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118269

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Chin Bagundol

This document summarizes a study comparing the abundance, diversity, and stable isotope signatures of benthic fauna between mangrove, seagrass, and sand flat habitats in Gazi Bay, Kenya. Replicate cores were taken from each habitat and analyzed. Mangrove and seagrass meadows had higher densities of benthic fauna than sand flats, and seagrass showed the highest species diversity. Stable isotope signatures ranged widely but showed no direct evidence that macrobenthic species consumed mangrove or seagrass tissues. Most species appeared to feed non-selectively on microalgae and seagrass detritus. Polychaete density and diversity varied between sampling stations,

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- 29 - COMMUNITY STRUCTURE AND TROPHIC RELATIONS IN AN EAST AFRICAN COUPLED MANGROVE-SEAGRASS ECOSYSTEM Dino De Waen1* , An Vanreusel2 , Judith Nyunja3, 4 and Steven Bouillon5,6 1 Ghent University, Maritime Institute, Universiteitsstraat 6, B-9000 Ghent, Belgium E-mail: Dino.dewaen@ugent.be 2 Ghent University, Marine Biology Section, Krijgslaan 281, Campus Sterre - S8, B-9000 Gent, Belgium 3 Kenya Marine and Fisheries Research Institute, PO Box 81651, Mombasa, Kenya 4 University of Nairobi, Department of Zoology, PO Box 30197, Nairobi, Kenya 5 Vrije Universiteit Brussel, Department of Analytical and Environmental Chemistry, Pleinlaan 2, B-1050 Brussels, Belgium 6 Netherlands Institute of Ecology, Centre for Estuarine and Marine Ecology (NIOO-CEME), Korringaweg 7 4401 NT Yerseke The Netherlands In Gazi Bay (Kenya), the abundance, diversity and stable isotope signatures of the benthic fauna was compared between the adjacent mangrove, seagrass and non- vegetated sand flats. Replicate cores were taken from each habitat in three sampling stations, during the period February-March 2005. Mangrove and seagrass meadows showed on average higher densities (11500 ind.m-2 ) than sand flats (3800 ind.m-2 ), while only seagrass showed a high species diversity (up to 23 spp.m-2 ). All stable isotope signatures ranged between -28.6 and -10.1‰ for δ13 C and -1.3 and 7.5‰ for δ15 N, the mean δ13 C value was -19.1‰. In this study, there was no direct evidence for mangrove or seagrass tissue consumption by the macrobenthic species sampled in Gazi Bay. Most species seem to feed non-selectively on microalgae and seagrass detritus or selectively on microalgae. The higher δ15 N values were found in omnivorous polychaetes and filter-feeders. Spatial shifts were investigated between the stations and habitats. Only polychaete density and diversity varied significantly between the stations, possibly mediated by diversity in seagrass features in the local seagrass beds. δ13 C enrichment of the species tissue was observed between the river mouth and the seaward side of the bay. Despite the large differences in isotope signatures of the dominant local primary producers, we found no consistent gradient in consumer δ13 C signatures between the different habitats.

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118269

  • 1. - 29 - COMMUNITY STRUCTURE AND TROPHIC RELATIONS IN AN EAST AFRICAN COUPLED MANGROVE-SEAGRASS ECOSYSTEM Dino De Waen1* , An Vanreusel2 , Judith Nyunja3, 4 and Steven Bouillon5,6 1 Ghent University, Maritime Institute, Universiteitsstraat 6, B-9000 Ghent, Belgium E-mail: Dino.dewaen@ugent.be 2 Ghent University, Marine Biology Section, Krijgslaan 281, Campus Sterre - S8, B-9000 Gent, Belgium 3 Kenya Marine and Fisheries Research Institute, PO Box 81651, Mombasa, Kenya 4 University of Nairobi, Department of Zoology, PO Box 30197, Nairobi, Kenya 5 Vrije Universiteit Brussel, Department of Analytical and Environmental Chemistry, Pleinlaan 2, B-1050 Brussels, Belgium 6 Netherlands Institute of Ecology, Centre for Estuarine and Marine Ecology (NIOO-CEME), Korringaweg 7 4401 NT Yerseke The Netherlands In Gazi Bay (Kenya), the abundance, diversity and stable isotope signatures of the benthic fauna was compared between the adjacent mangrove, seagrass and non- vegetated sand flats. Replicate cores were taken from each habitat in three sampling stations, during the period February-March 2005. Mangrove and seagrass meadows showed on average higher densities (11500 ind.m-2 ) than sand flats (3800 ind.m-2 ), while only seagrass showed a high species diversity (up to 23 spp.m-2 ). All stable isotope signatures ranged between -28.6 and -10.1‰ for δ13 C and -1.3 and 7.5‰ for δ15 N, the mean δ13 C value was -19.1‰. In this study, there was no direct evidence for mangrove or seagrass tissue consumption by the macrobenthic species sampled in Gazi Bay. Most species seem to feed non-selectively on microalgae and seagrass detritus or selectively on microalgae. The higher δ15 N values were found in omnivorous polychaetes and filter-feeders. Spatial shifts were investigated between the stations and habitats. Only polychaete density and diversity varied significantly between the stations, possibly mediated by diversity in seagrass features in the local seagrass beds. δ13 C enrichment of the species tissue was observed between the river mouth and the seaward side of the bay. Despite the large differences in isotope signatures of the dominant local primary producers, we found no consistent gradient in consumer δ13 C signatures between the different habitats.