Different Surrounding Landscapes may Result in Different Fish Assemblages in East African Seagrass Beds |
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Authors: | M Dorenbosch M G G Grol I Nagelkerken G van der Velde |
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Institution: | (1) Department of Animal Ecology and Ecophysiology, Institute for Water and Wetland Research, Faculty of Science, Radboud University Nijmegen, Toernooiveld 1, 6525, ED, Nijmegen, The Netherlands |
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Abstract: | Few studies have considered how seagrass fish assemblages are influenced by surrounding habitats. This information is needed
for a better understanding of the connectivity between tropical coastal ecosystems. To study the effects of surrounding habitats
on the composition, diversity and densities of coral reef fish species on seagrass beds, underwater visual census surveys
were carried out in two seagrass habitat types at various locations along the coast of Zanzibar (Tanzania) in the western
Indian Ocean. Fish assemblages of seagrass beds in a marine embayment with large areas of mangroves (bay seagrasses) situated
9 km away from coral reefs were compared with those of seagrass beds situated on the continental shelf adjacent to coral reefs
(reef seagrasses). No differences in total fish density, total species richness or total juvenile fish density and species
richness were observed between the two seagrass habitat types. However, at species level, nine species showed significantly
higher densities in bay seagrasses, while eight other species showed significantly higher densities in reef seagrasses. Another
four species were exclusively observed in bay seagrasses. Since seagrass complexity could not be related to these differences,
it is suggested that the arrangement of seagrass beds in the surrounding landscape (i.e. the arrangement on the continental
shelf adjacent to the coral reef, or the arrangement in an embayment with mangroves situated away from reefs) has a possible
effect on the occurrence of various reef-associated fish species on seagrass beds. Fish migration from or to the seagrass
beds and recruitment and settlement patterns of larvae possibly explain these observations. Juvenile fish densities were similar
in the two types of seagrass habitats indicating that seagrass beds adjacent to coral reefs also function as important juvenile
habitats, even though they may be subject to higher levels of predation. On the contrary, the density and species richness
of adult fish was significantly higher on reef seagrasses than on bay seagrasses, indicating that proximity to the coral reef
increases density of adult fish on reef seagrasses, and/or that ontogenetic shifts to the reef may reduce adult density on
bay seagrasses. |
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Keywords: | coral reef fishes seagrass beds mangroves nursery connectivity migration |
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