletta-Bergan A, Ekau W, Schories D (2000) Spatial and temporal distribution of Myrophis punctatus (Ophichthidae) and associated fish fauna in a northern Brazilian intertidal mangrove forest. Hydrobiologia 426:65–74
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Barletta-Bergan A, Barletta M, Saint-Paul U (2002) Community structure and temporal variability of ichthyoplankton in north Brazilian mangrove creeks. J Fish Biol 61(Suppl A):33–51 Beckley LE (1984) The ichthyofauna of the Sundays Estuary, south Africa, with particular reference to the juvenilie marine component. Estuaries 7:248–259 Bell JD, Pollard DA, Burchmore JJ, Pease BC, Middleton MJ (1984) Structure of a fish community in a temperate tidal mangrove creek in Botany Bay, New South Wales. Aust J Mar Freshw Res 35:33–46 Blaber SJM (1997) Fish and fisheries of tropical estuaries, vol 22, Fish and fisheries series. Chapman and Hall, London Blaber SJM, Milton DA (1990) Species composition, community structure and zoogeography of fishes of mangrove estuaries in the Solomon Islands. Mar Biol 105:259–267 Blaber SJM, Young JW, Dunning MC (1985) Community structure and zoogeographic affinities of the coastal fishes of the Dampier Region of Northwestern Australia. Aust J Mar Freshw Res 36:247–266 Blaber SJM, Brewer DT, Salini JP (1989) Species composition and biomasses of fishes in different habitats of a Tropical Northern Australian estuary: their occurrence in the adjoining sea and estuarine dependence. Estuar Coast Shelf Sci 29:509–531 Cervigo´n F (1985) La ictiofauna de las aguas costeras estuarinas del delta Rı´o Orinoco en la costa Atlantica occidental, Caribe. In: Ya´n˜ez-Arancibia A (ed) Fish community ecology in estuaries and coastal lagoons: towards an ecosystem integration. DR (R) Universidade Auto´noma de Me´xico Press, Mexico City, pp 57–78 Claridge PN, Potter IC, Hardisty MW (1986) Seasonal changes in movements, abundance, size composition and diversity of the fish fauna of the Severn estuary. J Mar Biol Assoc UK 55:229–258 Cyrus DP, Forbes AT (1994) The role of harbours in Natal, South Africa as alternative nursery sites for juvenile marine fish normally using estuaries. In: Systematics and evolution of IndoPacific fishes. Proceedings, Fourth Indo-Pacific Fish Conference, 28 November – 4 December 1993. International Conference on Indo-Pacific Fishes. Faculty of Fisheries, Kasetsart University, Bangkok, pp 340–353 Dahlberg MD, Odum EP (1970) Annual cycles of species occurrence abundance and diversity in Georgia Estuarine fish populations. Am Nat 83(2):382–392 Day JH, Blaber SJM, Wallace JH (1981) Estuarine fishes. In: Day JH (ed) Estuarine ecology with particular reference to southern Africa. Balkema, Rotterdam, pp 197–221 de Morais TA, de Morais TL (1994) The abundance and diversity of larval and juvenile fish in a tropical estuary. Estuaries 17:216–225 Haedrich RL (1983) Estuarine fishes. In: Ketchum BH (ed) Ecosystems of the World 26, Estuaries and enclosed seas. Elsevier, Amsterdam, pp 183–207 Harris SA, Cyrus DP (1995) Occurrence of larval fishes in the St. Lucia Estuary, KwaZulu-Natal, South Africa. S Afr J Mar Sci 16:351–364 Harris SA, Cyrus DP (1997) Composition, abundance and seasonality of larval fish in Richards Bay Harbour, Kwazulu-Natal, South Africa. S Afr J Aquat Sci 23(1):56–78 Heck KL Jr, Hays G, Orth RJ (2003) Critical evaluation of the nursery role hypothesis for seagrass meadows. Mar Ecol Prog Ser 253:123–136 Janekarn V, Boonruang P (1986) Composition and occurrence of fish larvae in mangrove areas along the east coast of Phuket Island, western peninsular, Thailand. Phuket Mar Biol Res Bull 44:1–22 Janekarn V, Kiørboe T (1991) The distribution of fish larvae along the Andaman coast of Thailand. Phuket Mar Biol Res Bull 56:41–61 Jenkins GP (1986) Composition, seasonality and distribution of ichthyoplankton in Port Philip Bay, Victoria. S Afr J Zool 37:507–520 Jones R (1978) Competition and co-existence with particular reference to gadoid fish species. Rapp P-V Reun Cons Int Explor Mer 172:292–300
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Krishnamurthy K, Jeyaseelan MJ (1981) Early life history of fishes from Pichavaram mangrove ecosystem of India. Rapp P-V Reun Cons Int Explor Mer 178:416–423 Lasserre G, Toffart JL (1977) Echantillonnage et structure des populations ichthyologiques des mangroves de Guadeloupe en septembre 1975. Cybium 2:115–127 Little MC, Rey PJ, Grove SJ (1988) Distribution gradients of ichthyoplankton in an East African Mangrove creek. Estuar Coast Shelf Sci 26:669–677 Loneragan NR, Potter IC (1990) Factors influencing community structure and distribution of different life-cycles categories of fishes in shallow waters of a large Australian estuary. Mar Biol 106:25–37 Loneragan NR, Adnan AN, Connolly RM, Manson FJ (2005) Prawn landings and their relationship with the extent of mangroves and shallow waters in western pensinsular Malaysia. Estuar Coast Shelf Sci 63:187–200 Manson FJ, Loneragan NR, Skilleter GA, Phinn SR (2005) An evaluation of the evidence for linkages between mangroves and fisheries: a synthesis of the literature and identification of research directions. Oceanogr Mar Biol Annu Rev 43:483–513 McHugh JL (1967) Estuarine nekton. In: Lauff GH (ed) Estuaries. AAAS, Washington, DC, pp 581–620 Meager JJ, Vance DJ, Williamson I, Loneragan NR (2003) Microhabitat distribution of juvenile Penaeus merguiensis de Man and other epibenthic crustaceans within a mangrove forest in subtropical Australia. J Exp Mar Biol Ecol 294:127–144 Melville-Smith R, Baird D (1980) Abundance, distribution and species composition of fish larvae in the Swartkops estuary. S Afr J Zool 15:72–78 Mongkolprasit S (1983) Fish in mangroves and adjacent areas. 1st Training course introduction to mangrove ecosystem, Thailand, 2–30 March 1983. UNDP/UNESCO regional projecttraining and research pilot program on the mangrove ecosystems of Asia and Oceania Ras/ 79/002/E/10/13, I-B Moore RH (1978) Variation in the diversity of summer estuarine fish populations in Aransas Bay, Texas, 1966-1973. Estuar Coast Mar Sci 6:495–501 Mumby PJ, Edwards AJ, Arias-Gonzalez JE, Lindeman KC, Blackwell PG, Gall A, Gorczynska MI, Harborne AR, Pescod CL, Renken H, Wabnitz CCC, Llewellyn G (2004) Mangroves enhance the biomass of coral reef fish communities in the Caribean. Nature 427:533–536 Neira FJ, Potter IC (1994) The larval fish assemblage of the Nornalup-Walpole estuary, a permanently open estuary on the southern coast of western Australia. Aust J Mar Freshw Res 45:1193–1207 Neira FJ, Potter IC, Bradley JS (1992) Seasonal and spatial changes in the larval fish fauna within a large temperate Australian estuary. Mar Biol 112:1–6 Odum EP, Heald EJ (1972) Trophic analysis of an estuarine mangrove community. Bull Mar Sci 22(3):671–738 Odum EP, Heald EJ (1975) The detritus based food web of an estuarine mangrove community. In: Carpenter EJ, Capone DG (eds) Nitrogen in the marine environment. Academic, New York, pp 565–649 Pittman SJ, McAlpine CA (2003) Movements of marine fish and decapod crustaceans: process, theory and applications. Adv Mar Biol 44:205–294 Plumstead EE (1990) Changes in ichthyofaunal diversity and abundance within the Mbashe estuary, Transkei, following construction of a river barrage. S Afr J Mar Sci 9:399–409 Robertson AI, Duke NC (1987) Mangroves as nursery sites: comparisons of the abundance and species composition of fish and crustaceans in mangroves and other nearshore habitats in tropical Australia. Mar Biol 96:193–205 Roper DS (1986) Occurrence and recruitment of fish larvae in northern New Zealand estuary. Estuar Coast Shelf Sci 22:705–717 Sheridan P, Hays C (2003) Are mangroves nursery habitat for transient fishes and decapods? Wetlands 23:449–458
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Taylor RH (1982) The St. Lucia estuary: the aquatic environment: physical and chemical characteristics. In: Taylor RH (ed) St. Lucia research review. Natal Parks Game and Fish Preservation Board, Queen Elizabeth Park, Pietermaritzburg, pp 42–56 Tricklebank KA, Jacoby CA, Montgomery JC (1992) Composition, distribution and abundance of neustonic ichthyoplankton of northeastern New Zealand. Estuar Coast Shelf Sci 34:263–275 Tzeng W, Wang Y (1992) Structure, composition and seasonal dynamics of the larval and juvenile fish community in the mangrove estuary of Tanshui River, Taiwan. Mar Biol 113:481–490 Wallace JH (1975) The estuarine fishes of the East Coast of South Africa. I. Species composition and length distribution in the estuarine and marine environments. Part 2: seasonal abundance and migrations. Investig Rep Oceanogr Res Inst 40:1–72 Whitfield AK (1989a) Fish larval composition, abundance and seasonality in a southern African estuarine lake. S Afr J Zool 24:217–224 Whitfield AK (1989b) Ichthyoplankton interchange in the mouth region of a southern African estuary. Mar Ecol Prog Ser 54:25–33 Whitfield AK (1999) Ichthyofaunal assemblages in estuaries: a South African case study. Rev Fish Biol Fish 9:151–186 Ya´n˜ez-Arancibia A, Linares FA, Day JW Jr (1980) Fish community structure and function in Terminos Lagoon, a tropical estuary in the southern Gulf of Mexico. In: Kennedy VS (ed) Estuarine perspectives. Academic, New York, pp 465–482
Chapter 14
Molecular Phylogenetic and Population Genetic Structuring of Macrodon sp., a Coastal and Estuarine Fish of the Western Atlantic Ocean I. Sampaio, S. Santos, and H. Schneider
14.1
Phylogenetic Studies in Fish Populations
Early studies have indicated that marine fish species have low levels of population genetic differentiation when compared to freshwater species (Ward et al. 1994; Gyllensten 2006). However, recent studies have shown deep divergences on marine species populations. In some cases, the degree of differentiation is so high that speciation events are proposed (Colborn et al. 2001; Muss et al. 2001; Planes et al. 2001; Chenoweth et al. 2002; Carlin et al. 2003). Marine organisms disperse much more due to high connectivity between their habitats. Therefore, the degree of genetic differentiation in this environment is attenuated. However, there are some other limits (spatial, directional or temporal) to dispersion that may promote the genetic differentiation in marine organisms. Amongst the different types of limits are physical barriers such as patterns of oceanic circulation, water temperature, gradients of salinity, restrict dispersion of eggs, larval or adults, phylopatry, selection, and historic events such as glaciations (Sinclair 1988; Palumbi 1994). Macrodon ancylodon (Bloch and Schneider 1801) (king weakfish) is the only species belonging to this genus described for the western Atlantic coast of the South Atlantic. This fish is a demersal species inhabiting marine and estuarine waters with muddy bottoms in tropical and subtropical regions, from Venezuela to Argentina. M. ancylodon is an estuarine-dependent species, with restricted migratory habit, spawning next to delta rivers, with their larval stages penetrating the estuary which serves as a nursery, and the juveniles remaining there until reaching the beginning of sexual maturation (Yamaguti 1979; Camargo-Zorro 1999). M. ancylodon is a very important economic resource, especially in Venezuela and northern and southern regions in Brazil due its abundance and great acceptance in the consumption market (Cervigo´n 1993; Haimovici et al. 1996; Isaac and Braga 1999). Previous genetic data (Santos et al. 2003) revealed remarkable genetic differences between northern and southern populations of Macrodon of the Atlantic coast of South America. Analyses from two mitochondrial DNA segments (Cytochrome b
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and 16S rRNA) revealed two distinct and reciprocal monophyletic lineages, defined by the authors as tropical (Venezuela to Pernambuco) and subtropical (Sa˜o Paulo to Argentina). High rates of divergence between the two groups were of the same order of magnitude that are observed among distinct species of the same genus, leading the authors to recommend the possible existence of two species for Macrodon inhabiting the western Atlantic coastal waters of South America. Additional sampling points covering the complete geographic distribution of Macrodon in the South American Atlantic coast confirmed this previous hypothesis. Parameters of population genetic variability are presented and discussed here, and from these more extensive analyses, the geographic limits of both stocks of Macrodon are now clearly visualized. Macrodon specimens were captured at 16 sites along the South American Atlantic coast: Venezuela, Amapa´, Para´, Maranha˜o, Ceara´, Pernambuco, Alagoas, Sergipe, Bahia, Espı´rito Santo, Rio de Janeiro, Sa˜o Paulo, Parana´, Santa Catarina, Rio Grande do Sul, and Argentina (Fig. 14.1). The specimens were carefully
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km 0
500 1000
Fig. 14.1 Collecting sites of Macrodon along the South America coast: Venezuela (VE), Amapa´ (AP), Para (PA), Maranha˜o (MA), Ceara´ (CE), Pernambuco (PE), Alagoas (AL), Sergipe (SE), Bahia (BA), Espirito Santo (ES), Rio de Janeiro (RJ), Sa˜o Paulo (SP), Parana´ (PR), Santa Catarina (SC), Rio Grande do Sul (RS), and Argentina (AR). Base map was created at Online Map Creations http://www.aquarius.geomar.de/omc/
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identified according to traditional keys based on morphology (Chao 1978; Menezes and Figueiredo 1980; Cervigo´n 1993), and a small piece of muscle tissue was removed and conserved in absolute ethanol or frozen for DNA analyses. Fragments of about 500 base pairs (bp) of 16S rRNA and 800 bp of Cytochrome b were isolated by PCR and sequenced using the ABI platforms (for details, see Santos et al. 2003, 2006). All sequences are deposited in GenBank under accession nos. AY253536–AY253656. DNA sequences were edited and aligned by Clustal W (Thompson et al. 1994) implemented on the BioEdit software (Hall 1999). Nucleotide divergences among the 16S haplotypes were estimated using Tamura and Nei method (1993) and phylogenetic trees based in Neighbor-Joining (Nei 1987) and Maximum Parsimony approaches were constructed using PAUP* version 4.0b10 (Swofford 2002) for this gene, using Cynoscion microlepidotus (Cmi) as outgroup in the 16S analyses. The most likely model of molecular evolution was determined in the MODELTEST version 3.06 (Posada and Crandall 1998) and the robustness of groupings was evaluated by 1,000 bootstrap pseudoreplicates (Felsenstein 1985). Phylogenetic trees generated for Cyt b sequence dataset depicted the same topology of the ones based in 16S (Cyt b tree is not shown). Divergence time was estimated assuming a rate of constant evolution of 1.0% of divergence of the sequences per million years for the 16S rRNA as calibrated by the molecular clock based on the Central American trans-isthmian geminate species of Centropomus (Tringali et al. 1999). Genetic diversity within populations of Macrodon was estimated with haplotype (h) and nucleotide diversities (p) (Nei 1987) using the software package DnaSP (Rozas et al. 2003). Genetic differentiation between pairs of populations was evaluated by pairwise fixation index (FST), using the Tamura and Nei distances and gamma value 0.01; significance of FST values was ascertained by 10,000 random permutations. The distribution of the variation within and between populations was inferred using an Analysis of Molecular Variance (AMOVA; Excoffier et al. 1992). With AMOVA, we also tested the variance (FCT) between the tropical and subtropical macro-geographic regions. These analyses were made with the program Arlequin version 2000 (Schneider et al. 2000).
14.2
Genetic Differentiation of Macrodon
There were generated 108 partial sequences of the mitochondrial 16S. The 422-bp alignment of this fragment showed 15 variable sites being 11 phylogenetically informative for parsimony. Only seven haplotypes (different sequences) were observed and their distributions are very peculiar among the populations of Macrodon. Haplotype 1, the most common in the populations from the north of South America, appears 47 times and is carried by specimens from Venezuela, Amapa, Para´, Maranha˜o, Ceara´, Pernambuco, Sergipe, Alagoas, and Bahia. Haplotype 2 (Maranha˜o) and Haplotypes 3 and 4 (Sergipe) are rare and appear just once.
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Haplotype 5 is the most common in the populations from the south, being observed in specimens from Espirito Santo, Rio de Janeiro, Sa˜o Paulo, Parana´, Santa Catarina, Rio Grande do Sul, and Argentina. Haplotype 6 occurs just once in a specimen from Sa˜o Paulo. Haplotype 7 occurs four times and is observed in the populations of Sa˜o Paulo and Parana´. Santos et al. (2003) named these two distinct groups of Macrodon as Tropical (north) and Subtropical (south). The tropical group occurs from Venezuela to Bahia while the subtropical group is distributed from Espirito Santo to Argentina. Surprisingly, besides the absence of apparent morphological differences, tropical and subtropical Macrodon are completely distinguished by 16S sequences, sharing no haplotypes. As can be seen in Table 14.1, 11 sites (2, 17, 28, 33, 91, 110, 122, 242, 266, 278, 370) show fixed mutations that may be utilized as diagnostics to discriminate tropical and subtropical groups of Macrodon. Site 177 is also diagnostic for the tropical group because all four haplotypes in this group present adenine, while those from the subtropical group (with exception of the haplotype 7) show guanine in this position (A in haplotype 7 is clearly a homoplasy). Table 14.2 shows nucleotide divergences calculated according to the Tamura– Nei algorithm. Divergences within locations and also within tropical and subtropical clades were always lower than 1%. However, nucleotide divergences between the two groups were much higher, varying from 2.4% to 3.2%. Neighbor-joining and Maximum Parsimony trees were in agreement, showing a clear separation between the tropical and subtropical groups, highly supported by bootstrap values above 90% (a consensus tree is shown in Fig. 14.2). The present analysis confirms the preliminary findings presented by Santos et al. (2003), showing two monophyletic and highly differentiated lineages of Macrodon Table 14.1 Seven different haplotypes found in a 422-base pairs fragment of the mitochondrial rRNA 16S gene, obtained for 108 specimens of Macrodon H Position where variation occurs Abbreviation for each n population 1 1 1 1 2 2 2 2 3 3 3 1 2 3 9 1 2 7 8 4 6 7 8 2 5 7 2 7 8 3 1 0 2 7 0 2 6 8 4 9 4 0 H1 A C T T A G A A C G G C T G G A VE, AP, PA, MA, CE, PE, SE, 47 AL, BA H2 . . . T . . . . . . . . C . . . MA 1 H3 . . . T . . . . T . . . . . . . SE 1 H4 . . . T . . . . . . . . . A . . SE 1 H5 G A A G A G G . A A T . . . G ES, RJ, SP, PR, SC, RS, AR 53 H6 G A A G A G G . A A T . . A G SP 1 H7 G A A G A G . . A A T . . . G SP, PR 4 Fifteen variable sites are shown above haplotypes (2, 17, 28, 33, 91. . .370). Dots represent the same nucleotide of haplotype H1. A deletion () is observed in site 33. Abbreviations of localities are: VE Venezuela, AP Amapa´, PA Para, MA Maranha˜o, CE Ceara´, PE Pernambuco, AL Alagoas, SE Sergipe, BA Bahia, ES Espirito Santo, RJ Rio de Janeiro, SP Sa˜o Paulo, PR Parana, SC Santa Catarina, RS Rio Grande do Sul, AR Argentina. n in the far right column means the number of specimens sharing the same haplotype
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Table 14.2 Nucleotide divergence matrix obtained according to Tamura and Nei (1993) based on haplotypes of the mitochondrial rRNA 16S gene of Macrodon (H1H7) and one haplotype of Cynoscion microlepdotus (Cmi) 16S Haplotypes Percentage of nucleotide divergence Cmi H1 H2 H3 H4 H5 H6 Cynoscion microlepidotus Macrodon ancylodon Haplotype 1 9.8 Macrodon ancylodon Haplotype 2 10.1 0.2 Macrodon ancylodon Haplotype 3 10.1 0.2 0.5 Macrodon ancylodon Haplotype 4 10.1 0.2 0.5 0.5 Macrodon sp. Haplotype 5 9.6 2.7 2.9 2.9 3.5 Macrodon sp. Haplotype 6 9.3 3.0 3.2 3.2 3.2 0.2 Macrodon sp. Haplotype 7 9.6 2.4 2.7 2.7 2.7 0.2 0.5
Fig. 14.2 Neighbor-joining consensus tree obtained according to the Tamura and Nei evolution model for 422 bp of the 16S rRNA of Macrodon. Numbers above nodes represent bootstrap values estimated from 1,000 pseudoreplicates. Cynoscion microlepidotus is the outgroup
populations in the western Atlantic Ocean. Interestingly, there was no overlap zone between the two groups, which were geographically separated in the region of south Bahia (Porto Seguro) and north Espirito Santo (Vitoria). Tropical and subtropical groups of Macrodon show nucleotide divergences for the 16S gene varying from 2.4 to 3.5%. This magnitude of genetic divergences is usually observed between distinct species of Sciaenidae, as demonstrated in the study of Vinson et al. (2004) for the assemblage of the Caete´ estuary river: Stellifer rastrifer and S. stellifer (3.3%); S. naso and S. microps (1.2%); and Cynoscion virescens and C. leiarchus (3.1%) (Vinson et al. 2004). Several families of Perciformes also show nucleotide divergences varying from 1 to 4% for congeneric species: Centropomidae (Tringali et al. 1999), Cichlidae (Farias et al. 2000), Pomacentridae (Tang 2001), Scaridae (Streelman et al. 2002), and Labridae (Mabuchi et al. 2004). The high values of divergence observed between the tropical and subtropical groups of Macrodon, coupled with the clearly geographic isolation between them, strongly support our conclusions that these groups should be
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considered distinct species. M. ancylodon Bloch and Schneider (1801) is the species of the tropical region (Venezuela to Bahia) and Macrodon sp. is the new species of the subtropical region (Espirito Santo to Argentina). Nucleotide divergence values among DNA sequences may be used based on a molecular clock to estimate divergence time for separation between two lineages (Avise 1994). For the present study, we applied this approach assuming a constant rate of 1% of divergence per million years for the 16S rRNA, an estimation obtained by the comparison of the Panama trans-isthmian geminate species of Centropomus (Tringali et al. 1999). Using this rate of molecular evolution, we estimate that the separation between the tropical and subtropical groups of Macrodon have possibly occurred between 2.4 and 3.5 million years ago, during the late Pliocene. Interestingly, theses estimations do not coincide with Pleistocene glacial events, which are usually considered by many authors as the major causes for genetic differentiation in fishes (Brunner et al. 2001; Hickerson and Ross 2001; Beheregaray et al. 2002; Grunwald et al. 2002; Kotlı´k et al. 2004). Cytochrome b sequences were obtained for 130 specimens of Macrodon from 12 geographic localities represented in Fig. 14.1 (samples from Ceara, Alagoas, Sergipe and Rio de Janeiro were not included in the Cyt b analyses). A total of 43 distinct haplotypes with 59 polymorphic sites were observed. M. ancylodon carries 20 haplotypes (Hp1Hp20), while Macrodon sp. carries 23 Cyt b haplotypes (Hp21Hp43). Similarly to the 16S database, no Cyt b haplotype is shared between M. ancylodon and Macrodon sp. This scenario shows clearly the two species as reciprocally monophyletic. Within each species, most haplotypes are specific to their collecting location, i.e., private alleles. Only eight haplotypes (1, 7, 13, 14, 21, 30, 39, and 40) are shared among populations inside each species (Table 14.3). Haplotype and nucleotide diversities of Cyt b for each population are shown in Table 14.4. Within M. ancylodon, the population of Para´ was the one with the lowest haplotype diversity (h ¼ 62%), while Pernambuco showed the highest one (h ¼ 84%). Within Macrodon sp., the smallest haplotype diversity was found in Espı´rito Santo (h ¼ 52%), while samples from Sa˜o Paulo presented the highest (h ¼ 91%). The nucleotide diversities (p) were very low (less than 0.3%) inside the species (Table 14.4), but quite high (4.5%) between the two species (for more details, see Santos et al. 2003). Significant separation of M. ancylodon and Macrodon sp. is depicted from the AMOVA (Table 14.5), with 93% of all variance resulting from differences between the two species (FCT ¼ 0.931, P < 0.005). Populations within the species also showed significant geographic structuring, although a much lower percentage of genetic variance was distributed among populations. Within M. ancylodon, 54% of genetic variance is attributed to differences within populations (FST ¼ 0.462, P < 0.001), and 44.5% of genetic variance attributable to the difference between the Brazil North Current and the Brazil Current populations (FCT ¼ 0.445, P ¼ 0.072). Although nonsignificant, almost half the total genetic variance among tropical populations is attributable to a contrast between populations in the Brazil North Current (Venezuela to Maranha˜o) and populations of the Brazil
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Table 14.3 Distribution of the 43 Cyt b haplotypes in Macrodon ancylodon and Macrodon sp. along the 12 localities of the South America Atlantic coast Cyt b Haplotype Macrodon ancylodon Macrodon sp. Total VE AP PA MA PE BA ES SP PR SC RS AR 1 6 6 7 8 27 2 1 1 3 2 2 4 1 1 5 1 1 6 1 1 7 2 1 4 7 8 1 1 9 1 1 10 1 1 11 1 1 12 1 1 13 1 4 3 8 14 2 1 3 15 1 1 16 1 1 17 1 1 18 1 1 19 1 1 20 1 1 21 12 3 4 1 3 23 22 1 1 23 1 1 24 1 1 25 1 1 26 1 1 27 1 1 28 1 1 29 1 1 30 3 4 7 31 1 1 32 1 1 33 1 1 34 1 1 35 1 1 36 1 1 37 1 1 38 1 1 39 4 5 6 15 40 2 2 4 41 1 1 42 1 1 43 1 1 Total 130
Current (Pernambuco and Bahia). AMOVA in Macrodon sp. shows 86% of the variance related to differences within populations and FST ¼ 0.136 (P < 0.001) indicating little population structuring inside this group.
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Table 14.4 Haplotype and nucleotide diversities of Cytochrome b in Macrodon ancylodon and Macrodon sp. populations along western Atlantic coast Populations n Different Cyt b Haplotype Nucleotide haplotypes diversity (h) diversity (p) Macrodon ancylodon 62 20 0.786 0.048 0.0026 0.0016 Venezuela 10 4 0.644 0.152 0.0012 0.0015 Amapa´ 10 4 0.644 0.152 0.0020 0.0013 Para´ 11 5 0.618 0.164 0.0020 0.0015 Maranha˜o 15 5 0.676 0.105 0.0017 0.0012 Pernambuco 10 6 0.844 0.103 0.0030 0.0020 Bahia 6 4 0.800 0.172 0.0021 0.0016 Macrodon sp. 68 23 0.831 0.033 0.0020 0.001 Espirito Santo 17 6 0.515 0.145 0.0010 0.0008 Sa˜o Paulo 12 8 0.909 0.065 0.0027 0.0018 Parana´ 11 5 0.782 0.093 0.0016 0.0012 Santa Catarina 9 5 0.806 0.120 0.0025 0.0017 Rio Grande do Sul 8 3 0.607 0.164 0.0021 0.0015 Argentina 11 4 0.673 0.123 0.0014 0.0011 All 130 43 0.906 0.014 0.0185 0.0003
Table 14.5 Analysis of molecular variance (AMOVA) for Macrodon using Cyt b haplotypes Source of variation Variance total F/F -statistics P All populations <0.004 Among groups 93.1 F/FCT ¼ 0.931 <0.001 Among populations within group 1.5 F/FSC ¼ 0.222 <0.001 Within populations 5.4 F/FST ¼ 0.946 Macrodon ancylodon ¼0.072 Among groups 44.5 F/FCT ¼ 0.445 ¼0.171 Among populations within group 1.6 F/FSC ¼ 0.029 <0.001 Within populations 53.9 F/FST ¼ 0.462 Macrodon sp. <0.001 Among populations within group 13.6 F/FST ¼ 0.136 Within populations 86.4 In All population”, the populations were grouped into Macrodon ancylodon and Macrodon sp. In Macrodon ancylodon the populations were grouped into the Brazil North Current (Venezuela to Maranha˜o) and the Brazil Current (Pernambuco and Bahia) populations. In Macrodon sp. all populations were treated as one group. This group organization was depicted from a Nested Clade Analyses (results not detailed here)
14.3
Consequences for the Taxonomy of Macrodon
The pattern of genetic differentiation of Macrodon along the western South Atlantic coast is similar to the type I phylogeographic pattern described by Avise (2000), characterized by the presence of highly divergent haplogroups, showing isolated alopatric lineages by effective barriers to gene flow. In marine environments, the barriers to the gene flow are less evident than in freshwaters or in terrestrial environments. However, amongst the factors that may promote genetic differentiation in the marine environment are the pattern of oceanic circulation, coastal
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topography, temperature and salinity gradients, mechanisms of larval retention, and limited dispersion of eggs, larval and adults, as well as phylopatry, selection and historical events (Sinclair 1988; Palumbi 1994; Dawson et al. 2001). Gold and Richardson (1998) analyzed populations of three Sciaenidae species (Sciaenops acellatus, Pogonias cromis and Cynoscion nebulosus) that show larval and juvenile stages inside the estuary and limited migration of adult specimens. They interpreted this differentiation pattern as the result of isolation by distance. Macrodon shares with those sciaenids a very similar life history, such as an estuarine-dependent larval stage as well as juveniles and adults with restricted migratory habits (Yamaguti 1979; Camargo-Zorro 1999). The isolation by distance model does not explain the results obtained with both 16S and Cyt b in Macrodon, once populations separated by at least 6,000 km (e.g., Venezuela and Bahia) share haplotypes, whereas populations from Bahia and Espı´rito Santo separated by only 500 km do not show any evidence of gene flow. These results indicate that additional factors may have contributed to the differentiation of western Atlantic Macrodon. The effect of oceanic circulation as a potential barrier restricting gene flow and favoring genetic differentiation for some marine fish species has been very well discussed (Hickerson and Ross 2001; Muss et al. 2001; Stepien et al. 2001). Macrodon distribution in the western South Atlantic is under the influence of three main current systems, the Brazil North Current or Guyana Current, the Brazil Current and the Malvinas Current. The Brazil North Current and the Brazil Current originate and diverge at 10 S, approximately, in the Brazilian northeast coast (Castro and Miranda 1998; Johns et al. 1998). The Brazil North Current flows towards the north and influences part of the Brazilian northeast coast and all the Brazilian north coast, whereas the Brazil Current flows towards south influencing part of the northeast, southeast and south of Brazil and some regions in Argentina. The Malvinas Current carries cold sub-antarctic waters northwards influencing the entire Argentina coast to the south of Brazil. Santos et al. (2003) suggested that the surface current systems of the Atlantic coast of South America could be a barrier to limit the gene flow between tropical and subtropical groups of Macrodon. However, in this more recent analysis, it was observed that Macrodon from south Bahia belongs to the tropical group (M. ancylodon); therefore, the pattern of currents in the west of the South Atlantic seems not to be the main factor that contributes to the isolation of the two Macrodon. According to Lowe-McConnell (1999), water temperature is one of the main factors influencing the distribution of marine fishes. M. ancylodon lives in an environment where the temperature varies from 24 to 29 C with vertical gradients of temperature of at least 1 C (Cervigo´n 1993; Castro and Miranda 1998), while Macrodon sp. inhabits regions where the water temperature varies from 4 to 27 C due to two important current systems: the Brazil Current, transporting tropical waters towards south to the Argentina’s coast and the Falklands Current that transports cold sub-antarctic waters north towards the coast of Parana´ (Thomsem 1962; Castro and Miranda 1998). It is possible that Macrodon groups may have developed local adaptations to the environmental temperature, which could have
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promoted the fragmentation and isolation of them along the time leading to the degree of differentiation observed nowadays. According to Palumbi (1994), mate preference, habitat specialization, and synchrony during spawning and fertilization are prezygotic mechanisms that may promote the reproductive isolation in organisms. It has been documented that Macrodon from north and south Brazil have distinct reproductive periods: Macrodon from the north coast shows parceled spawning from July through August and October through December (Camargo-Zorro 1999), while Macrodon from south Brazil shows two main peaks of spawning in December and February (Vazzoler 1963; Yamaguti 1967; Juras and Yamaguti 1989). Therefore, an asynchrony during the reproductive period may be one of the factors responsible for the present day isolation of M. ancylodon and Macrodon sp. The existence of two monophyletic and highly divergent lineages of Macrodon along the western Atlantic coast raises a question about the taxonomic status of this group. According to the allopatric speciation model, extrinsic barriers isolating conspecific populations reduce or eliminate the gene flow promoting genetic differentiation and reproductive isolation, which is the main characteristic of biological concept of species (Avise 2000). The genetic data so far accumulated for Macrodon suggest the existence of reproductive isolation, as evidenced by the absence of intergradations between M. ancylodon and Macrodon sp. Considering all the evidence discussed here, we strongly recommend a taxonomic revision of this estuarine-dependent group of fishes.
References Avise JC (1994) Molecular markers, natural history and evolution. Chapman & Hall, New York Avise JC (2000) Phylogeography: the history and formation of species. Harvard University Press, Cambridge MA Beheregaray LB, Sunnucks P, Briscoe DA (2002) A rapid fish radiation associated with the last sea-level changes in southern Brazil: the silverside Odontesthes perugiae complex. Proc R Soc Lond B 269:65–73 Brunner PC, Douglas MR, Osinov A, Wilson CC, Bernatchez L (2001) Holartic phylogeography of Arctic charr (Salvelinus alpinus L.) inferred from mitochondrial DNA sequences. Evolution 55:573–586 Camargo-Zorro M (1999) Biologia e estrutura populacional das espe´cies da famı´lia Sciaenidae (Pisces: Perciformes), no estua´rio do rio Caete´ municı´pio de Braganc¸a, Para´ – Brasil. MSc thesis, University of Para´, Bele´m Carlin JL, Robertson DR, Bowen BW (2003) Ancient divergences and recent connections in two tropical Atlantic reef fishes Epinephelus adscensionis and Rypticus saponaceous (Percoidei: Serranidae). Mar Biol 143:1057–1069 Castro BM, Miranda LBDE (1998) Physical oceanography of the western Atlantic continental shelf located between 4 N and 34 S, coastal segment (4, W). In: Robinson AR, Brink KH (eds) The sea, vol 7. Wiley, New York Cervigo´n F (1993) Los peces marinos de Venezuela, vol 2. Fundacio´n Cientı´fica Los Roques, Caracas Chao LN (1978) A basis for classifying western Atlantic Sciaenidae (Teleostei, Perciformes). NOAA Tech Rep Circ 415:1–64
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Chapter 15
Fisheries and Management V.J. Isaac, R.V. Espı´rito-Santo and U. Saint-Paul
15.1
Introduction
The Bragantine region of the state of Para´, Brazil, is naturally conducive to fishery activities. The protected areas within the estuary form natural ports where fishing vessels moor. The marine and estuary environments of the north Brazilian coast generally exhibit high productivity and considerable ichthyic diversity (Camargo and Isaac 2001), which is likely the consequence of the important contribution of organic matter originating from the mainland and the decomposition of the mangroves that dominate the coastal vegetation (Nittrouer and Demaster 1996). This sustains an important biomass of fishery resources, especially demersal organisms, many of which are commercially exploited, although their potential and the carrying capacity of stocks are as yet unknown (Isaac 2006). Fishery production on the north Brazilian coast represents 20% of the total volume of marine/estuary catches in the country and 10% of the total value of exported marine/estuary products (IBAMA 2005), surpassing US$ 40 million per year. Landings occur in at least six coastal communities of the Caete´ River estuary, as well as the cities of Braganc¸a and Augusto Correˆa. Fishery activities are exercised in estuary and coastal waters or on the broad continental shelf off the Amazon, which includes the marine region to the 200-m isobath between Sa˜o Marcos Bay (state of Maranha˜o) and the delta of the Oiapoque River (well north of the state of Amapa´) (PROVAM 1990) (Fig. 15.1). The city of Braganc¸a is located on the northeast coast of the state of Para´. It has over 100,000 inhabitants, nearly 60% of which live within the city limits and the remainder in the surrounding rural communities. The population is mainly occupied with agriculture (especially cassava, beans and fruit), livestock (chicken and cattle) and fishing activities. The city ranks third in marine-origin fishery production in the state (Brito and Furtado 2002). Catches serve as a food source for the local population and also constitute an important source of income through the commercialization of products in the local, regional and national markets.
U. Saint-Paul and H. Schneider (eds.), Mangrove Dynamics and Management in North Brazil, Ecological Studies 211, DOI 10.1007/978-3-642-13457-9_15, # Springer-Verlag Berlin Heidelberg 2010
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Fig. 15.1 Map of the coastal region of north Brazil, encompassing the states of Maranha˜o, Para´ and Amapa´.
Despite its relative importance, little was known regarding the fishery characteristics and measures in the Bragatine region until the end of the 1990s. Following the implantation of projects such as MADAM, which scientifically investigated these activities, we currently have a better knowledge of its dynamics and can better understand its complexity. Thus, we are in a position to propose fishery management alternatives designed to make the activity sustainable.
15.2
Methods
Data on catches were collected for all landings occurring from June 2000 to June 2001 at seven sites located on the margins of the Caete´ River estuary: Braganc¸a, Bacuriteua, Vila de Ajuruteua, Caratateua, Furo Grande, Tamatateua, and Vila do
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Fig. 15.2 Geographic location of landing sites in the Caete´ River estuary where the data collection forms were applied.
Treme (Fig. 15.2). Interviews were conducted with the captains or persons in charge of each vessel. Discussions with community leaders, associations, fishermen, and others linked to fishery activities were also carried out in order to typify the fishery production systems following the classification methodology proposed by Silva (2004). Along with a review of the fishery legislation, management issues were also discussed with authorities as well as with fishermen in diverse meetings.
15.3
Fisheries Structure and Situation
Approximately 1,076 different vessels operated at the landing ports between 2000 and 2001, from small rowing boats to industrial vessels more than 20 m in length. The fishery fleet demonstrates a wide variety of physical characteristics (Fig. 15.3), which are summarized in Table 15.1. Small boats are the most frequent type of
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Table 15.1 Physical characteristics of the fishing fleet operating at ports in the city of Braganc¸a. Adapted from Espı´rito-Santo (2002) and Braga (2002) Fleet
Feature
Size (m) (range; mean standard deviation)
Rowing boat
Built with wood. Propelled with rows Built with wood. Propelled with sail or rows and sail, with no deck or with semi-closed deck, generally with no cabin Built with wood. Propelled with motor, or motor and sail, with or without deck, generally with no cabin Built with wood. Propelled with motor, or motor and sail, closed or semi-closed deck, generally with cabin Built with wood. Propelled with motor, or motor and sail, closed deck and cabin Steel hull. Propelled with motor, possessing equipment for navigation, catch support and storage Small boat or motorized skiff that operates only transporting fish from other boats to the landing ports
3.0–6.5; 4.9 0.9
Load capacity (kg) (range; mean standard deviation) 100–800; 379 151
3.0–8.0; 4.2 1.5
100–500; 539 421
3.0–8.0; 6.9 0.8
250–3,000; 1,456 557
7.0–12.0; 8.5 1.1
500–10,000; 2,900 1,541
10–18; 12.9 1.4
4,000–25,000; 10,000 4,000
12–22; 16.0 2.9
10,000–22,000; 14,800 3,590
3.0–6.5; 8.3 0.9
1,200–6,000; 2,903 1,971
Skiff
Motorized skiff
Small fishing boat
Mid-size fishing boat Industrial fishing boat
Fish packer
Fig. 15.3 Illustration of the different types of fishing vessels at the fishery ports of the city of Braganc¸a: row boats and sailing skiffs; motorized skiffs; small fishing boats; mid-size and industrial fishing boats
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Table 15.2 Distribution of fishery fleet operating at ports in the city of Braganc¸a per type of vessel, length (mean) and number of fisherman (mean) Type of vessel Nr. of vessels Relative frequency (%) Length Nr. of fisherman Rowing boat 463 43.0% 4.9 2 Skiff 274 24.5% 4.2 3 Motorized skiff 136 12.6% 6.9 4 Small fishing boat 107 9.9% 8.5 4 Mid-size fishing boat 78 7.2% 12.9 7 Industrial fishing boat 13 1.2% 16 9 Fish packer 5 0.5% 8.3 3 Total 1,076 100% – –
vessel, making up 43% of the total (Table 15.2). The crew varies with the type of vessel; there is an average of nine fishermen on industrial boats, seven on mid-size boats, two on rowing boats, and between three and four on the remaining types. The structure of the fleet has been undergoing changes over the years. While mid-size vessels have increased in number as a result of government incentives for the purchasing of this type of fishing vessel, the number of rowing boats and skiffs has decreased. This change has been accompanied by increased fishing power, as the new boats are larger, giving them a greater load capacity and enabling them to carry a larger crew (Almeida et al. 2006). The different types of fishing vessels exploit partially distinct environments due to their physical characteristics and catch capacity. Larger boats with greater autonomy principally sail in waters on the continental shelf, north of the equator. Small boats are able to reach this area as well, but more frequently operate along the coast off the states of Para´ and Maranha˜o. Motorized skiffs are restricted to the coast off Para´ between the Maranha˜o Gulf and Marajo´ Bay. Rowing boats and sailing skiffs only operate in estuarine or coastal waters near the Bragatine ports (Fig. 15.4). Fishery activities in the region are performed with a large variety of methods, from modalities considered traditional to others that are more modern. The most frequently used fishing gear are gillnets, which were introduced in the Amazon region in the 1960s (Isaac 2006). They are placed in both the water column as well as on the bottom, either drifting or anchored, either in open waters or closing tide channels, depending upon their size and target species. Other types of gear are also used with a certain frequency, including hand lines, long lines, stationary uncovered pound nets, and mobile traps (Fig. 15.5). The fishery modalities in the region can be classified according to the type of vessel and technology employed into: (1) small-scale artisanal systems; (2) largescale artisanal systems; and (3) industrial systems (Espı´rito-Santo 2002; Braga 2002). Despite the fact that a number of steel-hull boats were observed, few units can be considered as pertaining to the industrial fishery category at the Bragatine ports. Thus, most of the fleet is classified in the two artisanal categories. Classification into just three categories fails to make explicit the great variability in forms of production. In a typification exercise using technological, socioeconomic and environmental criteria, the fishery production systems observed at landings in the
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4.00
4.00
2.00
2.00
0.00
0.00
–2.00
–2.00
– 52.00 – 50.00 – 48.00 – 46.00 – 44.00 – 42.00 – 40.00
– 52.00 – 50.00 – 48.00 – 46.00 – 44.00 – 42.00 – 40.00
Motorized skiff
Rowing boats and skiff 4.00
4.00
2.00
2.00
0.00
0.00
–2.00
–2.00
– 52.00 – 50.00 – 48.00 – 46.00 – 44.00 – 42.00 – 40.00
Small fishing boats
– 52.00 – 50.00 – 48.00 – 46.00 – 44.00 – 42.00 – 40.00
Mid-size and industrial fishing boats
Fig. 15.4 Area of operations of the fishery fleet that lands catches at ports in the city of Braganc¸a, according to type of vessel. Larger circles represent greater catch volumes.
city were subdivided into 16 categories, with just 1 on the industrial scale (Red Snapper fishery using traps), 4 of a large-scale artisanal nature (Acoupa Weakfish, Red Snapper, Lobster and Laulao Catfish), and 11 of a small-scale artisanal nature, targeting diverse fish as well as shrimp, crab and mussels (Table 15.3). Taking into consideration all vessels arriving at ports in the 13-month period from June 2000 through June 2001, we concluded that fishery production of Braganc¸a was 4,870 t. For only 12 months, from July 2000 through June 2001, production was 4,322 t. These estimates do not include the commercialization of the crab Ucides cordatus, which surpassed 900 t in 2003 (Arau´jo 2006), as fishermen from this system arrive to town using land-based paths. It should also be pointed out that lobster landings in Braganc¸a have only begun to occur fairly recently and therefore do not appear in the statistics for the period between 2000 and 2001. Thus, we can affirm that the total production of the Braganc¸a ports for all types of catch must be at most 6,000 t. The official statistics recorded by IBAMA (Brazilian Environmental Agency) report a total fishery production for the city ranging from 10,000 to 20,000 t per year from 1995 to 2004 (CEPNOR/IBAMA 2007). The considerable discrepancy between the official data and those obtained from our survey may be attributed to failures in government statistical collection methods, which use a sampling system (instead of a census), with less-than-strict monitoring by authorities. It appears evident that the large diversity and considerable dispersion of the fishery modalities in the region do not allow extrapolations for calculating the total production, which makes the official statistics inaccurate.
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Fig. 15.5 Principal fishing gear used by the Bragantine fishery fleet
Fishery production clearly presented a harvest period, which appears to be related to the hydrological cycle. On a monthly scale, landing volumes ranged from a maximum of 500 and 600 t/month during the early dry season from May to June to around 200 t/months from November to January, at the end of the dry season and beginning of the flood season (Fig. 15.6). Catches within the estuary of the Caete´ River represented about half of total landings. It was also observed that, during the rainy season, a large part of the
Net
Large-scale artisanal
Line
Long line
Trap
Industrial Panulirus argus; P. laevicauda; Scyllarides delfosi Cynoscion acoupa Aspistor parkeri Charcharhinus sp. Lutjanus purpureus
Lutjanus purpureus
Coast net Spanish Small-scale Net Scomberomorus brasiliensis; Mackerel artisanal Macrodon ancylondon Coast long line Line Bagre bagre Estuary net without Net Diverse fish motor Estuary net with motor Estuary long line Long line Estuary pound net Pound net Sardine Net Anchovia clupeoides Artisanal shrimp Litopenaeus schmitti Barrier net Diverse fish Mussel Manual Mytella sp. and other mollusks Crab collection Ucides cordatus a Average income of fishermen in relation to general income of the region b Degree of isolation of fishermen in relation to nearest urban center
Coast net Weakfish Long Line Gillbacker Sea Catfish Red Snapper with line
Red Snapper with traps Lobster
Mangrove; mud
Beach; sand
Estuary; sand and mud
Continental shelf, hard bottoms Coastal region; sand
Coastal region, sand and mud
Continental shelf, hard bottoms
Table 15.3 Fishery systems recorded at Braganc¸a landings and main classification characteristics System Fleet Gear Target species Environment
Family owned
Partnership
Boat owner
Lower
Equal
Lower
Equal
Isolated
Work relations Incomea Degree of isolationb Entrepreneurial Greater Not isolated
240 V.J. Isaac et al.
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Fig. 15.6 Fish landings and rainfall in Bragntine region from June 2000 to June 2001 from June 2000 to June 2001.
4.00
4.00
2.00
2.00
0.00
0.00
– 2.00
– 2.00
– 52.00 – 50.00 – 48.00 – 46.00 – 44.00 – 42.00 – 40.00
– 52.00 – 50.00 – 48.00 – 46.00 – 44.00 – 42.00 – 40.00
Rainy season – February to April
Transition to dry season Mai to July
4.00
4.00
2.00
2.00
0.00
0.00
– 2.00
– 2.00
– 52.00 – 50.00 – 48.00 – 46.00 – 44.00 – 42.00 – 40.00
– 52.00 – 50.00 – 48.00 – 46.00 – 44.00 – 42.00 – 40.00
Dry season – August to October
Transition to rainy season November to January
Fig. 15.7 Concentration of fishery production according to season.
production is obtained from northern fishing expeditions off the state of Amapa´. During the dry season, catches diminish and are concentrated along the coast of the states of Para´ and Maranha˜o (Fig. 15.7). A total of 62 fish and invertebrates categories were established for the landings (Table 15.4). This indicates that the richness of commercialized species is quite high. It should be considered, however, that some categories include various taxonomic groups, whereas others contain just a single species. The first ten species
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Table 15.4 Fishery production (kg) by species at ports of Braganc¸a from June 2000 to June 2001 in order of relative importance No Common name Scientific name Production % Accumulated 1 King Weakfish Macrodon ancylodon 1147,972 23.57 23.57 2 Red Snapper Lutjanus purpureus 884,737 18.17 41.74 3 Spanish Mackarel Scomberomorus brasiliensis 532,075 10.93 52.67 4 Acoupa Weakfish Cynoscion acoupa 333,108 6.84 59.51 5 Coco Sea Catfish Bagre bagre 318,470 6.54 66.04 6 Crucifix Sea Catfish Sciades proops 180,734 3.71 69.76 7 Bressou Sea Catfish Aspistor quadriscutis 177,738 3.65 73.41 8 Whaler shark Carcharhinus spp. 119,366 2.45 75.86 9 Couma Sea Catfish Sciades couma 97,320 2,00 77,85 10 Goliath Grouper Epinephelus itajara 93,878 1.93 79.78 11 Gillbacker Sea Catfish Aspistor parkeri 86,849 1.78 81.57 12 Pompano Trachinotus sp. 82,954 1.70 83.27 13 Skates Rajiformes 68,760 1.41 84.68 14 Sea trout Cynoscion virescens 67,881 1.39 86.08 15 Torroto Grunt Genyatremus luteus 53,140 1.09 87.17 16 Cobia Rachycentron canadum 51,941 1.07 88.23 17 Madamango Sea Catfish Cathorops spixii 47,377 0.97 89.21 18 Mullet Mugil spp. 47,038 0.97 90.17 19 Atlantic Bonito Sarda sarda 46,632 0,96 91,13 20 Leatherjack Oligoplites spp. 45,640 0.94 92.07 21 Grouper Epinephelus sp. 38,342 0.79 92.85 22 Snook Centropomus spp. 37,175 0.76 93.62 23 King Mackerel Scomberomorus cavala 25,850 0.53 94.15 24 Crevalle Jack Caranx hippos 18,898 0.39 94.54 25 Trench Mullet Mugil incilis 17,769 0.36 94.90 26 Tripletail Lobotes surinamensis 14,977 0.31 95.21 27 Dolphinfish Brachyplatystoma 12,948 0.27 95.47 rousseauxii 28 Tarpon Megalops atlanticus 11,287 0.23 95.71 29 Thomas Sea Catfish Notarius grandicassis 11,237 0.23 95.94 30 Pacuma Toadfish Batrachoides surinamensis 10,269 0.21 96.15 31 Whitemouth Croaker Micropogonias furnieri 10,124 0.21 96.36 10,038 0.21 96.56 32 Mutton Snapper Lutjanus analis; L. jocu 33 Yellowtail Snapper Ocyurus chrysurus 9,543 0.20 96.76 34 Grouper Mycteroperca sp. 8,979 0.18 96.94 35 Jacks, Pompanos Carangidae 8,451 0.17 97,12 36 American coastal pellona Pellona flavipinnis 8,219 0.17 97.28 37 Sharks Charcharhinus spp.; 6,294 0.13 97.41 Sphyrna spp. 38 Softhead Sea Catfish Arius rugispinis 5,945 0.12 97.54 39 French Angelfish Pomacanthus paru 3,063 0.06 97.60 40 Shrimp Penaeidae 2,984 0.06 97.66 41 South American Silver Plagioscion squamosissimus 2,780 0.06 97.72 Croaker 42 Wolf fish Hoplias malabaricus 1,386 0.03 97.75 43 Blue Crab Calinectes sp. 1,364 0.03 97.77 44 Bluefish Pomatomus saltatrix 1,136 0.02 97.80 45 Rock-Bacu Lithodoras dorsalis 913 0.02 97.82 46 Laulao Catfish Brachyplatystoma vaillantii 900 0.02 97.83 47 Mullet Mugil sp. 815 0.02 97.85 (continued)
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Table 15.4 (continued) No Common name 48 Sawfish 49 Lookdown 50 Pompanos 51 Blue Mussel 52 Kumakuma 53 Redtail Catfish 54 55 56 57 58 59 60 61 62 63
Knifefish Suckermouth Catfish Largescale Foureyes Oyster Croakers Arapaima Atlantic Cutlessfish Passany Sea Catfish Flatfish Others Total
243
Scientific name Pristis sp. Selene voˆmer Trachinotus spp. Mytella sp. Brachyplatystoma filamentosum Phractocephalus hemioliopterus Eigenmannia sp. Hypostomus plecostomus Anableps anableps Crassostrea rhizophorae Stellifer sp. Arapaima gigas Trichiurus lepturus Sciades passany Achiridae –
Production 761 466 279 180 102
% 0.02 0.01 0.01 0.00 0.00
Accumulated 97.87 97.88 97.88 97.88 97,89
54
0.00
97.89
42 37 31 30 30 23 18 11 2 102,624
0.00 0.00 0.00 0,00 0.00 0.00 0.00 0.00 0.00 2.11
97.89 97.89 97.89 97,89 97.89 97.89 97.89 97.89 0.00 2,11
4,869,986
represent 80% of the total volume, and Macrodon ancylodon alone accounts for nearly one-quarter of the recorded total. The King Weakfish (M. ancylodon) together with the Acoupa Weakfish (Cynoscion acoupa) present the greatest abundance in the transition to the dry season mid-way through the year, immediately following the rainy season. The Spanish Mackerel (Scomberomorus brasiliensis) exhibits its highest catch volumes in the first semester, during the rainy season, whereas the Red Snapper (Lutjanus purpureus) is caught more in the second semester at the beginning of the period of less rainfall in the region. Over 4,100 laborers operate in the Braganc¸a fishing fleet, representing 5% of the total number of fishermen in the state of Para´ (SEAP 2006). The number of fishermen was estimated based on an average number of crew members per type of vessel and not considering crab collectors, who, according to Arau´jo (2006), probably number about 1,200 laborers, nor considering mussel collectors, most of whom are women and the numbers for whom are unknown. Thus, over 5,300 people are directly linked to the exploitation of fishery resources. This means that fishery laborers represent 16% of the overall working population of the municipality (Source: 2000 demographic census of the IBGE – Brazilian Statistics Agency). According to Glaser (2006), considering only the rural communities of the Bragatine peninsula, about 60% of residents practice fishing or the collection of aquatic organisms, whether for subsistence or as a form of obtaining income. As each fisherman sustains an average of five persons, the number of people that depend upon fishery activities reaches over 25,000 in the city, representing approximately 25% of the population.
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The social situation of these laborers is quite precarious. The average monthly income per family depends upon the fishery modality and can be between US$ 300 and 500 for lobster or Red Snapper fisheries, but far below this amount (
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of vessels and fishermen from the northeast region of the country who have come to the city of Braganc¸a in search of more promising yields, especially in the targeting of snappers and lobster. This results in new social conflicts over resources, as well as feuding and competition between fishermen stemming from the superior training of the fishermen who come from far distances. The situation portrayed here is further aggravated by the lack of continuous monitoring and reliable information that would at least permit an accurate diagnosis of production tendencies and fishing efforts, as well as a true understanding of the state of stocks. The combination of these factors composes an alarming scenario for fishery activities in a not-too-distant future. Given the lack of information on the development of activities, a policy of precaution on the part of government actions would be the most sensible approach. Instead, government agencies have traditionally encouraged an increase in fishery efforts by way of measures that facilitate the purchasing of new boats and fishing gear in order to target stocks that are already sufficiently exploited. Even with very low interest rates, the implemented financing has high incidences of defaults on loans, which may surpass 90% of the total investments. The municipality of Braganc¸a has been particularly favored by this policy of subsidies. From 1996 to 2000, 159 fishing vessels of up to 3 t capacity were financed by the Bank of Amazoˆnia, corresponding to 36% of financing in the period for the entire coast of the state of Para´. In a multidimensional analysis of sustainability indicators considering social, economic, ecological, technological and political aspects of fishery production systems in the state of Para´, it was concluded that none of the fishery modalities has an adequate performance in all evaluation fields. It is therefore difficult to establish criteria for determining the fisheries that are more or less sustainable, as the different evaluation fields display opposing behaviors. Fishery systems that may be considered favorable from the social or economic perspective exhibit low sustainability indices regarding environmental criteria. Thus, industrial or largescale artisanal systems, such as Red Snapper or the Acoupa Weakfish, exhibit greater sustainability from the economic and social standpoints for having better yields and promoting a higher standard of living for their stakeholders. On the other hand, small-scale fishery systems exhibit a better performance regarding environmental indicators, as they employ fishing gear with less of an impact and an as yet low fishing pressure on stocks (Isaac et al. 2009). Considering the lack of control over increased efforts in industrial and largescale artisanal fisheries, and seeking to avoid situations of over-exploitation and over-capitalization, it appears evident that restrictive measures are needed regarding increases in fishing efforts, even if such measures are not well accepted by stakeholders. The high levels of loan defaults on the part of fishermen are an indication that these fisheries should be controlled in order to avoid economic bankruptcy and the negative social and environmental consequences. Otherwise, unemployment and the loss of environmental quality can very readily become real threats to the laborers of these systems.
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The survey of the fishery systems of Braganc¸a calls attention to the need for a greater investment in the monitoring of fisheries, as well as scientific research regarding the activities and impact of fishery efforts. We should bear in mind that, even when speaking of artisanal systems, those that target species of good economic yields, such as the Red Snapper (L. purpureus), Acoupa Weakfish (C. acoupa), and Gillbacker Sea Catfish (A. parkeri) can theoretically continue to grow limitlessly due to the open access with no restrictions regarding the obtaining of licenses, thereby placing at risk the integrity of these stocks. A policy of precaution should prevail over all economic and political interests in order to protect the workplace of these laborers as well as the natural resources of the ecosystems. The small-scale artisanal fishery modalities appear to have less impact on the ecosystem and resources. However, social sustainability seems to be seriously compromised by the lack of working conditions, housing, social security system, education, etc. The fishermen have low average incomes, lower even than the neighboring population. The aspirations of these laborers are directly linked to improving living conditions and a fairer distribution of the benefits stemming from the exploitation of resources in order to enable them to escape social marginality (Pereira 2004). Despite the fact that most of the stakeholders live in small, traditional communities, they do not necessarily exhibit adequate levels of social organization nor efficient incentives for participative management, which makes these laborers all the more underprivileged as well as socially and politically isolated.
15.4
Recommendations
The main problems facing the Bragatine fishery sector are linked to the lack of public policies directed at avoiding over-exploitation as well as the increases in governmental financing and laborers arriving from other states, which lead to a larger fishing fleet and greater numbers of fishermen. Further problems can be traced to the lack of opportunities for social inclusion that promotes improvements in the quality of life of fishermen. In addition, monitoring failures avoid better understanding of the real situation. Thus, the following recommendations can contribute toward establishing the political and social means necessary for the achievement of greater sustainability. 1. Reformulate the policy for the obtaining of fishing licenses, and establish quotas for the fleets of all fishery systems, including artisanal systems 2. Diminish efforts in fisheries in which stocks have been proven to show signs of over-exploitation, such as Red Snapper and Lobster 3. Monitor catches and especially fishing efforts; make available these georeferenced data to any user via the Internet, thereby facilitating research on the sector 4. Increase the aggregate value of the products and yields of fisheries through conservation and improvement technologies in order to obtain greater economic gains without an increase in effort
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5. Encourage the multiplicity of productive activities for small-scale artisan fishermen, introducing alternatives that generate income to compensate for low economic yields, such as craftwork and eco-tourism 6. Create mechanisms for the allocation of products (fish market) shortening and optimizing the productive chain, which should generate greater profits for fishermen 7. Encourage the organization capacity of the diverse stakeholders and their representation in management agencies 8. Increase the education levels of the stakeholders in order to increase their participation in research and resource management 9. Prioritize co-management systems based on ecosystem conservation to ensure greater levels of sustainability.
References Almeida MAC, Isaac VJ, Brito CSF, Nunes JLG (2006) Evoluc¸a˜o da frota pesqueira que desembarca em Braganc¸a, litoral paraense. II Semina´rio de Gesta˜o Socioambiental para o Desenvolvimento Sustenta´vel da Aq€ uicultura e da Pesca no Brasil. Universidade Federal do Rio de Janeiro. CD de Resumos Arau´jo ARR (2006) Fishery statistics and commercialization of the mangrove crab, Ucides cordatus (L.), in Braganc¸a – Para´ – Brazil. PhD thesis, University Bremen, Bremen Braga CF (2002) Atividade pesqueira de larga escala nos portos de desembarque do estua´rio do rio Caete´, Braganc¸a-Para´. MSc thesis, UFPA, Braganc¸, PA Brito CSF, Furtado I Jr (2002) Boletim estatı´stico da pesca marı´tima e estuarina do Brasil – 1997 a 2002. CEPNOR/IBAMA, Bele´m, PA, p 56 Camargo M, Isaac VJ (2001) Os peixes estuarinos da regia˜o norte do Brasil: Lista de espe´cies e considerac¸o˜es sobre sua distribuic¸a˜o geogra´fica. Boletim do Museu Paraense Emı´lio Goeldi, Bele´m 17:133–156 CEPNOR/IBAMA (2007) Estatı´stica Pesqueira do Estado do Para´ (anos 1995 a 2004). http:// www.ibama.gov.br/cepnor/index.php?id_menu¼52. Accessed 16 Mar 2007 Espı´rito-Santo RV (2002) Caracterizac¸a˜o da atividade de desembarque da frota pesqueira artesanal de pequena escala na regia˜o estuarina do rio Caete´, municı´pio de Braganc¸a-Para´-Brasil. MSc thesis, UFPA, Braganc¸a, PA Glaser M (2006) Inter-relac¸o˜es entre o ecossistema manguezal, a economia local e a sustentabilidade social no estua´rio do Caete´, Norte do Brasil. In: Glaser M, Cabral N, Ribeiro AL (eds) Gente, ambiente e pesquisa. Manejo transdisciplinar no manguezal. NUMA/UFPA, Bele´m, pp 37–49 Glaser M, Grasso M (2000) Pesca em manguezais: dinaˆmica e dependeˆncia entre a economia e o ecossistema da bahia Caete´, nordeste do Para´ – Brasil. In: May PH, Neto FCV, Pozo VC (eds). Valorac¸a˜o econoˆmica da biodiversidade. Estudos de caso no Brasil. Projeto Estrate´gia Nacional de Biodiversidade – MMA/GEF/PNUD. Programa Nacional de Diversidade Biolo´gica – PRONABIO. http://info.worldbank.org/etools/docs/library/117318/mma.pdf. Accessed 21 Mar 2007 IBAMA (2005) Estatı´stica da Pesca 2004. Brasil. Grandes regio˜es e estados da federac¸a˜o. Brası´lia. http://www.ibama.gov.br/rec_pesqueiros/download.php?id_download¼77 Isaac VJ (2006) Reflexo˜es sobre uma polı´tica de desenvolvimento da pesca na Amazoˆnia. In: ´ guas e Ilhas. CEJUP, Bele´m, pp 321–344 Castro E (ed) Bele´m de A
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Isaac VJ, Santo RVE, Silva BB, Fre´dou FL, Moura˜o KRM, Fre´dou T (2009) An interdisciplinary evaluation of fishery production systems off the State of Para´ in North Brazil. J Appl Ichthyol 25:244–255 Nittrouer CA, Demaster DJ (1996) The Amazon shelf setting: tropical, energetic, and influenced by a large river. Cont Shelf Res 16:553–573 Pereira F (2004) Avaliac¸a˜o de impactos so´cio-ambientais causados por projetos de extensa˜o no litoral bragantino, Braganc¸a, PA. PhD thesis, UFPa, Bele´m PROVAM (1990) Programa de desenvolvimento integral do vale do Araguari (Estado do Amapa´) OEA SUDAM. Estudos Ba´sicos: Recursos Naturais e So´cio-Economia. Recursos Pesqueiros 7:77 SEAP (2006) Resultados do Recadastramento Nacional dos Pescadores do Brasil. Secretaria Especial de Aq€uicultura e Pesca da Presideˆncia da Repu´blica, Brası´lia, p 104 Silva BB (2004) Diagno´stico da Pesca no Litoral Paraense. Dissertac¸a˜o de Mestrado, Museu Paraense Emı´lio Goeldi, Universidade Federal do Para´
Part VI Ecology and Fishery of Mangrove Crabs
Chapter 16
The Brachyuran Crab Community of the Caete´ Estuary, North Brazil: Species Richness, Zonation and Abundance K. Diele, V. Koch, F.A. Abrunhosa, J. de Farias Lima, and D. de Jesus de Brito Simith
16.1
Background and Scope
Brachyuran crabs are a prominent faunal component of mangrove forests, both in the Atlantic East Pacific and Indo West Pacific bioregions. They play important ecological roles, e.g., as bioturbators, leaf and litter feeders, propagule predators, and as prey for many fish species (for comprehensive reviews, see Lee 1998; Cannicci et al. 2008; Lee 2008; Kristensen 2008). As recently stated by Cannicci et al. (2008) and Alongi (2009), a paradigm shift has occurred during the last 20 years, with crabs and other fauna now regarded as important actors in the structuring and functioning of mangrove forests, in addition to abiotic processes that had formerly been seen as the principal drivers. For a comprehensive understanding of the functioning of any given mangrove ecosystem, knowledge about local geophysical factors as well as the community and ecology of crabs (and other fauna) living therein is thus essential. We examine species richness, zonation and abundance of brachyuran crabs in tidal creeks and mangrove forests of the north Brazilian Caete´ estuary (see Chap. 3 for site description). Our study site is located in Para´ state, which harbors approx. 8,000 km2 of mostly pristine mangroves (Souza-Filho 2005). Our results provide a reference for monitoring biodiversity changes at this site and for comparisons with more disturbed areas with similar geomorphologic settings.
16.2
Species Richness and Zonation
Braganc¸a peninsula has approx. 160 km2 of typical species-poor eastern Atlantic mangroves composed of Rhizophora mangle (Rhizophoraceae), Avicennia germinans (Avicenniaceae), and Laguncularia racemosa (Combretaceae), in order of deceasing importance (see Sect. 6.1). For our crab inventory, sampling was conducted between 1996 and 2007 at 12 stations all across the peninsula, including tidal creeks, and one at Ilha Canela, a small island located 5 km off the eastern coast U. Saint-Paul and H. Schneider (eds.), Mangrove Dynamics and Management in North Brazil, Ecological Studies 211, DOI 10.1007/978-3-642-13457-9_16, # Springer-Verlag Berlin Heidelberg 2010
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of the peninsula (for map, see Chap. 3, Fig. 2.1). Both aquatic and terrestrial crabs were captured and identified, yielding a total of 29 species belonging to 10 families and 16 genera (Table 16.1). Five (15%) of the species found (Arenaeus cribrarius, Austinixa bragantina, Austinixa aidae, Panopeus bermudensis, Pinnixa gracilipes) have not formerly been registered in Para´ state (based upon species lists provided by Coelho and Ramos 1972; Coelho and Ramos-Porto 1981; Koch 1999; Barros and Pimentel 2001; Koch and Wolff 2002; Viana et al. 2003; Araujo Silva et al. 2002). The pinnotherid crab A. bragantina is a new species finding and was subsequently described by Coelho (2005). With a carapace width (CW) of below 10mm, pinnotherid crabs are by far the smallest crab species found in the Caete´ estuary. Of all species present, 55% have a maximum CW between 10 and 40 mm, 17% are medium-sized (40–60 mm) and another 17% reach a maximum size larger than 60 mm CW (Table 16.1). The largest captured specimen was a male Ucides cordatus with a CW of 99 mm. Drawings of all species recorded in the Caete´ estuary (except Cardisoma guanhumi and A. aidae) are shown in Fig. 16.1. Crabs were found across the entire tidal profile of the Caete´ estuary (Table 16.1). The gecarcinid C. guanhumi is the only supratidal species and occurs in salt marsh vegetation. Three sesarmid, two ocypodid species and an ucidid species dominate the high intertidal zone of the mangrove forest, which is inundated only during spring tides for a few hours each day (Table 16.1). A total of 15 species from six families occur across the mid- and low-intertidal zone in the mangroves while five species from three families were exclusively found on sandy beaches and exposed mudflats. In the subtidal zone, three portunid crabs, A. cribrarius, Callinectes bocourti, and Callinectes danae were registered (Table 16.1). A total of 66% of the species are bioturbators, i.e dig burrows in the sediment into which they retreat for shelter, and the three pinnotherid crabs live in burrows of callianassid shrimps. The remaining species hide between oyster shells, under mangrove roots, deadwood, beach debris or dig themselves into the sediment, without constructing burrows (Table 16.1). Of the 29 recorded brachyuran species, 18 are categorized as typical “mangrove crabs” (Table 16.1), on which we will focus in the following. These species occur in the mangrove forest habitat and are at least partially active in air outside their shelters and burrows during ebb tides (see also Burggren and Mc Mahon 1988 for definition of land crabs). As in many other areas of the world, the mangrove crab community of the Caete´ estuary is dominated by Ocypodidae and Sesarmidae, which together account for 78% of the species. In terms of biomass and abundance, ocypodid and ucidid crabs are the most important ones (see below). The zonation of the mangrove crabs was studied between 1996 and 1998 in a R. mangle- dominated stand, the most common forest type on the Caete´ peninsula. Zonation is pronounced with many species being restricted either to the high intertidal forest (“Forest”, F) or to the mid- and low-intertidal areas near creeks (small creek, SC; large creeks, LC) (Table 16.1, Fig. 16.2; Koch 1999). Aratus pisonii is an exclusively aboreal species and ascends high into mangrove trees. These crabs are also regularly encountered on stilt roots of R. mangle from where they jump into the water when disturbed. Another species climbing on mangrove stilt roots is Armases rubripes, but unlike
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Table 16.1 Brachyuran crabs of the Caete´ estuary including Ilha Canela Family Species Size Tidal Habitat Burrowing Comments Zone Grapsidae Goniopsis M H M F SC n Shelters under mangrove cruentata* roots, often near small creeks, very rapid runner Pachygrapsus S L M SC y On mudbanks and on gracilis* branches and under bases of mangrove trees near small creeks Planes cyaneus S L B n Only one specimen found, sheltering under beach debris Sesarmidae Aratus pisonii* S HM F n Aboreal on trunks, branches and prop roots of mangrove trees. Very rapid climber Armases S M F y Under roots and on dead angustipes* trees of marginal seaward mangroves Armases S M L SC y Under roots and trunks of benedicti* mangrove trees near small creeks Armases S H F y Under trunks of mangrove rubripes* trees Sesarma S M SC y Often at creek margins curacaoense* Sesarma rectum* S HM F y Mostly in shaded areas Gecarcinidae Cardisoma L S SM y In sandy soils with saltguanhumi marsh vegetation Ocypodidae Ocypode M H B y On sandy beaches. Forages quadrata at the water line. Very rapid runner Uca cumulanta* S M L SC MF y Mostly in silty sediments, often on shaded creek banks Uca maracoani* S L M LC y On banks of unshaded mangrove creeks Uca mordax* S M L SC y In areas with fresh water influence Uca rapax* S H F y In shaded as well as less shaded forest areas Uca thayeri* S M L SC y Mostly in shaded areas Uca vocator* S H F y Mostly in shaded areas Ucididae Ucides cordatus* L H F y Often near Rhizophora mangle roots, mostly in shaded areas L SU B n On sand only Portunidae Arenaeus cribrariusa Callinectes L SU LC n Aquatic, in larger bocourti mangrove creeks and adjacent coastal waters (continued)
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Table 16.1 (continued) Family Species Callinectes danae Pinnotheridae Austinixa bragantinaa
Austinixa aidaea
Pinnixa gracilipesa
Menippidae Panopeidae
Menippe nodifrons* Panopeus americanos
Size Tidal Habitat Burrowing Comments Zone L SU LC n Aquatic, in larger mangrove creeks and adjacent coastal waters SS L B MF n Shelters in burrows of the thalassinids Lepidophtalmus siriboia and Callichirus major SS L MF n Shelters in burrows of the thalassinid Lepidophtalmus siriboia SS L B MF n Shelters in burrows of the thalassinids Lepidophtalmus siriboia and Callichirus major M L SC MF y Shelters under rocks M
L
SC
y
S Panopeus bermudensisa Panopeus M lacustris*
L
SC LC n
ML
SC
y
Often under pieces of deadwood on creekbanks Shelters between oyster shells Often under mangrove deadwood on creek banks, between oyster shells In silty substrates
Eurytium S M L SC MF y limosum* The species categorized as mangrove crabs (see text for explanation) are highlighted with an asterisk. Size categories refer to the largest specimens found of each species (in mm carapace width: SS < 10; S 10 < 40, M 40 < 60, L > 60). Tidal zones: S supratidal, H, M and L high, mid and low intertidal, Su subtidal. Habitat types: F forest, SC small creek, LC large creek, B beach, MF mudflat, SM saltmarsh. Habitat assignments were based on where each species was found most frequently. Keys provided by Chace and Hobbs (1969), Powers (1977), Abele (1992), Coelho-Filho and Coelho (1996), Melo (1996) and Young (1998) were used for species identification a New species recordings for the state of Para´ Xanthidae
A. pisonii these crabs retreat to burrows constructed between the roots in the high intertidal. Uca rapax, Uca vocator and Sesarma rectum also occur mostly in the high intertidal forest (F), as does U. cordatus. However, juveniles of the latter species are also regularly found on shaded mudbanks of SC. Sesarma curacaoense, Armases angustipes and Goniopsis cruentata occur in mid-intertidal forest areas and along creek margins. Uca mordax, Uca thayeri, Armases benedicti, Eurytium limosum, Pachygrapsus gracilis, Panopeus lacustris, Uca cumulanta and Uca maracoani are found mostly throughout the mid- and low-intertidal. The latter is by far the dominant species on unshaded mudbanks of LC.
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Fig. 16.1 (continued)
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The Brachyuran Crab Community of the Caete´ Estuary, North Brazil
Fig. 16.1 Drawings of brachyuran crab species recorded in the Caete´ estuary (except Cardisoma guanhumi and A. aidae). All illustrated specimens are males. Note different scales. All drawings provided by de Farias Lima (unpublished)
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Fig. 16.2 Vertical zonation of the predominant mangrove crab species in a R. mangle-dominated forest stand. Modified after Koch (1999). ST spring tide, NT neap tide, HW high water level, LW low water level
Fig. 16.3 Species clusters and MDS plot of the predominant species in three habitat types (forest, small creek, large creek) within a R. mangle-dominated forest stand
The zonation pattern corresponds well to the three mangrove habitat types (F, SC, LC) and is clearly reflected in the cluster diagram and MDS plot (Fig. 16.3). Abiotic factors among habitats differ significantly: Silt/clay content is lowest in LC, organic matter highest in SC, sediment water content lowest in F, and air temperature at the sediment surface is highest at LC (Koch et al. 2005). These parameters appear to be the most important factors determining crab distribution patterns (Macnae 1968; Warner 1969; Frith and Brunnenmeister 1980; Jones 1984; Macintosh et al. 2002; Robertson and Alongi 1992; Frusher et al. 1994; Dahdouh-Guebas et al. 2002; Lim et al. 2005), other biotic factors are, e.g., forest structure, competition, predation and food availability (Ashton and Macintosh 2002; Ashton et al. 2003; Nobbs 2003; Piou et al. 2007, 2009). For the deposit-feeding fiddler crabs, a strong
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relationship between sediment characteristics and species distribution was found, depending on morphological features of their feeding appendices (Koch et al. 2005; Chap. 17). The litter-feeding crab U. cordatus prefers R. mangle-dominated forest stands over those dominated by A. germinans in the Caete´ estuary, as indicated by much higher crab densities and larger average crab size in the former habitat (Wessels 1999). Within these forest stands, U. cordatus aggregates near tall R. mangle trees. The even distribution of the crabs underneath these trees indicates intraspecific competition (Piou et al. 2009). Competition for leaf litter (Nordhaus et al. 2006) seems to be a main factor driving their spatial distribution (Piou et al. 2009; Chap. 20).
16.3
Abundance and Biomass
Average yearly abundance and biomass of the most abundant species are shown in Fig. 16.4, ranked according to their biomass and habitat type (F, SC, LC). The highest biomass values were found in F, followed by SC and LC. Abundance was
Fig. 16.4 Biomass and abundance (average SE) of mangrove crabs in three habitat types (forest, small creek, large creek) within a R. mangle-dominated forest stand. Modified after Koch and Wolff (2002)
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highest in SC, followed by LC and the high intertidal forest (Koch 1999; Koch and Wolff 2002). The biomass dominance of U. cordatus in the forest is outstanding (84%), followed by the fiddler crabs U. rapax and U. vocator. Other species are only of minor importance. Single species dominance is even more pronounced in LC with U. maracoani contributing >95% to the total biomass/abundance in this habitat. In SC, on the other hand, biomass is more evenly distributed between four species. In terms of abundance, however, U. cumulanta and P. gracilis are clearly dominant in this habitat. The dominance of U. maracoani on shadeless mudbanks of LC, where surface temperatures reach up to 40 C, is probably due to the temperature tolerance of this species, as indicated by respiration measurements (Koch 1999). While U. maracoani displays normal respiration rates up to a temperature of 37 C, all other fiddler and P. gracilis crabs already show signs of metabolic stress at 30–32 C. It is thus likely that the latter cannot deal with the high temperatures occurring regularly in this habitat. With 172 g m 2 fresh mass (Koch and Wolff 2002), total epifaunal biomass in the Caete´ mangrove forest is high when compared to values reported for mangrove systems elsewhere (e.g., Macintosh 1977; Lalana-Rueda and Gosselck 1986; Lee 1998; Wiedemeyer 1997). Much higher values, however, were found in low intertidal Costa Rican mangroves with biomass values of up to 1,200 g m 2 for mobile and sessile epifauna (Buettner 1997). While crabs completely dominate the epifauna of the high intertidal mangroves of the Caete´ estuary, balanids, bivalves and other filter feeders were dominant in the Costa Rican mangroves, probably as a result of the prolonged inundation periods. Filter feeders only feed when inundated and remain inactive during times of exposure, whereas crabs mostly forage during ebb tide and are better adapted to desiccation stress higher on the shore.
16.4
Biogeographic Comparison
Crab species-richness at our eastern Atlantic study site is much lower than in mangroves of the Indo West Pacific (IWP). For example in Singapore, Tan and Ng (1994) found 76 species and thus 47 more than we did, despite much smaller mangrove land coverage compared to the Caete´ estuary. Differences are most pronounced regarding ocypodid (36 species vs 7 in the Caete´ estuary) and sesarmid crabs (46 species vs 6 in the Caete´ estuary). High versus low mangrove crab diversity is characteristic for IWP and Atlantic East Pacific (AEP) regions, respectively, and parallels biogeographic differences in the number of mangrove tree species (Ellison 2008; Lee 2008). When considering the ecological roles of mangrove crabs, however, it seems that lower species diversity however, it seems that a lower species diversity does not necessarily translate to lower functional diversity: For example, similar litter removal rates of crabs were observed in IWP and AEP mangroves (Macnae 1968; Tan and Ng 1994) versus mostly only Ucides occidentalis (Pacific side of the Americas; Twilley et al. 1997) or U. cordatus (Atlantic side of the Americas; Nordhaus et al. 2006) in the latter biogeographic region. In the
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Caete´ estuary, total faunal biomass is about 132 g/m2, including the benthic and the pelagic part (Wolff et al. 2000). U. cordatus alone contributes 61% and the other crabs a further 12%, indicating their great importance in the mangrove ecosystem (see Chap. 17).
References Abele LG (1992) A review of the grapsid crab genus Sesarma (Crustacea: Decapoda: Grapsidae) in America, with the description of a new genus. Smithson Contrib Zool 527:60 Alongi DM (2009) The energetics of mangrove forests. Springer, Heidelberg Araujo Silva KC, Ramos-Porto M, Cintra IHA, Muniz APM, Silva MCN (2002) Crustaceos capturados durante o programa revisee na costa norte Brasileira. Bol Tec-Cient Cepenor 2:97–108 Ashton EC, Macintosh DJ (2002) Preliminary assessment of the plant diversity and community ecology of the Sematan mangrove forest, Sarawak, Malaysia. For Ecol Manage 166:111–129 Ashton EC, Macintosh DJ, Hogarth PJ (2003) A baseline study of the diversity and community ecology of crab and molluscan macrofauna in the Sematan mangrove forest, Sarawak, Malaysia. J Trop Ecol 19:127–142 Barros MP, Pimentel FR (2001) A fauna de decapoda (Crustacea) do estado do Para´, Brasil: Lista preliminar das espe´cies. Bol Mus Para Emı´lio Goeldi Se´r Zool 17:15–41 ¨ kologie der Wurzelgemeinschaft der roten Mangrove Rhizophora mangle Buettner H (1997) Zur O L. an der Pazifikk€ uste Costa Ricas. PhD thesis, University of Bremen, Bremen Burggren WW, Mc Mahon BR (1988) Biology of the land crabs: an introduction. In: Burggren WW, McMahon BR (eds) Biology of land crabs. Cambridge University Press, Cambridge, pp 1–4 Cannicci S, Burrows D, Fratini S, Smith TJ III, Offenberg J, Dadouh-Guebas F (2008) Faunal impact on vegetation structure and ecosystem function in mangrove forests: a review. Aquat Bot 89:186–200 Chace FA, Hobbs HH (1969) The freshwater and terrestrial decapod crustaceans of the West Indies with special reference to Dominica. Bredin-Archbold-Smithsonian biological survery of Dominica. Bull US Nat Mus Washington 292:258 Coelho PA (2005) Descric¸a˜o de Austinixa bragantina sp. nov. (Crustacea, Decapoda, Pinnotheirdae) do litoral do Para´, Brasil. Ver Brasil Zool 22:552–555 Coelho PA, Ramos MA (1972) A constituic¸a˜o e distribuic¸a˜o da fauna de deca´podos do litoral leste da Ame´rica do sul entre as latitudes de 5 e 39 S. Trab Oceanogr Univ Fed Pernambuco 13:133–236 Coelho PA, Ramos-Porto M (1981) Grapsidae do geˆnero Sesarma do Norte e Nordeste do Brasil (Crusta´cea, Decapoda) com especial refereˆncia a Pernambuco. An Encontr Zool Nord 3:176–185 Coelho-Filho PA, Coelho PA (1996) Sinopse dos Crusta´ceos Deca´podes Brasileiros (Famı´lia Xantidae). Trab Oceanogr Univ Fed Pernambuco 24:179–195 Dahdouh-Guebas F, Verneirt M, Cannicci S, Kairo JG, Tack JF, Koedam N (2002) An exploratory study on grapsid crab zonation in Kenyan mangroves. Wetl Ecol Manage 20:179–187 Ellison AM (2008) Managing mangroves with benthic biodiversity in mind: moving beyond roving banditry. J Sea Res 59:2–15 Frith DW, Brunnenmeister S (1980) Ecological and population studies of fiddler crabs (Ocypodidae, genus Uca) on a mangrove shore at Phuket Island, western peninsula Thailand. Crustaceana 39:157–184
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Frusher SD, Giddins RL, Smith TJ III (1994) Distribution and abundance of grapsid crabs in a mangrove estuary: effects of sediment characteristics, salinity tolerances and osmoregulatory ability. Estuaries 17:647–654 Jones D (1984) Crabs of the mangal ecosystem. In: Por F, Dor I (eds) Hydrobiology of the mangal. Junk, The Hague, pp 89–109 Koch V (1999) Epibenthic production and energy flow in the Caete´ mangrove estuary, North Brazil. PhD thesis, University of Bremen, Bremen. ZMT Contribution 6, Koch V, Wolff M (2002) Energy budget and ecological role of mangrove epibenthos in the Caete´ estuary, North Brazil. Mar Ecol Prog Ser 22:119–130 Koch V, Wolff M, Diele K (2005) Comparative population dynamics of four sympatric fiddler crab species (Ocypodidae, Genus Uca) for a North Brazilian mangrove ecosystem. Mar Ecol Prog Ser 291:177–188 Kristensen E (2008) Mangrove crabs as ecosystem engineers; with emphasis on sediment processes. J Sea Res 59:30–43 Lalana-Rueda R, Gosselck F (1986) Investigations of the benthos of mangrove coastal lagoons in Southern Cuba. Int Rev Gesamten Hydrobiol 71:779–794 Lee SY (1998) Ecological role of grapsid crabs in mangrove ecosystems: a review. Mar Freshw Res 49:335–343 Lee SY (2008) Mangrove macrobenthos: assemblages, services, and linkages. J Sea Res 59:16–29 Lim SSL, Lee PS, Diong CH (2005) Influence of biotope characteristics on the distribution of Uca lactea annulipes (H. Milne Edwards, 1837) and U. vocans (Linnaeus, 1758) (Crustacea: Brachyura: Ocypodidae) on Pulau Hantu Besar, Singapore. Raffles Bull Zool 53:111–114 Macintosh DJ (1977) Quantitative sampling and production estimates of fiddler crabs in a Malaysian mangrove. Mar Res Indonesia 18:59 Macintosh DJ, Ashton EC, Havanon S (2002) Mangrove rehabilitation and intertidal biodiversity: a study in the Ranong mangrove ecosystem, Thailand. Estuar Coast Shelf Sci 55:315–341 Macnae W (1968) A general account of the fauna and flora of mangrove swamps and forests in the Indo-West-Pacific region. Adv Mar Biol 6:73–170 Melo GA (1996) Manual de identificac¸a˜o dos brachyura (Caranguejos e Siris) do litoral brasileiro. Editora Pleˆiade/FAPESP, Sa˜o Paulo Nobbs M (2003) Effects of vegetation differ among three species of fiddler crabs (Uca spp.). J Exp Mar Biol Ecol 284:41–50 Nordhaus I, Wolff M, Diele K (2006) Litter processing and population food intake of the mangrove crab Ucides cordatus in a high intertidal forest in north Brazil. Estuar Coast Shelf Sci 67:239–250 Piou C, Berger U, Hildenbrandt H, Grimm V, Diele K, D’Lima C (2007) Simulating cryptic movements of a mangrove crab: recovery phenomena after small scale fishery. Ecol Modell 205:110–122 Piou C, Berger U, Feller IC (2009) Spatial structure of a leaf-removing crab population in a mangrove of North-Brazil. Wetl Ecol Manage 17:93–106 Powers LW (1977) A catalogue and bibliography to the crabs (Brachyura) of the Gulf of Mexico. Contrib Mar Sci 20:122–183 Robertson AI, Alongi DM (1992) Tropical mangrove ecosystems. American Geophysical Union, Washington, DC Souza-Filho PW (2005) Costa de manguezais de macromare´ da Amazoˆnia: cena´rios morfolo´gicos, mapeamento e quantificac¸a˜o de a´reas usando dados de sensores remotos. Rev Bras Geofı´s 23:427–435 Tan C, Ng P (1994) An annotated checklist of mangrove brachyuran crabs from Malaysia and Singapore. Hydrobiologia 285:75–84 Twilley RR, Pozo M, Rivera-Monroy VH, Zambrano R, Bodero A (1997) Litter dynamics in riverine mangrove forests in the Guavas River estuary, Ecuador. Oecologia 111:109–122
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Viana GFS, Ramos-Porto M, Santos MCF, Silva KCA, Cintra IHA, Cabral E, Torres MFA, Acioli FD (2003) Caranguejos coletados no Norte e Nordeste do Brasil durante o Programa REVIZEE (Crustacea, Decapoda, Brachyura). Bol Te´cn Cient CEPENE 11:117–144 Warner GF (1969) The occurrence and distribution of crabs in a Jamaican mangrove swamp. J Anim Ecol 38:379–389 Wessels L (1999) Untersuchungen zur r€aumlichen Verbreitung bodenlebender Landkrabben (Ocypodidae) in der Mangrove von Braganc¸a, Para´, Brasilien. Dipl thesis, University of Bonn, Bonn Wiedemeyer W (1997) Analysis of a benthic food web in a mangrove ecosystem at Northeastern Brazil. PhD thesis, University of Kiel, Kiel Wolff M, Koch V, Isaac V (2000) A trophic flow model of the Caete´ mangrove estuary, North Brazil, with considerations of the sustainable use of its resources. Estuar Coast Shelf Sci 50:789–803 Young PS (1998) Catalogue of Crustacea of Brazil. Museu Nacional, Rio de Janeiro
Chapter 17
Feeding Ecology and Ecological Role of North Brazilian Mangrove Crabs V. Koch and I. Nordhaus
17.1
Feeding Guilds
In high intertidal mangrove forests, litter- and deposit-feeding crabs usually dominate (Jones 1984; Koch 1999; Chap. 16), followed by omnivores and predators. Many species have a broad diet and categorization may be difficult, and even herbivorous crabs can become scavengers to get extra nitrogen (Wolcott 1988). In Brazilian mangrove forests, Ucides cordatus (Ucididae) and Aratus pisonii (Grapsidae) are the most important leaf-consuming crabs, but other species, e.g., Sesarma rectum (Sesarmidae), also exploit this resource (Lacerda et al. 1991; Brogim and Lana 1997; Schories et al. 2003; Nordhaus et al. 2006). While U. cordatus is a benthic crab and feeds on litter (i.e., fallen leaves, flowers and stipules) and propagules which are shed by mangrove trees (e.g., De Geraldes and De Calventi 1983; Nascimento 1993; Nordhaus et al. 2006), A. pisonii is arboreal and feeds on fresh mangrove leaves (Beever III et al. 1979; Erickson et al. 2003) but has also been reported to prey upon insects and hence may be considered omnivorous (Beever III et al. 1979). In the Caete´ estuary (as elsewhere in Brazil), U. cordatus constructs burrows with up to 2 m in length in the intertidal zone that are subdivided into a leaf cavity, where collected litter is ingested, and a living cavity, which provides groundwater contact (Schories et al. 2003). U. cordatus has a small foraging radius (max. 1 m) and mainly collects mangrove litter near its burrow entrance (Nordhaus 2004). Stomachs contain mangrove leaves (61.2 17.5%), unidentified plant material and detritus (28.0 17.0%), roots (4.9 6.3%), sediment (3.3 3.4%), bark (2.5 4.1%), and animal remains (0.1 0.4%). Crabs prefer leaves of Rhizophora mangle over Laguncularia racemosa and Avicennia germinans and yellow and brown leaves over green leaves (Nordhaus and Wolff 2007). U. cordatus was also observed to feed on epiphytic green and brown algae with a high N content that probably represent an important part of the diet. Bacterial biomass in the sediment and on leaf surfaces is low and most likely does not contribute much to the nutrition of the crabs (Nordhaus and Wolff 2007). U. cordatus did not feed on dead fish or crustaceans. However, juvenile crabs do feed on infauna (e.g., polychaetes) in the
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laboratory during the first 4 months of life, after which they switch to mangrove litter Diele and Koch (in press). Fiddler crabs (Genus Uca, Family Ocypodidae) make up by far the largest part of the biomass and abundance of deposit-feeding crabs in the mangrove ecosystem of Braganc¸a, Para´, followed by Pachygrapsus gracilis (Grapsidae) and several sesarmid crabs (Koch 1999; Chap. 16). Stomach contents of all deposit feeders consist of fine particulate organic matter and a small fraction of sediment; no animal or plant remains other than microalgae were identified (Koch 1999). Other authors have reported Uca spp. to also ingest some vascular plant material and macroalgae (Marguillier et al. 1997; Meziane and Tsuchiya 2002; Hsieh et al. 2002), but this was not confirmed for the species present in the Caete´ estuary. Fiddler crabs ingest small amounts of sediment and fill their buccal cavity with water; the setae on the second maxillipeds (feeding appendages) are then used to clean sediment particles from attached bacteria, microalgae and detritus (Miller 1961). Sediment is spat out in the form of little balls, and the lighter organic matter is swallowed (Crane 1975). Species with abundant spoon-tipped setae (sturdy setae with spoon-shaped cups at the tip) feed mostly on sandy sediments with low organic content while species feeding on muddy sediments with high organic content have primarily plumose (flexible, featherlike) setae (Altevogt 1957; Miller 1961; Icely and Jones 1978). Microscopic examination showed that the proportion of spoon-tipped setae is highest in Uca maracoani, followed by Uca rapax and Uca cumulanta, while Uca vocator possesses only plumose setae. This pattern was clearly reflected in the zonation of individual fiddler crab species (Koch 1999; Chap. 16). The sympatric occurrence of U. vocator and U. rapax in the forest seems to be partly made possible by their different feeding preferences, as the latter prefers more sandy sediments with lower organic content (Koch 1999; Koch et al. 2005; Chap. 16). The most important omnivorous mangrove crab in north Brazil appears to be Goniopsis cruentata (Grapsidae). This species feeds on fiddler crabs, mud and mangrove seedlings in the Caete´ mangroves (Koch, personal observation) and also in Recife, northeast Brazil (Wiedemeyer 1997). The predatory mud crab Eurytium limosum (Xanthidae) usually forages during high tide but was also observed to feed on fiddler crabs during ebb tides (Koch, personal observation). Stomachs of mud crabs contain mostly carapace fragments from fiddler crabs and in minor quantities pieces of polychaetes and infaunal bivalves (Koch 1999), suggesting that this species also digs for infaunal prey. These food items are consistent with those reported elsewhere in the world (Kneib and Weeks 1990; Lee and Kneib 1994).
17.2
Feeding Periodicity
The feeding periodicity was measured for the most abundant mangrove crabs in the Caete´ mangrove ecosystem to provide a better understanding of their feeding ecology and the factors that influence foraging behavior. Feeding periodicity of U. cordatus is not diurnal or tide-related, at least during neap tides when the forest is
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not inundated (Nordhaus et al. 2006). The species feeds more or less continuously as indicated by similar gastrointestinal contents throughout the 24-h period (Fig. 17.1). However, foraging activities outside the burrows are clearly light-dependent,
Fig. 17.1 Average gastrointestinal content (GIC) in dry weight (DW) as % of dry bodyweight of five deposit-feeding crabs (Uca spp., P. gracilis), a predatory crab (E. limosum) and a litter-feeding crab (U. cordatus) over a 24-h cycle (Data from Koch 1999 and Nordhaus 2004). Error bars are 95% confidence intervals, the broken line indicates tide level during the sampling period. Note that the y-axes have different scales
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increasing at dawn and decreasing after dusk, and litter was mostly collected during daytime. Thus, crabs feed inside their burrows on the collected litter at any time of day (Nordhaus 2004). During spring tides, U. cordatus stays more time inside burrows and rarely collects litter at the sediment surface, even when the forest is not inundated. All deposit feeders (Uca spp. and P. gracilis) showed a clear feeding periodicity over a 24-h cycle with the main feeding peak occurring during the day (Fig. 17.1). Secondary feeding peaks at night were present in all species dwelling in the lower intertidal (U. maracoani, U. cumulanta and P. gracilis). Here, feeding during the night is probably needed because foraging time during the day is restricted due to prolonged inundation (Macintosh 1988; Koch 1999). Feeding in all deposit-feeding species ceases when their burrows were covered by the tide, probably to avoid aquatic predators such as blue crabs, mud crabs, snake eels, catfish and pufferfish (Montague 1980; Warren 1990; Koch 1999). The predatory mud crab E. limosum also feeds more intensively during the day, with a secondary feeding peak at night. In contrast to the deposit-feeding species, it was more active when covered by water. Specimens were observed foraging under water and entering burrows of other crabs (mostly Uca spp.) where they probably consumed the inhabitants. However, E. limosum was also observed foraging and feeding when not covered by water (Koch, personal observation).
17.3
Food Intake
Average daily food intake (DFI in % of body weight) was calculated for all species. Egger’s model (Eggers 1977) was applied as it is statistically robust and provides good estimates of daily ration for various feeding regimes (Boisclair and Leggett 1988). DFI-values are highest for the five deposit-feeding species (22–32%), followed by U. cordatus (6.4%), and the predatory mud crab (6.2%) (Table 17.1). Consumption rates and energy intake of U. cordatus are at the high end of the range reported for litter-consuming sesarmid and gecarcinid crabs (Emmerson and Mc Gwynne 1992; Greenaway and Linton 1995; Greenaway and Raghaven 1998). The high DFI of U. cordatus is made possible by a large stomach, a moderate evacuation rate, and more or less continuous feeding. This, in combination with high assimilation efficiencies (38.6% of the energy in senescent R. mangle leaves), results in an efficient utilization of food, partly compensating for the low energy and N content of mangrove leaves (Nordhaus and Wolff 2007). Food storage in burrows by U. cordatus does not exceed several days (Nordhaus and Wolff 2007), contradicting studies on several sesarmid crabs that are assumed to let leaves age in burrows for several weeks to increase their nutritive value (e.g., Steinke et al. 1993). High litter removal and consumption rates and a low litter quantity in burrows suggest that the local crab population is food limited, at least during certain periods of the year (Nordhaus et al. 2006). The short-term storage of leaves allows crabs to
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Table 17.1 Average daily food intake (DFI) in DW, calculated with the Egger’s (1977) model Species Size range (mm) ER (h1) n DFI (% of DW 95% CI biomass) Ucides cordatus 65–75 0.31 243 6.4 4.8–8.4 Uca cumulanta 7–12 0.60 29 23.4 20.0–27.1 U. maracoani 10–32 0.47 32 30.6 26.4–35.2 U. rapax 11–21 0.59 26 32.2 28.2–35.9 U. vocator 13–21 0.62 23 22.1 17.8–26.1 Pachygrapsus gracilis 7–14 0.53 31 28.3 25.9–30.4 Eurytium limosum 10–36 0.33 31 6.2 5.2–7.4 Size range of animals used is given in mm carapace width; ER evacuation rate h1; n number of animals used to calculate ER; 95% CI confidence intervals. Data are based on Nordhaus (2004) for U. cordatus and on Koch (1999) for all other species
feed inside burrows, where they avoid predation and competition and where feeding is also possible during forest inundation (Nordhaus and Wolff 2007). Consumption rates of U. cordatus are significantly higher for yellow than for green R. mangle leaves, and are lowest for yellow and green A. germinans leaves. Surprisingly, assimilation rates for C and N are higher for senescent R. mangle than A. germinans leaves (Nordhaus and Wolff 2007). The latter have lower C/N ratios and a much lower tannin content (Nordhaus and Wolff 2007; Schmitt 2006) and should thus have a higher nutritive value. On the other hand, feces analyses showed that A. germinans leaves are tougher and more difficult to masticate and digest than Rhizophora leaves, thus lowering assimilation efficiencies (Nordhaus and Wolff 2007). Food preference of U. cordatus is therefore not determined by the C/N ratio, bulk N, and tannin content of litter material, which is in contrast to several studies on sesarmid crabs (e.g., Camilleri 1989). The higher assimilation rates for leaves with high tannin content indicate that endogenous enzymes or gut bacteria degrade tannin compounds (Nordhaus 2004). This is supported by Schmitt (2006) who found enzymes in the gut of U. cordatus that break down hydrolysable tannins. Deposit-feeding crabs have a much higher food consumption in comparison with all other species, which can be explained mainly by two factors: (1) the overall low nutritional value of the ingested food (detritus + sediment), and (2) the fact that they assimilate mainly bacteria, fungi, protozoa and some microalgae, which represent only a small fraction of the ingested material. The plant detritus itself is not digested, as fiddler crabs apparently lack the necessary enzymes and gut passage times are much too short to permit the breakdown of cellulose (Montague 1980; Robertson and Newell 1982b; Dye and Lasiak 1987). The lower DFI estimates of the fiddler crabs U. cumulanta and U. vocator, when compared to U. rapax and U. maracoani, can probably be explained by the different feeding adaptations described above. While the former two species are adapted to feeding on muddy sediments with a high organic content, the latter feed on sandy sediments with lower organic (and energy) content and their food intake is consequently higher. The total amount of food consumed by the five deposit-feeding species in forest, small and large creek habitats is 562, 431 and 2,146 g DW m2 year1 respectively
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Table 17.2 Total food consumption (FC) in dry weight (g DW m2 y1) of seven crab species (deposit-feeders ¼ D, Predators ¼ P, Leaf consumers ¼ L) from three mangrove habitats FC 95% CI Habitat Feeding Species FC guild (g DW m2 y1) (g DW m2 y1) Forest (F) L Ucides cordatus 1,419.4 1,159.3–1,663.5 D Uca cumulanta 41.1 35.1–47.6 D U. rapax 279.1 244.4–311.2 D U. vocator 242.3 195.2–286.2 Small Creek (SC) D U. cumulanta 76.5 65.4–88.6 D U. maracoani 196.6 169.62–226.2 D Pachygrapsus 158.0 144.6–169.7 gracilis P Eurytium limosum 43.8 40.1–52.4 Large Creek (LC) D U. maracoani 2,145.7 1,851.2–2,468.3 Calculations are given with 95% confidence intervals, calculated from the original DFI-estimates. Data are based on Nordhaus (2004) for U. cordatus and on Koch (1999) for all other species. Biomass data refer to Chap. 16 and Koch and Wolff (2002)
(Table 17.2; for biomass values see Chap. 16). The total quantity of sediment processed by the crabs is much higher as fiddler crabs retain <10% of the sediment taken in their buccal cavities (Robertson and Newell 1982a) and spit out the inorganic fraction. Thus, multiplying total consumption by 10 and converting to wet weight, about 9,000, 5,100 and 34,300 g of sediment (wet weight m2 year1) pass through the mouthparts of deposit feeding crabs in the high intertidal forest (F), small shaded creeks in the forest (SC), and unshaded banks of large creeks (LC), respectively (see Chap. 16). The average quantity of sediments for all habitats combined (weighed by their contribution to total area) was 10,400 g m2 year1, pointing towards the important role of deposit feeding crabs in nutrient remineralization and sediment chemistry (Koch 1999).
17.4
Ecological Role
To better understand why litter-consuming and deposit-feeding crabs are so important for nutrient cycling and energy flow in the Caete´ mangrove ecosystem, we will follow the fate of mangrove litter: part of the litter production is exported by the tides (Schories et al. 2003), but most mangrove litter and propagules (81 15%) are eaten by U. cordatus (Nordhaus et al. 2006). Litter retention is at the higher end of the values reported for sesarmid crabs in IndoWest Pacific mangroves, which bury 9–99% of the annual litter fall (Lee 1989; Robertson and Daniel 1989; Emmerson and Mc Gwynne 1992; Steinke et al. 1993). In our study area, a large part of the litter and propagule production (43.51% in a R. mangle-dominated forest stand) is returned to the sediment as finely shredded detritus through feces (7.13 t dm ha1 year1) by U. cordatus (Nordhaus and Wolff 2007). Feces have low C/N ratios and provide an excellent growth medium for microorganisms. Consequently, microbial biomass in feces of U. cordatus is
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much higher when compared to the sediment (Nordhaus 2004). Deposit-feeding crabs eat the litter detritus produced by U. cordatus and grind it into still smaller pieces, further increasing the surface area. The detritus thus serves as a culture medium for microorganisms rather than as an actual food source for the fiddler crabs (Montague 1980; Dye and Lasiak 1986, 1987). It appears to be a renewable resource in the sense that detritus particles can be repeatedly ingested and cleared from the bacteria growing on it, which has also been reported for other detritivores (Begon et al. 1996). As a result, litter-consuming and deposit-feeding crabs appear to enhance overall bacterial production in the mangrove soil by: (1) shredding of litter and enlargement of particle surface area through fragmentation in the cardiac stomachs, (2) concentration of organic matter in fecal pellets, (3) rejuvenation of microbial populations by grazing, and (4) oxygenation of the sediment through frequent overturn of the upper layers by feeding and by construction and maintenance of burrows (e.g., Montague 1980; Macintosh 1988; Genoni 1991; Nordhaus 2004). Hence, litter-consuming and deposit-feeding crabs seem to fulfil a function in the mangrove ecosystem that is similar to that of earthworms in terrestrial ecosystems (Koch and Wolff 2002). The mechanisms described above suggest that mangrove trees, crabs and bacteria form a positive feedback loop (Koch and Wolff 2002), where increased activity of any participant also benefits either directly or indirectly the activity of all others (Ulanowicz 1997). U. cordatus retains a large fraction of mangrove primary production within the forest, but assimilates only part of the available energy (Koch and Wolff 2002; Nordhaus and Wolff 2007). Mangrove trees benefit from the activity of crabs and bacteria because (1) nutrients and energy are retained, (2) nutrient remineralization is enhanced, and (3) the soil is aerated by the burrowing activity of the crabs, diminishing anoxic conditions and production of phytotoxins in the sediment (Smith III 1987). The existence of the positive feedback mechanisms is also strongly supported by the fact that mangrove primary production and secondary production of mangrove benthos in the Caete´ estuary are at the high end when compared to other mangrove ecosystems (Koch 1999; Wolff et al. 2000; Mehlig 2001; Koch and Wolff 2002; Bouillon et al. 2008). Also, fisheries yield of U. cordatus in the area is exceptionally high (7 tons km2) (Chap. 19). This underlines the important role of positive feedback mechanisms for the cycling and efficient use of energy and nutrients in the ecosystem (Koch and Wolff 2002).
References ¨ kologie und Physiologie indischer WinkerkAltevogt R (1957) Untersuchungen zur Biologie, O ¨ kol Tiere 46:1–110 rabben. Z Morph O Beever JW III, Simberloff D, King LL (1979) Herbivory and predation by the mangrove tree crab Aratus pisonii. Oecologia 43:317–328 Begon M, Harper JL, Townsend CR (1996) Ecology. Blackwell, Oxford Boisclair D, Leggett WC (1988) An in-situ experimental evaluation of the Elliott and Persson and the Eggers models for estimating fish daily rations. Can J Fish Aquat Sci 45:138–145
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Bouillon S, Borges AV, Diele K, Dittmar T, Duke NC, Kristensen E, Lee SY, Marchand C, Middelburg JJ, Rivera-Monroy VH, Smith TJ III, Twilley RR (2008) Mangrove production and fate: a revision of budget estimates. Global Biogeochem Cycles 22:GB2013, [2011–2012]. 4201 Brogim RA, Lana PC (1997) Espectro alimentar de Aratus pisonii, Chasmagnathus granulata e Sesarma rectum (Decapoda, Grapsidae) em um manguezal da Baia de Paranagua´. Parana´ Iheringia Ser Zool 83:35–43 Camilleri JC (1989) Leaf choice by crustaceans in a mangrove forest in Queensland. Mar Biol 102:453–459 Crane J (1975) Fiddler crabs of the world. Ocypodidae: genus Uca. Princeton University Press, New Jersey De Geraldes MG, De Calventi IB (1983) Estudios experimentales para el mantenimiento en cautiverio del cangrejo Ucides cordatus. Cienc Interam 23:41–53 Diele K, Koch V (in press) Growth and mortality of the mangrove crab Ucides. cordatus in N-Brazil. J Exp Mar Biol Ecol Dye AH, Lasiak TA (1986) Microbenthos, meiobenthos and fiddler crabs: trophic interactions in a tropical mangrove sediment. Mar Ecol Prog Ser 32:259–264 Dye AH, Lasiak TA (1987) Assimilation efficiencies of fiddler crabs and deposit-feeding gastropods from tropical mangrove sediment. Comp Biochem Physiol 87A:341–344 Eggers DM (1977) Factors in interpreting data obtined by diel sampling of fish stomachs. J Fish Res Board Can 34:290–294 Emmerson WD, Mc Gwynne LE (1992) Feeding and assimilation of mangrove leaves by the crab Sesarma meinerti de Man in relation to leaf-litter production in Mgazana, a warm-temperate southern African mangrove swamp. J Exp Mar Biol Ecol 157:41–53 Erickson AA, Saltis M, Bell SS, Dawes CJ (2003) Herbivore feeding preferences as measured by leaf damage and stomatal ingestion: a mangrove crab example. J Exp Mar Biol Ecol 289:123–138 Genoni GP (1991) Food limitation in salt marsh fiddler crabs Uca rapax (Smith) (Decapoda: Ocypodidae). J Exp Mar Biol Ecol 87:97–110 Greenaway P, Linton SM (1995) Dietary assimilation and food retention time in the herbivorous terrestrial crab Gecarcoidea natalis. Physiol Zool 68:1006–1028 Greenaway P, Raghaven S (1998) Digestive stragegies in two species of leaf-eating crabs (Brachyura: Gecarcinidae) in a rain forest. Physiol Zool 71:36–44 Hsieh H, Chen C, Chen Y, Yang H (2002) Diversity of benthic organic matter flows through polychaetes and crabs in a mangrove estuary: 13C and 34S signals. Mar Ecol Prog Ser 227:145–155 Icely JD, Jones DA (1978) Factors affecting the distribution of the genus Uca (Crustacea: Ocypodidae) on an East African shore. Estuar Coast Shelf Sci 6:315–325 Jones D (1984) Crabs of the mangal ecosystem. In: Por F, Dor I (eds) Hydrobiology of the mangal. Junk, The Hague, pp 89–109 Kneib RT, Weeks CA (1990) Intertidal distribution and feeding habits of the mud crab Eurytium limosum. Estuaries 13:462–468 Koch V (1999) Epibenthic production and energy flow in the Caete´ mangrove estuary, North Brazil. PhD thesis, University of Bremen, Bremen. ZMT Contribution vol 6 Koch V, Wolff M (2002) Energy budget and ecological role of mangrove epibenthos in the Caete´ estuary, North Brazil. Mar Ecol Prog Ser 22:119–130 Koch V, Wolff M, Diele K (2005) Comparative population dynamics of four sympatric fiddler crab species (Ocypodidae, Genus Uca) for a North Brazilian mangrove ecosystem. Mar Ecol Prog Ser 291:177–188 Lacerda LD, Silva CAR, Rezende CE, Martinelli LA (1991) Food sources for the mangrove tree crab Aratus pisonii: a carbon isotopic study. Rev Brasil 51:685–687 Lee SY (1989) The importance of sesarminae crabs Chiromanthes spp. and inundation frequency on mangrove (Kandelia candel (L.) Druce) leaf litter turnover in a Hong Kong tidal shrimp pond. Journal of Experimental Marine Biology and Ecology 131(1):23–43
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Lee SY, Kneib RT (1994) Effects of biogenic structure on prey consumption by the xanthid crabs Eurytium limosum and Panopeus herbstii in a salt-marsh. Mar Ecol Prog Ser 104:39–47 Macintosh DJ (1988) The ecology and physiology of decapods of mangrove swamps. In: Fincham A, Rainbow PS (eds) Aspects of decapod crustacean biology. Symp Zool Soc Lond, vol 59, pp 315–341 Marguillier S, van der Velde G, Dehairs F, Hemminga MA, Rajagopal S (1997) Trophic relationships in an interlinked mangrove-seagrass ecosystem as traced by 13C and 15N. Mar Ecol Prog Ser 151:115–121 Mehlig U (2001) Aspects of tree primary production in an equatorial mangrove forest in Brazil. Ph. D. thesis, University of Bremen, Bremen, ZMT Contribution vol 14 Meziane T, Tsuchiya M (2002) Organic matter in a subtropical mangrove-estuary subjected to wastewater discharge: origin and utilisation by two macrozoobenthic species. J Sea Res 47:1–11 Miller DC (1961) The feeding mechanisms of fiddler crabs, with ecological considerations of feeding adaptations. Zoologica 46:89–101 Montague CL (1980) A natural history of temperate Western Atlantic fiddler crabs (genus Uca) with reference to their impact on the salt marsh. Contrib Mar Sci 23:25–55 Nascimento SA (1993) Biologia do caranguejo-uc¸a´ (Ucides cordatus). ADEMA, Aracaju´ Nordhaus I (2004) Feeding ecology of the semi-terrestrial crab Ucides cordatus cordatus (Decapoda: Brachyura) in a mangrove forest in northern Brazil. Ph.D. thesis, University of Bremen, Bremen. ZMT Contribution vol 18 Nordhaus I, Wolff M (2007) Feeding ecology of the mangrove crab Ucides cordatus (Ocypodidae): food choice, food quality and assimilation efficiency. Mar Biol 15:1665–1681 Nordhaus I, Wolff M, Diele K (2006) Litter processing and population food intake of the mangrove crab Ucides cordatus in a high intertidal forest in northern Brazil. Estuar Coast Shelf Sci 67:239–250 Robertson AI, Daniel PA (1989) The influence of crabs on litter processing in high intertidal mangrove forests in tropical Australia. Oecologia 78:191–198 Robertson JR, Newell SY (1982a) Experimental studies of particle ingestion by the sand fiddler crab Uca pugilator (Bose). J Exp Mar Biol Ecol 59:1–21 Robertson JR, Newell SY (1982b) A study of particle ingestion by three fiddler crab species foraging on sandy sediments. J Exp Mar Biol Ecol 65:11–17 Schmitt BB (2006) Characterization of organic nitrogen compounds in sediment and leaves of a mangrove ecosystem in North Brazil. PhD thesis, University of Bremen, Bremen Schories D, Barletta-Bergan A, Barletta M, Krumme U, Mehlig U, Rademaker V (2003) The keystone role of leaf-removing crabs in mangrove forests of North Brazil. Wetl Ecol Manag 11:243–255 Smith TJ III (1987) Seed predation in relation to tree dominance and distribution in mangrove forests. Ecology 68:266–273 Steinke TD, Rajh A, Holland AJ (1993) The feeding behaviour of the red mangrove crab Sesarma meinerti De Man, 1887 (Crustacea: Decapoda: Grapsidae) and its effect on the degradation of mangrove leaf litter. Afr J Mar Sci 13:151–160 Ulanowicz RE (1997) Ecology, the ascendant perspective. Complexity in ecological systems. Columbia University Press, New York Warren JH (1990) Role of burrows as refuges from subtidal predators of temperate mangrove crabs. Mar Ecol Prog Ser 67:295–299 Wiedemeyer W (1997) Analysis of the benthic food web of a mangrove ecosystem at northeastern Brazil. Ph.D. thesis, Kiel University, Germany Wolcott TG (1988) Ecology. In: Burgren WW, McMahon BR (eds) Biology of the land crabs. Chapter 3. Cambridge University Press, Cambridge, UK, pp 55–96 Wolff M, Koch V, Isaac V (2000) A trophic flow model of the Caete´ mangrove estuary, North Brazil, with considerations of the sustainable use of its resources. Estuar Coast Shelf Sci 50:789–803
Chapter 18
Comparative Population Dynamics and Life Histories of North Brazilian Mangrove Crabs, Genera Uca and Ucides (Ocypodoidea) K. Diele and V. Koch
18.1
Individual Size, Population Size Structure and Sex Ratio
Ucides cordatus (Ucididae) and fiddler crabs (genus Uca, Ocypodidae) co-occur in Atlantic mangrove forests of the Americas. With a maximum size of more than 90 mm, Ucides is the largest mangrove crab species, while fiddler crabs are small to medium sized. Here, we present findings obtained in the north Brazilian Caete´ estuary, where both groups experience similar environmental conditions and were studied simultaneously. All crabs live in burrows dug in the intertidal zone and emerge when the forest is not inundated (Chap. 16.2). When outside their burrows, Ucides remains immobile half of the time (Nordhaus et al. 2009) and thus appears sluggish compared to the very active fiddler crabs. The population size structure of U. cordatus and of the four fiddler crabs differs strongly (sampling was conducted over 1 year in Rhizophora mangle-predominated forest stands, the most frequent forest type in the study area). All Uca populations are dominated by juveniles and smaller adults (positively skewed distributions), which is characteristic for fastgrowing and short-lived species (Hartnoll 1982; Hartnoll and Bryant 1990). In contrast, the population sampling of U. cordatus indicates a dominance of the larger specimens (Fig. 18.1; 81% of the crabs sampled in the forest have a carapace width, CW, of 50 mm or above; Diele et al. 2005). In this species, small crabs are abundant in peripheral habitats, such as larger forest gaps and along forest and creek margins. Here, 80% of all crabs have a CW of below 45 mm (n ¼ 1,396; Diele et al. 2005, and unpublished data). However, these habitats only cover approx 10–15% of the total area and therefore the effect on the size frequency distribution is rather small. The overall negatively skewed sizefrequency distribution of U. cordatus is typical for slow-growing and long-lived species, where crabs accumulate in the large size classes due to decreasing growth rates with age (Hartnoll 1982; Diele 2000; Diele and Koch, in press). The low number of large U. cordatus specimens in peripheral habitats reflects their preference for inner forest areas underneath mangrove trees and roots (Piou et al. 2009) that provide food and shelter. In peripheral habitats, smaller individuals
U. Saint-Paul and H. Schneider (eds.), Mangrove Dynamics and Management in North Brazil, Ecological Studies 211, DOI 10.1007/978-3-642-13457-9_18, # Springer-Verlag Berlin Heidelberg 2010
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Fig. 18.1 Population size structure of Ucides cordatus and four Uca species in the Caete´ estuary, north Brazil (U. cumulanta, U. maracoani, U. rapax, U. vocator). Modified after Diele et al. 2005 and Koch et al. 2005
benefit from the absence of the competitively dominant larger crabs, as the latter often suppress the foraging activity of smaller conspecifics in the forest (Diele 2000; Nordhaus et al. 2009). Intraspecific competition for food thus seems to be a driver for the observed spatial distribution of large versus small crabs in U. cordatus (Diele 2000; Piou et al. 2009; Chap. 20). In contrast, in the four Uca species, no spatial separation of juveniles and adults is apparent, possibly due to a lack of asymmetric competition for food.
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Fig. 18.2 Von Bertalanffy growth curves of the long-lived Ucides cordatus and the four shortlived fiddler crab species (Uca spp.), Caete´ estuary, north Brazil (see Table 18.1 for growth parameters). Growth curves of the latter are plotted in the small graphs which also show the initial part of the respective U. cordatus curve for better comparison. The large graph shows the entire U. cordatus growth curves. Growth curves are plotted until the age at which 95% of the maximum size is reached
Sex ratios in Uca maracoani and Uca vocator are approximately 1:1, while females significantly predominate in U. cumulanta (59%) and Uca rapax (56%) (Koch et al. 2005). In his review on sex ratio in marine crustaceans, Wenner (1972) outlined that deviations of the generally expected 1:1 sex ratio (Fisher 1930; Wilson and Pianka 1963) are the rule rather than the exception. A female dominance is not surprising in fiddler crab species such as U. cumulanta and U. rapax that have a promiscuous mating system where males compete for females (Wilson and Pianka 1963; Emlen 1973). U. cordatus is also promiscuous, but males are more abundant in the inner forest habitat (56%), while females dominate only in the peripheral areas (57%). In this species, males grow much larger and live longer than females (see Table 18.1 and Fig. 18.2), which results in the so-called anomalous sex ratio (sensu Wenner): Females are more abundant in intermediate size classes and males in large size-classes (Diele et al. 2005).
18.2
Growth and Mortality
Ocypodid and Ucidid crabs do not have a terminal molt, but continue molting after reaching sexual maturity. Growth increments of U. cordatus and Uca spp. were measured for specimens kept in field enclosures. For Ucides, the growth increment
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Table 18.1 Parameters of the von Bertalanffy growth function (L1 maximum size; K curving parameter) for males (M) and females (F) ucidid and ocypodid crabs of the Caete´ estuary, north Brazil, and the total mortality value (Z) K (year1) Max age F0 Z Species Sex Size range L1 (mm) (years) (mm) Ucides cordatus M 1.4–82.4 92.0 0.17 17.54 1.16 0.69 F 1.4–69.6 71.0 0.25 11.9 1.10 0.49 Uca cumulanta M 6.0–12.5 13.1 4.22 0.71 0.86 10.1 F 6.0–10.9 11.1 4.24 0.70 0.72 9.1 Uca maracoani M 7.0–24.6 35.2 2.03 1.47 1.40 4.9 F 7.0–25.3 31.0 2.44 1.23 1.37 6.0 Uca rapax M 6.9–18.0 20.5 2.08 1.44 0.94 4.6 F 7.1–18.0 20.0 2.15 1.40 0.93 5.5 Uca vocator M 6.6–20.0 21.6 2.71 1.10 1.10 5.7 F 6.5–19.3 20.6 2.91 1.01 1.09 7.6 The premolt size range over which growth was measured is shown. Maximum age is defined as the age where 95% of L1 is reached; F0 is Munros growth performance index (Pauly and Munro 1984; calculated basing upon L1 in cm and natural logarithm). Modified after Koch et al. (2005), Diele (2000), Diele and Koch (in press)
was measured for individually tagged crabs, while growth data in the smaller Uca spp. were analyzed indirectly with cohort analysis. The crabs released into the enclosures covered most of the size range for each of the five species, permitting a reliable calculation of growth curves (Table 18.1 and Fig. 18.2) (Koch et al. 2005; Diele and Koch, in press). The parameters calculated with the von Bertalanffy growth function are given in Table 18.1. The calculated maximum body size (L1) of Ucides is 86% and 62% larger than the one of the smallest (U. cumulanta) and largest fiddler crab species (U. maracoani), respectively. Males grow distinctly larger than females in Ucides (23%), Uca cumulanta (15%) and U. maracoani (12%), while maximum sizes in U. rapax and U. vocator differ by less than 5% between sexes. The growth coefficient K (curving parameter of the growth function) is 12–25 times lower in U. cordatus than in Uca spp. (Fig. 18.2 and Table 18.1), which translates into large differences for longevity: Ucides reaches 95% of L1 (¼tmax95) in 11.9–17.5 years, while tmax95 occurs in less than a year in U. cumulanta, and within 1–1.5 years in the remaining three Uca species (Table 18.1 and Fig. 18.2). Despite the very large differences in K and hence in longevity between Ucides and Uca spp., the growth performance index, F0 (Pauly and Munro 1984) which allows comparison of the growth of different species and taxonomic groups, varies only a little between the two genera. In Ucides, the low K value is compensated by the high L1. Overall, F0 is highest in U. maracoani and lowest in U. cumulanta (Table 18.1). Ucides shows intermediate values. Total annual mortality Z, calculated by the use of length-converted catch curves (Ricker 1975; Sparre et al. 1989; Koch et al. 2005; Diele and Koch, in press), varies both intra- and interspecifically. In Ucides and U. cumulanta, Z is 28 and 10% higher in males than in females, respectively, while a 16–25% higher female mortality was observed in the remaining fiddler crabs. Differences between Ucides
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and Uca spp. are large. Total mortality in the long-lived U. cordatus is 7- to 17-fold lower than in the shorter-lived fiddler crabs (Table 18.1). Crab racoons (Diele, personal observation) and estuarine fishes (Rozas and LaSalle 1990; Giarrizzo and Saint-Paul 2008) seem to be important natural predators of Ucides, followed by the less abundant capuchin monkeys and crab hawks. The much smaller fiddler crab species are also eaten by predatory crabs and by wading birds such as the scarlet ibis and egrets (Koch and Wolff 2002; Koch and Diele pers. observ). According to model assumptions of Wolff et al. (2000) (underlined by field observations by Giarrizzo and Saint-Paul 2008), consumption of fiddler crabs by natural predators can be at least 15 times higher than consumption of Ucides. In the Caete´ estuary, fiddler crabs thus play an important role as an alimentary base for many estuarine species (Koch 1999). Likewise, crabs of the family Sesarmidae are extensively preyed upon by estuarine fishes in Australia (Sheaves and Molony 2000). By offshore migration of cancrivorous fishes, substantial productivity of the mangrove ecosystem sequestered by crabs may be exported (Sheaves and Molony 2000). In contrast to the smaller Uca spp., the large Ucides is also exploited by man for subsistence and commercial use in the Caete´ estuary (Glaser and Diele 2004; Diele et al. 2005; Chap. 19) as elsewhere in Brazil (e.g. Ivo and Gesteira 1999; Alves et al. 2005). Its slow growth and long life span, however, suggests a high vulnerability to overfishing (Diele 2000; Diele et al. 2005; Chap. 19).
18.3
Reproduction
In U. cordatus, reproduction is characterized by cyclic mass mate-searching events (Alves 1975; Alcaˆntara-Filho 1978; Nascimento 1993; Nordi 1994; Diele 2000). In the Caete´ estuary, 4–5 of these locally called “andanc¸a”-events occur each year during the rainy season between January and May, with a clear peak in January or
Fig. 18.3 Breeding seasons and peak reproductive activity (striped fields) of Ucides cordatus and four fiddler crab species (Uca spp.) in the Caete´ estuary. Basing upon frequency of ovigerous females captured during population sampling (Koch et al. 2005; Diele et al. 2005)
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February (Fig. 18.3; Diele 2000). Unlike most of the year, when crabs show high burrow fidelity and quickly retreat when disturbed, during andanc¸a the forest floor is scattered with crabs, mostly males, walking around in search for mates, and males often fight with each other. Some crabs (both sexes) were also found climbing on roots 1–1.5 m above ground, a behavior never seen during non-andanc¸a times. Both males and females are hard-shelled during the breeding season, which allows copulations to take place outside the water, e.g., in entrances of burrows or on the forest floor (Diele, personal observation). Andanc¸a-events have a lunar or semilunar rhythm in the Caete´ estuary and elsewhere: crabs begin to exhibit matesearching behavior 1 or 2 days after full or new moon for up to 4 days (Nordi 1994; Diele 2000). Towards the end of andanc¸a, many weak and dead crabs, mostly males, are found on the forest floor (Diele, personal observation), suggesting that energy expenditure for this reproductive strategy is high. The latter is underlined by conspicuous foam production of crabs during andanc¸a days (Nordi 1994; D’Lima 2005), a behavior normally not displayed unless crabs are stressed, e.g., when handling them (Diele, personal observation). Foam may increase aerial ventilation in response to increased metabolic rates during stressful situations, such as andanc¸a (D’Lima 2005). During the last 2 days of andanc¸a events, females were often found inside their burrows or hidden underneath or on roots. There, they extruded the freshly fertilized egg mass. During subsequent egg incubation, which lasts for 3.5–4 weeks (Diele 2000), females are hidden and rarely seen. Larvae are released synchronously at spring tides when the mangrove forest is inundated (Diele 2000). From laboratory observations, we know that females can produce two broods per year, even without a new copulation in between (Diele, personal observation), corrobor` nna et al. ating the finding that spermatophores are stored in spermathecae (SantA 2007). However, field sampling of ovigerous females (and larvae) throughout the breeding season indicates that most females only breed once per year (Diele 2000). A low frequency of reproductive activities reduces nitrogen requirements per unit time (Linton and Greenaway 2007) and may thus be an adaptation of U. cordatus to its nutrient-poor diet (see further discussion in Sect. 18.4). Unlike in Ucides, mate searching in fiddler crabs is not restricted to just a few days per month. Male Uca spp. waving their distinctly enlarged cheliped can almost always be observed in the field, at least during the breeding season of the four species. U. rapax reproduces year-round, U. cumulanta during 9 months and the remaining two species during 6 months of the year (Fig. 18.3). Hence, breeding seasons in Uca spp. are prolonged in comparison to Ucides, enabling them to reproduce several times within a year. This explains the strong dominance of juvenile crabs in all Uca populations and ensures sufficient reproductive output despite short life spans (Table 18.2). As a result of the different body sizes and longevity, absolute size and age at the onset of maturity in females (OM, defined as the average size or age of the 5% smallest ovigerous crabs captured during population sampling; Koch et al. 2005) differs distinctly between Ucides and Uca spp. (Table 18.2). However, size and age at OM relative to maximum size (L195) and age (tmax95) are within the same range.
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Table 18.2 Reproductive parameters of Ucides cordatus and Uca spp. (average SD) females in the Caete´ estuary, north Brazil Species Size at OM (mm) Age at OM (years) n broods (year1) Ucides cordatus 39.6 0.4 (58.7%) 3.18 0.55 (26.7%) Mostly one Uca cumulanta 6.2 0.1 (58.5%) 0.20 0.01 (28.6%) Several Uca maracoani 18.0 0.3 (61.0%) 0.36 0.01 (29.3%) Several Uca rapax 7.4 0.2 (39.0%) 0.22 0.01 (15.7%) Several Uca vocator 9.9 1.0 (50.5%) 0.23 0.03 (22.7%) Several Size and age at the onset of maturity (OM) is defined as the average size or age of the 5% smallest ovigerous crabs captured during population sampling (Koch et al. 2005; Diele et al. 2005). Numbers in parentheses indicate size or age at OM relative to 95% of maximum size (L195) or 95% of maximum age (tmax95)
Ucides and most Uca species mature when they attain between 50 and 61% of L195 and 23–29% of tmax95; only U. rapax reaches maturity a little earlier (Table 18.2). Our definition of OM yields a similar value as for gonadal maturity in U. cordatus (the size at which 50% of the females are physiologically mature); however, we may have slightly overestimated OM in this species because smaller Ucides crabs, in contrast to the fiddler crabs (Koch et al. 2005), were probably not sampled quantitatively to the full extent (see 18.1). Even when considering only the smallest ovigerous Ucides female found in the field (29 mm; Diele 2000), the resulting relative size and age at OM still fall into the range of Uca spp. Both U. cordatus and the four fiddler crab species produce large numbers of small eggs and larvae (Vale 2003; Hattori and Pinheiro 2003; Koch, personal observation). Brood-care is restricted to incubation time, during which females actively moisture, oxygenate and clean their egg-clutches (Diele, personal observation). All species release their brood into estuarine waters. Due to the large tidal amplitude and strong currents prevalent in the study area (Chap. 3), it is very likely that the pelagic larvae, which undergo normal unabbreviated development, are exported to coastal waters and develop offshore, as shown for U. cordatus (Diele 2000; Diele and Simith 2006, 2007; Oliveira-Neto et al. 2007).
18.4
Contrasting Life Histories: Large, Long-Lived and Litter Feeding Versus Small, Short-Lived and Deposit Feeding
The five co-occurring mangrove crabs studied here live under very similar environmental conditions. Aspects of their life histories, however, differ fundamentally, reflected by the size frequency distributions of the crabs (negatively skewed in U. cordatus, positively skewed in Uca spp.), as well as their growth and mortality rates. We showed that the large mangrove crab U. cordatus grows slowly and has a long life-span in north Brazil, which is also reported from south Brazil (Pinheiro et al. 2005). In the Caete´ estuary, this species has a 12- to 25-fold lower growth
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coefficient (K) than the co-occurring fiddler cab species, a 7- to 17-fold lower total mortality (Z) and consequently individual life span is much longer (Table 18.1). However, the growth performance index of all five crab species is similar, which is in line with Pauly and Munros’ (1984) prediction for F0 for closely related species. In contrast to the marked differences in size and longevity, life history traits associated with reproduction are similar between Ucides and the fiddler crabs (except for the different mating behavior and the duration of the breeding seasons, see Table 18.3): Females mature at a roughly comparable size or age relative to maximum size or total life span, respectively, and produce large numbers of small eggs. The larval ecology of the five species also seems to be similar with larvae being exported to coastal waters, where probably only a very small fraction of them survive, as is assumed for planktotrophic larvae of benthic marine invertebrates (0.01%: Thorson 1946; 0.04%: Warner 1967 (Aratus pisonii); 0.16–3%: McConaugha 1992). The differing life history traits (except for reproduction) in Ucides and Uca spp. suggest that the crabs’ diets, which diverge markedly, may have contributed to the evolution of the observed differences. The combination of large body size, low metabolism and slow growth, as in Ucides, is typical for many semi-terrestrial and terrestrial crabs that feed mostly on leaf litter or salt marsh plants. It is likely to be an adaptive response to nitrogen limitation, long digestion times and poor energy content of their preferred food (Wolcott and Wolcott 1987; Wolcott and O’Connor 1992; Linton and Greenaway 2007). U. cordatus feeds more or less continuously on nutrient-poor and hard to digest tannin-rich mangrove leaf-litter (Nordhaus et al. 2006; Nordhaus and Wolff 2007; Chap. 17). This should select for a large stomach (and thus body size), increased gut length and volume and slow gut clearance time (Sibly 1981 in Wolcott and O’Connor 1992; Greenaway and Raghaven 1998; Diele 2000; Diele and Koch, in press) (it takes U. cordatus over 72 h to empty its digestive tract, see Nordhaus 2004 for review; Nordhaus and Wolff 2007). The poor nutrient quality and low digestibility of the food probably also explains the slow growth of Ucides. This is corroborated by a field study showing that crabs fed with a supplementary diet of fish and vegetable rich in nitrogen grew faster than those fed with leaf-litter only (Ostrensky et al. 1995). In contrast to Ucides, the deposit-feeding fiddler crabs process sediment and detritus. Overall, the sediment/ detritus mixture also has a low nutrient content, but fiddler crabs only assimilate the nutrient-rich microorganisms, such as bacteria, fungi, protozoa and microalgae. Their diet is thus much easier to digest than mangrove litter (Chap. 17). However, fiddler crabs must process large amounts of sediment and detritus to obtain sufficient nutrients. This is facilitated by very short gut passage times when compared to Ucides (3–4 h in Uca spp., Koch 1999, approx. 95% faster than in U. cordatus) and 1.5- to 2-fold higher evacuation rates (see Table 17.1). For a deposit-feeder, a smaller absolute body, a fast metabolism and rapid digestion thus seems to be advantageous when compared to large litter feeders with low metabolic rates and slow digestion. Hence, the diverging life histories of the fiddler crabs and U. cordatus can be better understood when considering their diets.
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References Alcaˆntara-Filho P (1978) Contribuic¸a˜o ao estudo da biologia e ecologia do caranguejo-uc¸a´, Ucides cordatus cordatus (Linnaeus, 1763) (Crustacea, Decapoda, Brachyura), no manguezal do Rio Ceara´ (Brasil). Arq Cienc Mar 18:1–41 Alves MMI (1975) Sobre a reproduc¸a˜o do caranguejo, Ucides cordatus (Linnaeus), em mangues do estado Ceara´ (Brasil). Arq Cienc Mar 15:85–91 Alves RRN, Nishida AK, Herna´ndez MIM (2005) Environmental perception of gatherers of the crab ‘caranguejo-uc¸a´’ (Ucides cordatus, Decapoda, Brachyura) affecting their collection attitudes. J Ethnobiol Ethnomed 1:1–8 D’Lima DCF (2005) Movement ecology of the mangrove crab Ucides cordatus (L.) (Decapoda: Brachyura) in the Caete´ estuary, N-Brazil. MSc thesis, University of Bremen, Bremen Diele K (2000) Life history and population structure of the exploited mangrove crab Ucides cordatus cordatus (Linnaeus, 1763) (Decapoda: Brachyura) in the Caete´ estuary, North Brazil. PhD thesis, University of Bremen, Bremen. ZMT Contribution vol 9 Diele K, Simith D (2006) Salinity tolerance of northern Brazilian mangrove crab larvae, Ucides cordatus (Ocypodidae): necessity for larval export? Estuar Coast Shelf Sci 68:600–608 Diele K, Simith D (2007) Effects of substrata and conspecific odour on the metamorphosis of mangrove crab megalopae, Ucides cordatus (Ocypodidae). J Exp Mar Biol Ecol 348:174–182 Diele K, Koch V (in press) Growth and mortality of the exploited mangrove crab Ucides cordatus (Ucididae) in north Brazil. J Exp Mar Biol Ecol Diele K, Koch V, Saint-Paul U (2005) Population structure, catch composition and CPUE of the artisanally harvested mangrove crab Ucides cordatus: indications for overfishing? Aquat Living Resour 18:169–178 Emlen JM (1973) Ecology: an evolutionary approach. Addison-Wesley, Reading, MA Fisher RA (1930) The genetical theory of natural selection. Clarendon, Oxford Giarrizzo T, Saint-Paul U (2008) Ontogenetic and seasonal shifts in the diet of Pemeceu sea catfish Sciades herzbergii (Siluriformes: Ariidae) from a macrotidal mangrove creek in the Curuc¸a´ estuary (North Brazil). Rev Biol Trop 56:861–873 Glaser M, Diele K (2004) Asymmetric outcomes: assessing central aspects of the biological, economic and social sustainability of a mangrove crab fishery, Ucides cordatus (Ocypodidae), in North Brazil. Ecol Econ 49:361–373 Greenaway P, Raghaven S (1998) Digestive strategies in two species of leaf-eating crabs (Brachyura: Gecarcinidae) in a rain forest. Physiol Zool 71:36–44 Hartnoll RG (1982) Growth. In: Abele LG (ed) The biology of Crustacea, vol 2, Embryology, morphology and genetics. Academic, New York, pp 111–196 Hartnoll RG, Bryant AD (1990) Size-frequency distributions in decapod crustacea – the quick, the dead, and the cast-offs. J Crustac Biol 10:14–19 Hattori GY, Pinheiro MAA (2003) Fertilidade do caranguejo do mangue Ucides cordatus (Linnaeus 1763) (Crustacea, Brachyura, Ocypodidae) em Iguape (Sa˜o Paulo, Brasil). Rev Bras Zool 20:309–313 Ivo CTC, Gesteira TCV (1999) Sinopse das observac¸o˜es sobre a bioecologia e pesca do caranguejo-uca Ucides cordatus cordatus (Linnaeus 1763) capturado em estua´rios de sua a´rea de occorencia no Brasil. Bol Tech Cient Cepene 7:9–51 Koch V (1999) Epibenthic production and energy flow in the Caete´ mangrove estuary, North Brazil. PhD thesis, University of Bremen, Bremen. ZMT Contribution vol 6, Koch V, Wolff M (2002) Energy budget and ecological role of mangrove epibenthos in the Caete´ estuary, North Brazil. Mar Ecol Prog Ser 22:119–130 Koch V, Wolff M, Diele K (2005) Comparative population dynamics of four sympatric fiddler crab species (Ocypodidae, Genus Uca) for a north brazilian mangrove ecosystem. Mar Ecol Prog Ser 291:177–188
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Linton SM, Greenaway P (2007) A review of feeding and nutrition of herbivorous land crabs: adaptations to low quality plant diets. J Comp Physiol B 177:269–286 McConaugha JR (1992) Decapod larva: dispersal, mortality and ecology. Am Zool 32:512–523 Nascimento SA (1993) Biologia do caranguejo-uc¸a´ (Ucides cordatus). ADEMA, Aracaju´ Nordhaus I, Wolff M (2007) Feeding ecology of the mangrove crab Ucides cordatus (Ocypodidae): food choice, food quality and assimilation efficiency. Mar Biol 151:1665–1681 Nordhaus I, Wolff M, Diele K (2006) Litter processing and population food intake of the mangrove crab Ucides cordatus in a high intertidal forest in north Brazil. Estuar Coast Shelf Sci 67:239–250 Nordhaus I, Diele K, Wolff M (2009) Activity pattern, feeding and burrowing behaviour of the crab Ucides cordatus (Ucididae) in a high intertidal mangrove forest in North Brazil. J Exp Mar Biol Ecol 374:104–112 Nordi N (1994) A captura do caranguejo-uca´ (Ucides cordatus) durante o evento reprodutivo da espe´cies: O ponto de Vista dos caranguejeiros. Rev Nordest Biol 9:41–47 Nordhaus I (2004) Feeding ecology of the semi-terrestrial crab Ucides cordatus (Decapoda: Brachyura) in a mangrove forest in Northern Brazil. Phd thesis, University of Bremen, Bremen. ZMT Contribution vol 18 Oliveira-Neto JF, Boeger WA, Pie MR, Ostrensky A, Hungria DB (2007) Genetic structure of populations of the mangrove crab Ucides cordatus (Decapoda: Ocypodidae) at local and regional scales. Hydrobiologia 583:69–76 Ostrensky A, Sternhain US, Brun E, Wegbecher FX, Pestana D (1995) Technical and economic feasibility analysis of the culture of the land crab Ucides cordatus (Linnaeus, 1763) in Parana´ coast, Brazil. Arq Biol Technol 38:939–947 Pauly D, Munro JL (1984) Once more on the comparison of growth in fish and invertebrates. Fishbyte 2:85 Pinheiro MAAP, Fiscarelli AG, Hattori GY (2005) Growth of the mangrove crab Ucides cordatus (Brachyura, Ocypodidae). J Crustac Biol 25:293–301 Piou C, Berger U, Hildenbrandt H, Grimm V, Diele K, D’Lima C (2007) Simulating cryptic movements of a mangrove crab: recovery phenomena after small scale fishery. Ecol Model 205:110–122 Piou C, Berger U, Feller IC (2009) Spatial structure of a leaf-removing crab population in a mangrove of North-Brazil. Wetl Ecol Manage 17:93–106 Ricker WE (1975) Computation and interpretation of biological statistics of fish populations. Bull Fish Res Board Can 191:1–382 ` nna BS, Pinheiro MAA, Mataquueiro M, Zara FJ (2007) Spermathecae of the mangrove crab SantA Ucides cordatus: a histological and histochemical view. J Mar Biol Assoc 87:903–911 Sheaves M, Molony B (2000) Short-circuit in the mangrove food chain. Mar Ecol Prog Ser 199:97–109 Sibly RM (1981) Strategies of digestion and defecation. In: Townsend CR, Calow P (eds) Physiological ecology: an evolutionary approach to resource use. Sinauer, Sunderland, pp 109–139 Sparre PU, Ursin E, Venema SC (1989) Introduction to tropical fish stock assessment part 1. FAO Fisheries Technical Paper 306/1, Rome Thorson G (1946) Reproduction and larval development of Danish marine bottom invertebrates, with special reference to the planktonic larvae in the sound (Oresund). Meddelser fra Kommissionen for Danmarks Fiskeri- og Havunderogelser, Serie Plankton vol 4, CA Reitzels, Kopenhagen Vale PAA (2003) Biologia reprodutiva do caranguejo Ucides cordatus cordatus (Linnaeus 1763), num manguezal do estua´rio do rio Caete´. MSc thesis, University of Para´, Bele´m Warner GF (1967) The life-history of the mangrove tree crab, Aratus pisonii. J Zool (Lond) 153:321–335 Wenner AM (1972) Sex ratio as a function of size in marine crustacea. Am Nat 106:321–350
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Wilson MF, Pianka ER (1963) Sexual selection, sex ratio and mating systems. Am Nat 97:405–407 Wolcott DL, O’Connor NJ (1992) Herbivory in crabs: adaptations and ecological considerations. Am Zool 32:370–381 Wolcott DL, Wolcott TG (1987) Nitrogen limitation in the herbivorous land crab Cardisoma guanhumi. Physiol Zool 60:262–268 Wolff M, Koch V, Isaac V (2000) A trophic flow model of the Caete´ mangrove estuary, North Brazil, with considerations of the sustainable use of its resources. Estuar Coast Shelf Sci 50:789–803
Chapter 19
Artisanal Fishery of the Mangrove Crab Ucides cordatus (Ucididae) and First Steps Toward a Successful Co-Management in Braganc¸a, North Brazil K. Diele, A.R.R. Arau´jo, M. Glaser, and U. Salzmann
19.1
Background and Scope
In Brazil, the large semi-terrestrial mangrove crab Ucides cordatus sustains an artisanal fishery of considerable economic and social significance. In contrast to many other fisheries, this crab species can be captured without costly equipment, thus providing an important income opportunity for the coastal poor. Between 2001 and 2005, the average national annual yield was 10,644 1,251 tons (IBAMA 2003, 2004a, 2004b, 2005, 2007), and 50% of the crabs were landed in the northern state of Para´, which harbors approx. one-third of the country’s mangroves (3,894 km2; calculated after Kjervfe and Lacerda 1993). U. cordatus, nationwide referred to as caranguejo-uc¸a´, is also of substantial cultural importance. Its fishery may reach back into pre-historic times as suggested by a 1,000- to 3,000-year-old ornamented clay artefact of a Ucides cephalothorax excavated on the Island of Marajo (Fig. 19.1). Today, thanks-giving festivals with dancers dressed in costumes made entirely of crab legs and shells are held annually in many villages along the coast of northern Brazil (Fig. 19.2). In recent years, Brazilian media have frequently reported on declines in mangrove crab populations. U. cordatus is a long-living species with slow growth and is thus potentially vulnerable to environmental impacts (Diele et al. 2005; Chap. 18). Significant population declines have occurred in several north-eastern and southern states of Brazil, mostly due to forest degradation and a fungal disease causing massive crab mortalities (Boeger et al. 2005). As a result, fisheries in affected areas are collapsing, leaving numerous dependent rural coastal families with reduced protein supplies and income. In northern Brazil, Ucides populations have not yet been affected by the fungus. The district of Braganc¸a in Para´ state (Fig. 19.3) still sustains an artisanal crab fishery with the considerable yield of 7 tons per km2 (Diele and Simith 2007; calculated after Arau´jo 2006), despite commercial exploitation ongoing for over 30 years. This region thus offers a unique opportunity for examining the functioning of this small-scale crab fishery in a “healthy” mangrove forest. Here, we present the main outcomes from our fisheries monitoring
U. Saint-Paul and H. Schneider (eds.), Mangrove Dynamics and Management in North Brazil, Ecological Studies 211, DOI 10.1007/978-3-642-13457-9_19, # Springer-Verlag Berlin Heidelberg 2010
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Fig. 19.1 1,000- to 3,000year-old clay artefact of the mangrove crab U. cordatus (Museo Forte do Castelo, Bele´m, Para´). Excavated at Marajo´ Island near the mouth of the Amazon river, Brazil (Museo Forte do Castelo, Bele´m, Para´, personal communication). Photo K. Diele
Fig. 19.2 Girl dancing at thanksgiving festival in Acarajo´, north Brazil. Her dress is made entirely out of the shell from U. cordatus legs. Photo K. Diele
programme conducted in Braganc¸a district between 1997 and 2005, and outline the significance of our participatory approach.
19.2
Capture Areas, Capture Techniques and Effort
A census in 1997 revealed that 42% (n ¼ 1,050) of all rural coastal households in Braganc¸a district are collecting and selling crabs (Glaser 2003). Current U. cordatus fisheries legislation permits crab capture most of the year (further details in sec. 19.4)
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Fig. 19.3 Capture grounds of crab collectors living in Braganc¸a district (modified after Arau´jo 2006). Dashed lines: district borders, Stretched lines: border of the Caete´-Taperac¸u Extractive Reserve
and does not contain spatial restrictions. The capture areas of Braganc¸a district extend over approximately 100 km of coastline, comprising the Braganc¸a and Taperac¸u´ Peninsulas and also mangrove forests of the adjacent western and eastern districts such as Tracuateua and Agosto Correia (Fig. 19.3; Arau´jo 2006). The coast is mostly undeveloped by man, but the forests are reachable through rivers and tidal creeks with canoes or small motorised boats. Only Braganc¸a peninsula has a paved road which greatly facilitates access for motorised vehicles. During the 9 years of our fisheries monitoring, the capture of U. cordatus was of an overall open access nature. However, residency and capture areas are generally linked since this provides easier access for crab collectors. Overlaps between villages are mostly avoided (Fig. 19.3). For example, crab collectors from Tamatateua village exploit the western mangroves
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only, while those from Treme work in eastern mangroves, including the eastern shores of the Braganc¸a peninsula (Arau´jo 2006; Fig. 19.3). The Braganc¸a peninsula is also the main capture area for people from Braganc¸a, Acarajo´ and Bacuriteua, who exploit the central and northern mangroves of this area. Villagers from Caratateua also collect crabs on the Braganc¸a peninsula but focus on its south-eastern as well as western shores (Arau´jo 2006). However, in 1998 and 1999, Caratateua crab collectors began to harvest the northern part of the peninsula (Furo Grande; Fig. 19.3), which provoked a conflict with already established resource users (Glaser and Diele 2004). As a result, people from Caratateua ceased to work in these areas in subsequent years. This demonstrates that informal local tenure arrangements and self-organization do, to some extent, regulate access to capture grounds in Braganc¸a district, despite the overall open access nature of this crab fishery. U. cordatus is harvested during daytime and ebb tide, when the forest floor is not inundated. Crab collectors spend an average of 4 h for capture. Depending upon distance and tidal phase, up to 4 h are additionally needed for travelling to and from capture locations and also for other capture preparations such as making strings for tying crabs (see below) or rolling cigarettes whose fumes act as a mosquito repellent (Arau´jo 2006). Crabs dwell in up to 2-m-deep burrows and crab collectors use either the full length of their arm (“brac¸eamento”; Fig. 19.4a) or a wooden stick with an iron hook (“gancho”) to grab them (Diele et al. 2005). The work is physically
Fig. 19.4 (a) Crab collector catching with “brac¸eamento”-technique (note that his right arm is fully inserted into the sediment) Photo K. Diele. (b) Participants of the crab fisheries monitoring programme. Photo K. Diele. (c) Crab collectors with “cambadas”. Photo R.M. Saraiva. (d) Women picking crab meat. Photo A.R. Arau´jo
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demanding and therefore only conducted by men. “Brac¸eamento” and “gancho” are long-established traditional capture techniques and Braganc¸a district is one of the few areas nationwide where they are still exclusively used today. In other areas of Para´ state (e.g., Sa˜o Caetano de Odivela), an illegal technique called “lac¸o” is now more popular. Here crabs are caught by deploying a nylon string onto their burrow entrances which entangles them when they emerge. The use of “lac¸o” facilitates the work of the crab collectors as it renders it unnecessary to reach down into the crabs’ burrows. However, a severe disadvantage of the “lac¸o” and other more recent capture techniques is that they can be deployed to any type of crab burrow (including small ones and those obstructed by roots, see below), thereby increasing the risk of overfishing (Diele et al. 2005). In forest areas such as near Sa˜o Caetano de Odivela, where these new capture techniques are used, crab populations have suffered distinct declines. “Brac¸eamento” and “gancho”, in contrast, only allow the catching of crabs from burrows that are not obscured by roots and thus easily penetrable. Hence, dense patches of mangrove roots act as natural refugia and buffers against rapid overfishing when using these traditional techniques (Diele et al. 2005; see also Chap. 20). In 2003, we determined the effort and yield of crab collectors from Braganc¸a district for all capture grounds (Fig. 19.3.; Arau´jo 2006). Each day and at all major landing points, contracted students from the fishing villages interviewed crab collectors returning from work (Fig 19.4b) about capture and landing locations, number of working men and collected crabs, hours of capturing etc. Truck and bus drivers who pick up landed crabs along the road were also involved in this monitoring. Prices at first level of commercialization and information about crab marketing systems were also noted (see Sect. 19.5). More than 60,000 datasets were collected on 353 days in 2003 and processed in a GIS-Access database. The results show that the Braganc¸a peninsula is only exploited by the district’s own crab collectors. The average daily number of working men (¼ man-days) on the peninsula in 2003 was 120.79 104.62 (maximum: 988, minimum: 2) with a total annual number of 42,758 man-days (Arau´jo 2006). When referring to the ca. 140 km2 of fishable mangrove forest on the Braganc¸a peninsula (Diele et al. 2005), this translates into 305 man-days per km2 per year and thus to less than a man per day per km2. It is noteworthy that 12% of the total peninsula crab fishery man-days in 2003 occurred on only 8 days. These were the days of the annual mate-searching events (locally called “andanc¸a”; see Chap. 18). In addition to the work performed by regular crab collectors, many “non-professionals” go crab fishing during “andanc¸a” days, as mate-searching crabs can be easily collected on the ground rather than from the burrows. Capture of U. cordatus during andanc¸a-events is, however, prohibited by law (see Sect. 19.4), but enforcement is virtually non-existent.
19.3
Standing Stock and Fishery Yields
Average density of U. cordatus in Rhizophora mangle-dominated forest stands of the northern part of Braganc¸a peninsula is about 1,650,000 indiv. km1 (data derived from crab sampling conducted over 13 months; Diele 2000; Diele et al. 2005).
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Considering the entire fished mangrove area on the peninsula (approx. 140 km2), this adds up to a population size of approx. 232 million crabs. Compared to other large semi-terrestrial or terrestrial crabs (e.g., Gecarcinus ruricula on San Andres Archipelago, Colombia: 217,400 indiv. km2, Hartnoll et al. 2006; Cardisoma carnifex on Aldabra, Seychelles: 360,000 indiv. km2, Alexander 1979; Gecarcoidea natalis on Christmas Island, Australia: 1,190,000 indiv. km2, Hicks 1985; Gecarcinus planatus on Clipperton Atoll, France: 6,000,000 indiv. km2, Ehrhardt 1968), the above values are at the higher end and underline the high productivity of the Braganc¸a mangroves (see also Chap. 17). Between 1997 and 2005, a resident fisherman was engaged by the MADAM project to monitor the daily crab landings at the tidal channel Furo Grande, a major landing point in the northern part of the Braganc¸a peninsula (noted information included: number of fishermen, number of crabs caught per person, name of capture locations, type of transportation, time spent for capture and time spent for travel, sex of the crabs, price at first commercialization level; carapace width of the landed crabs was additionally measured once per week) (Fig. 19.3). During the 9 study years, only male crabs for the live crab marketing system (see 19.5) were harvested at Furo Grande. When asked about the reasons for their preference for male crabs, crab collectors typically answer: “we will deplete caranguejo-uc¸a´ if we take the females” or “we want only large crabs, but females are smaller” (for different maximum sizes of males and females, see Chap. 18). Average annual landings observed at Furo Grande between 1997 and 2005 were 817,418 58,782 specimens (Diele et al. 2005; Diele, unpublished), which is 22% below the annual maximum sustainable yield estimated by the Sch€afer model (1,044,881 crabs). Arau´jo (2006) showed that, in 2003, 36% of all crabs captured on the peninsula originated from Furo Grande, underlining the importance of this capture area. The fact that fisheries landings at Furo Grande were well below the calculated maximum sustainable yield suggests that this area is still not overexploited. This is also indicated by a 9 years analysis (1997–2005) of catch per unit effort data (CPUE; the unit of effort considered here is one man-day). While in three consecutive years (1998–2000) CPUE decreased by anually 5–7%, it increased again during the last 5 years of the monitoring programme by annually 0.54–5.2% (Diele et al. 2005; Diele, unpublished data; 4.2% total decline between 1997 and 2005). Another time series focusing on the size of the captured crabs further indicates that the fishery is still biologically sustainable. Between 1998 and 2005, the mean size (carapace width, CW) of crabs captured at Furo Grande for the live market (males only) was 74.04 0.43 mm CW (data pooled, n ¼ 81,456; current legal minimum capture size is 60 mm; see Sect. 19.4). Annual averages differed at the most by 2.5 mm, without showing any particular trend in either direction (Glaser and Diele 2004; Diele et al. 2005; Diele, unpublished). In contrast to the crab collectors working for the live crab market, those supplying the meat processing market (see Sect. 19.5) are less size and sex selective: average size of males landed between 1998 and 2000 was 64.5 0.68 mm (n ¼ 3,400, sampling location Caratateua village) and 5.7% of the measured crabs were females (mean CW 55.5 0.41, n ¼ 204). Irrespective of the destined marketing system, overall
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crab collectors of Braganc¸a district mainly target large and mature specimens, allowing crabs to reproduce before being captured: The size at which 50 and 100% of the males are estimated to be physiologically mature is 35.1 and 51 mm CW, respectively (Vale 2003) and thus well below the realized average capture sizes. It is still unknown, however, at which size crabs are fully functionally mature. Mating success may depend on the size of the males and be lower in smaller or intermediate-sized ones than in larger males which are usually competitively dominant. Future studies will investigate this matter in more detail. In an unexploited population, the slow-growing crab U. cordatus (Diele et al. 2005; Chap. 18) is likely to accumulate in upper size classes over the years (Diele 2000). This results from decreasing growth with age, the species’ longevity and asymmetric competition, which favors larger conspecifics (Diele 2000; Diele et al. 2005; Chap. 18). When resources are limited and intraspecific competition occurs (see Nordhaus et al. 2006; Piou et al. 2007), the population growth rate is likely to decline. In contrast, size-selective fishery can have a reverse effect by specifically reducing the number of large, dominant specimens. It must be considered, however, that a possible initial over-proportional availability of large crabs in U. cordatus populations may mask the first negative effects of its fishery until their over-theyears accumulated biomass has been skimmed (Diele 2000). We therefore recommend that fishery yields of U. cordatus should precautionarily be kept well below the estimated maximum sustainable yield in order to prevent a sudden non-linear down-fishing of the economically valuable upper size classes in this slow-growing species. Furthermore, the targeted large males may be particularly important for fertilizing the large females.
19.4
Legislation
In 1997, the state of Para´ launched a first Preservation Programme for Ucides cordatus (Programa de Preservac¸a˜o do Caranguejo-Uc¸a´, Lei 6.082, 13.1.1997) including a total capture ban for females. It also became illegal to catch crabs during mass mate-searching events (“andanc¸a”) in order to reduce the high fishing pressure by non-professionals during these particular days. A subsequent state legislation released in 2002 (COEMA N 020 OF, 26.11.2002) then defined a minimum capture size of 70 mm CW, thus banning the use of auxiliary means such as “gancho” and “lac¸o“ (see sec. 19.2). However, a federal legislation for north and northeast Brazil (IBAMA N 034/03-N, 24.06.2003), released a year later, overruled the state legislation in most regards: minimum capture size was now set to 60 mm CW, female capture was banned between December and May only, males must not be captured at days of mass mate-searching events, and in addition to capture by hand (“brac¸eamento”), the traditional hook (“gancho”) was again permitted. In 2005, a new state legislation (Gerencia Executiva no Para´, N -2, 20.10.2005) widely agreed with the federal law.
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Marketing Systems
Half the crabs landed in Braganc¸a district in 2003 (see Sect. 19.2 for details on the fisheries monitoring) supplied a market for live crab and the other half a market for processed crab (crab meat or claws, see below; Arau´jo 2006). In both systems, crab collectors are either self-employed or employed. Depending on their access to infrastructure, villages favor either one or the other marketing system: While crab collectors from Braganc¸a, Acarajo´, Bacuriteua and Tamatateua (Fig. 19.3) almost exclusively catch crabs for the live market, all specimens landed in Treme and Caratateua today are entering the processed crab market (Arau´jo 2006). Originally, the latter two villages also exclusively supplied the live crab market. They only switched to crab processing in the 1980s, when the paved road from Braganc¸a to the beaches of Braganc¸a peninsula was built, and newly establishing road villages (e.g., Bacuriteua) with better access to Braganc¸a quickly took over the live crab market with its fresh and quickly perishable product. Specialization on the processed crab market enabled the more distant villages of Caratateua and Treme to take advantage of the fact that crab meat can be refrigerated or frozen until sold to middlemen. Crabs for the live market are sold in strings of 14 specimens (cambada; Fig. 19.4c) that are generally traded and consumed within 3 days at the most. The majority of the crabs (80%) are sold on local rather than regional markets (Arau´jo 2006). In the processed crab market, sales prices of the crab landings refer to weight (or volume) rather than to number of crabs. Crabs are processed by the women of the fishing households (Fig. 19.4d) who aggregate further value to the catch, playing an important role in this marketing system (Magalha˜es et al. 2007). Claws (sold separately) and the picked crab meat are transported by middlemen as refrigerated or frozen products to the final trading locations, mostly regional (approx. 250 km, 97%) and national markets (<3%) (Arau´jo 2006). Consumers of processed and live crabs differ in regard to their impact on capture sizes. Live crab consumers prefer to eat large specimens, due to the labor involved in eating whole crabs. As a result of this size-selectivity, cambadas with large specimens sell better, which has a positive feedback on the overall capture size of the crabs (Diele et al. 2005). In contrast, in the processed crab marketing system, where a prepared product instead of crab in natura is purchased, there is no direct link between the consumer’s preference and capture size. Average monthly net income of crab collectors supplying the live crab and the processed crab market reached US$ 122 (R$ 367) and up to US$ 196 (R$ 590) in 2003, respectively (Arau´jo 2006). This was well above the official Brazilian minimum wage of US$ 80 (R$ 240) in that year. However, it should be considered that this is generally the only or by far the largest single income of a crab collector’s household, which in the Braganc¸a district has an average size of five members. Crab landings in the entire Braganc¸a district in 2003 generated a total of US$ 331,000 (R$ 994,000) for live crabs and US$ 293,000 (R$ 878,000) for processed crabs at the first level of commercialization. Information on prices in subsequent levels of the commercialization chain was obtained through weekly interviews with
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local and regional mercantile agents (Arau´jo 2006). In the processed crab market system, the price paid by the final consumer was always more than double the price at first commercialization. In the live crab market, final consumer prices ranged between 32 and 150% of the initial producer prices, depending upon the number of actors involved in the commercialization chain and on whether crabs were sold locally or regionally. A more detailed analysis of the commercialization chains of the two systems, including mark-ups and marketing margins at different levels is under preparation (Arau´jo and Diele, unpublished).
19.6
Significance of Community Participation in Research and Management
Our research within the MADAM project greatly enhanced the knowledge about the biology and ecology of U. cordatus in northern Brazil. Together with our longterm fisheries monitoring programme, these data provide a scientific baseline for elaborating management plans. In 2005, the extractive reserve “Caete´-Taperac¸u´” (see Fig. 19.3) comprising 42,068 ha was created in our study area. Many mangrove extractive reserves (Reservas Extratevistas - RESEX) have recently been established by the Brazilian Federal Environmental Agency IBAMA (Instituto Brasileiro de Meio Ambiente e dos Recursos Naturais Renovaveis), aiming at maintaining and improving livelihoods of traditional users and ensuring sustainability of the natural resources and ecosystem integrity. RESEX are established at the request of traditional populations who participate in the elaboration and implementation of a co-management plan, giving them use rights to resources (see Chap. 21.5). Responsibility for the RESEX is shared between user groups and government. The RESEX approach is relatively new for coastal areas (Glaser and Oliveira 2004), and the communities living here thus lack experience and confidence in dealing with the steps involved. However, their participation in decision-making is central to the general acceptance of management measures and thus the success of the RESEX, particularly when considering the large size of the extractive reserve and the difficulty in controlling activities therein. By planning and conducting our fisheries monitoring programme jointly with crab collectors and other local stakeholders of Braganc¸a district, an important first step toward active and competent community participation was made. We witnessed an increasing selfconfidence of the members of the monitoring programme (fishermen, village students) during our regular workshops, triggered by the participants’ new experience that their profession and traditional knowledge is valued. Crab collectors were also, for the first time, invited to workshops organized by regional and federal governmental institutions. Despite many promising first steps, the implementation of the RESEX management plan in our study area is still incomplete, partly due to inadequate legislation. For example, it is presently impossible to compensate crab collectors during the few
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days of capture bans at mate-searching days, as compensation benefits are only paid on a full month basis. Many crab collectors are also not yet officially documented as professionals, which undermines their option to participate in fisheries management on a formal basis. Registration of crab collectors in the fisherfolk association of Braganc¸a (Colonia de Pescador) is only possible since 2003, offering them access to social benefits for the first time. However, their registration is often hampered as many are illiterate, do not possess birth certificates, and are discouraged by membership fees. Greater efforts are needed to organize crab collectors, as official recognition and registration would, for instance, render them able to obtain compensation payments in the future, an important incentive for implementing essential fisheries management measures. Registration is also a prerequisite for evolving the potentials of the active co-management approach which has become possible on Brazilian coasts under the RESEX concept. Acknowledgements We thank Domingos de Arau´jo, Aldo de Melo, Katia de Melo, Rosa Maria Saraiva, Cidiane Soares, Felipe Saraiva and crab collectors, students, bus and truck drivers and many other helpers from Braganc¸a city and the villages of Braganc¸a district for their participation.
References Alexander HG (1979) A preliminary assessment of the role of the terrestrial decapod crustaceans in the Aldabra ecosystem. Philos Trans R Soc Lond B 286:241–246 Arau´jo AR (2006) Fishery statistics and commercialization of the mangrove crab, Ucides cordatus (L.), in Braganc¸a – Para´ – Brazil. PhD thesis, University of Bremen, Bremen Boeger WA, Pie MR, Ostrensky A, Patella L (2005) Lethargic crab disease: multidisciplinary disease: multidisciplinary evidence supports a mycotic etiology. Mem Inst Oswaldo Cruz 100:161–167, Available online at: http://www.scielo.br Diele K (2000) Life history and population structure of the exploited mangrove crab Ucides cordatus cordatus (Linnaeus, 1763) (Decapoda: Brachyura) in the Caete´ estuary, North Brazil. PhD thesis, University Bremen, Bremen. ZMT Contribution vol 9 Diele K, Simith D (2007) Effects of substrata and conspecific odour on the metamorphosis of mangrove crab megalopae, Ucides cordatus (Ocypodidae). J Exp Mar Biol Ecol 348:174–182 Diele K, Koch V, Saint-Paul U (2005) Population structure, catch composition and CPUE of the artisanally harvested mangrove crab Ucides cordatus: Indications for overfishing? Aquat Living Resour 18:169–178 Ehrhardt JP (1968) Recensement en 1968 de la populacio´n de gecarcinus planatus Stimpson sur la´toll de Clipperton. Rapport particulier no 40 CRSSA/BIOECO, Paris Glaser M (2003) Interrelations between mangrove ecosystems, local economy and social sustainability in Caete´ Estuary, North Brazil. Wetl Ecol Manage 11:265–272 Glaser M, Diele K (2004) Asymmetric outcomes: Assessing central aspects of the biological, economic and social sustainability of a mangrove crab fishery, Ucides cordatus (Ocypodidae), in North Brazil. Ecol Econ 49:361–373 Glaser M, da Silva Oliveira R (2004) Prospects for the co-management of mangrove ecosystems on the North Brazilian coast: Whose rights, whose duties and whose priorities? Nat Res Forum 28:224–233 Hartnoll RG, Baine MS, Grandas Y, James J, Atkin H (2006) Population biology of the black land crab, Gecarcinus ruricola, in the San Andres Archipelago, Western Caribbean. J Crust Biol 26:316–325
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Hicks JW (1985) The breeding behavior and migrations of the terrestrial crab Gecarcoidea natalis (Decapoda, Brachyura). Aust J Zool 33:127–142 IBAMA (2003) Estatı´stica da Pesca 2001. Ministe´rio do Meio Ambiente, Instituto Brasileiro do Meio Ambiente e dos Recursos Naturais Renova´veis, Diretoria de Fauna e Recursos Pesqueiros, Centro de Pesquisa e Gesta˜o de Recursos Pesqueiros do Litoral Nordeste – CEPENE, Tamandare´-PE IBAMA (2004a) Estatı´stica da Pesca 2002. Ministe´rio do Meio Ambiente, Instituto Brasileiro do Meio Ambiente e dos Recursos Naturais Renova´veis, Diretoria de Fauna e Recursos Pesqueiros, Centro de Pesquisa e Gesta˜o de Recursos Pesqueiros do Litoral Nordeste – CEPENE, Tamandare´-PE IBAMA (2004b) Estatı´stica da Pesca 2003. Ministe´rio do Meio Ambiente, Instituto Brasileiro do Meio Ambiente e dos Recursos Naturais Renova´veis, Diretoria de Fauna e Recursos Pesqueiros, Centro de Pesquisa e Gesta˜o de Recursos Pesqueiros do Litoral Nordeste – CEPENE, Brası´lia IBAMA (2005) Estatı´stica da Pesca 2004. Ministe´rio do Meio Ambiente, Instituto Brasileiro do Meio Ambiente e dos Recursos Naturais Renova´veis, Diretoria de Fauna e Recursos Pesqueiros, Centro de Pesquisa e Gesta˜o de Recursos Pesqueiros do Litoral Nordeste – CEPENE, Brası´lia IBAMA (2007) Estatı´stica da Pesca 2005. Ministe´rio do Meio Ambiente, Instituto Brasileiro do Meio Ambiente e dos Recursos Naturais Renova´veis, Diretoria de Fauna e Recursos Pesqueiros, Centro de Pesquisa e Gesta˜o de Recursos Pesqueiros do Litoral Nordeste – CEPENE, Brası´lia Kjervfe B, Lacerda LD (1993) Mangroves of Brazil. In: Lacerda LD (ed) Conservation and sustainable utilization of mangrove forests in Latin America and African regions. Part 1: Latin America. Mangrove Ecosystems Technical Report, pp 245–272 Magalha˜es A, da Costa RM, da Silva R, Periera LCC (2007) The role of women in the mangrove crab (Ucides cordatus) production process in North Brazil (Amazon region, Para´). Ecol Econ 61:559–565 Nordhaus I, Wolff M, Diele K (2006) Litter processing and population food intake of the mangrove crab Ucides cordatus in a high intertidal forest in north Brazil. Estuar Coast Shelf Sci 67:239–250 Piou C, Berger U, Hildenbrandt H, Grimm V, Diele K, D’Lima C (2007) Simulating cryptic movements of a mangrove crab: Recovery phenomena after small scale fishery. Ecol Modell 205:110–122 Vale PAA (2003) Biologia reprodutiva do caranguejo Ucides cordatus cordatus (Linnaeus, 1763), no manguezal do Estua´rio do Rio Caete´, Braganc¸a – Para´ – Brasil. MSc thesis, University of Para´, Bele´m
Chapter 20
Simulating Ucides cordatus Population Recovery on Fished Grounds C. Piou, U. Berger, and K. Diele
20.1
The Individual-Based-Ucides Model
The Ucides cordatus population of the Caete´ Peninsula does not seem to be biologically threatened and the sustainability of the fishery appears to be still secured (Chap. 19; Diele et al. 2005). However, the processes at scales of few meters responsible for the recovery of fishing grounds with crabs of harvestable size are still enigmatic. Fishermen reported that such recovery occurs within approximately 2 weeks. However, individual crabs grow too slowly (Chap. 18) for this recovery to be caused by recruitment, and movement of harvest-sized crabs into new burrows, although obviously happening, is difficult to observe in the field. Therefore, we chose an approach called pattern-oriented modeling (Grimm et al. 1996, 2005; Grimm and Berger 2003) to infer from higher levels of information (i.e., patterns at population level) the processes happening at the individual level (i.e., how the crabs might be moving). An individual-based model was specifically developed for this analysis: the individual-based-ucides or IBU model (Piou et al. 2007). The IBU model was developed to analyze potential factors influencing the recovery of U. cordatus in harvested areas. In this individual-based model, the behavior of crabs, their relations to their burrows, and their movement trajectories were developed as computer algorithms from field observations and expert knowledge. The model simulated small areas of mangrove floor (in general 225 m2) densely populated (>3 ind. m 2) by U. cordatus individuals of mean sizes 6 cm 1 SD cm. Thus, these areas of the mangroves corresponded to densely populated patches within highly productive tall Rhizophora mangle forests, which are the preferred fishing grounds of local crab collectors with the highest density of big crabs (Diele et al. 2005; Chap. 16; Piou et al. 2009). The IBU model included several submodels: two submodels of reason for movement, one submodel of walking behavior, one of reason for stopping movement, and a submodel describing the disappearance of unoccupied burrows from the mangrove floor.
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Inferences with the Pattern-Oriented Modeling Approach
With the pattern-oriented modeling approach in a first study, parameters such as life-time of unoccupied burrows, angle of correlation of the walking direction or perception of burrows by the walking crabs were tested with different values to analyze the most probable range in nature (Piou et al. 2007). These parameters led to model parameterizations fitting better the results of recovery field experiments with specific values: long unoccupied burrows’ life-time (values corresponding to a maximum of 5–20 days), short perception ranges of burrows (
Fig. 20.1 Description of the field-of-neighborhood (FON) approach in the IBU model and the calculation leading to the estimation of the probability of movement of individual crabs (Pmove) in a submodel of reason for movement. Rint is the radius of interaction, dependent on crab size, FA is the integrated FON effect of all neighbors on a focus crab, and Fmin is the minimum value of FON at the borders of the interaction zone
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Fig. 20.2 Recovery of harvested areas (12.25 m2) with (black) or without (gray) removing the burrow entrances after the fishery. Triangles show the results of the field experiment as pattern to be reproduced by the IBU model. The lines present the results of the same experiment done during simulations of the IBU model (continuous median result, dashed maximum and minimum results) with the best fitting configuration found in Piou (2007) using a submodel of reason for movement with a zone of influence approach and intermediary radius of interaction
The version including the competition-induced movement of crabs (FON submodel) led to more realistic conditions and better reproduced recovery patterns. In particular, this FON submodel better reproduced the linearity of the recovery patterns seen in the field, with a frequency of movement below 1 move every 15 days per crab. From these results, Piou et al. (2007) concluded that the main reason of burrow change in U. cordatus is intraspecific competition. This indirectly means that the movement frequency would be density-dependent. In a second study, Piou (2007; Chap. 8) tried to fit the IBU model to a spatial distribution pattern at a small scale (<10 m; see Fig. 20.3), while still fitting the recovery patterns but not considering their linear aspect (see Fig. 20.2). In this study, several competition-inducing movement submodels were tested representing different types of behaviors of the crabs. They were set to test if the patterns are better reproduce when (1) competition is asymmetric in relation to the size of the crabs, and (2) when competition for resources close to burrows is more intense than for resources further away from the territorial area. This study used an information criterion enhancing the detection of evidence of the different model parameterizations to fit the field patterns. The results showed that competition was definitely needed to reproduce the regular organization of crab burrows observed in the field (Fig. 20.3). Additionally, this study could show that resources close to the burrows were of much higher importance and competed for than the ones further away. However, by fitting the recovery patterns without considering their linear aspect, equal evidence was found for a random process of decision to move as for a competition-induced decision of movement. Finally, the competition asymmetry
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Fig. 20.3 Spatial point pattern analysis of position of burrow entrances on a nonrooted area of 15 m2 with the L-Ripley function (Ripley 1977). The solid black line presents the result from a plot mapped in the field and the black dashed lines are the corresponding 95% confidence envelope for complete spatial randomness (CSR) using 999 Monte Carlo randomisations (Piou et al. 2009). The pattern to reproduce is the part of the black line running below the confidence envelope which means a regular organization of the burrow entrance with a mean distance of about 25 cm. The solid gray line presents the mean L-Ripley function resulting from the same analysis in 30 simulations of the IBU model with the most realistic configuration for this pattern: using the FON approach and an intermediary radius of interaction. The gray dashed lines are the corresponding maximums and minimums of the simulation results
did not present a higher evidence of fitting the patterns than with symmetric competition. This study underlines the need for investigating some additional patterns of movement in the field, such as size-dependent frequency of change of burrows, for a better understanding of the symmetry of competition.
20.3
Importance of Movements Induced by Density-Dependent Processes
In summary, both studies demonstrate the importance of competition in a situation of spatial reorganization of the crab population. The reason to move due to competition was shown to be of major importance for the recovery of fished areas on the Caete´ peninsula, where densities of harvest-sized U. cordatus are high (Piou et al. 2007). Competition may in fact force crabs to move from preferred and therefore densely populated areas under tall R. mangle trees (with many roots and thus unfishable) toward fishable grounds (forest areas with fewer roots) first, and secondarily toward peripheral habitats (e.g., canopy gaps, under small R. mangle
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trees, in Avicennia germinans- or Laguncularia racemosa-dominated areas). Therefore, this density-induced movement may be an important aspect for the sustainability of the crab fishery. The densely R. mangle rooted areas inaccessible to crab collectors may act as local buffers for nearby fishable grounds, as hypothesized by Diele (2000) and Diele et al. (2005). In the peripheral habitats of the peninsula, smaller crabs accumulate, probably resulting from competition with larger conspecifics in the most favorable habitats (see Chap. 18). But these peripheral habitats, being not at all or less intensively harvested, may then act as a buffer over a longer time scale. With increasing growth and competitiveness, crabs may then move back into the preferred habitat type (Diele 2000). In addition, other processes such as food limitation or lack of moisture may also force individual crabs to move within and out of these peripheral habitats (Piou 2007). Piou et al. (2007) concluded that, if the overall density of U. cordatus decreases too much, these hierarchal buffer systems may slow down resulting in a much slower recovery of harvested areas, despite the presence of harvest-sized crabs in the population. Further analysis at multiple scales and integrating the influences of forest structure on the crab population as demonstrated by Piou et al. (2009) is needed for a more comprehensive understanding of the processes leading to recovery of fished areas on the Caete´ Peninsula.
References Berger U, Hildenbrandt H (2000) A new approach to spatially explicit modelling of forest dynamics: spacing, ageing and neighbourhood competition of mangrove trees. Ecol Modell 132:287–302 Diele K (2000) Life history and population structure of the exploited mangrove crab Ucides cordatus cordatus (L.) (Decapoda: Brachyura) in the Caete´ estuary, North Brazil. PhD thesis, University of Bremen, Bremen. ZMT Contribution vol 9 Diele K, Koch V, Saint-Paul U (2005) Population structure, catch composition and CPUE of the artisanally harvested mangrove crab Ucides cordatus (Ocypodidae) in the Caete´ estuary, North Brazil: Indications for overfishing? Aquat Living Res 18:169–178 Grimm V, Berger U (2003) Seeing the wood for the trees, and vice versa: pattern-oriented ecological modelling. In: Seuront L, Strutton PG (eds) Handbook of Scaling Methods in Aquatic Ecology: Measurement, Analysis, Simulation. CRC Press, Boca Raton, pp 411–428 Grimm V, Frank K, Jeltsch F, Brandl R, Uchmanski J, Wissel C (1996) Pattern-oriented modelling in population ecology. Sci Total Environ 183:151–166 Grimm V, Revilla E, Berger U, Jeltsch F, Mooij WM, Railsback SF, Thulke H, Weiner J, Wiegand T, DeAngelis DL (2005) Pattern-oriented modeling of agent-based complex systems: lessons from ecology. Science 310:987–991 Piou C (2007) Patterns and individual-based modeling of spatial competition within two main components of Neotropical mangrove ecosystems. PhD thesis, University of Bremen, Bremen, http://nbn-resolving.de/urn:nbn:de:gbv:46-diss000106712 Piou C, Berger U, Hildenbrandt H, Grimm V, Diele K, D’Lima C (2007) Simulating cryptic movements of a mangrove crab: Recovery phenomena after small scale fishery. Ecol Modell 205:110–122 Piou C, Berger U, Feller IC (2009) Spatial structure of a leaf-removing crab population in a mangrove of North-Brazil. Wetl Ecol Manage 17:93–106 Ripley BD (1977) Modelling Spatial Patterns. J R Stat Soc Ser B (Methodol) 39:172–212
Part VII Mangroves and People
Chapter 21
Mangroves and People: A Social-Ecological System M. Glaser, G. Krause, R.S. Oliveira, and M. Fontalvo-Herazo
21.1
The Social-Ecological System (SES) Concept
Marion Glaser The analysis of social-ecological systems (SES) seeks to identify system configurations which produce sustainable futures for major stakeholders at various system levels and scales. Our point of departure for SES analysis has to be a clear generic definition of the concept. For the purposes of our sustainability-oriented social-ecological analyses, a social-ecological system is comprised of three elements. These are: 1. A bio-geophysical system (e.g., ecosystem, coastal territory); 2. The associated social agents (individual and collective) with their institutions;1 3. An identified problem context (e.g., resource overuse, pollution or ecosystemrelated degradation of human livelihoods). At the core of the SES approach to managing human–nature relations is the concept of resilience. Resilience is a system’s ability to reorganize and renew itself without loss of functions or diversity when disturbed (Alcorn et al. 2003). The resilience of any living (including social-ecological) system is centrally affected by the way the system reacts to change. As famously presented by James Lovelock in his virtual “daisyworld”, self-reinforcing negative system feedbacks can reduce and stop an ongoing change. On the other hand, “positive” self-re-enforcing mechanisms, such as the mutual feedbacks between population numbers and rising birth rates over time, will speed up ongoing system changes (Folke et al. 2002). Thus, the character of the self-reinforcing mechanisms of an SES affects its resilience (Olsson et al. 2004b). Resilience also depends on the capacities of an SES for learning and adaptation (Berkes et al. 2003).
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SES resilience analysis needs to be undertaken in relation to a spatially defined unit. Feedbacks which determine the future trajectory of SES development can occur within and between ecological and social system components as well as across spatial and organizational scales. In our current age of the anthropocene (Crutzen and Stoermer 2000; Crutzen 2002), humankind is becoming an ever-more central driver of social-ecological dynamics (Schellnhuber 1999; Berkes and Folke 2002). In line with this, the governance and management of human interactions with nature has become increasingly important for sustainability. This chapter shows how, after assuming a “pristine” mangrove ecosystem in the Caete´ peninsula at the outset of a 10-year research period, the MADAM socio-economic research program constructed a differentiated picture of a complex system in which human–nature interactions are the predominant drivers of mangrove-based social-ecological dynamics (Fig. 21.1). The research program on “Mangrove Dynamics and Management” (MADAM) was initiated and led by biologists. In order to investigate natural dynamics in a “pristine” environment, the work was explicitly located in the Braganc¸a mangrove peninsula, a region which was regarded as relatively free of human interference. During the first few years of research, natural and social scientists worked on different topics and spatial scales in the research region. The socioeconomic research group, whose work is reported here, was a late-comer, initially expected to provide quantitative data for natural science-led questions, which had
GTZ GEF Western hemisphere mangroves
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Fig. 21.1 The social ecological system Braganc¸a/Caete´ mangroves (adapted from Berkes and Folke 2002)
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been formulated during project design with only minor participation of social scientists. The social science point of departure in the interdisciplinary MADAM program was therefore a study area defined by natural scientists: This was translated into the SES concept as follows. Bio-geophysical area: the 130 km2 of mangroves on the Caete´ peninsula between the town of Braganc¸a and the coast on both sides of the Caete´ river (see Chap. 2, Fig. 2.1). Associated social agents: the local communities whose residents extract resources – for subsistence or sale – from the mangroves of this area reside in the ecosystem’s socio-economic impact area (SEIA) The SEIA (Glaser 2003) was spatially delimited through interviews with local leaders and other key informants in over 50 mangrove-near villages in the region about the livelihood strategies of inhabitants. The SEIA geographic boundaries surround the 21 villages whose human population engaged in production/extraction in the mangrove study area. The combination of the spatially defined mangrove study area and its associated SEIA thus produces the spatially explicit delineation of the local/regional part of our social-ecological system (SES) (see Krause et al. 2001; and area map in Chap. 2). This SES contains actors and institutions at multiple nested levels from the local to the national level and beyond, and social and ecological subsystems are connected by drivers and feedbacks (see Fig. 21.1). Although higher-scale drivers were not excluded, most of our analysis here centers on the local and regional levels. Problem context: the overall concern of our research was to identify the major drivers of the Caete´ SES, and especially those drivers which generate identified SES problems such as mangrove deforestation and low incomes for mangrove producers, and to analyze the available options for steering the SES into more sustainable directions.
21.2
Mangrove Values and Livelihoods
Marion Glaser Knowledge about how much of which resources people extract from a biogeophysical system is central in social-ecological assessment. A household survey was carried out which covered 69% of the approximately 2,500 households in the 21 local villages whose residents extract resources from our study mangroves. Figure 21.2 lists the mangrove resources used for subsistence and sale in order of their importance for local households and shows a complex picture of human– nature interdependence. Residents named 20 products and product types, the most important ones for the local household economies being crabs (Ucides cordatus
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Mangrove product
Fig. 21.2 Percentage of households using mangrove products for subsistence and sale (source: Glaser 2003)
and Callinectes sp.), fish, woodworms (Teredo sp.), mussels (Mytilidae) and mangrove wood.2
21.2.1 Mangrove Dependence The major resource, and a keystone species of our ecosystem, is the mangrove crab U. cordatus (Diele 2000; and Chap. 17). Well over 60% of households in the SES catch and directly consume or barter (subsistence) and over 40% also sell this crab. When crab processing and trading activities are included, over 80% of households in the socio-economic impact area derived material benefits (in money or in-kind) from U. cordatus (Glaser and Diele 2004). As crab collectors have few other income sources and are among the poorest coastal dwellers in the region, the subsistence and sale incomes from the U. cordatus crab have a particularly important poverty alleviation function. This is reflected in Fig. 21.2 and in Table 21.1 both of which also show the wide range of other mangrove products which local residents reported to have consumed or sold. 2
There are three mangrove species (see Chap. 5) whose utilization is likely to be much higher than in the data reported here due to persistent underreporting of illegal uses of mangrove resources (for further discussion of tree use see Glaser et al. 2003).
Table 21.1 Mangrove-related income generation for local ecosystem users (1998–1999) 1 2 3 4 5 6 Subsistence Annual value Product % of households (hh) No of hhs with sale/ Sale income income (R$ per (subsistence subsistence income (R$ per hh/ Subsistence Sale hh/month) production) from mangrove month)a U. cordatus (mangrove crab) 64 42 1,026/1,565 159.20 19 356,820.00 Fish (general) 54 31 758/1,320 348.00 35 554,400.00 Callinectes sp. (“siri crab”) 50 6 147/1,223 104.00 83 1,218,108.00 Teredinae (woodworm) 48 6 147/1,174 30.00 244 3,437,472.00 Mytella falcata (mangrove 45 6 147/1,100 60.00 70 924,000.00 estuary mussel) Eleotiedae guavina sp. 36 3 73/808 3.00 12 116,352.00 (“amore´ fish”) 43 (3) 73/1,051 – 13 163,956.00 Mangrove woodb All mangrove productsd 83 68 1,663/1,863 332.00 30 7,305,840.00 a One Brazilian Real (R$) was equivalent to US$ 0.5 at the time of the study b Beams, posts and fuelwood c As the extraction of mangrove wood is illegal, little reliable interview information was available on it (see Glaser et al. 2003) d As in Figure 20.2
n/ac 6,622,764.00
2,628.00
7 Annual value (production for sale) 1,960,070.40 3,165,408.00 1,833,456.00 52,920.00 105,840.00
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21.2.2 Economic Value and Poverty Table 21.1 shows the economic value of the mangrove ecosystem3 based on one year of fortnightly information of household-level production in 250 households in 10 villages. A total of 67 mangrove products including 56 mangrove-dependent fish species4 were differentiated by local households (Grasso 2000). Grasso (2000) also priced the subsistence and sale production values of major products and showed that, while the U. cordatus does deliver major monetary incomes to local households (see row 3 of Table 21.1), as a whole, mangrove subsistence production values actually surpass the sale value of mangrove products (see totals of columns 6 and 7 of Table 21.1). While commercial mangrove wood exploitation increased the percentage of those living below the poverty line, i.e. further impoverished local households (Glaser et al. 2003), the subsistence-oriented exploitation of the mangrove ecosystem created additional welfare (i.e. a 20% income increase) in the study area (Grasso 2000). There are thus strong incentives for local residents near mangroves to use “their” local mangrove ecosystem sustainably and to protect it from “outside” exploitation. Strong and persistent conflicts between locals and “outsiders” around illegal mangrove logging in the study area (Glaser et al. 2003) confirm this. Poverty alleviation is thus a central social function of the mangroves. For poor ecosystem users, and in particular for female-headed households, the mangrove system provides important subsistence and emergency fall-back foods (see Table. 21.1, and nonshaded bars in Fig. 21.2). Conventional economic valuation, however, disregards subsistence production and focuses only on production which passes through markets. This fails to capture the full poverty alleviation impacts of ecosystems and runs the danger of supporting policies that undermine the social functions of ecosystems. The analysis of ecosystem values therefore needs to adopt a comprehensive view of the services these systems provide to humankind. The three major socio-economic functions of our mangrove ecosystem are (1) income generation, (2) poverty alleviation, and (3) the provision of rural food security.
21.2.2.1
Income Generation
The Caete´ peninsula mangrove ecosystem generates between R$ 773 and 1,005/ year/ha of producer income, depending on method of calculation (Grasso 2000: 89).
3
Mangroves are here understood as encompassing the diversity of flora and fauna associated with the ecosystems in which this tree species predominates. 4 Including 56 mangrove-dependent fish species that were mostly summarized as “fish” in Fig. 20.2.
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This translates into at least R$ 14 million5 of subsistence and commercial product value for the study area mangroves (cf. totals of columns 6 and 7 in Table 21.1). 21.2.2.2
Poverty Alleviation
Half of mangrove-dependent households in our study area lived below the poverty line (R$ 50/month per capita). As mangrove resources degraded, labor productivity, i.e. catch per unit effort in crab collection, decreased (Glaser and Diele 2004). Crab collectors thus needed to invest more time and effort to achieve the same physical production results. Between 1998 and 2001, these productivity falls translated into a lower purchasing power for crab collectors (see Fig. 21.6). Unless producer prices rise or more rewarding alternative income sources are adopted by the concerned households, lower catch per unit effort will further impoverish crab collectors, who are already among the poorest inhabitants of the study area. 21.2.2.3
Food Security
As many as 83% of households in our rural coastal study area directly consumed or bartered crabs, fish, wood and other mangrove products without passing through any market transactions. Eighteen of the 20 mangrove products presented in Fig. 21.2 served as emergency back-up food for the collecting household during hard times. Socio-economic risk insurance, including the mitigation or prevention of hunger, is therefore an important function of the mangrove ecosystem. While the total economic value of the production in question is already high, its socioeconomic importance for the poorest residents on north Brazilian mangrove coasts is even higher (Glaser 2003). 21.2.2.4
Socio-Economic Context and Local Priorities
Mangrove dependence in our SES needs to be seen in the context of locally perceived problems and development priorities. In 1996 at the start of our research programme, less than half the 21 villages in our SES were connected to mains electricity, or had access to basic medical care through a local health post. Only slightly over half the villages had a community centre and only three had partial access to piped water. Fecal coliform bacteria in the drinking wells of households and village schools were the norm (in 21 of 22 sampled domestic wells; R. Lara, personal communication). Most village schools provided only the first years of primary schooling. At a series of village meetings, local residents prioritized village problems in order of importance as follows: 1. The lack of quality education restricts alternative income options. Even after years at the village school, children are unable to read or write. 5
At the time of our survey, this was roughly equivalent to US$ 7 million.
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2. Women are restricted to working in the house and in agriculture. In some villages, women also work in low-paid crab meat processing. 3. The lack of medical facilities. This is especially serious for pregnant women and those afflicted by malaria and dengue fever. 4. Low prices paid to producers. Patronclient relations between fish and crab traders provide an informal risk insurance for crab collectors, fishermen and other mangrove producers against sickness and other sudden financial needs. But producers are obliged to accept prices below those on the open market. 5. No electricity is available in most communities. 6. Scarcity of competent local leaders. Village groups find it difficult to access municipal, state, banking and other “bureaucracies”. Since there are few competent village leaders, there are few community initiatives and disunity prevails. Further problems mentioned in village meetings were the lack of public transport, low drinking water quality, and the absence of childcare facilities to free women to engage in gainful employment. Villages in beach locations were described as exposed to locally unpredictable destructive coastal erosion processes. This reduced investment in agriculture and horticulture as well as physical and social infrastructure (Krause and Glaser 2003).
21.3
The Coevolution of Natural and Social System Drivers at the Local Level
Gesche Krause and Marion Glaser Social and ecological systems are indivisibly linked and co-evolve. Here, we examine two cases of co-evolutionary development in the mangrove-based SES under study. Both areas were subject to efforts by the Brazilian government in the mid-1970s to improve access to mangrove resources. However, after the construction of an access road in the study area, our two example sites moved along very different developmental paths, influenced by their particular combinations of natural and/or social and institutional drivers: In the coastal village of Ajuruteua, site-specific beach morphodynamics and socio-economic processes drove a mangrove fishing village into weakening social-ecological resilience, increasing impoverishment and socio-economic polarization. In the mangrove-adjacent, agricultural/extractivist6 village of Tamatateua, the spatial vicinity to the mangrove ecosystem has allowed the ecosystem to assume the function of buffer or risk insurance so that successful agricultural innovations and investments could be undertaken by community members.
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In the context of this chapter, extractivism describes the collection or capture of mangrove resources.
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21.3.1 Ajuruteua: A Coastal Village 21.3.1.1
Boundaries and Properties of the SES
The village of Ajuruteua is separated from the Atlantic Ocean by a flat sandy beachdune ridge system, which is known to respond rapidly to changing environmental conditions. Landward shifts of the beach-dune ridge of up to 15 cm/day were observed (Krause and Soares 2004). This moving “barrier” plays a key role for the evolution and protection of the adjacent mangrove area. The village is situated at the northern point of the mangrove peninsula in relative spatial isolation and developed during the mid-1970s following the construction of an access road. Currently, access is possible by boat or along the paved road, which dissects the peninsula in a northsouth direction (Krause et al. 2001). Ajuruteua consists of three spatially separated neighborhoods Praia, Vila dos Pescadores, and Bonifacı´o (Fig. 21.3), each with a distinct hydrodynamic signature.7 Fisheries are the main source of income, followed by tourism: the splendor of the beaches in this area promotes tourism along the coastline (Cabral 1997), while the
Fig. 21.3 Schematic map of the three village sections of Ajuruteua. Each village section exhibits specific hydrodynamic signature(s) indicated by roman numerals as different coastal cells Source: Krause and Glaser 2003
7 Following Short (1999) the hydrodynamic signature is defined as the sum of all driving forces (wind direction and force, wave type and frequency, tidal amplitude, etc.) acting on a specific coastline.
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mangrove ecosystem continues as a key source of income for the local population (Glaser and Grasso 1998; Grasso 2000; Glaser 2003). If tourism as an alternative source is to be successful, knowledge of local coastal dynamics and their impact on beach topography is required. A large set of sequential beach profiles was therefore collected on a fortnightly basis from 1997 to 2001 to assess the co-evolution of coastal morphodynamic processes, residential distribution, and the development of local social infrastructure (Krause and Soares 2004). Further information was obtained from remote sensing analysis, a household census, and semi-structured interviews, covering the key themes of erosion, resettlement and local strategies in the village sections (Krause et al. 2004). Three community meetings were held to identify local problems and people’s perceptions of local geo-morphological dynamics and associated socio-economic strategies, and to discuss strategic future options. In order to address gender-specific issues, one of these community meetings was held exclusively for women (Krause and Glaser 2003).
21.3.1.2
Co-evolutionary Outcomes
The predominant beach profile at each survey site did not change significantly but all profile types were subject to some erosion. The site-specific hydrodynamic signatures, e.g., major wave direction and forcing, were rather stable over the course of time (Krause and Soares 2004). However, human strategies of coping with erosion increased the future likelihood of erosion events. Local residents identified erosion-linked socio-economic risks that are discussed below. Praia: This beachfront area was the main destination for tourism in this region. There were 166 households in 1997. Since the access road was completed in 1983, wealthier absentee owners who arrived from other areas of the state of Para´ and from the north-east of Brazil, make up the majority of residents. With additional income options in tourism, only 55% of households of this village section still depend mainly on artisanal fishery. The residences of artisanal fishers and tourism workers have shifted to a “second row” of houses, further inland towards the mangroves, having been ousted from beachside locations by better-off tourism entrepreneurs and land speculators. Tourist accommodation is generally more attractive close to the shore (Nordstrom et al. 2002). At Praia, houses were constructed immediately on the dune system, or even in front of the first dune ridge. Natural vegetation generally stabilizes and fixes dune sediments, and its removal for house construction can therefore contribute to increased dune erosion. If this natural fixation is destroyed, the sediment is able to shift freely according to the degree of incoming wind and waves. Tourism activities (in the peak season up to 7,000 people per day on the approx. 2 km2 tourist beach area) may have further decreased dune stability, as dunes have been leveled in parts to make room for housing directly on the shoreline. In places, local hotel owners constructed a row of wooden piles as some measure to hamper the impact of the waves and thus to prevent further cutting back of the dune system. However, they did
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not implement any measures to protect or to promote vegetation growth as a natural stabilizer on the dunes. At the end of our monitoring program, only the rear parts of the stilt houses were still situated on dune sands along the tourism part of the village (Praia). The front stilts were fortified but exposed to the high tide swash. This reduced the income of the local hotel owners: hotels could no longer be accessed from the beach during high tides, and thus the facilities could no longer be fully utilized (Krause and Soares 2004). Vila dos Pescadores: The oldest section of the village is inhabited by the poorest artisanal fishers of the village and by old people. This village section has the most dilapidated and low quality wooden housing with all the signs of low-cost impermanence and the most neglected social infrastructure among the three village sections. A number of households do not have access to freshwater due to saline intrusion into their shallow, hand-dug wells (Krause and Glaser 2003). At Vila dos Pescadores, continuous erosion of 34 cm/year was observed. Flooding at extreme spring high tides of the backwash area caused massive damage to the local fishing families’ housing. The construction of fish traps in the tidal channel opposite the harbor in this village section also added to the erosion problem. These large structures have the shape of isosceles triangles (approx. 200 m side lengths), and accumulated sediments then narrow the tidal channel and increase current velocities (Krause and Soares 2004). Over the past decade, this village section has suffered a continuous population exodus towards the better-protected village section of Bonifacio. With continuous erosion, the number of households fell from 300 in 1987 (Maneschy 1995) to 119 in 1997, of which 73% were engaged in artisanal fishery. In contrast to Praia, the wealthier inhabitants of Vila dos Pescadores moved further inland to avoid the recurrence of losses through erosion. The poor were forced to stay on the eroding shores and live in primitive shelters, as they lacked the financial resources to construct better housing facilities in safer areas. Bonifa´cio: This village section was only formed around 1995, receiving the relatively better-off and/or better networked artisanal fishing households. There were only 74 houses in 1997, but population continuously immigrated from other parts of the State and from Vila dos Pescadores. In Bonifacio, 81% of resident households engage in commercial artisanal fisheries. Over the past decade, a large number of substantial wooden and part-concrete houses were constructed by migrants from Vila dos Pescadores. In 2001, a new health centre and a school were erected with public funding. The village leader resides here, associations and village clubs have moved in, and this neighborhood is increasingly becoming the location for local social meetings (Krause and Glaser 2003). Residents’ migration to Bonifa´cio was accompanied by the removal of large patches of mangroves (Krause et al. 2004). A new harbor was established in the vicinity of this village section, sheltered from the waves but exposed to strong tidal currents. The shore-most mangroves were clear-cut to construct the new harbor, so that the “natural” level of erosion was measurably enhanced through human action.
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Driving Forces in the SES
Interestingly, the beach profile monitoring showed that very different types of beach profiles existed in close proximity. This may be related to the socio-economic features of the different sections of the study village. We found that, in Ajuruteua, income source diversity was lower than the regional average of 1.9 income sources per household. Interviews suggested a direct causal link between low income source diversity and erosion. The fear of erosion reduced local incentives to invest in trees, horticulture, annual crops and any construction. Local statements on the failure to invest in local infrastructure, such as “It will all be washed away anyway, nobody knows what the sea will do” showed a high degree of fatalism (Glaser 2003). Results of interviews and public meetings indicate that the local inability to predict the temporal spacing and impacts of erosion events is a major reason why locally available surpluses are not channeled into investments in future household productivity. The observed lack of knowledge of coastal dynamics, the so-called “ecological illiteracy”, of recent migrants causes some undesirable back-loops in our SES. Natural sedimentation dynamics and the deforestation of mangrove areas close to the levee increased erosion so that the need for relocation becomes more likely (Krause 2002). In this sense, there is a negative co-evolutionary link between geomorphological and social elements that clearly weakens systemic resilience. The repetition of dysfunctional societal reactions to erosion is a case in point. For instance, inoperative fish traps, which are abandoned rather than removed, enforce undesirable local erosion by artificially trapping sediments (Krause and Soares 2004). Erosion, and the particular way in which the local population reacts to it in its presently uninformed situation, plays the central role in a vicious circle: Income diversity is reduced by erosion, and this diminishes socio-economic stability and diversity and increases poverty which in turn renders beach populations’ livelihoods ever more vulnerable to the dynamic nature of the beach morphology. A better-informed local population, able to appraise geomorphological dynamics, would be able to generate positive co-evolutionary links in this SES. Finally, since settlements in beach and mangrove areas are prohibited in Brazil (Glaser and Krause 2005), there is no public support for relocating the households affected by coastal erosion. Resettlement costs have to be entirely covered by the families affected by coastal erosion in these areas so that the full effects of erosion events most threatens the lives and assets of those who are most vulnerable.
21.3.2 Tamatateua: An Agricultural Village 21.3.2.1
Boundaries and Properties of the SES
Tamatateua is located in the transition zone between the high plateau and the coastal lowland in the direct vicinity of the mangrove peninsula at Braganc¸a
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Fig. 21.4 Subset of a LANDSAT 7etm+ Scene. Canal 3, 2, 1, (RGB). Lat/Long-Projection. The image of 07. 08 1999 displays the coastal area of Braganc¸a. The light patch in the lower part of the image indicates the city of Braganc¸a. The red circuit is the Campo do Tamatateua. The dark areas represent the mangroves. The light colors of the Atlantic Ocean in the upper part of the image result from the high load of suspended material (source: Klose 2004)
(Fig. 21.4). Due to the topographic features of the area and the high groundwater level, the lower parts of the land (campos) are inundated during the wet season, restricting the village settlements and cultivation of agricultural products to six “islands” (elevated land areas surrounding by seasonally flooded lowlands) of roughly 10 km2 in total (Klose 2004). Economic activities encompass mainly subsistence agriculture. Typical crops like manioc, beans and tobacco are cultivated with traditional shifting cultivation techniques. The vicinity of the mangroves supports multi-occupational income structures, such as artisanal fishery, crab collection and honey production. Due to its “island” character, the village has limited space for the further expansion of agriculture. Until the 1990s, the inhabitants of Tamatateua were without reliable access to other rural villages and to Braganc¸a city during the wet season. In the wake of the political interest to facilitate access to coastal resources, sandy embankments which link the islands were established, enabling access to Braganc¸a town throughout the year. Although most of Tamatateua’s natural products are still exchanged or sold in the village itself, the improved infrastructure has increased the potential to sell on regional markets and to invest in the commercialization of agricultural products.
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In order to assess the co-evolutionary dynamics between mangrove ecosystem, agricultural production and livelihoods, a remote sensing analysis focused on the changing dynamics between 1986 and 2003. Further information was obtained from several household censuses and semi-structured interviews, covering the themes of livelihoods, perception of mangroves and local agricultural production strategies. In addition, several community meetings were organized to identify local problems and community perceptions of mangroves and local socio-economic strategies.
21.3.2.2
Co-evolutionary Outcomes
The land-use types in Tamatateua are unevenly distributed between the islands. An increase in agricultural areas and an intensification of cultivation has occurred since the construction of the road. Our interviews confirmed a strong link between improved infrastructure and increases in marketing activities. Two new activity types were introduced in response to the establishment of the main road that allows year-round mobility: 1. Establishment of little shops that provide goods for basic needs; 2. Trade with mangrove products such as fish, crabs and honey. The latter is drawn on mangrove products as a new income option for the village. Most former fishermen and crab collectors declared that they had given up artisanal fishery and moved into the trade with mangrove products (Klose 2004). The road has gained relevance for local livelihoods throughout the years as reflected in the steadily increasing number of little shops. Most buildings and lands permanently under agricultural crops are concentrated on the central “islands” of Tamatateua. The preferred but limited arable land along the main street is today under permanent agriculture. These fields, locally called pastos com leira, are cultivated with an innovative method which was invented locally only recently. After one year of fallow, land is cleared of vegetation, and livestock fertilize the soil for 1–2 weeks before elevated rows of earth are shaped and then are sown or planted. In the subsequent year, up to two harvest cycles are possible before the next year-long fallow period. This cultivation method is only implemented in Tamatateua. It produces higher yields than the traditional shifting cultivation that is still used in the neighboring villages, which are further away from the mangrove forest. This kind of local development of new – and therefore risky – agricultural methods has only been observed in a handful of areas worldwide (Siegmund-Schultze, personal communication). In Tamatateua, it is supported by the proximity of the mangrove ecosystem and its resources. The more remote “islands” at the edge of the village are covered with secondary forests (caporeira) and cultivated with traditional slash and burn techniques as is still common in many rural areas in the tropics (Hiroaka 1995; Conklin 1961; Fox et al. 2000). The improved infrastructure which facilitates communications is an important driver of agricultural innovation in Tamatateua. Mangrove goods and services act as an economic buffer and fall-back option in times of crisis for local households.
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This reduces the risk associated with innovation and has allowed the necessary local scope for experimentation with new production techniques (Klose et al. 2005). Not only agricultural innovation but also the collectively established mangrove honey house in the village demonstrates this. The charismatic village leader who acted as a key steward and source of information in the transformation of the local agricultural system was a further important support to the transformative innovations that occurred in Tamatateua. A key steward, or “policy entrepreneur” (Kingdon 1995), is a person who improves problem perception of a community and initiates key processes (Olsson et al. 2004a), vis-a´-vis attaining a political objective. As such a key steward, the village leader of Tamatateua was able to communicate the potentialities of novel production techniques and maintaining mangroves according to the State regulations effectively among the local residents. The co-evolution of Tamatateua’s agricultural system with the adjacent mangrove system has promoted innovation and higher productivity in land and labor use (e.g., crop intensification, development of better tools). The perception of mangroves not only as an important source of alternative livelihood but also as a “piggy bank” or form of risk insurance has generated additional room for manoeuvre for villagers. A high level of cooperation and social cohesion within the village, probably promoted by the joint work in agriculture, also promoted innovative transformation. The establishment of a village radio station, where local affairs are discussed, is an example. After the village leader unexpectedly died in 2003, other locals took over as stewards and maintained the village development momentum, underlining the importance of local social capital. The strong local quest for sustainable well-being made families and especially adolescents decide to remain resident in Tamatateua. This stands in marked contrast to the general trend of rural migration to the cities elsewhere in Brazil (Fischlowitz and Engel 1969; Henkel 1994).
21.3.2.3
Driving Forces in the SES
The current social-ecological system of Tamatateua was shaped by the government decision to facilitate better road access to coastal resources in the mid-1970s. Since then, this local SES has been moving along an innovative and positive development path. The relatively high level of social capital in the village, in combination with local innovative leanings, and a higher incidence of social and occupational diversity in Tamatateua acted as key drivers of change. Innovation, especially in creating new alternative sources of income in agriculture, was possible because, in the context of open access to nearby mangroves, the perceived risk to livelihoods was low. In Tamatateua, the late village leader, Elias da Silva, was an important key steward who perceived and used the advantages of the public policy move to facilitate better access to coastal resources, whilst at the same time was capable of effectively communicating these to the local residents. This leader promoted new local system perceptions by focusing on the formerly underestimated role of mangroves for local livelihoods. This initiated social-institutional key processes,
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which triggered innovations in agricultural production techniques and supported the realization of new income options from the mangrove ecosystem. These processes have direct links to local resource use dynamics and ecosystem state. Changes in environmental perceptions, socio-economic dynamics and local mangrove use and protection are interlinked. The interviews and public meetings showed that high local social cohesion and the local willingness to protect mangroves and their goods and services are the major reasons that locally available surplus is directed towards more productive innovative forms of agriculture.
21.3.3 Social-Ecological Systems as Co-evolving Entities Co-evolutionary trajectories can vary substantially between natural entities, within small geographic areas and over time. Such differences can be analyzed by carefully tracing the rationales and actions of human agents in their feedbacks with natural dynamics. Social structure and processes are thus co-evolving components of socialecological systems. They play a similarly central role as indicators for the state of a coastal system as for instance the hydrodynamic signatures have come to play. The need to include nature and its dynamics in the analysis of the sustainability of human uses of nature is evident in both our village examples. To the construction of an access road, which was the original force driving the transformation for both villages, Ajuruteua and Tamatateua, each responded with very different trajectories of development. While the interactions between human activities and natural forces reenforced erosion with a host of associated problems, which drove Ajuruteua to its current negative path, the inhabitants of Tamatateua developed their own initiatives and succeeded in driving their local SES onto a positive transformative new trajectory. However, Tamatateua’s positive trajectory of change was only possible with a change in the perception of the nearby mangrove area. From the local viewpoint, it changed from a source of subsistence for the poorest to an emergency resource for innovative farmers. Thus, what appears to be a typically homogenous agricultural frontier development at first glance is driven by local land-use decisions and perceptions of the specific environment in which people are located. The recognition of the connectedness between socio-economic well-being and the mangroves provided security so that the risks of experimenting with innovative agricultural approaches were locally rated as acceptable. The identified undesirable linkages (or, in systems language, mutually reinforcing “positive” feedbacks) between geomorphological and socio-economic instability in Ajuruteua are, however, not cast in stone. Local empowerment with available research knowledge may facilitate more desirable co-evolutionary patterns. Better knowledge, for instance, on the patterns and drivers of local erosion, would enable local people to increase their adaptive capacities and strategies vis-a`vis the natural sources of instability so that alternative options for action may surface for the local residents.
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In both villages, local knowledge systems appear as a central element in the search for desirable social-ecological co-evolution patterns.
21.4
Sustainability Visions and Indicators
21.4.1 Introduction Marion Glaser and Martha Fontalvo-Herazo In order to support the governance and management of social-ecological dynamics, an integrated and comprehensive vision of an ecologically and socially sustainable future for the regional mangrove-people complex was needed. This required: 1. The participatory and – ideally consensual – envisioning of desirable future(s) for the SES; and 2. A long-term monitoring system to ascertain whether important system variables are developing in desirable directions. To pursue these objectives, we initially assessed the societal interpretations and aims relating to possible sustainable future(s) for our mangrove SES. For this, major stakeholders in our system, such as the MADAM natural and social scientists, environmental administrators and political decision-makers, ecosystem users and other groups interested in or affected by coastal management, were interviewed on an individual, household or focus group basis (Glaser et al. 2006). Table 21.2 shows the diversity of coastal management objectives identified for the major coastal management stakeholders. Stakeholders0 rationalities and their objectives differed greatly and Table 21.2 necessarily presents a simplified picture: The number of stakeholder groups in our social-ecological system was much larger than listed,8 and differences in coastal management objectives existed not only between but also within stakeholder groups. For instance, the attitudes and perceptions between MADAM scientists from different disciplines differed. While some included the satisfaction of human basic needs, participation and human well-being into their definition of the goals of sustainable system management, most natural scientists associated sustainable mangrove management exclusively with levels of resource exploitation. Social scientists, on the other hand, saw the objectives of sustainable management as
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Seven spatial/organizational levels with over 30 different stakeholder groups, each with a specific combination of coastal management priorities, were identified over the 10-year duration of the research program in a long-term iterative process (Glaser and da Silva Oliveira 2004).
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Table 21.2 Stakeholder-specific sustainable coastal management objectives for the mangrove coast of Braganc¸a, Para´, North Brazil Stakeholder Sustainable coastal management aims in the research area MADAM program Create new system knowledge, protect mangrove ecosystem GTZ/ProRenda Decentralize administrative structures, create alternative incomes for poor rural residents United Nations Development Program Sustainable coastal resource management (UNDP) through the promotion of income alternatives for mangrove-adjacent communities Federal University of Para´ State (UFPA) Build human capacity, generate new knowledge Federal environmental authority Effectively administrate federal protected areas (IBAMA/CNPT) State Development Bank (BASA) Effective funding of production Federal administration of land (DPU) Administrate territories, prevent extractive use of mangrove areas National and State Associations of Improve quality of life, productivity and social Fisherfolk (MONAPE and MOPEPA) organization of coastal fisherfolk Socio-environmental NGOs (e.g. FASE) Organize poor coastal dwellers, promote environmentally sound production Ministry of Health of Para´ State (SESPA) Improve public health in coastal areas Ministry of the Environment of Para´ State Administrate nature and protected areas, promote (SECTAM) environmental education and research Military police of Para´ Implement nature protection laws and guarantee public safety Municipal school office Provide primary and environmental education Municipal agriculture and environment Promote agricultural development and office environmental protection Fisherfolk cooperative (Colonia dos Improve access of fisherfolk to old age and health Pescadores) security Rural workers’ cooperative (Sindicato dos Improve quality of life, productivity and social Trabalhadores Rurais) organization of rural workers Local social-environmental NGO Promote social organization and environmental (AMOVMARE´) education of mangrove-adjacent rural populations
related to the level of human quality of life, to a balance between human needs and the limits of nature, equity and justice and to the need for participatory structures. Over time, the scientists of the various disciplines learnt much from each other and the MADAM researcher team generated an important base for productive interdisciplinary research. However, even after years under the umbrella of the same research program and working within the same geographical region, the definition of sustainable coastal management remained somewhat contested between the natural and social scientists on the program (for more details, see Glaser et al. 2006).
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21.4.2 Case Study: An Indicator System as an Integrative and Transdisciplinary Tool To ensure transparency and to facilitate the management of social-ecological dynamics according to agreed objectives, the ability to monitor change over time is essential. In the context of our work on the north Brazilian coast, the first step was to define sustainability in the specific regional social, ecological and cultural context of our regional SES taking into account the diversity of stakeholder viewpoints shown in Table 21.2. Sustainability thresholds then needed to be established, and the combined functioning of the social-ecological system needed to be regularly monitored and analyzed. We thus started the development of an integrated indicator system for the Caete´ mangrove SES (Fontalvo-Herazo 2004; FontalvoHerazo et al. 2007). Sustainability criteria were our second step towards indicator development. Good indicators provide relevant information about important changes to guide future decisions and actions. Indicators are valuable when spatial and temporal coverage is sufficient to allow meaningful comparisons. Central criteria for a good indicator are: scientific validity and reliability of statistical measurement, resonance with decision-makers and ecosystem users, responsiveness to change, and data availability with affordable inputs (Ehler 2003; Bossel 1999). Many early ecosystem and coastal management indicator systems were resource-specific and eco-centric (e.g., IUCN 2001). Thus, human “consumption” was only interpreted as “ecosystem predation”, and “social” indicators reflected an exclusive orientation towards the preservation of ecosystems in their “pristine” state (Kumari 1995; Ruffino and Isaac 1995). Human well-being, on the other hand, was frequently omitted from management objectives in such approaches. Data on people’s perceptions of and responses to changes in their natural environment and equity and distribution issues surrounding the regulation of human uses of nature were scarce to nonexistent (Bradbury and Rayner 2002). Our indicator development for the sustainable management of our mangrove SES (Fontalvo-Herazo 2004; Fontalvo-Herazo et al. 2007) aimed to move beyond this. Visions of a desirable future and a set of corresponding coastal management indicators were developed by natural and social scientists as well as by different village groups (of men and women, with different occupations) in an iterative, participatory way. Participatory workshops for problem identification, future visioning and interactive indicator development were held with villagers. This was followed by a period of technical indicator development which also used a system-based “filtering process” to reduce the indicators to a manageable number without losing the ability to assess the fulfillment of central stakeholder concerns and of social-ecological system viability conditions (Fontalvo-Herazo 2004; Glaser 2007; Fontalvo-Herazo et al. 2007). The resulting set of indicators was merged into an incipient SES monitoring system.
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Criteria (Second level) High education, culture and recreation are accessible to everybody
Well - being of coastal population is assured
Governance performance is assured
Population health and social security are guaranteed
•Percentage of people studying •School facilities •Number of cultural and recreation events
•Health resources and facilities •Number of malaria and dengue cases •Mortality rate under 5 years old
Basic infra-structure facilities are guaranteed
•Density of people by house rooms •House quality
Empowerment of coastal population is guaranteed
•Number people that belongs to an association •Participation in research and technology projects •Citizen participation
Social conditions
•Mean family income •Employment rate •Number of inhabitants
Governance mechanisms are established
•Formulated and implemented local development plans ratio •Village representation at municipality council
Coastal ecosystem status is maintain
•Land use change over time •Species diversity •Percentage of mangroves trees area cut •Percentage of secondary forest trees area cut •Percentage of seasonal field wetlands area burned •Percent of beaches and dunes area •Coastal and marine protected areas •Fisheries grounds •Mangrove areas differentated by mangrove types
Ecosystem use is sustainable
•Mangrove extractivisim •Number of crabs collected •Quantity of fish specles landing at the villages
Coastal ecosystems integrity is assured
Economic diversification is needed Economic structure is assured
Indicator (Third level)
•Number of income alternatives
Production level is maintained
•Amount of agriculture products for sale •Financial support to small producers and fishermen •Amount of fish for sale •Amount of crabs for sale
Market structure is guaranteed
•Number of commercial products •Number producers selling directly to the market
Fig. 21.5 Indicators for monitoring the sustainability of a mangrove-based social-ecological system (adapted from Fontalvo-Herazo 2004 and Fontalvo-Herazo et al. 2007)
Our case study process and the resulting indicator system (Fig. 21.5)9 are thus prototypes for a generic approach to the participatory visioning and monitoring of sustainable SES futures. Our assumption was that stakeholders whose decisions determine the future of their natural and social environment need a central role in
9
Figure 20.5 shows just the social dimension which was elaborated by all stakeholders groups.
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determining what this future might be and how its attainment might be assessed. Monitoring systems and the data they provide have an impact on system governance and management. Our hypothesis was that a participatively designed and implemented monitoring system will empower SES stakeholders to take an active part in sustainable management. In our study area, the continuing self-organization of previously disorganized village and mangrove producers beyond the time horizons of the MADAM program confirmed this hypothesis (Glaser and Diele 2004; Glaser 2007). The aim of implementing participatory SES monitoring on a long-term basis remained far from achieved in our study region in late 2005, by the end of the MADAM program. However, local residents in mangrove-adjacent areas, crab collectors and fisherfolk, honey collectors, and also young researchers at the regional university had clearly gone through important learning processes related to local self-organization for coastal management. Village development programs had moved onto a self-sustaining basis, villages were maintaining their own support networks (including a community radio, a number of associations and training programs), and regional associations of mangrove stakeholders were forming and continuously increasing the scope of their activities and ambitions, accompanied by the supporting analysis of regionally based academics. Different uses of the locally rooted integrated sustainability monitoring system that we propose are possible. The “star diagram” or “sustainability wheel” in Fig. 21.6, for instance, achieved the visualization, in an integrated comparable manner, of some central biological, social and economic indicators on the sustainable development of the crab fishery in our study region over a 4-year period (1998–2001). As indicator values move towards the outer edges of the four data axes,10 sustainability increases. The choice of indicators in Fig. 21.6 is problem-based and transdisciplinary, i.e. it includes the priorities of nonacademic stakeholders as well as social and natural science criteria. Thresholds of concern distinguish those dimensions of sustainability that remain within the absolute limits of SES viability and sustainability from those that do not. For instance, the crab fishery income passed its threshold of concern in our monitoring period when full-time work no longer provided incomes equivalent to the minimum wage level to the crab collector.11
21.4.3 The Social Dimension The most striking difference between the indicator system we developed in our case study and many other indicator systems of sustainable coastal management 10
More data axes are possible, so that such visualizations could take the shape of a star or a wheel with many “spokes” or even an amoeba as Bell and Morse (1999) have named such dynamic integrated presentations of multi-faceted change. 11 Brazilian minimum wages are based on the regularly assessed cost of a “basket” of goods for the satisfaction of basic local needs.
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concerns the relative importance of the social dimension of ecosystem management. The “social” in our case study system is an integral and coevolving part of the social-ecological system. In our participatory analyses, a clear primacy of social aspects emerged: 50 of the 77 indicators of “a desirable future for the region and community” which were developed by residents related to social issues. This should not surprise us: as local system stakeholders gain a voice in ecosystem management, their priorities are likely to move center stage. While the ordering of social priorities differed between men and women in our case study SES,12 all village respondents emphasized health, transport and communications infrastructure, political representation and better education as required for local communities to maintain a viable mangrove ecosystem. In contrast to this, early social indicators merely monitored the human consumption of ecosystem goods and services. For this, bio-physical indicators – for instance on rates of fish reproduction or tree growth – were combined with social data such as human population size and growth and resource use rates. Effective ecosystem management, however, also needs to include the priorities of those who depend on the ecosystem. Indicators on social-ecological sustainability therefore also need to provide information on social sustainability. Transdisciplinary approaches which involve the active participation of different system actors Social School attendance ( %) 100
2001
1998
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Sustainability thresholds 80 70 1,8
1.4
Economic Crab fishery income (% of minimum wage)
1,2
0,8
0,6
6
7
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60 80 110
9
10
Biological Capture size of U. cordatus crabs(cm)
140
170 200
Economic Productivity of labour (crabs per man day)
Fig. 21.6 “Star diagram” or “sustainability wheel” for the visual integration of indicators
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On gender issues and changing female room for manoeuvre in the MADAM program area, see Henrique (2005).
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Box 21.1. Interlinked Vicious Circles: Social-Ecological Dynamics in a Mangrove-Based SES Rural people living near the mangroves around Braganc¸a see low family income, little formal education, high risks to health, and a decrease in natural resources availability as their major problems. For many young people and most women, this goes hand in hand with the lack of employment. This increases their dependence on mangrove resources. Most of those who work in the mangroves do not have their own means of transporting products to markets and lack the resources (including public social insurance and formal lines of credit) to cope in difficult times such as illness in the family. In exchange for support in such times of emergency, they therefore accept lower prices for their products from “patron” traders on a one-to-one basis. As their parents only earn near minimum survival incomes, many children drop out of school to contribute to family subsistence. Few manage to finish secondary school and none get to university. Lack of technical training further reduces occupational options. As a result, most rural youth remain unemployed or – unwillingly – take up their parents’ occupations in fishing or mangrove crab collection. This pushes successive generations into the same dependence on the traders of mangrove products and, with growing numbers of local people, it also increases the pressure on local mangroves. Alcoholism, prostitution and drugs consumption are becoming more common among the young. Health services, social security, and sanitary conditions are deficient. Many female-headed households can only afford one meal per day. Especially for poorer local households, mangrove areas are an important emergency buffer, supplying food and other resources. . .
and which combine ecological with economic and social criteria are required to understand the linkages between socio-economic and ecological dynamics. For our mangrove SES, some of the more important social-ecological linkages are described in Box 21.1. Our study SES thus displays a number of “vicious circles” of interlinked, mutually re-enforcing social-ecological dynamics surrounding mangrove use, which clearly undermine social, economic and ecological sustainability. These vicious circles contain important feedback loops between different mangrove resources and mangrove-based livelihoods. Sustainability indicators will improve our understanding of these dynamics over time and prepare the ground for more efficient governance and management. They will also allow an assessment of the various social, institutional, economic and ecological aspects of sustainability and their interconnections. If indicators reflect stakeholder interests, participatory longterm monitoring should support sustainable development. In the final stage of MADAM work in our mangrove SES, we assessed which local organizations might be interested and able to monitor different selected indicators on a regular basis. Residents’ associations, local public health officials
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and youth groups, and school classes were identified. Time will tell whether this participatory monitoring survives over the longer term. However, the indicator system developed for our mangrove SES combines the different priorities and knowledge types of a wide circle of system stakeholders, including local residents and researchers, who jointly defined problems, objectives and criteria, dealt with conflicts, and combined their relevant forms of knowledge. The research results of the MADAM program were thus brought into a longer-term inter- and transdisciplinary knowledge generation process. The indicator system lays the foundations for system stakeholders to pursue improved outcomes according to transparently developed sustainability criteria.
21.5
Participatory Management of Coastal Ecosystems
Marion Glaser and Rosete da Silva Oliveira In one of the best known articles on natural resource management, Hardin (1968) argues that common access to a resource always leads to its degradation since the benefits of (over)use accrue in proportion to resource use, while the costs of (over) use are shared equally between all users. Hardin overlooked that social capacities can prevent such “tragedies of the commons”. Since then, the social mechanisms which promote cooperation in the commons have been investigated by hundreds of researchers.13 The clear differentiation between open access and common pool resource management regimes has become crucial in these investigations, and the appropriate degree of participation under different economic, social and ecological conditions has become a central theme. It is agreed today that effective participatory resource management regimes need to be closely matched to regional and local social, economic and ecological conditions (Cinner and Aswani 2007; Ferse et al. 2010; Glaser et al. 2010). However, the active participation of local stakeholders (i.e. community management) is no panacea. Thus the concept of comanagement gained ground. Co-management refers to arrangements where “. . .responsibility for resource management is shared between government and user groups” (Sen and Nielsen 1996). Different degrees of participation for natural resource users are possible under co-management ranging from between “being informed of decisions already taken” to “actively taking and implementing decisions” (sensu Arnstein 1969). Rights and duties in resource management can thus be distributed in different ways between public authority, user groups and other actors implying a range of possible interactions between public and private co-managers under co-management. Co-management has become the main approach in the increasingly common situations of open resource access with a growing human population, rising 13
See homepage of the International Association for the Study of the Commons (IASC).
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unemployment, new technologies, and increasing demand for nature’s products and services. Such conditions also prevail in our study area on the north Brazilian coast. At the same time, the survival strategies of rural people are also still highly dependent on the subsistence goods and services provided by the mangrove ecosystem. Growing commercial pressures on the ecosystem and the failure of coercive, top-down conservation approaches are increasingly obvious features of our system. There are strong and consistent contrasts between the aims of legislation and the outcomes in land use, fisheries and the use of mangrove trees. The implementation of environmental legislation that was developed and “handed down” by the State has failed, and unsustainable outcomes prevail. Inequity with particularly negative social sustainability implications, such as the criminalization of firewood collection by the poor, a lack of social protection for logging workers, and hostility of locals towards conservation authorities have resulted from top-down resource governance and management regimes which ignore local social needs. The Brazilian ban on the use of mangrove wood and its counterproductive on-the-ground outcomes provide a particularly stark example of the negative coevolution of top-down environmental legislation, resource use and social outcomes14: Current Brazilian legislation totally prohibits the use of any mangrove flora. However, on top of a diverse range of mangrove wood uses (Glaser et al. 2003), about 90% of rural residents in mangrove-adjacent areas rely on mangrove wood as their only option for domestic cooking.15 Our investigations concluded that even the best equipped public authority is unlikely to stop the cutting of mangrove trees if it ignores the socio-economic needs of local populations associated with the use of this resource. In accordance with studies elsewhere (Ruddle 1989; Pomeroy 1995; Johannes 1998), dynamics in our north Brazilian mangrove SES thus confirm that resource management which portrays people only as “predators”, without recognizing legitimate livelihood objectives behind human ecosystem uses, has poor implementation prospects. The lack of user participation in the planning and implementation of mangrove management legislation has caused implementation failures for numerous legal restrictions on the exploitation of natural resources. The conclusion that “the laws are good but implementation has to be enforced” needs to be revised where institutional development has occurred in a top-down manner. Without a voice in the development of rules for the conservation and management of their own immediate natural livelihood support system, ecosystem-dependent rural communities have and will continue to devise and implement their own alternative rules and practices. 14
For other examples, see Glaser and Diele (2004) and Chap. 17 on the management of the mangrove crab Ucides cordatus; and Krause and Glaser 2003 on the regulation of coastal land use in our mangrove SES. 15 This result is not reflected in Fig. 21.2 since interviewed rural dwellers do not tend to admit these practices which, though locally considered legitimate, are against the law. Our subsequent, more unconventional investigations allowed us to obtain a more realistic approximation to the real rate of mangrove wood use in the study area (Glaser et al. 2003).
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In the context of considerable empowerment of traditional natural resource users (e.g., rubber tappers, indigenous forest dwellers) since the late 1980s (Simonian 2000; Simonian and Glaser 2002), this conclusion has come to be shared by many Brazilian coastal policy-makers and legislators. Under the national constitution of 1988, user participation in the co-management of natural resources thus became possible under the RESEX concept (Allegretti 1994, p. 19). The RESEX explicitly breaks with the top-down, centralized “keep people out” ecosystem conservation which had thus far characterized Brazilian conservation policy. For some experts (Diegues 2007), the RESEX creates an “alternative map of conservation in Brazil”. Its historical roots lie in the late 1980s, when extractive workers, mainly rubber-tappers from the Brazilian Amazon forest, struggled for local resource rights so that they could stop the encroachment of commercial logging companies and instead continue to use ecosystem resources in locally determined socially and ecologically sustainable ways (Allegretti 1989, 1994; Mendes 1989; Menezes 1989). The formal RESEX concept was a response by the Brazilian federal government to growing local and regional social organization, resistance from rainforest people to the loss of their customary rights as well as to growing international criticism of the destruction of tropical forests and local livelihoods. The introduction of the RESEX approach to Brazilian coastal areas and thus the inclusion of coastal fisherfolk began in the late 1990s. The objectives of the RESEX are: 1. 2. 3. 4.
To protect nature through sustainable utilization To improve the living conditions for the traditional users of natural resources To integrate traditional users into national development processes To promote participation in the sense of users deciding and acting together
Under RESEX co-management, local communities develop local resource management rules and development plans and then form regional associations for wider conservation and development purposes. The federal conservation authority (IBAMA) passes the regionally developed rule framework through a national level approval process and assumes management responsibilities in case of serious infractions, which local communities cannot handle on their own. This bottom-up process of institutional development offers considerable scope for the integration of local priorities. Indeed, the formation of coastal RESEX is only undertaken at the request of local communities, which usually occurs in the context of a natural resource-related conflict or problem. Coastal RESEX belongs to a “second generation” of co-management initiatives in Brazil. In contrast to the “first generation” rainforest RESEX, they are generated within a formal institutional environment, which offers various forms of public support to rural residents. Coastal RESEX, such as that in our study area, are also implemented in much more densely populated, economically and socially more diverse environments than the pioneer rainforest initiatives with their ethnically homogenous isolated and internally cohesive small groups of forest populations (Simonian and Glaser 2002).
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The development of coastal co-management under the RESEX approach in Brazil is an ongoing process. While new local and regional governance and management potentials are apparent, there are also a number of possible problems. The major limitations of the approach in our study area were: Resource scarcity at the state and community level: Beyond the question of who gains from and who bears the costs of coastal co-management, the reoccurring problem of scarce financial and human resources for management at the public and at the community level raises the question: when does co-management become “unaffordable” to community co-managers? A lack of funding for transport and personnel responsible for the RESEX arrangements leaves communities alone with problems they cannot solve (e.g., the encroachment of powerful outsiders) and endangers the chances of successful co-management. Weak public knowledge: There was a need for better public information on the rights and duties associated with the RESEX concept, on legal options and on the limitations of the co-management concept posed by pre-existing legislations. Weak community organization and leadership: Communities themselves identified the inability of local players to assume leadership positions in co-management as a limiting factor and they initiated planning for leadership training. Future success in local self-organization may well hinge on these learning initiatives. Obstacles from powerful official players: The RESEX model was developed in the context of a power struggle between federal and state institutions in Brazil (Glaser and Krause 2005). As public agencies compete for spheres of influence, they eliminate each others’ successes in the process and create serious obstacles to successful co-management. At the time of our study, a reportedly very rare period of cooperative relationships in coastal management existed between the environmental authorities of State of Para´ (SECTAM) and those at the federal level (IBAMA). This allowed local communities to develop their capacities for participatory management under the federal RESEX concept without obstruction from the state level. However, such cooperative relations between state and federal authorities depend on good interpersonal relations between the concerned federal and state officeholders and are extremely vulnerable to political change. Our hesitantly optimistic conclusion is that, during such temporary “windows of opportunity”, local resource co-managers might be sufficiently capacitated and empowered to defend their management rights in periods when federal and state authorities are less cooperative.
21.5.1 Outlook In our co-management case study, alliances in support of coastal co-management had formed behind different, relatively powerful political/ideological interests. Local agents and groups then rallied behind these as client constituencies. Under the coastal RESEX model, the State delegates management responsibilities to local ecosystem users while these gain the right to formulate, but also the obligation to
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implement and monitor resource management rules. A particularly important incentive for system users to participate in mangrove management in our study area was the right to exclude outsiders from access to mangrove resources. However, this right, which local users assume to be contained in the RESEX comanagement model, stands in contradiction to other, older Brazilian environmental legislation. The resolution of such ambiguities and increased transparency on the rights of local co-managers now under way will greatly improve the prospects of mangrove co-management in Brazil.
21.6
Scenarios for Mangrove-Based Social-Ecological Systems: Linking Futures Across Stakeholder Rationalities
Gesche Krause and Marion Glaser Since it involves multiple actors with multiple views and interests, the participatory management of social-ecological dynamics needs to be supported by the formulation of group visions of possible and of desirable futures. Scenario-building is a tool for this task. It helps to reveal underlying ambiguities, to improve the transparency and outcomes of local management decisions, and it promotes the understanding of the rationalities and choices of the multiple actors involved.
21.6.1 Setting Up Social-Ecological Scenarios Alternative management options for social-ecological systems can be explored via the participatory development of scenarios. Scenarios are descriptors of what the future could be, rather than predictions of what it will be (Walker et al. 2002). The participatory exploration of plausible futures discloses stakeholder-specific decision-making rationalities. Such scenarios allow for an emphasis on societal values, perceptions, networks and system user priorities (Manuel-Navarrete et al. 2004; Hosang et al. 2005; Bodin et al. 2006). It also allows the exploration of alternative livelihood options. Moreover, ecological feedbacks and management policies influence local livelihood options and can intensify the human modification of ecosystems, creating a vicious circle of poverty and ecosystem degradation (see Box 21.1). The scenario approach focuses on the causes of changes that matter for sustainable management. Such causes of change could be, e.g., ecosystem shifts, which can occur rapidly but may alter the availability of ecosystem services for generations. Therefore they pose special challenges for long-term thinking (Carpenter et al. 2006). In our scenario study, we used interviews with key stewards, local leaders and outcomes of several workshops at village level as well as natural science findings to
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help identify the main contrasts between major possible futures. Although many imaginable futures might be explored, scenarios are most powerful as a small set of clear and strikingly different options (van der Heijden 1996). Assumptions about the future tend to cluster. Therefore, we developed three coherent scenarios in which we placed a special focus on management policies. We based the scenarios on a mixture of qualitative and quantitative analyses of various complex dynamic components of our SES and expert opinions on their interactions. The management scenarios, which will described in more detail below, were (1) “business as usual”, the system polarization scenario, (2) the “worst case”, or threshold shifts scenario which indicates transformation into an unsustainable system, and (3) the “desirable” or adaptive change scenario towards sustainability. The management scenarios focused on two main system drivers: (1) changes in legislation, and (2) the enforcement of mangrove use bans. Here, we explore how management conditions generate SES outcomes. We consider the different rationalities of various mangrove ecosystem user groups and the potential outcomes of their choices of ecosystem use under different management and governance regimes, including various interpretations of social equity in adaptive management. A detailed discussion is found in Krause (2002) and Krause et al. (2008).
21.6.2 Possible Futures of the Mangrove-Based SES 21.6.2.1
SES Boundaries and System Actors
The spatial boundaries of our SES follow the geographic definitions given in Chaps. 1 and 9. As elsewhere in the tropics, our SES agents are mainly children and adolescents, with over 63% of the total population less than 20 years old (IBGE 2000). Most SES residents rely on subsistence production. Land, mangrove and institutional dynamics are the three central arenas where natural and social dynamics co-evolve. A broad definition of institutions, derived from the sociological and anthropological literature, is taken here. They comprise formal and informal norms and rules of the system users. In our SES, crab collectors, fisherfolk, traders, tourists, female-headed households, and other stakeholders interact with each other and the mangrove system on different levels (Glaser 2003). In order to reduce the complexity of this scenario analysis, the following discussion considers only the rationalities of “rich” and “poor” local agents. The majority of the agents are risk takers who live within the SES boundaries. However, an increasing number of agents live outside the local SES in the adjacent town of Braganc¸a or even in Bele´m, the capital of Para´ State. Changes in the local SES do not threaten their livelihood, SES-related risk for them relates to loss of luxury assets, such as weekend housing (personal interviews with residents, 1997–2001). Ecosystem user knowledge, defined as the factor that provides human societies with the means to deal with their natural environment and to actively
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modify it (Holling et al. 1998), is not well established in the area. This can be attributed partly to the increasing number of agents who live for the most part of their lives outside the SES, and therefore are not well acquainted with the natural system processes, but also to the rather recent immigration of the local agents in the early 1970s. However, local SES actors share several informal communication arenas: churches, fishing/agricultural associations and football grounds. The football ground is a central component of contemporary rural social capital in Brazil (Mitlewski, personal communication) and local churches play a key role for the degree of social cohesion, social networking and conflict in rural areas (Krause 2002; Krause et al. 2008).
21.6.2.2
Scenario 1: System Polarization
Our first scenario assumes that the observed trends persist; the mangrove ecosystem remains viable, but it is subject to strong exploitation. Management policies are not enforced. Continuous coastal migration and tourism growth create mutual dynamics of self-organized relationships without any prospect of consolidation or management. Such mutual relationships also occur between mangrove productivity and fisher folk survival. The State of Para´ supports ongoing change. Its regulatory efforts are mirrored for instance in the establishment of a permanent health post in the fishing village of Ajuruteua and by a public safety police patrol during peak seasons. Management efforts are mainly directed towards public safety, but aggravate local social disparities as they increase the unequal distribution of incomes and opportunities (Glaser and Krause 2005). The social polarization under illegality continues (Krause et al. 2008). Those agents who are well-connected within the political arena maintain “client” relationships with the local decision-makers. These system dynamics can be described by the adaptive cycle model, in which the temporal changes of a system proceed through phases of growth (r), conservation (k), release (Ω), and reorganization (a) (Gunderson and Holling 2002). The current system characteristic of our SES can be linked to the “r-phase” in which the brief initial stage of development, the r stage, consists of the rapid exploitation and garnering of resources by system components. Since “ecologically illiterate” actors predominate, the SES displays a very limited social memory. Social memory is understood here as the accumulation of experiences concerning management practices and rules-in-use that ensures the capacity of social systems to monitor changes and to build institutions that enable appropriate responses to environmental signals (McIntosh 2000). As newcomers to the system have little option but to use mangrove resources unsustainably, socioeconomic inequality is worsened and the SES may move beyond the limits of sustainability. A case in point here is the intensive use of the mangrove crab (U. cordatus): This does not threaten biological sustainability, but the social sustainability of crab collectors’ households, as the financial returns from crab
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collection decrease below the legal minimum wage which covers the crab collectors’ basic needs (see Fig. 21.6 and Glaser and Diele 2004). At this threshold of concern, territorial disputes between crab collectors increase. This economic overfishing, caused by “business-as-usual” behavior, intensifies polarization and disparities between mangrove crab collectors and other groups. Social polarization, enforced by lack of political representation and formal social rights (e.g. old-age pensions) for crab collectors are a key feature of this scenario. The widening social disparities could eventually propel the SES into a threshold shift scenario. 21.6.2.3
Scenario 2: Threshold Shifts
Management policies are a key influence on the dynamics of this scenario – they can either be poorly designed with respect to ecological and social system thresholds, or attempt to rigorously enforce locally unrealistic policy objectives. For instance, for the latter, if both the State of Para´ and the Federal Government rigorously enforce the legislative objective of nonuse of mangroves as a reaction to the recognition that key mangrove resources have moved beyond a threshold of concern, then social sustainability thresholds are passed. Such a management measure would aim to avoid a system shift towards an ecologically unsustainable situation. The State might confront elites (e.g., tourist entrepreneurs, land speculators and logging companies) and take action against legislative abuses by these powerful groups. The motivation for strict law enforcement may be to warn other mangrove users to respect the law. This may support the ecological sustainability of the system. On the other hand, the resulting de facto expropriation of local communities would cause current livelihood strategies to disintegrate. Thus, a “worst case” scenario for the social system results. However, since it still remains possible to access the mangroves for visiting purposes, such a change of policy may also open novel opportunities. For example, boat access to mangroves for eco-tourism could be established, providing local fishermen with new means of income generation. However, the authorities must provide human resources and support in the initial stages of such an alternative use scenario. At the same time, the mangroves would experience a phase of renewal and self-reorganization, as ecosystem resilience is likely to remain intact. If successfully implemented, this would be a powerful management measure of the State, to achieve a more even distribution of economic wealth. However, since State and other elites are closely intermeshed, this type of change is rather unlikely. The threshold shifts scenario underlines the importance of better understanding the underlying rationalities human resource use as drivers of management decisions and SES dynamics. 21.6.2.4
Scenario 3: Adaptive Change
Our adaptive change scenario assumes that cooperation and community-focused values gain prominence in management efforts prior to a system crisis. System
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agents’ norms and values are sustainability-oriented and go beyond mere competition to maximize individual gains (Krause et al. 2008). Our central hypothesis for this scenario is that human reflective capacity is sufficient to establish locally rooted adaptive management and that this can generate a positive SES trajectory. In this scenario, the Brazilian Federal Government overrules the current objective of the State of Para´ on the nonuse of mangroves by supporting the RESEX (Reservas Extrativistas) program. Under the RESEX, the government delegates user-rights to local coastal system users (see Sect. 21.5). This window of opportunity could generate local co-management schemes under the Federal Environmental Agency, IBAMA. This co-management approach focuses on the extent and quality of user participation in mangrove management and facilitates a more equitable distribution of benefits. The federal authorities would support local co-managers financially and technically to develop a mangrove utilization plan. The right to formulate rules locally is a central incentive for local participation. Cooperatives are established by different mangrove producers. Social structures and communication improve. Social capital strengthens and the locally perceived value of mangroves increases. In the long term, local capacity building is improved by schools and professional education. Regional vocational schools are established where mechanics, sales personnel, builders, cooks and nurses are trained. Local access to sources of income other than mangroves thus increases. The University of Braganc¸a intensifies environmental education. This enhances the attractiveness of local mangroves and beaches and contributes to community health. Local agents learn to better reflect on how their behavior influences environmental risks to livelihoods and how innovation generates positive livelihood outcomes. Participatory ecosystem and community management are essential in achieving this desirable trajectory for our SES. Yet, this may be undermined by low social memory and community cohesion in the villages of our SES, caused by high rates of immigration into the region and a range of other factors. Social capacities to cooperate, reflect and adapt are often underestimated in natural resource management (Glaser 2006). The potentials of participation and self-governance have been successfully explored and implemented in the Amazonian rainforest (Simonian and Glaser 2002). The transfer of such a management approach to the coast, although beset with a range of difficulties (Glaser and da Silva Oliveira 2004), is therefore a realistic scenario.
21.6.3 Inclusion of “the Social Dimension” as Central Element of Sustainability in SES The MADAM research area is an excellent place to compare different coastal and ecological processes and their interactions with various types of human resource use in a rather confined SES setting. Thus, what are the lessons of this short scenario exercise for decision-making in an integrated coastal management framework?
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Clearly, in the particular SES presented here, there is ample need to facilitate collective action for local common-pool resource management supported by the administrations on Municipal, State and Federal level. The scenarios show that, next to the ongoing natural processes, the behavior and choices of different actor groups strongly determine the future of the SES. In which future ways the SES is likely to proceed is strongly based on the options the local agents perceive. For all types of human activities, the ecosystem will set the limits to how large an activity can grow in relation to its resource base. Within this ecosystem framework, the social system with all its institutional and cultural aspects will determine how fast an activity is approaching these limits. This highlights the emerging demand for complex system analysis, which moves away from the spatial-sectoral disposition of ecosystem analysis to more realistic, dynamic and integrative studies of coastal systems. So far, the major costs of environmental degradation are borne to a disproportionally high degree by economically disadvantaged groups (Krause and Glaser 2003). This undermines social justice and causes social tension (Krause et al. 2008). The inability of poor crab collector families to engage in alternative income generation activities is an example. Crab collectors remain locked in the vicious circle of degradation of their very own resources. In the current SES trajectory, there are several thresholds of concern towards the stage where a “worst case” scenario may occur. In contrast, it is surprisingly difficult to imagine a trajectory redirecting the current social polarization trends directly towards a sustainable, resilient SES future. The scenario exercise implies that poverty mitigation is of priority over ecological concerns in this case study. Thus, the social structure has to be viewed as an active component of the SES. The type of social organization of a coastal community may play a similarly important role as an indicator for the state of a SES as the important ecological processes. Therefore, oversimplified definitions of local “community” are at the root of many co-management failures. The importance of social capital and of social and economic diversity and divisions in diverse community types is often ignored and communities are simplistically conceptualised (Davis and Bailey 1996). As every society is as poor as its poorest members (Lakshmi and Rajagopalan 2000), successful management strategies must acknowledge that poverty is both a cause and a consequence of short-term survival strategies and limited long-term perspectives. Especially in the tropical coastal areas, approaches need to keep pace with strong population growth, migration of ecological illiterate agents into the SESs, and with weak institutional enforcement of regulated resource use. The life-support values of many coastal SESs are at risk of being driven to threshold limits, where system shifts are likely. Conflicts over the control of natural resources, inevitably rise when direct and active participation of local agents does not take place so that the groups that retain their traditional access to resources, may find them less productive in the long run. There is therefore a need to establish clearer user-rights regimes for common-pool resources, as well as a well-defined, integrated scientific framework to support active participation and co-management in coastal areas.
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Local ability to predict and to affect local life circumstances, to rely on trusted networks in the community and the personal skills to participate, are prerequisites to successful system co-management (Jentoft 2000). Scenarios, such as those in this section, can help decision-makers to assess the positive and negative implications of alternative management regimes. Our scenarios are not forecasts or predictions, but plausible stories about how the future might unfold under alternative management strategies. They illuminate the possible consequences of different policies on the co-evolutionary interaction between stakeholder rationales and values and “their” associated natural systems.
21.7
Appropriate Knowledge for a Mangrove-Based SocialEcological System: Outlook for Future Work
Marion Glaser The major task of science is knowledge generation. The relevance of that knowledge to societal problems is a central challenge. This chapter closes by proposing seven challenges to a science which aims to support the sustainable governance and management of human–nature relations. These challenges were identified during the 10-year research on our mangrove-based social-ecological system on the north Brazilian coast. They are, however, also of more general relevance for the governance and management of the increasingly tightly interlinked social-ecological systems on current-day tropical coasts. Most tropical coastal regions are characterized by rural poverty and natural resource dependence of increasing numbers of resident human populations. Thus, throughout the different sections of this chapter, our mangrove research area, which had originally been selected for study as relatively “pristine” (i.e. untouched by human activities), appears as a tightly interlinked co-evolving social-ecological system whose development path is determined by human–nature interactions. Thus, the great majority of residents on and near the Braganc¸a mangrove peninsula depend on the mangrove ecosystem for important economic, social and cultural aspects of their lives including monetary and subsistence income. Our study area is therefore clearly part of the “mangrove cultures” of coastal north Brazil. The priorities, rationalities, values and knowledge of the direct users of our mangrove ecosystem centrally determine its development trajectory. Moreover, ecosystem changes also feed back into the change trajectory of the social system thus generating coevolving social-ecological change patterns. The seven challenges discussed below all require scientists to identify and generate knowledge and to connect different forms and types of knowledge with each other.
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21.7.1 Identify Undesirable Feedback Loops and Modes of Addressing Them In the language of systems theory and cybernetics, we have shown that the connections between social and natural components of the system display important feedback loops. There is, for instance, strong mutual enforcement between the lack of any social rights (pensions, healthcare, labor rights) for crab collectors and mangrove loggers and the increased resource exploitation levels these groups engage in to secure their survival with the help of patron–client relationships with product traders. A similar “vicious circle” of undesirable feedback loops surrounds the children of mangrove producers. Child labor in the mangroves such as collection of crabs, line fishing, wood collection and bird hunting supports poor mangrove producer families’ subsistence livelihoods; children find the daily food for their families while the crabs, fish or mangrove logs which their parents collect are sold for monetary needs. The products collected by parents are usually marketed through patronclient ties where producers receive low prices in exchange for basic security from their patrons. To complement insufficient family incomes, mangrove producers’ children are therefore responsible for providing daily family meals with their subsistence gathering and fishing activities. These children are therefore hardly able to attend school. Their consequently low levels of formal education leave them little option later but to – unwillingly16 – follow their parents into mangrove production (i.e. crab collection, fishing and/or charcoal-making). This vicious circle renders successive generations of unwilling mangrove producers vulnerable to the same poverty trap. Such “positive”17 feedback loops within our mangrove-based social-ecological system and their undesirable social and ecological implications need to be addressed at the root, as is being currently attempted by the Brazilian bolsa familia which financially supports poor families in return for their children’s regular school attendance.18 To increase the chances of breaking the type of dysfunctional social-ecological circle described here, science needs to provide political decision-makers with a comprehensive understanding of the rationales behind human behaviors towards nature and of non-human nature’s reaction to these. Novel interdisciplinary research approaches, such as participatory multi-agent modeling are being developed for this (Wilson et al. 2007; Yan et al. 2008; Glaser 2011).
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In over 100 interviews with crab collectors conducted by the MADAM socio-economic research team in the year 2000, none wanted their offspring to become crab collectors but almost all said they themselves collected crabs since no other options had been available to them. However, the great majority of crab collectors’ sons were starting in their fathers’ occupation. 17 Speaking strictly in systems language here. 18 While it is beyond the scope of this chapter to discuss these programs, they been reported to significantly reduce child labor and increase school attendance (Yap et al. 2001).
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21.7.2 Assign Adequate Values to Poverty Alleviation Functions The mangrove ecosystem is of central importance for the residents of our study region. Our quantitative findings on the subsistence and commercial value of the mangrove ecosystem were enforced by local residents’ statements such as “The mangrove preserves life in the village,” or “When there is nothing, we go there.” “It is our money tree.” and “We don’t have other work, we are all crab collectors”. The mangrove ecosystem decreases poverty and urban-bound migration from coastal areas, it increases household productivity and promotes social resilience. Indirectly, even criminality, another major alternative to destitution in our case study environment, is presumably mitigated by poverty alleviation through the use of mangrove resources. For the above reasons, we argue that, when poor human populations are heavily and directly dependent on ecosystem resources, the classic concept of economic value underrates the social functions of the mangrove ecosystem. Where the ecosystem assumes major poverty alleviation functions, only the explicit valuation and weighting of this essential social dimension can provide the basis for adequate management. In the context of widespread rural poverty such as in north Brazil, natural resource management needs to carefully take into account subsistence production, i.e., those ecosystem uses which never pass through the market but which nonetheless are central to local populations’ livelihoods. We have shown in Sect. 21.2 that, although commercially exploited species such as the U. cordatus possess a high monetary value, the subsistence production of this species, together with that of a range of minor mangrove resources (listed in Fig. 21.2) is essential for the food security of the majority of poor residents in north Brazilian coastal mangrove villages. In fact the monetary value, and even more so, the poverty alleviation impact of the subsistence production of the mangrove ecosystem surpasses its commercial importance. Mangrove management should therefore pay special attention to subsistence production including the “hunger-abatement foods for the poor” of mangrove origin which are neither marketed nor readily listed in open interviews19 but which buffer the most marginal rural coastal households in situations of absolute need. Not undermining the basis of livelihood security for the poorest SES stakeholders will need to be part of any viable management approach. While even the most holistic ecosystem management cannot achieve all social development objectives, the management of mangroves in our study area needs to at least maintain the current social and poverty alleviation functions of the ecosystem, or to identify workable alternatives for the mangrove-adjacent human populations. That this is not simple humanitarianism is shown by the large number of failed eco-centric approaches to the management of humannature relationships (Brandon and Wells 1992; Ghimire and Pimbert 1997; Glaser et al. 2003; Glaser 2006) These demonstrate that even the achievement of purely ecological objectives 19
Interviewees tended to be ashamed of admitting to be resorting to the consumption of some products (as one interviewee stated proudly “This is poor people’s food, we do not eat it”).
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of ecosystem management will be undermined if the social functions of the ecosystems in question are simply lost without countermeasures or compensation to those affected. As human populations increase in coastal areas and demands for ecosystem resources from often distant markets grow, mangrove management without social objectives will either have disastrous implications for the economic and social sustainability of the majority of ecosystem-dependent households or remain unimplemented and ineffective. Sustainable and feasible ecosystem management strategies need to recognize the social functions of ecosystem in their particular socio-economic context, value them according to agreed priorities, and take this into account in planning. Identification and valuation are thus clearly part of problem-focused scientific knowledge production and an essential input into the planning and decision-making.
21.7.3 Develop Alternatives to Unsustainable Forms of Behavior Towards Nature Our studies over the years repeatedly and showed that working in the mangroves is not what the overwhelming majority of those who rely on it desire for the future. Crab collectors and other mangrove workers were clearly stating that they hoped for a life less dependent on the physically hard and economically unrewarding extraction of mangrove resources for themselves and for their children. Such local aspirations for change are an opportunity for mangrove governance and management. Within a holistic approach to sustainable coastal life, better quality education and social infrastructure, in combination with scholarships and technical training for village children, would enable households in mangrove-adjacent areas to break the various vicious social-ecological circles surrounding their mangrove dependence which force generations of local people to continue resource extraction from the mangroves against their expressed desires. Addressing the explicit local wish to reduce economic dependence on the mangrove ecosystem would improve socio-economic as well as ecological perspectives. Education on its own will not generate employment and income alternatives in rural areas, but local people prioritize better quality education because without it, the prospects for local youth are bleaker still.
21.7.4 Recognize, Evaluate and Link Knowledge Systems An exclusive focus on the social functions of ecosystems does not ensure sustainable social-ecological dynamics. Natural and social science as well as knowledge from outside the sciences need to be interlinked to create useful synergies.
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Local user knowledge is often based on decades or even generations of experience with the behavior of ecosystems. However, even where ecosystem use by heavily nature-dependent subsistence populations predominates, good quality local user knowledge cannot be assumed. Our research on the co-evolution of erosion and local livelihoods (Sect. 21.3) shows evidence of “ecological illiteracy” among ecosystem users in our study area: With a high number of migrants who arrived over the past generation from inland agricultural areas, many local users of the mangrove coast had little knowledge of coastal morphological dynamics including the consequences of their own, often deleterious interactions with it. Since migration is high to most coastal regions across the globe, this is unlikely to be an isolated phenomenon. Failures in ecosystem management in areas with high immigration are more likely, the more the recent arrivals lack experience of living with the type of ecosystems predominant in their new environment. Lacunae in local knowledge can lead to local misconceptions about environmental dynamics and its interactions with human behavior among those whose day-to-day decisions centrally determine the pathways of social-ecological system dynamics. A societally responsible science needs to point out gaps in local knowledge systems and provide the tools to remedy them. New important roles for scientists in the construction of functioning communication between scientists and ecosystem users and in the facilitation of collective learning processes are implied in this. In our example, the “ecological illiteracy” of migrant populations in our coastal SES vis-a`-vis their coastal environments can be addressed by well-designed co-management approaches which include the transfer of systemic knowledge about erosion and its natural and anthropogenic causes from scientists to local “neo-traditional” populations. We have also demonstrated that patterns of social-ecological change can vary substantially within small geographical areas. The origins of such differences can be traced to the different rationales and actions of human agent types in interaction with their dynamic natural environments. Multi-agent-based modeling approaches offer a promising and as yet underexplored way to understand human–nature dynamics in mangrove and other coastal SES. The modeling of the actions and interactions of human and nonhuman living agents is the central innovative feature here. Moreover, the iterative and participatory development and use of multi-agent models can also encourage discussions and interactions among system stakeholders, serve as a didactic instrument in management, and act as a tool for linking different systems of knowledge (Castella et al. 2005; Glaser 2010).
21.7.5 Build an Effective Social Base Our experience in north Brazil shows that long-term research such as the MADAM program can spark off interlinked and complementary processes of knowledge generation and support iterative, adaptive co-management. Inclusive and democratic approaches can support self-organizational dynamics which enable local and
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other stakeholders to jointly identify problems and desirable visions of the future. This appears to be a precondition for moving human–nature systems onto more desirable trajectories of change. Long-term research which has the flexibility which was enjoyed by the 10-year MADAM program to respond to (at least some of) the priorities of local stakeholders can contribute to desirable social-ecological change. Another necessary component of sustainable social-ecological dynamics is the fulfillment of a range of social functions in management. For a social-ecological system, this requires both boundaries and bridging organizations (Olsson et al. 2007) as well as people to assume local key stewardship functions such as trust building, local social coordination and maintenance of information flows (Olsson et al. 2004a). Our case example of Tamatateua with the charismatic key steward in Sect. 21.4 shows how the initial stage of local capacity building, which often relies on key individual leaders, can, in a learning-oriented community, be succeeded by a distribution of stewardship functions among members of ecosystem user communities. Resilience management is a central feature of sustainability-enhancing work in a complex system under conditions of uncertainty. From a social-ecological systems point of view, resilience is system ability to reorganize and renew itself without loss of functions and diversity when disturbed (Alcorn et al. 2003), and while building learning and adaptation capacities (Berkes et al. 2003). Resilience resides in self-reinforcing mechanisms. Social-ecological systems may be slow to change due to their mutually stabilizing self-reinforcing mechanisms (Olsson et al. 2004b). In the context of low predictability, nonlinearity and surprise in complex social-ecological systems, increasing the resilience of desirable system configurations supports either the protection of agreed upon sustainability functions or it enables appropriate adaptation or transformation processes where these are deemed necessary or unavoidable. Scientists need to identify the sources of social and ecological resilience and to identify resilience-supporting measures where ecosystems are to be protected and resilience-weakening measures where undesirable system shifts such as large-scale deforestation or impoverishing ecosystem-dependent populations need to be addressed.
21.7.6 Collectively Envision Desirable Futures Our sections on envisioning and monitoring sustainable developments (Sect. 21.4) and on the participatory management of coastal ecosystems (Sect. 21.5) show that it is necessary and possible to obtain transparency, and even agreement, on the desired functions and outcomes of SES dynamics. Participatory methods for the definition of indicators confront ecosystem users with their current situations and likely futures and stimulate local inventiveness on how to work towards more desirable futures. Given participatory settings with clearly agreed rights and responsibilities for local ecosystem users, sustainable social-ecological systems may thus be successfully pursued with local and regional level system user
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participation. Section 21.6 explores a number of plausible future scenarios for our mangrove SES and outlines the management decisions needed to attain them. These alternative scenarios focus on the causes behind events and trajectories of change. Management and governance is then called upon to strengthen the resilience of those structures and processes which produce desirable and sustainable socialecological outcomes and to weaken the resilience of those which generate undesirable outcomes. The “scenario section” (21.6) also emphasizes the importance of group-specific rationalities of different types of mangrove ecosystem users, and the way these depend on the organization of everyday life, on culture and the development of group identities and on communication. We thus interpret human behavior towards nature as the outcome of context-dependent individual choices which greatly depend on the particular social and economic position of the agents in question. This approach allows us to include both the classical dimensions of social inequality such as income and education, as well as cultural and ethical dimensions of resource use rationales such as aesthetics, world views and norms, into deliberations on governance and management. All these dimensions of human–nature systems are subject to interactions between individuals and society, and they are dynamic over time. Our analysis shows that human behavior towards ecosystems and their resources can differ between groups and individuals and that it includes innovative and conservative as well as sustainable and unsustainable aspects. Resource use decisions by individuals, households, companies and other ecosystem stakeholders evolve iteratively and in conjunction with ecological processes. An integrated systems view thus contributes appropriate knowledge for the management of human–nature relations. To promote integrated social-ecological management with such knowledge, innovative knowledge-sharing and decision-making networks and platforms are needed. With our action-oriented research on the north Brazilian coast, we have shown how such platforms can be supported at the local and regional level. Further work needs to be done to upscale such bottom-up approaches to the analysis of local human–nature dynamics to higher institutional scales, which link to decision-makers’ priorities at those levels.
21.7.7 Achieve Relevance and Sustainability at Multiple Scales from the Local to the Global Throughout our 10 years of research work on the north coast of Brazil, the focal scale of our analysis has been the Braganc¸a SES, that is the local and regional spatial level (Fig. 21.1). Our investigations focused on the active stakeholders at this focal level and on the rationales behind their behavior toward the mangrove ecosystem. The local and regional specificity of such analyses is indispensable if governance and management are to be relevant to the problems most pressing to primary stakeholders and decision-makers.
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However, to support the sustainable governance and management of global social-ecological dynamics, analyses of stakeholder values, rationales and behaviors, and of their co-evolutionary interaction with natural dynamics, are also essential at higher spatial levels up to and including the earth system level. Global environmental change (Glaeser 2002), earth system analysis (Schellnhuber 1999; Schellnhuber et al. 2004) and global climate change drive local and regional processes of change in multiple ways. To become relevant to small and medium scale decision-making, global change needs to be analyzed in its specific manifestations at the local and regional level. The creative combination of diverse forms and systems of knowledge, including local, regional, academic and user knowledge, is now needed to develop the regionally specific but globally “nested” adaptive governance and management approaches which are required to persue sustainable futures for ecosystems and humanity who depends on them. Acknowledgements Important members of the MADAM socio-economic research group (1996–2005) were Neila Cabral, Drs Aquiles Simo˜es, Iran Veiga and Adagenor Ribeiro from the Federal University of Para´, Lucinaldo Blandtt, Cidiane Soares Tatiana Santiago, Dyane´s Cunha, Ana-Claudia Duarte, Rosangela Macedo, Rozilda Henrique Drude, Freya Klose and Do¨rte Segebart. Our research group metamorphosed into various forms between 1996 and 2005. In cooperation with residents of the villages of Abacateiro, Acarajo´, Aciteua, Ame´rica, Bacuriteua, Camuta´, Caratateua, Furo Grande, Japeta´, Jiquiri, Patalino, Ponta do Urumajo´, Praia de Ajuruteua, Retiro, Rio Grande, Tacuandeua, Tamatateua, Treme, Vila Bonifa´cio, Vila de Ajuruteua and Vila que Era, we worked on obtaining better common understandings of human–nature relations and produced this and other publications (for Portuguese language, see Glaser et al. 2005). Special thanks are due to Prof Dr Gotthilf Hempel whose concise and insightful comments and great sense of language made this chapter much more readable.
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Part VIII Data Synthesis and Assessment Tools
Chapter 22
The Mangrove Information System MAIS: Managing and Integrating Interdisciplinary Research Data U. Salzmann, G. Krause, B.P. Koch, and I. Puch Rojo
22.1
Introduction
Regular and efficient exchange of data between investigators is essential for the progress of interdisciplinary and integrative scientific research. Research data have to be easily accessible and retrievable in a structured and understandable format in order to facilitate comparative studies and make them available to a wider community. Both intra-scientific communication and transfer of scientific knowledge to stakeholders have been integral parts of the interdisciplinary research project MADAM (Mangrove Dynamics and Management) that aims at supporting environmental management in northern Brazil (Berger et al. 1999). In order to ensure data availability, quality and exchange, a central GIS database called MAIS (Mangrove Information System) has been developed during the initial stage of the MADAM project (Koch 1997). MAIS archives and synthesizes heterogeneous data collected during 10 years of interdisciplinary research in biology, geography, biogeochemistry, socio-economy and meteorology in north Brazil. Facilitated by modern computer performance and memory capacity, the typical scientist stores and analyzes research data on his personal workstation or local server using the resources and applications of his local system. If data are regularly backed up, this method of scientific “data management” is relatively secure and straightforward. However, the volume of valuable and often unique information and data continually increases throughout the “life cycle” of a scientific project, which should result in publications in peer-reviewed journals. Journal publications contain figures, tables and interpretations, whereas digital primary data are rarely published. The primary (raw) data and supporting information (metadata), which are stored in the investigators’ personal file system, become rapidly unmanageable and are, at the end of each research project, in danger of being permanently “buried” in private archives. This equates to an effective loss of data and knowledge to the scientific community (Helly et al. 2003). Raw or primary research data are unique and must be stored and managed for the long-term. Concerted initiatives to prevent research data loss have started more than 40 years ago with the
U. Saint-Paul and H. Schneider (eds.), Mangrove Dynamics and Management in North Brazil, Ecological Studies 211, DOI 10.1007/978-3-642-13457-9_22, # Springer-Verlag Berlin Heidelberg 2010
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establishment of large data repositories such as the World Data Center System (WDC), which promotes open access and exchange of scientific data (e.g. Mounsey and Tomlinson 1988; Alverson and Eakin 2001, http://www.ngdc.noaa.gov/wdc). Today, numerous archiving facilities for environmental scientific data are available worldwide, ranging from large central data repositories to rather small databases addressing specific research fields, disciplines or even single research projects (e.g., Baba et al. 2004; Diepenbroek et al. 2002; Ko¨nnen and Koek 2005). However, to date, there are no internationally binding regulations for scientific data management. The subject of an ongoing debate is how scientific data should be managed and made available to the general scientific and public community (Klump et al. 2006; Dittert et al. 2001). Here, we present a description of concept, design and functionality of the GISdatabase MAIS of the MADAM project. Our main objective is to highlight the potential of such a central data management system for improving interdisciplinary research. In regard to the ongoing debate on the freedom of scientific information, we also discuss the challenges in running a project database and outline the necessary conceptual prerequisites for a successful management of heterogeneous research data.
22.2
Implementation of a GIS-Database
During the initial planning stage of MAIS, questionnaires were distributed and meetings organized to fully assess the project collaborators’ needs and expectations in regard to scientific data management. The interdisciplinary character of the MADAM project resulted in the production of extremely heterogeneous datasets, developed from zoological, botanical, geochemical and meteorological measurements as well as the socio-economic census. This heterogeneity made high demands on the design of the MAIS database. The following major requirements and objectives for a central project data management were identified: (1) (2) (3) (4) (5) (6) (7)
Long-term data availability in Brazil and Germany (preferably via the Internet) Secure and long-term data storage High quality of supporting information (metadata) Protection of scientific ownership (data privacy) Use of geo-referenced data to facilitate spatial data comparison Flexibility and adaptability to specific project requirements User-friendly graphical user interface (GUI) for data search and visualization
As the program MADAM aims at delivering its scientific outcomes to relevant stakeholders, the project database has also been regarded as a tool for supporting management decisions in north Brazil. Therefore, considerable effort has been devoted to the development of an user-friendly GUI and a clear description of metadata, which should also be understandable to non-scientists. MAIS was implemented in 1995 when standards in information technology were relatively low
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compared with today, and when MADAM was still in its initial programme phase. This necessitated the design of an upgradeable, flexible database, adaptable to varying project requirements and progress in information technology.
22.3
Database Model and Data Management
Research data within the MADAM project were managed on different levels. Data storage and processing on the investigators’ personal computers guaranteed a maximum of data privacy and adaptability to individual research needs. Specific data analyses and individual software was employed at this level. If necessary, users were advised by database administrators on how to archive data professionally to facilitate a subsequent data transfer to the central project database. Before importing into MAIS, the investigators raw data were restructured and redundancies were removed. Each dataset was catalogued and documented using standardized metadata, which assured internal consistency and unambiguous description. Data were distributed through the intranet and thereby could be made accessible to all project members. The MAIS database was initially developed on Microsoft Access Version 97–2000 for Windows. Access is one of the most popular relational database management systems, which is easily programmable and has a very user-friendly interface and fast search engine (Viescas 2004). The Access database was connected to ArcView 3.2 using a special GIS-interface, programmed in Avenue, which enabled a visualization and basic analysis of geo-referenced data. The master version of the MAIS database and GIS-interface was based in Germany and copies were regularly distributed to servers in Brazil. In 2002, we migrated MAIS onto a platform-independent and entirely internet-based data management system, which facilitated data distribution and did not require expensive software licensing. We employed the open source software MySQL (http://www.mysql.com) for database management and MapServer (http://mapserver.gis.umn.edu) for the visualization of geo-referenced data. The technical update also increased data security and privacy. Protection against plagiarism was a major concern of many project members storing their research data in a central data management system. Therefore, if requested by the author, unpublished data were protected with a username and password. Such a protection of data ownership is particularly important for ongoing research projects as they contain high numbers of sensitive and unpublished research data or preliminary work. While many datasets in MAIS are password protected, its meta-information is still accessible for all users providing information about the status of ongoing research within the MADAM project. The design and implementation of the MAIS database followed general standards for software and database development (e.g., Lang and Lockemann 1995). The database was fully normalized and structured using a relational data model (Codd 1990). A full normalization implies (e.g., Carleton et al. 2005): (1) elimination of repeating groups and redundant data; (2) elimination of columns not dependent on
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Fig. 22.1 Schematic design of MAIS database showing grouping of main data and metadata and accessibility through different graphical user interfaces
key fields, which uniquely identify each record; and (3) isolation of independent and semantically related multiple relationships. MAIS-data are grouped in three main units: natural science, social science, and climate data (derived from climate data loggers) (Fig. 22.1). A separate publication unit links project papers and reports with respective research data. The primary data are described by metadata standardized following the “Global Change Master Directory” (http://gcmd.nasa.gov). MAIS metadata provide information on project, staff, method, parameter, equipment and sample type. Geographical latitudes and longitudes are assigned to each dataset, which allows a spatial synthesis and comparison of research results. An internal species key connected to each biological dataset enables data retrieval on different taxonomic levels. The species key follows the nomenclature provided by the Integrated Taxonomic Information System, ITIS (http://www.itis.gov). The heterogeneity of datasets generated by the MADAM project was a major challenge and required a flexible and dynamic data model. This was particularly true for the integration of fishery and socio-economic census data for which we had to denormalize the relational database to optimize performance and size of database queries and applications. For the same reason, most data on the mangrove crab Ucides cordatus were managed in a separate database unit, which is used for fisheries assessments (Araujo 2006; Chap. 19). A multilevel menu-based, user-friendly web interface with applications for advanced data retrieval was developed and made accessible through the intranet of the Leibniz-Center of Tropical Marine Ecology in Bremen and Brazil. The MAIS graphical user interface consists of data retrieval forms and a graphical tool
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MAIS Security Login MAIS Menu & Description
Data Retrieval & Metadata Information Visualisation in Dynamic Maps
Fig. 22.2 MAIS examples showing login page, main menu, data retrieval form and thematic map of study area
supported by MapServer to visualize geospatial data (Fig. 22.2). After login, different web-based forms provide for each data unit (climate data logger, publication, social and natural science data) access to all data tables of the relational system. The forms allow the user to retrieve individually queried subsets of research results. Queries are based on the combination of the following fields, which can be selected using drop-down lists of available values: (1) project; (2) researcher, (3) parameter/parameter group, (4) site/station, (5) method, (6) taxon/group (with advanced search on different taxonomic levels); (7) time period (start, end); (8) author (for publication); (9) title and year of publication; (10) keywords (publication). The result pages are interactive in providing additional metadata, such as advanced project or parameter descriptions for every dataset on point-and-click in
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a pop-up window. A mapserver module allows the integration and visualization of geo-referenced data in thematic maps (Fig. 22.2). MapServer was developed by the University of Minnesota as an Open Source development environment for building spatial enabled Internet applications (http://mapserver.gis.umn.edu). With MapServer, we created thematic maps, which allowed the user to browse through GISdata stored in MAIS. The maps are fully dynamic and different layers can be added and zoomed (see example in Chap. 19, Fig. 19.3). However, the mapping tool provided by MapServer does not replace a full geographical information system and we still employed ArcView to conduct advanced geospatial analyses and used MapServer to publish the thematic maps.
22.4
MAIS: A Tool for Supporting Interdisciplinary Research?
Archiving and managing scientific data in central databases is a time consuming and costly endeavor. A professional scientific data management requires a clear separation of data archiving and integration from “data gathering” and analysis, which is the responsibility of the respective investigator. In particular, in fixed term projects, both tasks, database management and research, often compete for the same funding and databases were managed at the expense of “real” science. This raises the question whether a central project data management is really worthwhile in terms of costs and benefits. Besides assuring long-term data storage, MAIS aimed at being flexible and dynamic to actively support interdisciplinary research within the running project. This was particularly important for bridging natural science and social science data. The flexible design of MAIS greatly facilitated the storage of heterogeneous datasets, including those originating from social science and fisheries biology. Instead of reorganising the data to fit into a predefined archive structure, we modified the project database to meet the requirements of specific scientific demands. This flexibility made MAIS a useful tool for supporting interdisciplinary science. MAIS was successfully applied by MADAM researchers to analyze, synthesize and visualize project data (e.g., Glaser and Diele 2004, 2005; Goch et al. 2005; Krumme et al. 2005, 2007; Araujo 2006; Chap. 19). Close cooperation and regular communication between database administrators and researchers was a prerequisite for successful data management. Both sides actively benefited from this cooperation. While administrators needed to understand the structure of research data, staff and in particular MSc and PhD students took advantage by receiving professional advice in scientific data management and analysis. Although MAIS had a great potential for initiating and supporting interdisciplinary science, the overall number of project investigators who regularly used the project database was rather limited. The problems of acceptance of research databases are well known in the scientific database management community (e.g., French et al. 1990; Gray et al. 2005; Grobe and Diepenbroek 2006). The reasons for these problems are manifold, and combined efforts towards a better collaboration
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can be made on both the investigator and database management side. Several attempts were made to make MAIS more popular by introducing user-friendly and efficient applications. In the following, we will discuss three major problem areas that we identified while working with MAIS. We will also define the prerequisites which are needed to ensure a successful scientific data management within research projects.
22.4.1 Quality Control and Improved Analysis Tools MAIS put much effort into metadata quality and the design of a user-friendly GUI. Advanced metadata standards, which facilitate the exploration of existing data, as well as improved analysis and visualization tools, are key factors for a successful scientific data management in the coming decade (Gray et al. 2005). The increasing heterogeneity of data in interdisciplinary projects puts even higher demands on the quality of metadata. Data must be self-describing and must follow international standards. Good metadata are central for data analysis, data visualization and data sharing among different disciplines (Gray et al. 2005). However, to recognize the benefits of a central scientific data management, the user must also be able to retrieve, interchange, compare, analyze and visualize data in a most efficient way. Unfortunately, available database applications are often insufficient and cumbersome and do not address the investigators’ specific needs. Failures in the design of a user-friendly man machine interface are not only caused by technical limitations but also by a lack of communication between database managers and scientists. Whereas in MAIS, metadata standards reached highest levels, database tools for retrieving, analyzing and visualizing geo-referenced data were rather limited. More sophisticated applications could have significantly increased the viability of MAIS for project investigators, but its implementation would have surpassed the financial and technical scope of the MADAM project.
22.4.2 Appropriate Support and Funding One of the biggest nontechnical barriers, which hamper an efficient operation of scientific databases, is the often low attention researcher and funding bodies pay to scientific data management. This results in an insecure funding situation, which is a major threat to long-term archives. Whereas the production of data is often wellfunded, its management is chronically underfunded (French et al. 1990). As a result, scientific databases are often managed part-time by regularly changing scientific staff and students, which are primarily interested in data production rather than in its management. MAIS was also affected by this lack of continuity.
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22.4.3 Intellectual Property Rights and Better Incentives for Data Sharing Protection of intellectual property rights and free exchange of information are subjects of an ongoing controversy debate within the scientific community (e.g. Dittert et al. 2001; Klump et al. 2006). In fact, researchers have only little incentives to release their unpublished datasets into central data management systems. The fear of plagiarism combined with the lack of binding standards for citing database sources are major reasons that prevent researchers from publishing their data in central databases. However, the ability of investigators to share data is vital to the progress of interdisciplinary and integrative scientific research (Helly et al. 2003). In MAIS, we protected the property rights by offering an optional password system, which could be selected by researchers to protect their unpublished data. While most project members, in particular PhD students, felt confident with this solution, it had the major drawback that the number of password-protected datasets quickly exceeded those freely accessible. Once protected by a password, it appeared to be very difficult to receive permission from authors to release data thereafter. The high number of password-protected data finally reduced the capability and usability of MAIS. Our experience underlined that, within a research project, binding rules for data transfer and release are essential for a successful central data management. These regulations must include timetables and deadlines. Today, many funding agencies, research organizations or projects actively encourage data sharing and transfer to data centres (e.g., National Environmental Research Council, http:// www.nerc.ac.uk/research/sites/data/policy.asp, or US Geological Survey, http:// www.usgs.gov/foia/). Internationally binding regulations, however, are still missing and many principal investigators still refuse to archive their data in appropriate databases (Dittert et al. 2001). As long as standards for data citations are missing and data collectors are not adequately credited in a way comparable to journal publication standards, internationally binding rules are not applicable.
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Concluding Remarks
There is a growing need for central and integrative data management solutions in interdisciplinary research projects, where research data must be continuously available and freely exchangeable. The Mangrove Information System (MAIS) has proven to be a useful tool for promoting interdisciplinary research and data syntheses within the MADAM project. The GIS database MAIS managed heterogeneous datasets on biology, chemistry, geography and socioeconomics collected in north Brazil over a period of 10 years. Research data were accessible for the Brazilian and German project members through the Internet by a user-friendly graphical user interface.
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Although MAIS has been successfully used for research data synthesis, the project database did not work to full capacity and some project investigators showed little interest in a further use of a central data management system. A general unwillingness of investigators to share data, coupled with a critical attitude towards databases, is a common phenomenon in the scientific community. Binding regulations, such as making data sharing part of the funding policy, are an effective way to improve data availability and to increase the quality of scientific databases. However, the introduction of such regulations (and sanctions) must be accompanied by efforts to give better incentives for scientists to release their data into central data management systems and to create the necessary metadata. Such key incentives include binding standards and regulations for the citation of archived datasets, which should be supported by technical mechanisms to track usage of archived data.
References Alverson K, Eakin CM (2001) Making sure that the world’s palaeodata do not get buried. Nature 412:269 Araujo A (2006) Fishery statistics and commercialisation of the mangrove crab, Ucides cordatus (L.), in Braganc¸a – Para´-Brazil. PhD thesis, University of Bremen, Bremen Baba S, Gordon C, Kainuma M, Ayivor JS, Dahdouh-Guebas F, Brown M (2004) The Global Mangrove Database and Information System (GLOMIS): present status and future trends. In: Vanden Berghe E, Costello MJ, Heip C, Levitus S, Pissierssens P (eds) Proceedings ‘The Colour of Ocean Data’: international symposium on oceanographic data and information management with special attention to biological data Brussels, Belgium, November 25–27, 2002. IOC Workshop Report 188. UNESCO, Paris, pp 3–14 Berger U, Glaser MEL, Koch BP, Krause G, Lara R, Saint-Paul U, Schories D, Wolff M (1999) An integrated approach to mangrove dynamics and management. J Coast Conserv 5:125–134 Carleton CJ, Dahlgren RA, Tate KW (2005) A relational database for the monitoring and analysis of watershed hydrologic functions: I. Database design and pertinent queries. Comput Geosci 31:393–402 Codd EF (1990) The relational model for database management, version 2. Addison-Wesley, Reading Diepenbroek M, Grobe H, Reinke M, Schindler U, Schlitzer R, Sieger R, Wefer G (2002) PANGAEA – an information system for environmental sciences. Comput Geosci 28:1201–1210 Dittert N, Diepenbroek M, Grobe H (2001) Scientific data must be made available to all. Nature 414:393 French JC, Jones AK, Pfaltz, JL (1990) Scientific Database Management (Final Report). Report of the Invitational NSF Workshop on Scientific Database Management, Technical Report 90–21, Department of Computer Science, University of Virginia, Charlottesville, VA Glaser M, Diele K (2004) Asymmetric Outcomes: Assessing the biological economic and social sustainability of a mangrove crab fishery, Ucides cordatus (Ocypodidae), in North Brazil. Ecol Econ 49:361–373 Glaser M, Diele K (2005) Resultados assime´tricos: Avaliando aspectos centrais da sustentabilidade biolo´gica, econoˆmica e social da pesca de caranguejo, Ucides cordatus (Ocypodidae). In: Glaser M, Cabral N, Ribeiro AL (eds) Gente, ambiente e pesquisa: Manejo transdisciplinar no manguezal, Bele´m, pp 51–68
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Goch YG, Krumme U, Saint-Paul U, Zuanon JAS (2005) Seasonal and diurnal changes in the fish fauna composition of a mangrove lake in the Caete´ estuary, north Brazil. Amazonia 18:299–315 Gray J, Liu DT, Nieto-Santisteban M, Szalay AS, DeWitt D, Heber G (2005) Scientific data management in the coming decade. CTWatch Quarterly 1(1). http://www.ctwatch.org/ quarterly/articles/2005/02/scientific-data-management/ Grobe H, Diepenbroek M (2006) Der Wert von Daten liegt in ihrer Nutzung. GMIT Geowissenschaftliche Mitteilungen 25:31–32 Helly J, Staudigel H, Koppers A (2003) Scalable models of data sharing in the earth sciences. Geochem Geophys Geosyst 4:1010 Klump J, Bertelmann R, Brase J, Diepenbroek M, Grobe H, Ho¨ck H, Lautenschlager M, Schindler U, Sens I, W€achter J (2006) Data publication in the Open Access initiative. Data Sci J 5:79–83 Ko¨nnen GP, Koek FB (2005) Description of the CLIWOC database. Clim Change 73:117–130 Koch BP (1997) Konzeption und Abgleich der Projektdatenbank f€ ur das o¨kosystemare Forschungsprojekt “Mangrove Dynamics and Managament”. Dipl thesis, University of Oldenburg, Oldenburg Krumme U, Keuthen H, Barletta M, Saint-Paul U, Villwock W (2005) Contribution to the feeding ecology of predatory wingfin anchovy Pterengraulis atherinoides (L.) in north Brazilian mangrove creeks. J Appl Ichthyol 21:469–477 Krumme U, Keuthen H, Saint-Paul U, Villwock W (2007) Contribution to the feeding ecology of the banded puffer fish Colomesus psittacus (Tetraodontidae) in north Brazilian mangrove creeks. Braz J Biol 67:383–392 Lang SM, Lockemann PC (1995) Datenbankeinsatz. Springer, Heidelberg Mounsey H, Tomlinson RF (eds) (1988) Building databases for global science. Taylor & Francis, London Viescas JL (2004) Microsoft access 2003. Inside out. Microsoft, Redmond, WA
Chapter 23
Coastal Zone Management Tool: A GIS-Based Vulnerability Assessment to Natural Hazards C. Szlafsztein and H. Sterr
23.1
Coastal Zone-Dynamic and Vulnerable Environment
In general, Socio-economic and environmental conflicts among various types of users of the coastal zone are inevitable. Among the resulting problems, such as conflicting exploitation of coastal resources, population growth and urbanization, pollution and environmental degradation as well as natural hazard impacts (i.e., events with high damage potential for people, property and environment) are the most severe. In particular, low-lying areas, which are strongly affected by coastal flooding or by active processes of shoreline erosion and sedimentation, pose the most serious consequences for local communities. These problems are accentuated due to rapidly increasing population pressures which often lead to inconsiderate or poorly planned development in natural hazard-prone areas or a potential sea-level rise. In consequence, functions and values of the coastal system have been degraded, and public safety and economy have been impacted. In order to understand its magnitude, Bird (1985) describes that more than 70% of the world’s coastal areas have shown net erosion over the past decades. Particularly in Brazil, approximately 30% of the coastline has been suffering from erosion processes (Mascarenhas and Augusto Filho 1997). The description of many coastal areas as highly dynamic and vulnerable zones by scientists has led to increasing attention by government and administrations on the risks and on attempts to understand and mitigate them. The concept of integrated coastal zone management (ICZM) is considered a good approach for this purpose, because it can simultaneously combine the control of Socio-economic development patterns, hazards prevention, and natural resource conservation (Clark 1995). According to Kay and Alder (1999), most of the wide range of administrative, social and technical instruments used in an ICZM program could be analyzed through a simplified organizational framework, the P-S-I-R cycle (Pressure-StateImpact-Response). Figure 23.1 shows the P-S-I-R cycle as a continuous feedback process in coastal areas (modified from Klein and Nicholls 1999). All coastal areas face a growing
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PRESSURES Climatic and Non-climatic
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Fig. 23.1 P-S-I-R framework: continuous feedback process in coastal areas (modified from Klein and Nicholls 1999)
range of stress and shock when, for natural or human-related reasons, some factors present certain behavioral change. When climatic and man-made Pressures (P) cause partial or total imbalance of the coastal system, the first effects are changes of the environmental State (S) such as pollution of soil and water, degradation of habitats, changes in land cover and land use, etc. This disequilibrium results in a number of Impacts on natural processes and resources as well as Socio-economic activities that take place in coastal areas. The Impacts (I) are also a function of the system’s Vulnerability or Susceptibility (Socio-economic and Natural). Assessments of vulnerability and impacts also provide a starting point for the determination of effective remedial action to diminish impacts and to re-establish the original conditions as soon as possible by supporting spontaneous or planned policies of Response Measures and Strategies (R). This means that either total or partial mitigation of the causes of the imbalance or adaptation to the new conditions are necessary. Adaptation responses mainly aim to reduce the system vulnerability; however, they can also cause changes on the pressures, thus collaborating indirectly with mitigation policies. Definitions of vulnerability to environmental stress vary considerably. However they show a clear separation between the Biophysical or Natural dimension and the Socio-economic dimension. In terms of the first one, vulnerability is defined as “the susceptibility of resources to negative impacts from hazard events” (NOAA 1999). The second dimension is defined as “the state of individuals, groups or communities characterized in terms of their capacity or ability to (1) be physically or emotionally wounded or hurt, and (2) anticipate, cope with, resist, and recover from the impact
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of natural hazards or unexpected changes placed on their livelihoods and wellbeing” (Adger and Kelly 1999). The coastal zone of the State of Para´ (north Brazil) represents such a system affected by natural hazards and risks, especially by flooding and erosion, which can lead to loss of land, severe property damage, and alteration of its ecological characteristics. Therefore, in the context of the P-S-I-R framework, this work aims to support the coastal zone program of the State of Para´ describing natural hazards impacts (mainly from erosion and flooding), in order to identify, assess and classify Natural and Socio-economic vulnerabilities of the area by means of a geographic information system (GIS)-based Coastal Vulnerability Index.
23.1.1 The Northeast Part of Coastal Zone of the State of Para´: The Study Area The coastal zone of the State of Para´ (82,596 km2, 6.5% of the State) is divided into three sectors by the National Coastal Zone Management Plan (Plano Nacional de Gerenciamento Costeiro): (1) Atlantic sector, (2) Continental-Estuarine sector, and (3) Insular-Estuarine sector (Fig. 23.2). The study area of this work, i.e., the Atlantic or NE sector, comprises 22 municipal districts over an area of 16,215 km2 which is 19.5% of the total area of the coastal zone of Para´. From the geological point of view, the region shows a Late Cenozoic sedimentary evolution defined by three litho-stratigraphic units: the Pirabas (late Oligocene–early Miocene) and the Barreiras (late early Miocene–mid-Miocene) Formations, and the Po´s-Barreiras sediments (Rosseti 2001). Geomorphologically, the study area is an irregular estuarine coast where the high relief of the protruding cliffs (Barreiras Formation) descends into indented inlets which extend about 50 km inland and are about 20 km wide at the mouths. The estuaries are characterized by a fringe of muddy sediments, which have been deposited in front of a higher hinterland and are covered by mangroves (Szlafsztein et al. 1999). The NE Para´ climate could be described as tropical warm and humid (mean annual temperature of 26.1 C), with a drier period (less rainfall) that occurs from June through November. The registered mean annual precipitation is more than 2,100 mm (Martorano et al. 1993). The tides, as the main hydrodynamic feature of the region, are of semidiurnal nature, with a maximum tidal range of 5.5 m (in Salino´polis) characterizing a (low) macrotidal regime (DHN 1994). While most of the flora belongs to the well-developed mangrove ecosystem (Rhizophora mangle, Avicennia germinans, and Laguncularia racemosa), the vegetation in the saline marshes is predominantly Aleucharias sp. Crop farms with secondary growth and forest are the most dominant vegetation types in the inland area of the coastal zone (Szlafsztein et al. 1999). This area with very low industrial development is moderately used for agricultural purposes and cattle farming. Socio-economic surveys show that a large
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Fig. 23.2 Map of the north coast of Brazil showing location of the study area, the “Sector 1 or Atlantic”, defined by the Coastal Zone Management Program of the State of Para´
percentage of the inhabitants earn their living from the mangrove ecosystem (crab collection and fishing are the economically most important activities) and tourism. As part of the government tourism policy and in order to facilitate access to coastal resources for the local population, roads have been constructed to connect beaches with the hinterland (Szlafsztein 2003). The National Coastal Zone Management Plan (PNGC – Plano Nacional de Gerenciamento – Federal Law 7661/1988) most important objectives are the elaboration and execution of norms for the rational use of the coastal zone resources, the contribution to improve local population well-being, and the conservation of the natural, historical, cultural and ethnical heritage. The Federal Constitution (Brasil 1991) indicates that the three governmental levels are involved in regulating environmental problems, public patrimony administration, and natural resource conservation (art. 24). Therefore, the State of Para´ established its
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Environmental Policy (State Law 5587/95), including the Coastal Zone Management Program of the State of Para´ (GERCO/PA – Programa de Gerenciamento Costeiro do Estado do Para´), which has been designed in order to plan and manage Socio-economic activities that control, conserve and recuperate the coastal natural resources and ecosystems, and exert an effective control over pollution sources or other forms of environment degradation that affect or could affect the coastal zone. The limited success in the implementation of the coastal management program in the Para´ coastal zone is caused by several factors such as (1) the weak support from the society and local communities, (2) conflicts of jurisdiction and lack of coordination among institutions at the three governmental levels, and (3) lack of available information and financial resources.
23.1.2 The Natural Hazards Impacts The coastal zone of the State of Para´ is a system affected strongly by natural hazards, principally flooding and erosion, which can lead to loss of land, severe property damage and ecosystem degradation. In the municipality of Braganc¸a, the beaches have been narrowed by erosive processes. In Vila dos Pescadores, successive flooding and erosion events have constantly affected the residents’ life, and in the last 5 years, about 500 m of the village area next to the estuary have been eroded (Souza Filho 2001). Alves (2001) and Krause (2002) have shown that on the beach of Ajuruteua, the NW sector has been impacted by rapid erosion processes (up to 50 m in 1 year of observation). On Farol and Buc¸ucanga beaches, erosion is also causing massive shoreline retreat, developing beach cliffs (10 m maximum height) sculpted in coastal longitudinal dunes. In the municipality of Marapanim in the Maruda´ region, Silva (1995) and Santos (1996) estimate an erosion rate of 15 m/year and report a cliff retreat rate of 200 m on Algodoal Island. A large storm-surge event – February 2001 – was the origin of a disaster situation along the Crispim Beach impacting the local population, their houses and economic activities. Human settlements in hazard-prone areas can also be found in several sectors of the municipalities of Sa˜o Joa˜o de Pirabas, Vigia, and Maracana˜. Several authors (Franzinelli 1982; Mendes 1998) describe numerous erosion events in different sectors of the coast of the municipality of Salino´polis – Atalaia and Mac¸arico beaches. Similarly, Muehe and Neves (1995a) indicate that this region, which is the tourism center of the northern coast of Brazil, is the sector with a high Socio-economic susceptibility to the impacts of potential sea-level rise. Unfortunately, official data revealing the economic impacts (damages and recovery costs) from the natural hazards in Para´ do not exist. However, their effects must be considered as major problems in the coastal region of the State.
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23.1.3 GIS-Based Composite Vulnerability Index for the Coastal Zone There are a variety of coastal zone vulnerability assessments (VA) and most of them agree on the following points: (1) the coastal zone is no homogeneous system; (2) there is a need to integrate different kinds of information; (3) the definition and quantification of vulnerability should not be handled subjectively, and (4) the results have to provide a valid instrument for effective risk management and coastal zone planning. Even adjacent coastal areas behave in quite different ways, varying according to social, economic and environmental conditions, prompting efforts to classify the coastline and subdivide it into relatively homogeneous units (Inham and Nordstrom 1971). Once subdivided, most of the approaches applied to quantify coastal vulnerability use multidisciplinary and multivariate data. The need to easily integrate various complex datasets has called for the development of numerous indices in order to assess the sensitivity of the areas to threats, and presenting information in a simple format (Cooper and Mc Laughlin 1998). The definition of the indices of vulnerability can be determined, for example, as a function of coastal erosion (Ricketts 1986), a variation of sea level (Gornitz and Kanciruk 1989), or an ecological and cultural context (Dal-Cin and Simeoni 1994). Considering the importance that coastal vulnerability indices have when used as management tools for implementation strategies, diverse efforts have been made in order to apply them at different spatial scales, e.g., in several studies at local scale (El-Raey 1997), regional scale (Lanfredi et al. 1998), and international scale (Quelennec 1989). In a detailed VA on German coastal regions, a comparison of scale-dependent methods has proven useful (Sterr et al. 2003). In general, relatively few studies have dealt specifically with the risks situation and VA of the Brazilian coast. At the global scale, Brazil carried out some steps of the IPCC’s Common Methodology (IPCC 1991), and their results ranks the Brazilian coastal area as a region of medium vulnerability (Hoozemans et al. 1993). Schnack (1993) has assessed the vulnerability of the east coast of South America and has analyzed some potential adjustment strategies. At the national scale, Muehe and Neves (1995) have conducted pioneer work on the comprehension of the vulnerability and potential effect of sea level on the Brazilian coast. It would be foolish to suggest that there is a single “correct” method for conducting a VA. Experience with several methodologies has yielded not only successful results but their applications also revealed many problems and deficiencies (Klein and Maciver 1999). Considering the Natural and Socio-economic characteristics of the coastal zone of the State of Para´ and the few relevant Brazilian studies, it is therefore suggested to develop a specific methodology for regionalscale VA which is better adapted to local needs.
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The coastal zone should be subdivided into units that exhibit similar attributes or characteristics, and a particular response or range of responses to hazardous events may be designed for each of these coastal sections. A CVI could be defined as a means to combine a number of separate variables to create a single indicator. In this case, these selected parameters reflect natural and socio-economic characteristics that contribute to coastal vulnerability from natural hazards. Once selected, they are aggregated according to an appropriate set of weights. Such combinations of all the information and coastal classification have been greatly aided by GIS capability as well as integrated remote sensing applications. With these techniques, storing of multidisciplinary data and examining the relationships between them could be performed on various scales and in a digital format (Burrough 1986). In this study, the SPRING 3.6 program of the Brazilian Institute of Spatial Research (INPE), and Arc View GIS 3.2 (ESRI) are used.
23.2.1 Data Problems and Shortcomings in Northeast Para´ Considering that coastal processes and vulnerability are strongly determined by local, regional and sometimes global conditions, a good understanding of the physical, biological and social system characteristics is required as well as climatological and hydrological data. While realizing its significance, developing countries such as Brazil often lack reliable information and basic data of this kind or, if such data exist, they are faced with problems with acquisition, storage and accessibility which are often immense. For example, data gathering is a neglected and under-resourced activity, because it must compete with (higher-ranked) economic and social development priorities. Therefore, such problems often result in very sparse networks and short or discontinuous data series as well as in errors and inconsistencies due to the diverse instruments or methodologies used. Datasets are often not readily available in digital format due to pre-computer era datasets and poor database practices. Also, data acquisition is often constrained by the related costs and by security and property issues. Data problems mentioned here are most evident in the Amazon region because of its vast area, the limited accessibility of several regions, the low population density and the lack of economic and scientific resources. In this study, it is recognized that many other factors could be used as components of the CVI. Among the data most badly missed are the following: High-resolution elevation data: There have been some attempts to improve the precision of the topographical cartography on the NE coast of the State of Para´ (currently 50-m contour lines), but unfortunately they are limited to only a few coastal sectors (Pereira 1995; Cohen et al. 2000). The data of the SRTM (Shuttle
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Radar Topography Mission) are of low vertical resolution for the region (approximately 90 m). Therefore, we had to utilize satellite imagery to delineate the inner (landward) boundary of the mangrove ecosystem, which is clearly distinguishable from other vegetation, in order to identify the flood-prone coastal lowlands. As mangroves grow only in a salt-water influenced regime, it is legitimate to assume that the area covered by mangroves is flooded from the open sea or from the estuaries more or less frequently. Climatic and oceanographic data: Relevant information usually referred to a rather large area and lacking the spatial resolution required for differentiating coastal types and responses as desired by VA (Cohen 2001; Geyer et al. 1996). Erosion rates: Only one study has been undertaken in this sense on a small sector of the coast of Para´ (Cohen and Lara 2003; Souza Filho and Paradella 2003) over a span of 25 years, which limits reliability of the morphological rates of change. Population growth: Number and boundaries of the municipal and census collection districts have remained constant over time in Para´.
23.2.2 Design of Composite Vulnerability Index, Based on GIS In spite of these difficulties and data limitations, a strong effort was made to develop a GIS-based CVI consisting of four basic modules (Fig. 23.3). The first step includes the gathering spatial (e.g., satellite images, regional and detailed maps), and nonspatial (e.g., statistical records, Socio-economic parameters) data. Some data result from the visual and digital interpretation and analysis of the cartography and remote sensing products (LANDSAT TM5 and airborne RADAR band X). Field work, carried out during 2001 and 2005, made it possible to georeference the natural or man-made elements, to identify morphological features and processes, to confirm the results obtained from the analysis of satellite images, and finally, to design and calibrate the Composite Vulnerability Index (CVI) (Table 23.1). The data input and preprocessing phase covers: (1) all aspects of transforming the data captured into a compatible digital form; (2) the activities to remove data errors; and (3) updating some data. The third phase consists of data storage and processing. Two models have been adopted for achieving the linkage between data: the Geo-Relational and the Composite Map Model (Shepherd 1991). In the first model, attribute information is associated with points, lines or any kind of polygons that could describe features occurring in the real world, using a unique identifier assigned to each spatial element. From a database design point of view, sets of attribute information are stored in different 2-D linked according to the relational join. The second model is based on the “Overlay Concept”, defined by the idea that the Real World is portrayed as a series of overlays, each with one aspect of the reality recorded in (Burrough 1986). Data integration consists in combining attribute values for geographical features that lie above or below in a “stack” of superimposed layers.
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Fig. 23.3 Scheme of Geographical Information System applied to elaborate the Composite Vulnerability Index of the NE coastal area of the State of Para´
Table 23.1 Secondary data, sources and types, used in the construction of the CVI of the Coastal Zone of Para´ Data source Data type Brazilian Institute of Geography and Statistics Census sectors maps and statistic data, (IBGE) topographic maps Brazilian Institute of Spatial Research (INPE) Remote Sensing Image LANDSAT TM5 Library of the University Federal of Para´ Geologic and geomorphologic maps, RADAR photograph Tribunal of Financial Issues of the Municipal Statistical data Districts of the State of Para´ “O Liberal” newspaper and Official Gazette Natural disasters and protection measures of the State of Para´ (DOE) record Civil Defense Coordination of the State Natural disasters record and protection of Para´ measures record Special Secretary of Planning and Statistical data, infrastructure maps Management of Para´
In order to facilitate the use of the CVI in coastal zone management activities, all the attribute data of each one of the geographical features are interpolated spatially and assigned to only two types of spatial polygonal elements, the municipal and the census collection districts.
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Natural Vulnerability Index = S Natural Vulnerability Variables/N° variables S Natural Vulnerability Variables = 1(a1)xy + 0,5(a2)xy + 0,25(a3)xy Socio-economic Vulnerability Index = S Socio-economic Vul. Variables/N° variables S Socio-economic Vulnerability Variables = 1(a1)xy + 0,5(a2)xy + 0,25(a3)xy
Total Vulnerability Index = (Natural Vuln. Index + Socio-economic Vuln. Index)/2
Fig. 23.4 Definitions of Natural, Socio-economic and Total Vulnerability Indices
With respect to the two existent vulnerability dimensions, the parameters that characterize them can also be classified as Natural and Socio-economic variables. The data of each variable are classified – a rank between 1 and 5 according to their relative vulnerability, 5 being the most vulnerable. The classification method used the so-called “Natural Breaks” (ESRI 1996). As it is clear that not all data used have the same relevance for the aims of the study, thus each of these variables is weighed according to its importance in determining the vulnerability of coastal areas to natural hazards. These coverages are then overlaid and the variable scores combined into Natural and Socio-economic CVI. Total Vulnerability Index is defined as the combination of both of them. All these CVI rank coastal sectors in a five-level scale based on the degree of susceptibility, classifying them as: very low vulnerability, low, moderate, high, and very high vulnerability (Fig. 23.4). Data output and presentation phase: Data are presented as maps, tables and charts, or transferred to another computer system.
23.3
Socio-economic and Natural Vulnerability
The following tables describe the several individual criteria used to characterize Natural (Table 23.2) and Socio-economic (Table 23.3) aspects of the coastal zone, their significance in order to VA, procedure of measure or calculation, and kind of geographical element linked to. The spatial and statistical analysis of the data of each one of the variables that characterize natural vulnerability yields the following results: The coastline of the NE of the State of Para´ has a length of approximately 2,625 km. The eastern area (Viseu and Augusto Correˆa) has the biggest share (800 km). Curuc¸a´, Salino´polis and Quatipuru are the municipalities where the coastal area has a great relevance (continentality). Higher values of coastline complexity are found in Braganc¸a, Quatipuru and Viseu and some islands (municipalities of Curuc¸a´ and Marapanim). The flood-prone areas of the NE coast of Para´
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Table 23.2 Parameters used to assess the natural dimension vulnerability Parameters Significance Calculation method – indicator Coastline length (km)
Degree of exposition
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The relative importance of the coastal area in the municipal context Degree of exposition
Coastline Complexity
Coastal Features
Coastal Protection Measures
Emergency Relief – Historic Cases
Fluvial Drainage
Energy environment High (seafront beaches and cliffs) Low (estuaries and bays) Degree of protection
Indication of past and present problems, likely indication of future problems In low-lying coastal areas, the extension and low gradient of the rivers favor tidal propagation
Measured on existent cartography 1:250,000 Total coastline length (km)/ Total municipal area (km2) Sinuosity ¼ L/Da Circularity ¼ island area/area of a circle having the same perimeter as the island Marine/estuarine ratio (%) ¼ (estuarine-coast length km/marine-coast length km) 100 Field trips inventory and records of the Civil Defense Coordination of Para´ (1991–2002) The record of the Civil Defense Coordination of Para´ (1991–2002) 1. Total length of the fluvial system (km) 2. Drainage density (km/ km2) ¼ length of the stream channels per M 3. Split ratio (1/km) ¼ total number of stream segments/ total length of the fluvial network 1. The total flooding area per CCD (km2) 2. Percentage flooded of each district (%)
Spatial feature M M
M
M
CCD
CCD
M
CCD Indication of past and present problems, likely indication of future problems M Municipal district, CCD Census collection district a L Total coastline length (km) and D distance (km) between the start and end points of the coastline Flooding Areas
cover an area of 2,342 km2 (14.15% of the study area). However, this coast is not a homogeneous geomorphologic unit, with sectors of 66% flood-prone land (from Viseu to Sa˜o Joa˜o de Pirabas), and others as Vigia and Colares without significant low-lying areas. From the total census collection districts in direct contact with marine or estuarine waters, only 9% have the coastline protected by some engineering stabilization measures, and only one, the town of Crispim (Marapanim), has registered emergency relief conducted by the Civil Defense, in the period 1991–2002. The great majority of the districts that are entirely or partially influenced by floods are near the coastline, and even some distant ones are also affected (e.g., part of the municipalities of Viseu and Marapanim). Of concern, 34 districts have more than
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Table 23.3 Parameters used to assess the socio-economic dimension vulnerability Parameters Significance Calculation method – Spatial indicator features CCD Demographic People in hazard prone areas 1. Total population (2000) increase society’s 2. Total population affected vulnerability even when by floods (2000) ¼ (total disaster reduction measures population) are adopted (% inundated area of CCDa) Population density Rough measure of historic and Total population per M M present urban development (2000)/area of M pressures in the coast Children population They suffer disproportionately 1. Total population (2000) CCD (0–4 years-old and are among the first 2. Population affected by populationb) causalities in emergencies Floods (2000) ¼ (children population) (% of the inundated area of the CCDa) They suffer when their houses 1. Total population (2000) Elderly population CCD having to be evacuated and 2. Population affected by (population older find difficulties to recover than 70 years old)c floods (2000) ¼ (elderly from property and other population) (% of the economic losses inundated area of CCDa) “Non-local” CCD Living permanent or 1. Total population (2000) population or temporarily, they are not 2. Population affected by people born in a familiar with the local floods (2000) ¼ (“nondifferent place that hazards, settling in risk local” population) they live now prone areas (% of the inundated area of the CCDa) Poverty Disproportionate consequences Human Development Index M on the poor, due to their values social marginalization and lack of access to resources M Municipal wealth Higher economic activities, Percentage of the tax on properties, and “circulation of goods and infrastructure works services supply” (ICMS)d exposed to the impacts M Municipal district, CCD Census collection district a % inundated area of CCD ¼ (flooded area/total area) 100 b The youngest group in the Brazilian Demographic Census is 0–4 years old c Brazilian population life expectancy is 616.5 years, for women d ICMS´s Tax (Imposto sobre Operac¸o˜es relativas a` Circulac¸a˜o de Mercadorias e sobre a Prestac¸o˜es de Servic¸os) is applied to the circulation of products and services of interstate and intermunicipal transport. 25% of the collection belongs to the municipalities, following criteria as area, population, and value of the goods
75% of their total area flooded. The fluvial network, which extends for 3,632 km, describes its larger extension in the municipalities of Viseu, Augusto Correˆa and Braganc¸a. However, the higher values of fluvial drainage density are represented in a region located between the municipalities of Tracuateua and Curuc¸a´. The spatial and statistical analysis of the data of each one of the variables yields a characterization of the Socio-economic vulnerability in the NE Para´ region:
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The total number of about 539,000 inhabitants (according to last census in 2000) in the study area represents approximately 8% of the total population of the State of Para´. The spatial distribution of the population is not homogeneous, major concentrations being observed in urban areas. A total of 172,000 people reside in the capital cities of the municipalities of Braganc¸a, Capanema, Vigia, Salino´polis, Viseu and Igarape´-Ac¸u. The coastal zone has a very low demographic density (33 inhabitants/km2); there are, however, sectors where this parameter exceeds the number of 3,000 inhabitants/km2 reached almost 10,000 inhabitants/km2 at the localities of Primavera, Braganc¸a, Emborai (Augusto Correˆa), Caratateua (Braganc¸a), Colares, Vigia, Viseu, Salino´polis and Fernando Belo (Viseu). Of the total population of children (114,000), about 30% of them were concentrated in the capital cities of Braganc¸a and Capanema as well as in some districts of Viseu. The total population of elderly is only 3,913 people, and 47% of these are concentrated in the districts of Salino´polis, Sa˜o Joa˜o de Pirabas, Marapanim, Viseu, Maracana˜, and Fernando Belo (Viseu). Finally, from the 5,095 “nonlocal population”, 61% concentrate in industrial (Capanema), tourist (Salino´polis), agricultural (Igarape-Ac¸u), and port (Vigia, Braganc¸a, Sa˜o Joa˜o de Pirabas and Augusto Correˆa) districts. Approximately 85,172 people live in flood-prone areas, and 40% of them are concentrated in the urban areas of only three municipalities (Salino´polis, Sa˜o Joa˜o de Pirabas and Marapanim). There are 16,775 children living in affected areas; however, 45% of them are grouped in six districts.1 Of the elderly affected 91.4% are concentrated principally in the urban area of Salino´polis and coastal districts of the municipality of Viseu. There are 907 “nonlocal” people affected, living mainly in few coastal districts – Salino´polis, Sa˜o Joa˜o de Pirabas, Quatipuru and Marapanim. As a general trend, very low values of the Human Development Index and economic resources are shown for every municipality of the coastal zone of the State of Para´. Taking into account the relevance of each variable in the construction of the CVI for natural hazards (Table 23.4) and the definition explained in Fig. 23.4, the Natural, Socio-economic and Total Vulnerability of the NE coast of the State of Para´ is analyzed. Considering the values of the Socio-economic dimension of CVI, it is possible to identify two regions, (1) near the coastline, with moderate to very high vulnerability values, and (2) distant from coastline, with very low to low vulnerability values (Fig. 23.5). The first region consists of 51 districts (14% of the total) and an area of 1,909 km2 (12% of the total area). The urban area of the municipality of Salino´polis is the only one characterized as very highly vulnerable. The others are the capital cities of the municipalities of Sa˜o Caetano de Odivelas, Salino´polis, Sa˜o Joa˜o de Pirabas, Sa˜o Joa˜o da Ponta, Marapanim, Quatipuru, Maracana˜, Braganc¸a, Viseu, and Augusto Correˆa, as well as a few districts.2
1
Salino´polis, Sa˜o Joa˜o de Pirabas, Viseu, Marapanim, Quatipuru and Fernando Belo (Viseu). Fernandes Belo and Sa˜o Jose´ do Piria (Viseu), Caratateua (Braganc¸a), Emborai and Itapixuna (Augusto Correˆa), Japerica (Sa˜o Jo˜ao de Pirabas), Muraja´ (Curuc¸a´), and Cafezal (Magalha˜es Barata).
2
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Table 23.4 Classification and weight of each variable, considering their relevance in struction of the CVI Variables Socio-economic Affected population (total; non-local population; children, and vulnerability elderly) Population density Non-local population, children, elderly Total population 2000; municipal budget 2000; poverty Natural vulnerability Coastline length, flooding area; protection measures, emergency relief historic cases; total length of fluvial system Coastal features Continentality; coastline complexity; proportion of flooding area; drainage density; split ratio
the conWeight 1 0.5 0.25 0.125 1 0.5 0.25
SOCIO-ECONOMIC VULNERABILITY INDEX Very Low Vulnerability Low Vulnerability Moderate Vulnerability High Vulnerability Very High Vulnerability 0
N
60 Kilometers
Fig. 23.5 NE coastal zone of the State of Para´: spatial distribution of the Socio-economic Vulnerability Index
Considering the values of the natural dimension of CVI, it is possible to identify three regions that are characterized by (1) high and very high vulnerability, (2) moderate vulnerability, and (3) very low and low vulnerability (Fig. 23.6). The first region, located near the coastline, is a continuous area of 5,357 km2 (33% of the total area) consisting of the capital cities of Viseu, Marapanim, Maracana˜, Curuc¸a´, Braganc¸a, Augusto Correˆa, Tracuataeua and, Quatipuru, as well as some districts.3 The second sector – 5,581 km2 or 35% of the total area – is concentrated in the SE 3
Fernandes Belo and Sa˜o Joa˜o do Piria (Viseu), Japerica (Sa˜o Joa˜o de Pirabas), Ponta de Ramos, Lauro Sodre and Muraja´ (Curuc¸a´), Aturai and Itapixuna (Augusto Correˆa), Maruda (Marapanim), Sa˜o Roberto and Boa Esperanc¸a (Maracana˜), and Caratateua and Tijoca (Braganc¸a).
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NATURAL VULNERABILITY INDEX Very Low Vulnerability Low Vulnerability Moderate Vulnerability High Vulnerability
N
Very High Vulnerability 0
60 Kilometers
Fig. 23.6 NE coastal zone of the State of Para´: spatial distribution of the Natural Vulnerability Index
area and some discontinuous districts on the NW area of the coastal zone. Finally, the third sector, which represents very low and low values of vulnerability, is defined at SW and W area of the coastal zone. In this category, the municipalities of Vigia and Colares deserves special attention due to their geographical position near to the coastline and their low natural vulnerability. The analysis of the total vulnerability of the NE coastal area of the State of Para´ (Fig. 23.7) indicates that it is possible to define two regions with (1) moderate to very high vulnerability, and (2) very low and low vulnerability. The area of the first region (8,614 km2, 54% of the total) is distributed among 158 CCD (42% of the total) most of them near the coastline. This sector, where around 270,600 persons live (50% of the total population), is represented by the capital cities of Viseu, Sa˜o Joa˜o de Pirabas, Salino´polis, Marapanim, Maracana˜, Braganc¸a, Tracateua, Quatipuru, Curuc¸a´, Augusto Correˆa, Sa˜o Joa˜o da Ponta, and Sa˜o Caetano de Odivelas, as well as a number of districts.4 In most districts, the variables related to natural vulnerability dimension prevail, while in a few sectors, mainly in the urban areas and/or capitals of the municipalities (e.g., Salino´polis, Sa˜o Joa˜o de Pirabas, Marapanim, Quatipuru), those which prevail are the variables of the Socio-economic Vulnerability dimension. 4
Fernandes Belo and Sa˜o Joa˜o do Piria (Viseu), Japerica (Sa˜o Joa˜o do Pirabas), Caratateua, Nova Mocajuba and Tijoca (Braganc¸a), Aturai, Emborai and Ipixuna (Augusto Correˆa), Boa Esperanc¸a and Sa˜o Roberto (Maracana˜), Ponta de Ramos, Lauro Sodre and Muraja´ (Curuc¸a´), and Maruda´ (Marapanim).
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TOTAL VULNERABILITY INDEX Very Low Vulnerability Low Vulnerability Moderate Vulnerability High Vulnerability Very High Vulnerability 0
N
60 Kilometers
Fig. 23.7 NE coastal zone of the State of Para´: spatial distribution of the Total Vulnerability Index
23.4
Conclusions
The results obtained in this study have a high confidence and are confirmed by field validation and thus should be a solid base to launch and support the ICZM program of the State of Para´. However, the conclusions presented here should be carefully considered, always remembering that they are the result of a “reality model” and not of the reality itself. The validity of the results obtained through this method is limited to the study area (changing the area examined, the values of the variables can notably differ); degree of system understanding (characterize the variables chosen and their relative significance weight), and subject to GIS errors (related to the age of the data, density observations, classification systems, position accuracy and interpolation of points or linear data into polygon boundaries that do not have the same dimensions). It is not possible to guarantee the identification of all the processes or parameters that determine Natural and Socio-economic Vulnerability, and some key variables that are desirable for VA have not been available. Most urgently needed data are those on (1) low-lying topography, (2) climatic and hydrographic data of higherresolution, and (3) incremental erosion rates. It can hardly be expected that these reliable information will be available in the near future, imposing some limitation to a strictly quantitative VA for north Brazil. On the other hand, the proposed
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method allows flexibility for utilizing a wide range of data and for adding more data as they appear. Likewise, additional indicators could perhaps be added as more/ better information becomes available. Vulnerability is defined by a combination of social and environmental factors that could change over shorter or longer time spans. Thus, the current vulnerability (expressed as CVI values) should not be considered as constant; they are likely to change through time as well. Changes in the social causes of vulnerability often happen much more rapidly (e.g., in a few decades) than many environmental changes. Yet some studies also intended to evaluate and predict of possible changes in coastal morphology (Woodroffe 1990) and mangrove ecosystems (Ellison 1994) over time scales from decades to a century. That is why future adjustments in the values and distribution of coastal vulnerability might be expected in NE Brazil, considering also the potential impacts of scenarios of future climate change and of regional Socio-economic development. Thus, an update of this first analysis presented here should be done periodically (e.g., every 10 years). Even when taking into consideration the shortcomings of the present-day results and the absence of some “hard” variables, why is it so important to assess this coastal zone’s overall vulnerability to natural hazard? The answer is that a VA is crucial for starting and supporting a program of ICZM in the study region. To approach the ICZM perspective, basic research on vulnerability aspects is a key element; it is needed for the outline and implementation of management guidelines as well as for the development of disaster relief policies. Because some response options to natural hazard impacts, both technical and institutional, might take decades to become fully effective, it is crucial to describe and implement response strategies and measures as soon as possible, even with some gaps in information and system’s knowledge remaining. It is not advisable to wait the full time in order to obtain all the information and knowledge on vulnerability or to resolve the existent uncertainties. This general rule is even more relevant for a rapidly developing region such as the northeast coastal zone of the State of Para´. Therefore, the following spatial distribution for the implementation of strategies and measures against natural hazards is suggested for each one of the planning and management units without excluding other strategies and measures (Fig. 23.8). The non-action strategy (not to interfere in the action of the natural processes) is suggested in those regions that are near to the coastline or flooding areas, poorly inhabited (less than 600 people), with difficult or nonexistent terrestrial access, and where the Natural Vulnerability Index is higher than the Socio-economic one. Some exceptions are indicated in areas with important tourist activity (e.g., Algodoal Island, municipality of Maracana˜). Planned retreat strategies and measures are recommended in regions that are near to the coastlines or flooding areas, moderately inhabited (total population over 600 people and under 1,500 people), with difficult terrestrial access, and where the Natural Vulnerability Index is higher than the Socio-economic one. The implementation of a protection instrument (hard and soft stabilization measures) is suggested in the densely populated areas, i.e., major cities and important urban nuclei with high degree of Natural and Socio-economic vulnerability, and
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Fig. 23.8 Map showing the recommended localization for the implementation of different adaptation strategies and measures
where hard-stabilization measures already exist, or natural hazard impacts are already evident. Accommodation measures and strategies are recommended for the sectors that fulfill some of the following requirements (1) bordering a capital city or important urban nuclei where hard-stabilization measures already exist, and (2) integrating the transition zone (10 km buffer) of the conservation units to be defined in the region. The remaining sectors, distant from the coastline or flooding areas, and not belonging to the transition zone, have been classified as moderate to very low vulnerability areas according to their Total Vulnerability Index values. For these areas, any kind of adaptation strategy and measure are indicated. The results of this proposal (Fig. 23.9) show that, although only 1% of the total area (117 km2 and 16 units) is indicated to implement protection measures, these would affect 28% of the total population (approximately 150,000 people). On the other hand, the large extensions where no action is suggested (2,388 km2 and 96 units) or the retreat strategy is indicated (1,383 km2 and 36 units) are poorly inhabited – 41,000 and 32,000 people, respectively. The 122 units where the accommodation strategies and measures prevail have the largest area (5,283 km2) and population (150,000 people). Finally, it is possible to plan to use these indices for (1) identifying vulnerable sectors in areas previously classified as nonvulnerable on a large scale analysis, (2) adapting the index to detailed studies, (3) repeating the VA process in all municipalities that integrate the Coastal Zone Management Program of the State of Para´, and (4) developing predictive impact models (e.g., assessment of the population at risk using trends of population change).
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Fig. 23.9 Sectors, area and people affected by recommended different kinds of strategies and measures
References Adger W, Kelly M (1999) Social vulnerability to climate change and the architecture of entitlements. Mitig Adapt Strateg Glob Change 4:253–266 Alves M (2001) Morfodinaˆmica e sedimentologia da praia de Ajuruteua – NE do Para´. MSc thesis, University of Para´, Bele´m Bird E (1985) Coastline changes: a global review. Wiley, London Burrough P (1986) Principles of GIS for land resources assessment. Monographs on Soil and Resources Survey. Clarendon Press, Oxford Clark J (1995) Coastal zone management handbook. Lewis, Boca Raton Cohen J (2001) Projeto Desmata: Impacto junto ao litoral atla´ntico da Amazoˆnia. Bola Soc Bras Meteorol 25:27–31 Cohen M, Lara R (2003) Temporal changes of mangrove vegetation boundaries in Amazonia: Application of GIS and remote sensing techniques. Wetl Ecol Manag 11:223–231 Cohen M, Lara R, Szlafsztein C, Dittmar T (2000) Digital elevation model as a GIS tool for the analysis of mangrove coasts, Amazon region, Brazil. Int J Environ Creat 3:31–42 Cooper J, Mc Laughlin S (1998) Contemporary multidisciplinary approaches to coastal classification and environmental risk analysis. J Coast Res 14:512–524 Dal-Cin R, Simeoni U (1994) A model for determining the classification, vulnerability and risk in the southern coastal zone of the Marche (Italy). J Coast Res 10:18–29
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DHN (1994) Tabuas de mares, costa do Brasil e alguns portos estrangeiros. Direc¸a˜o de Hidrografia Naval, Rio de Janeiro Ellison J (1994) Climate change and sea level rise impacts on mangrove ecosystems. In: Pernetta J, Leemans R, Elder D, Humphrey S (eds) Impacts of climate change on ecosystems and species: implications for protected areas, 4th World Congress on National Parks and Protected Areas (February 10–21, 1992: Caracas, Venezuela). IUCN, Gland, pp 11–30 El-Raey M (1997) Vulnerability assessment of the coastal zone of the Nile delta of Egypt, to the impacts of sea level rise. Ocean Coast Manag 37:29–40 ESRI (1996) ArcView GIS. Environmental System Research Institute, Redlands Franzinelli E (1982) Contribuic¸a˜o a` geologia da costa do Estado do Para´ (entre a baia de Curuc¸a´ e Maiau). IV Simp Quaterna´rio no Brasil, Rio de Janeiro, pp 305–322 Geyer W, Beardsley R, Lentz S, Candela J, Limeburner R, Johns W, Castro B, Soares I (1996) Physical oceanography of the Amazon Shelf. Cont Shelf Res 16:575–616 Gornitz V, Kanciruk P (1989) Assessment of global coastal hazards from sea level rise. In: Coastal Zone ’89: Proceedings of the sixth symposium on Coastal and ocean management, American Society of Civil Engineers, New York, pp 1345–1359 Hoozemans F, Marchand M, Pennekamp H (1993) Sea level rise. A global vulnerability assessment. Delft Hydraulics, Delft Inham D, Nordstrom C (1971) On the tectonic and morphological classification of coastal. J Geol 79:1–27 IPCC (1991) The seven steps to the vulnerability assessment of coastal areas to sea level rise – guidelines for case studies. Intergovernmental Panel on Climate Change. Response Strategies Working Group, Netherlands Kay R, Alder J (1999) Coastal planning and management. Spon, London Klein R, Maciver D (1999) Adaptation to climate variability and change: methodological issues. Mitig Adapt Strateg Glob Change 4:189–1916 Klein R, Nicholls R (1999) Assessment of coastal vulnerability to climate change. Ambio 28:182–187 Krause G (2002) Coastal morphology, mangrove ecosystem and society in North Brazil. PhD thesis, University of Stockholm, Stockholm Lanfredi N, Pousa J, D’Onofrio E (1998) Sea-level rise and related potential hazards on argentine coast. J Coast Res 14:47–60 Martorano L, Perreira L, Cezar E, Pereira I (1993) Estudos clima´ticos do Estado do Para´: classificac¸a˜o clima´tica (Ko¨ppen) e deficieˆncia hı´drica (Thornhtwhite, Mather). Sudam/ Embrapa/SNLCS, Bele´m Mascarenhas M, Augusto Filho O (1997) Landslides and coastal erosion hazards in Brazil. Int Geol Rev 39:756–763 Mendes A (1998) A expansa˜o urbana e sus efeitos danosos ao meio ambiente da Ilha do Atalaia – Salino´polis/Pa. Contrib Geol Amazoˆnia 364–365 Muehe D, Neves C (1995) The implications of sea level rise in the Brazilian coast: a preliminary assessment. J Coast Res 14:54–78 NOAA (1999) Community vulnerability assessment tool – New Hanover County – North Carolina. National Oceanic and Atmospheric Administration, Coastal Service Center, Charleston, NOAA/CSC/99044-CD Pereira S (1995) Mapeamento plani-altimetrico e morfotopogra´fico da microrregia˜o do Salgado Paraense a partir de procedimentos fotograme´tricos. MSc thesis, University of Para´, Bele´m Quelennec R (1989) The CORINE coastal erosion project. Identification of coastal erosion problems and data base on the littoral environment of eleven European countries. In: Coastal Zone ’89, American Society of Civil Engineers, New York, pp 4594–4601 Ricketts P (1986) National policy and management responses to the hazard of coastal erosion in Britain and the United States. Appl Geogr 6:197–221 Rosseti D (2001) Late Cenozoic sedimentary evolution in Northeastern Para´, Brazil, within the context of sea level changes. South Am Earth Sci 14:77–89
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Santos V (1996) Estratigrafia holoceˆnica e morfodinamica atual da planı´cie costeira da Ilha de Algodoal e Maruda. MSc thesis, University of Para´, Bele´m Schnack E (1993) The vulnerability of the east coast of South America to sea level rise and possible adjustment strategies. In: Warrick R, Barrow E, Wigley T (eds) Climate and sea level change: observations, projections and implications. Cambridge University Press, Cambridge, pp 336–348 Shepherd I (1991) Information integration and GIS. In: Maguire D, Goodchild M, Rhind D (eds) Geographical information systems: principles and applications, vol 1. Longman, Harlow, pp 337–360 Silva C (1995) Caracterizac¸a˜o geolo´gica–geomorfolo´gica das margens da Baia de Marapanim, NE do Para´. MSc thesis, University of Para´, Bele´m Souza Filho P (2001) Impactos naturais e antro´picos na planı´cie costeira de Braganc¸a (NE do Para´). In: Prost M, Mendes A (eds) Ecossistemas Costeiros. Impactos e gesta˜o ambiental. Museo Paraense Emilio Goeldi, Bele´m, pp 113–125 Souza Filho P, Paradella W (2003) Use of synthetic aperture radar images for recognition of coastal geomorphological features, land-use assessment and shoreline changes in Braganc¸a coast, Para´, Northern Brazil. An Acad Bras Cienc 75:341–356 Sterr H, Klein R, Reese S (2003) Climate change and coastal zones: an overview on the state-ofthe-art of regional and local vulnerability assessments. In: Giupponi C, Shechter M (eds) Climate change in the Mediterranean. Edward Elgar, Cheltenham, UK, pp 245–278 Szlafsztein C, Lara R, Cohen M (1999) Coastal management: some studies of the past and present of the Braganc¸a region (Para´, Brazil). The MADAM project. J Int Environ Creat 2:51–58 Szlafsztein C (2003) Vulnerability and response measures to natural hazard and sea level rise impacts: long-term coastal zone management, NE of the State of Para´, Brazil. ZMT Contributions 17:1–192, University of Bremen (Germany) Woodroffe C (1990) The impact of sea level rise on mangrove shorelines. Prog Phys Geogr 14:483–520
Part IX Closing Remarks
Chapter 24
Epilog U. Saint-Paul and H. Schneider
Mangrove forests are becoming smaller and smaller worldwide. Estimates of global losses during the last 25 years range between 35 and 86%. In Science, Duke et al. (2007) protested against a world without mangroves, noting that the full implications of mangrove loss to mankind are not fully appreciated. The MADAM project clearly confirmed most of what Duke et al. (2007) summarized as the “goods and services” provided by mangrove forests: l
l
l
l l
A dual capacity to be both a sink for atmospheric CO2 and an essential source of oceanic carbon. Deforestation of mangrove forests with their extraordinary high rates of primary productivity drastically reduces these capacities. The vital support that mangrove ecosystems provide for terrestrial as well as marine food webs is impaired, affecting, as only one example, the fishing industry. The loss of mangroves imperils the mangrove-dependent fauna with their complex habitat linkages, and jeopardizes natural environmental protections such as the buffering effects of seagrass beds and coral reefs. Mangroves prevent the impact of river-borne siltation. Mangroves protect coastal communities from the sea-level rise, or storm surges and tsunamis. A positive consequence of the 2004 Asian tsunami is that, finally, the importance of preserving coastal vegetation such as mangroves is understood as a vital protection against tsunamis, hurricanes and other natural disasters. Yet it is not just the existence of any green belt along the coastline that is important, the degree of protection seems to depend to a large extent on the quality of the mangrove forest. There were fewer losses and less damage to property by the 2004 tsunami where mangroves were dense and structurally complex (Barbier 2006). However, as stated by Dahdouh-Guebas et al. (2005), there is surprisingly little reliable data available to test such an observation. More investigation is necessary to determine how to fully restore the structural complexity of mangroves to a well-functioning ecosystem, and to improve their potential as a means of coastal protection.
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With damaged mangrove ecosystems, communities living in or near mangroves would endure a significant loss of access to a wide array of resources such as food, fibers, timber, chemicals and medicines. However, the path, to reaching these findings was long and rocky. The interdisciplinary nature of the MADAM research project initially generated a huge need for discussion on the divergent perspectives originating from the different research disciplines and the scientists involved. From our experiences, it is almost impossible to outline such a project in detail at its very beginning. Depending on the specialists involved, local conditions, political changes and recommendations from scientific board adjustments in structure and course are inevitable. A main theme at the beginning was the definition and the geographical delineation of the system to be studied, and thus the selection of the most appropriate scale. Each discipline presented its own ideas and requirements. While social scientists wanted to study the cross-linkages of the population inhabiting the whole peninsula, biogeochemists and biologists followed an exact sample design on a limited area. This is one example for such a conflict. As a consequence, the concept of a shared definition was eventually abandoned in favor of granting each scientific discipline a specific time scale according to the individual research aims. Despite this consensus, respective scientists were not free to decide their preferences for, for example, working on a point or area basis, or per seasonal or annual cycles, etc. The researchers were obliged to determine operational scales from the overall project objectives. It was essential that the research aims recognized spatial and temporal patterns in the particular fields of research. Depending on the scale used for an issue, it was necessary to find techniques and methods for compiling the mass of data from the various components of the MADAM sub-projects in a manner by which the data of the various subprojects could be compiled in a meaningful manner and could be analyzed and interpreted in relation to the respective questions. The principal instrument to achieve this was the project database, together with the geographical Mangrove Information System (MAIS). Analysis of aerial pictures (taken from satellites and aircraft) served to establish a suitable cartographic basis and also helped to detect and interpret structures that were characteristic of the system. However, expectations for this central database failed to be met as financial support for MADAM ended before this could be achieved. A good way for achieving the research goals was to involve a combination of different modeling approaches aimed at combining the respective benefits of global system analyses (trophic model of biomass flows), detailed process studies (“forest model” simulation package), and a risk assessment, combining both ecological and socio-economic aspects. In this way, it is possible to respond to the constant advances in scientific knowledge of all the participant research disciplines. On the one hand, the empirical work can be well-focused on key processes and sensitive parameters as they become apparent, while on the other hand, it is also possible to develop and refine the overall concept. As mentioned before, MADAM began as a multidisciplinary program in which social science played only a kind of service function. During the third and last
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phase, however, the project began to address complex life-world problems. By this, MADAM became more transdisciplinary. This is an integrative form of research, drawing the perspectives of public agencies, the business community and civil society into the research process. As stakeholders are being involved, transdisciplinarity is more complex than just a multidisciplinary approach. The Ucides topic is such an example. Many of the outcomes are used for sustainable management recommendations, improving the living conditions of the crab collectors. However, working together in a transdisciplinary way was difficult as the participating scientists were often overwhelmed by the amount of data amassed by all researchers. Differences in the specialized languages in each field of expertise were further obstacles. The MADAM project was initiated to provide a scientific basis for understanding and predicting mangrove growth patterns in the Caete´ estuary under changing environmental conditions, and to assess and compare the socio-economic implications and feasibility of different potential, ecologically sustainable mangrove resource management approaches. As shown in the previous chapters, these objectives were accomplished in many aspects, but not in all. The project did not cover all fields, such as entomology, microbiology, or climatology. In addition, not all researchers contributed their results to the book. MADAM was a program of partnership. German MSc and PhD students worked under local supervision by Brazilian professors, while Brazilian students went to Bremen to write up their results under the guidance of German professors. In this way, a total of 25 PhD and more than 50 MSc theses were produced and successfully defended. In addition, innumerable graduation theses were defended in Brazil. Altogether 161 publications in peer-reviewed journals were published, many of them jointly by German and Brazilian scientists. As there are still results to be published, the number will increase. For a couple of years after the formal end of MADAM in 2005, the German International Bureau and the Brazilian CNPq facilitated the bilateral exchange of scientists with special travel grants. Actually, a new Memorandum of Understanding between the ZMT and the UFPa was signed to provide the legal basis for continued cooperation. This clearly shows that MADAM initiated a sustainable long-lasting cooperation. At the beginning of MADAM, the Braganc¸a campus offered only some undergraduate courses for school teachers, on geography, history, art, mathematics and education. But during the past 15 years, the University Campus of Braganc¸a expanded and its academic qualification increased significantly. Actually, almost 30 PhDs are lecturing and working on environment-related topics including mangroves. A masters and a PhD program were established with emphasis on life science. This development was promoted by MADAM. Despite recognition of the importance of mangrove ecosystems and despite efforts made both locally and internationally, the loss and degradation of mangrove areas continue even today (FAO 2007). The related loss of biodiversity cannot be regained, and species might become locally extinct due to excessive fragmentation of habitats (Alongi 2002). However, because of the 2004 tsunami shock,
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reforestation programs have been reinforced and are likely to increase in the future. Yet, as reforestation is often implemented as a monoculture for timber production, a functional ecological restoration is not likely by such a process (Bosire et al. 2008). For environmental reasons, the goal should be the restoration of a mixed species forest cover with a dynamic equivalent to that of an adjacent reference forest (Lewis 2009). Field (1998) defined three criteria to achieve a successful mangrove rehabilitation: first, effectiveness of planting, in other words the extent to which the objectives of the rehabilitation program are met; second, rehabilitation efficiency which can be measured in the amount of labor, resources and material that were used; and third, the recruitment rate of associated flora and fauna, indicating the recovery of ecosystem structure and function. Continuous monitoring of the forest development and its ecological functions should be carried out over a period of at least five years. If not, mistakes are repeated and lessons learned are lost. More importantly, all these activities must be implemented with the involvement of the local community as an integral component of the mangrove system (Ro¨nnb€ack et al. 2007). A management plan must be developed which is community-oriented, and focused on participatory, holistic and integrated approaches. Community management of natural resources became an official policy in Brazil under the term “reserva extrativista” (RESEX). It was originally developed for the sustainable development of rainforest areas, but now it has been expanded to coastal regions. Those semi-protected areas were created on the demand of traditional and indigenous communities with the objective of using public land to extract natural resources in a sustainable way, thereby preserving both the natural environment and the local communities with their culture and traditions. MADAM scientists contributed in forming the Braganc¸a peninsula into a marine extractivist reserve (Glaser and Krause 2003). By giving current users the option to exclude newcomers, RESEX has the potential to turn non-viable open-access resource use on the mangrove coast into user-regulated common property management. Including socioeconomic priorities of resource users may provide an essential impetus to move away from the current widespread illegal use of mangroves. Marine reserves in Brazil are important instruments for fisheries management, including certification of origin and fair trade, and responsible tourism development, and play an important role in integrated coastal management, based on scientific knowledge, such as has been developed by MADAM.
References Alongi DM (2002) Present state and future of the world’s mangrove forests. Environ Conserv 29:331–349 Barbier EB (2006) Natural barriers to natural disasters: replanting mangroves after the tsunami. Front Ecol Environ 4:124–131 Bosire JO, Dahdouh-Guebas F, Walton M, Crona BI, Lewis RR III, Field C, Kairo JG, Koedam N (2008) Functionality of restored mangroves: a review. Aquat Bot 89:251–259
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Dahdouh-Guebas F, Jayatissa LP, Di Nitto D, Bosire JO, Lo Seen D, Koedam N (2005) How effective were mangroves as a defence against the recent tsunami? Curr Biol 15:R443–R447 Duke NC, Meynecke JO, Dittmann S, Ellision AM, Anger K, Berger U, Cannicci S, Diele K, Ewel KC, Field CD, Koedam N, Lee SY, Marchand C, Nordhaus I, Dahdouh-Guebas F (2007) A World without mangroves? Science 317:41–43 FAO (2007) The world’s mangroves. FAO Forestry Paper 153, FAO, Rome Field CD (1998) Rehabilitation of mangrove ecosystems: an overview. Mar Pollut Bull 37:383–392 Glaser M, Krause G (2003) User-based mangrove co-management in Brazil. In: CIP-UPWARD (ed) Conservation and sustainable use of agricultural biodiversity. A Sourcebook, vol 3. International Potato Center, Los Ban˜os, Laguna, pp 559–564 Lewis RR III (2009) Methods and criteria for successful mangrove forest restoration. In: Perillo GME, Wolanski E, Cahoon DR, Brinson MM (eds) Coastal wetlands: an integrated ecosystem approach. Elsevier, Amsterdam, pp 787–800 Ro¨nnb€ack P, Crona B, Ingwall L (2007) The return of ecosystem goods and services in replanted mangrove forests: perspectives from local communities in Kenya. Environ Conserv 34:313–324
Index
A Abundance, 251–261 Acanthaceae-Avicennioideae, 71 Acarajo´, 74, 77, 80, 81, 84, 85, 89, 90 Acrostichum aureum, 72 Adaptive capacities, 322 Adaptive change, 335, 337–338 AEP. See Atlantic–East Pacific African, 176, 184 Agricultural production, 320, 322 Aizoaceae, 72 Ajuruteua, 314–318, 322, 336 Ajuruteua beach, 77, 84, 85 Ajuruteua Peninsula, 71, 72, 74–79, 81, 84, 85, 88, 90, 91, 102 Amaranthaceae, 72 Amaryllidaceae, 72 Anableps anableps, 5–6 andanc¸a, 291, 293 Apocynaceae, 72 Appropriate knowledge, 340–347 Aratus, 252, 253 ArcView, 357, 360 Arenaeus, 252, 253 Ariidae, 6, 194 Armases, 252–254 Artisanal fishery, 287–296 Asian, 176 Assimilation efficiencies, 268–269 Associated social agents, 307, 309 Asymmetric competition, 148 Atlantic–East Pacific (AEP), 251, 260 Atlantic Ocean, 221 Austinixa, 252, 254 Avicennia, 86, 89, 92, 96–102, 128, 131, 132, 135–139
A. germinans, 71–76, 79, 80, 84, 88–91, 103, 147, 303 A. schaueriana, 71, 72, 77, 79, 84 B Barnacles, 110, 115–117, 119, 120 Barrier islands, 71 Bataceae, 72 Batis maritima, 72, 76 Beach profiles, 316, 318 Beach seine, 191, 192 Benthos, 109, 110 Biodiversity, 251 Bio-geophysical area, 309 Biomarker, triterpenols, 50, 51 Biomass, 171–181, 183, 186, 252, 259–261 Block nets, 191, 192, 194, 196, 201, 202 Blutaparon spp., 72, 76 Brachyuran crabs, 251–261 Braganc¸a coastal region administrative centre, 29 Amazon Oriental, 21 estuary, 21–23, 27 mangrove peninsula, 20–22, 25, 26, 28, 29 Braganc¸a district, 287–291, 293–295 Bremen criteria, 10, 11 Bridging organizations, 345 C Caete´ estuary, 171–180, 184, 185 Calcium, 93, 96 Callinectes, 252, 253 Canopy CII, 92, 96–97 size, 96–97 Canopy interception index (CII), 92, 96–97
395
396 Capture bans, 293, 296 Capture grounds, 289–291 Capture techniques gancho, 290, 291, 293 lac¸o, 293 Carapace width, 292 Carbon, 93 Cardisoma, 252, 253, 257 Catchment areas, 129 Catch per unit effort (CPUE), 292 Catch rates, 184 Cathorops agassizii, 175, 180, 183, 185 Channel width, 175, 176 CII. See Canopy interception index 14 C isotope content, 86 CO2, 389 Coastal zone co-management, 333 State of Para´, 367–371, 373, 374, 377–382 Coastal zone management, 365–383 new management tools, 165 planning process, 163 Coastline, 133–135, 139 beaches, 23, 30 beach profile monitoring, 24 erosion, 24–25, 30 littoral transport, 24 tourism, 24–25, 29 Coevolution, 314–323 trajectories, 322 social-ecological change, 340 Co-management, 330, 334, 338–340, 344 Combretaceae, 71, 72 Commercialization, 287, 291, 292 chain, 294–295 Communication arenas, 320, 328, 336, 344 Community participation, 295–296 Competition asymmetric, 301 intraspecific, 301 and predation, 186 Conflicts, 312, 330, 332, 336, 339 Connectivity, 193 Conocarpus erectus, 72 Consumers, 294–295 Consumption rates, 268–270 Coverage loss, 133–135 CPUE. See Catch per unit effort Crab fiddler, 275, 277–282 landings, 287–296 Uca, 275–282 Ucides, 275–282
Index Crenea maritima, 72 Crinum americanum, 72 Current, 190, 191, 195–197, 201, 202 Curuc¸a, 204 Cynoscion, 6 D Database, 355–363 Decision support scheme, 138 Degradation, 391 microbial, 51, 54, 61, 63 photo, 61–63 DEMs. See Digital elevation models Dendrochronology, 85–91, 103 Density, 171–181, 183, 186 94,713, Benthic macrofauna, 114 Dependence on mangrove resources, 329 Deposit feeding crabs, 265–267, 269–271 Diet detritus, 282 leaf-litter, 282 nitrogen, 280, 282 Digital elevation models (DEMs), 129 Dissolved organic carbon (DOC), 45, 46, 49, 50, 52–57, 60–63 Dissolved organic nitrogen (DON), 45, 57, 58 Distribution, 258, 259 DNA sequences, 223, 226 Driver of agricultural innovation, 320 Drivers of change, 321 Dwarf, 128, 131 Dysfunctional social-ecological circles, 329, 341, 343 Dysfunctional societal reactions, 318 E Earth system, 320, 347 Ebb tide, 191, 195–197, 202 Ecocline, 176, 184, 185 Ecological illiteracy, 318, 336, 344 Ecological roles, 251, 260 Economic value, 312–314 Ecosystem user knowledge, 335 Ecotone shifts, 133–140 Eleocharis mutata, 92 El Nin˜o, 136 Empowerment, 322, 326, 332 Energy, 143, 144, 146, 149, 150 flow, 270 Engraulidae, 194, 204 Environmental perceptions, 322
Index Estuaries, 171–186, 233, 234, 235, 237, 239, 240 Estuarine-dependent, 176, 185 Eurytium, 254 E. limosum, 266, 269–270 Evacuation rate, 268–269 Evolution, 282 of coastal vegetation, 133–134 Export rates, 45, 52, 53, 60 Extractive reserves (RESEX), 7, 289, 295–296, 392 obstacles from powerful official players, 333 resource scarcity at the state and community level, 333 weak community organization and leadership, 333 weak public knowledge, 333 F Fabaceae-faboideae, 72 Farfantepenaeus subtilis, 6 ´ rga˜os para Assisteˆncia Social Federac¸a˜o de O e Educacional (FASE), 14 Feedback loops, 271, 329, 341 Feeding, 189, 193, 194, 202–203 periodicity, 266–268 preferences, 266 Fiddler crabs, 266, 269–271 Fields-of-Neighborhood (FON), 147, 148 Fish Anableps anableps, 192, 194, 195, 197, 202–204 Anchovia clupeoides, 194, 202 assemblage, 189–205 biomass, 192–193, 196, 204 Cathorops, 194, 202 Colomesus psittacus, 194, 197, 199, 202, 203 density, 192–193, 204 Myrophis, 192 Pseudauchenipterus nodosus, 194, 202, 203 Pterengraulis atherinoides, 202 Sciades herzbergii, 194, 199, 202–204 Fisheries sector artisanal, 23, 237, 238, 240, 244–246 crab fisheries, 26, 27 fishermen, 235, 237, 238, 240, 243–247 fleet, 235–240, 243, 246 industrial fishery, 237, 244, 245 legislation, 288 management, 233–247 mangrove, 23, 26
397 ports, 233, 235, 236, 237, 238, 242–243 production systems, 233, 235, 237, 238, 239, 241–243, 245 resources, 233, 243, 244 subsistence, 23–24, 26, 27 yields, 287–296 Flood tide, 196, 197, 202, 203 Flushed system, 180 Focal level, 346 FON. See Fields-of-Neighborhood Food consumption, 269–270 Food intake, 268–270 Food preference, 269 Food security, 312–313, 342 Frequency, 139 Functional diversity, 260 Furo Branco, 74, 77 Furo do Meio, 74, 79, 81, 85, 90, 178, 180, 183, 185 Furo do Para´, 114 Furo Grande, 75, 79, 84, 87, 89, 90, 92 H’, 112, 114 Fyke nets, 191 G Gecarcinidae, 253 Geobotanical units, 132, 133 Geographic Information System (GIS), 365–383 Geomorphology of the estuary, 185 Gill nets, 191 GIS. See Geographic information system Global social-ecological dynamics, 308, 323, 325, 329, 334, 343, 345, 347 Goniopsis, 253, 254 Governance of coastal SESs, 339, 344 Grapsidae, 253 Growth, 275, 277–279, 281, 282 Growth rings, 86–87 H Herbaceous vegetation, 135, 136 Holocene, 35, 37–43 Hurricanes, 389 Hyblaeapuera, 80 Hydro-acoustics, 191, 198 Hydrological cycle dry season, 239, 241, 243 flood season, 239, 241 I IBAMA, 287, 293, 295 Ichthyoplankton Anchovia clupeoides, 210, 213, 215, 216
398 Ichthyoplankton (cont.) Cynoscion acoupa, 210, 214, 216–217 estuaries, 209, 210, 212–217 estuarine, 209, 210, 212–214, 217 estuarine and coastal marine science, 19 estuarine residents, 209 Guavina guavina, 185, 210, 213–216 juvenile, 209, 214, 217 larval stage, 213, 217 life cycle, 210, 214 life-history, 209 life stages, 209 marine-estuarine species, 209 marine stragglers, 209 Myrophis punctatus, 212 nursery site, 209, 210, 217 Poecilidae, 211, 212 postflexion stage, 214, 217 re-recruitment, 214 spawners, 210, 213 Inability to predict, 318 Income, 287, 294 Indicators, 132, 322–324, 339, 345 system, 325–327, 330 Individual-based models, 143, 149–150 Indo–West Pacific (IWP), 251, 260 Innovation, 314, 320–322, 338 Integrated Taxonomic Information System (ITIS), 358 Interdisciplinary, 390 research, 309, 324, 341 Intermediate disturbance hypothesis, 148 Intertidal, 252, 254, 260 creek, 190, 191, 194, 197, 198, 204 zone, upper salt marshes, 25 Intraspecific competition, 276 Inundation, 127, 129 frequencies, 71–73, 76, 81, 91, 93–96, 102, 103, 127–133, 136, 139 IWP. See Indo–West Pacific K Key steward, 321, 335, 345 KIWI model, 143, 144, 146, 148–150 Knowledge systems, 323–324, 343–344 L Laguncularia, 71, 77, 78, 92, 97 L. racemosa, 72, 76, 147, 303 Laguncularia racemosa, 71–77, 79, 84, 88–90 Leaf-consuming crabs, 265 Legislation, 288, 293, 295 Life histories, 275–282
Index Life span, 279–282 Lift nets, 191 Lignin, 45, 48–51, 53, 54 Litter fall rates, 79–82, 101 temporal patterns, 85, 103 Litter removal, 268 Littoral drift, 135 Live crab market, 291, 292, 294, 295 Livelihoods, 307, 309–314 security, 342 Local mangrove use, 312, 322, 329, 338 Local priorities, 313–314, 332 Local user knowledge, 344, 347 Long-term monitoring system, 323, 329 Low waters, 189, 190, 192, 193 Lythraceae, 72 M Macrodon ancylodon, 221, 226–230 collecting sites, 222 cytochrome b, 221, 223, 226, 228 estuarine-dependent, 221, 229, 230 king weakfish, 221 PCR, 223 16S rRNA, 222–226 MADAM. See Mangrove Dynamics and Management Magnesium, 79, 80, 82, 83, 93, 96 MAIS. See Mangrove Information System Malpighiaceae, 72 Management, 127, 129, 137–140 objectives, 323–325 Mangrove Dynamics and Management (MADAM), 308–309, 323–324, 327–330, 338, 341, 344–345 socio-economic reasearch program, 308, 341 Mangrove Information System (MAIS), 355–363, 390 Mangroves age structure, 88–91 co-management, 334 crabs, 252, 254, 258–260, 287–296 dependence, 310–311, 313, 343 detritus, 196, 197 ecosystems Atlantic mangrove province, 20 Avicennia germinans/black mangrove, 160, 162 canopy cover, 153 changes, 157 commercial and subsistence, 24, 26
Index goods and services, 19, 22 Laguncularia racemosa/white mangrove, 160–162 mosaic-like distribution, 25 mosaic of habitat patches, 159 product, 22, 26 Rhizophora mangle/red mangrove, 160, 162 species, 22, 25 tree heights, 25 validation of the KiWi model, 160 fine root production, 91, 92, 99, 100, 103 forest structure, 71–77, 81, 88, 91, 96–102 forest type, 72, 73, 76, 77, 103 leaf size, 97–98, 102 resources, 309–310, 313–314, 329, 334, 336–337, 342–343 structure, 153, 154, 159, 160, 163, 164, 165 values, 309–314 vegetation, 25, 30, 71–103 MapServer, 357, 359–360 Maranha˜o, 204, 205 Marine, 233, 244 Marine and freshwater species, 184 Marine seascape salinity, 23, 25, 27 tidal allochthonous estuary, 23 Marketing systems, 291, 292, 294–295 Matter flows, 143 Maximum sustainable yield, 292, 293 Menippe, 254 Menippidae, 254 Mercantile agents, 295 Metabolism, 282 Metadata, 355–359, 361, 363 Minimum capture size, 292, 293, 294 Minimum wage, 294 Mitochondrial, 221, 223–225 Modeling Braganc¸a mangrove development, 40–42 field-of-neighborhood (FON), 300–302 individual-based, 299 L-Ripley function, 301–302 pattern-oriented, 299–302 Mortality, 189, 191, 194, 203 value (Z), 278, 282 Muellera frutescens, 72 Mugilidae, 194, 204 Multi-agent model, 314, 344 Multi-scale segmentation (MSS), 155, 160 Mussels, 110, 115–120 Myrophis puncta, 178, 185, 186 MySQL, 357
399 N Natural hazards erosion, 365, 367, 369–371, 380 flood, 357, 365, 369, 372, 374–378, 381, 382 Neap tides, 190, 191, 195, 197–200, 202, 203, 205 Nested adaptive governance and management, 347 Nitrogen, 92, 93, 98–99, 101–103 Nitrogen fixation, 57–60 Non-linear down-fishing, 293 Norms and rules, 307, 335, 338, 346 North Brazilian coast Braganc¸a, 233, 234, 236–238, 240, 242, 243, 245, 246 Bragantine, 233, 239 State of Para´, 233, 237, 241, 243–245 Nursery, 189, 194, 205 Nutrients, 45, 46, 54–61 availability, 132 composition of leaves, 98–99 retranslocation efficiency (RE), 92, 98–99, 103 O Ocypode, 253 Ocypodidae, 252, 253 Open access, 289, 290 Ophichthidae, 192 Organic carbon, 45–50, 52, 53, 61–63 Outwelling, 45, 52–63 Over fishing, 291 Oysters, 110, 115–120 P Pachygrapsus, 253, 254 P. gracilis, 266, 269–270 Palaeoenvironmental reconstruction, 35–43 Panopeidae, 254 Panopeus, 252, 254 Paranagua´ estuary (south Brazil), 185 Participatory approach, 288 Participatory management, 330–334, 345 Participatory SES monitoring, 327 Particulate organic carbon (POC), 45, 53, 54, 57 Particulate organic nitrogen (PON), 45, 58 Partnership, 10, 13, 15, 391 Patron–client relations, 314, 341 Penaeidae, 194 Perception, 316, 320–323, 325, 334 Periodic oscillation, 135
400 Phenology, 73, 77–86 Phosphorus, 93, 98–99, 101–103, 132 Phylogenetic bootstrap, 223–225 divergence time, 223, 226 haplotype, 223–229 maximum parsimony, 223, 224 neighbor-joining, 223–225 Phytoplankton, 195, 202 Pilot program, 14 Pinnixa, 252, 254 Pinnotheridae, 254 Platforms, 346 Poaceae, 72 POC. See Particulate organic carbon Poecilia, 179, 186 PON. See Particulate organic nitrogen Population, 275–282 Porewater, 46, 53–58, 60–63 salinity, 128–135 Portunidae, 253 Possible future, 335–338 Potassium, 93, 101–103 Poverty alleviation, 310, 312–313, 342 Primacy of social aspects, 328 Primary production, 143, 144, 145 Processed crab market, 291, 292, 294, 295 Programa de renda familiar (PRORENDA), 14, 15 Projetos demonstratives, 14 Property, 127, 137 Property rights, 362 Protection areas, 137, 138, 139 Pteridaceae, 72 Public relations, 13 R Rainfall, 81, 84, 86, 129, 135, 136, 171, 172, 175, 178, 180, 184, 185 Rationalities, 323, 334–335, 337, 340, 346 Recolonization, 135, 139 Reforestation, 392 Refugia, 291 Remote sensing aerial survey analysis, 159–161 change algorithms, 156 change dynamics, 154, 156–159, 165 classification of mangrove patterns, 159 coastal land cover types, 161 fuzzy logic algorithm, 156 fuzzy member approach, 161
Index ground truth data, 153, 154, 157, 161 high resolution satellites, 159 IKONOS images, 159, 161, 162, 164 local scale analysis, 157–159 mangrove forest patterns, 154, 156, 160 MSS, 155, 160 object based approaches, 154, 155, 159, 163 object-oriented classification procedures, 160, 162 pixel-based approaches, 154, 155 post-classification methods, 157, 158 regional scale analysis, 156–157 separation of mangrove species, 161 uncertainty, 154, 161 very high resolution (VHR) images, 155, 159 Reproduction breeding season, 279, 280, 282 egg incubation, 280 eggs, 281, 282 larvae, 280–282 mate-searching, 279, 280 maturity, 277, 280, 281 ovigerous, 279–281 RESEX. See Extractive reserves Residents, 192–194 Resilience, 307–308, 314, 318, 337, 342, 346 supporting measures, 345 weakening measures, 345 Resource utilization, 137, 138, 139 Respiration, 260 Rhabdadenia biflora, 72 Rhizophora, 74, 77, 78, 86, 91, 92, 96–103 Rhizophoraceae, 71 Rhizophora mangles, 71–76, 79, 81, 85–91, 103, 143, 299, 302–303 age, 85–91, 103 growth rings, 86–87 Rhizophora mucronata, 86, 87 The right to exclude outsider, 334 Rise, 134 Risk insurance, 313–314, 321 River flow basin drainage, 185 The rural hinterland crab processing, 26, 27 income diversity, 27 innovative cultivation method, 28 monetary income, 27 multi-occupational structures, 27 shifting cultivation, 27–28 slash-and-burn cultivation, 27–28
Index S Salinas Dos Roques, 74, 80 Salinity, 127–132, 135, 136, 171, 172, 175–180, 183–185 index, 129 porewater, 71, 72, 76, 81, 86 Salt stress, 131, 132 Sand deposition, 133, 135 Satellite images Ikonos, 77 Scenarios, 334–340, 346 Sciaenidae, 6, 194, 198, 204 Sea-level rise, 128, 131, 133–136, 138, 389 Seasons of the year, 176, 180 Sediment, 127–133, 135, 139 water, 46, 52–60 Self-organization, 327, 333–334 Self-reinforcing mechanism, 307, 345 Self-thinning, 139, 148, 149 SES. See Social-ecological systems Sesarma, 253, 254 Sesarmidae, 252, 253 Sesuvium, 128, 131, 132 Sesuvium portulacastrum, 72, 76, 135 Sex ratios, 275–277 Size frequency distribution, 275, 281 Size-selective fishery, 293 Small-scale fisheries, 22, 23, 30 Social and economic diversity, 327, 339, 346 Social base, 344–345 Social capacities, 330, 338 Social capital, 321, 336, 338–339 Social cohesion, 321–322, 336 The social dimension, 326–330, 342 Social-ecological linkages, 329 Social ecological mangrove system anthropogenic interference, 30 dependence, 22, 27, 29, 30 knowledge, 30 linkages, 24, 29 shift, 27, 28, 30 Social-ecological scenarios, 334–335 Social-ecological system drivers, 307–347 Social-ecological systems (SES), 307–347 problems, 309 viability conditions, 325 Social-economic dynamics, 322 Social function, 312, 342–343, 345 Social indicator, 325, 328 Social justice, 339 Social memory, 336, 338 Social sustainability, 328, 331, 336–337, 343 Socio economic risk, 313, 316
401 Soil bulk density, 92, 93, 96, 102 SSC, 93, 94 Soil specific conductance (SSC), 93, 94 Sonar, 191, 192 South American water salinity, 176, 184 Spatial scales, 153 Species dominance, 254, 258, 260 richness, 251–261 Sporobolus virginicus, 72, 76, 135 Spring tides, 190, 195, 197–203 SSC. See Soil specific conductance Stakeholders, 307, 323–330, 334–340, 342, 344–347 Star diagram, 327–328 Stigmaphyllon bannisteroides, 72 Stomach contents, 266 Stomach fullness, 196, 202–204 Storm surges, 389 Stress, 129, 130, 136 Subsistence production, 311–312, 335, 342 Subtidal, 252, 254 Supratidal, 252, 254 Suriname, 135 Sustainability criteria, 325, 330 Sustainable futures, 307, 323, 347 Synoptic analysis spatial coverage, 153–155 spatial information technology, 154 spatial resolution, 154, 155, 159, 161 Synthesis, data, 358, 363 System perceptions, 321 System polarization, 335–337 T Tamatateua, 314, 318–322, 345 Taperac¸u Bay, 71 Taxonomic diversity, 260 Taxonomic, 230 Temperature litter samples, 71, 79 mean air, 81 regime, 84 Tetraodontidae, 194, 204 Threshold shifts, 335, 337 Topography, 127, 134, 135 heights, 128 Tourism, 139 Tracuateua, 84 Transdisciplinary, 389, 391 Transients, 191–204 Transperancy, 325, 330, 334, 335
402 Tree extraction, 137, 138 Tree height, 130, 131, 132, 136 Trophic modeling, 143, 144, 145, 149, 150 Tsunamis, 389, 391 U Uca, 253, 254 U. cumulanta, 266, 268–270 U. maracoani, 266, 267, 269, 270 U. rapax, 266, 269, 270 U. vocator, 266, 269, 270 Ucides, 252, 253, 260, 358, 391 Ucides cordatus, 6, 143, 265–271, 287–296, 299–303, 309–312, 328, 331, 336, 342 Ucididae, 253 User participation, 331–332, 338 V Vegetation coverage, 133, 135 height, 128–132
Index units, 127–129, 131, 133–140 Vessels, 233, 235–238, 243, 245 Vicious circles, 318, 329, 334, 339, 341 social-ecological dynamics, 329 Visual fish census, 192, 195 von Bertalanffy K, 278 L, 278 Vulnerability, 136, 139 indices, 367, 370, 372–374, 376–382 natural, 365–383 socio-economic, 365–367, 369–372, 374–382 total, 365–367, 374–382 X Xanthidae, 254 Z Zonation, 251–261 Zone-of-influence, 147 Zooplankton, 202, 205
