Trophic ecology and ecomorphology of fish assemblages in coastal lakes of Benin, West Africa

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Abstract
The feeding ecology and morphological diversification of fish assemblages of two coastal lakes in southern Benin (West Africa) were examined to compare patterns of community organization. Though located only 18 km apart, the two fish assemblages had dissimilar species composition, and this is largely derived from differences in connectivity to the Gulf of Guinea, salinity and pH. Among the 35 and 20 species sampled from Lake Nokoue (connected with a sea) and Lagoon Toho-Todougba (no sea connection), respectively, only a few species dominated each system. Lake Nokoue was dominated by the perciform Gerres melanopterus and the clupeiform Ethmalosa fimbriata, and Lagoon Toho-Todougba was dominated by the characiform Brycinus longipinnis. In Lake Nokoue, the akadja habitat (dense stands of woody debris installed by humans to attract fishes) had high species richness compared to the other lake habitats. Multivariate procedures were used to examine trophic guilds and the relationship between morphology and diet. Overall, thirteen trophic guilds were identified, with detritivore and piscivore guilds having the most species. Lagoon Toho-Todougba was dominated by detritivorous and insectivorous species and Lake Nokoue, a larger lake with a connection to the sea, was dominated by piscivores. In Lagoon Toho-Todougba, consumption of vegetation and insects was common, but these items were very rare in Lake Nokoue fish diets, possibly because the destruction of its fringing mangroves has reduced their availability for fishes. Despite major differences in taxonomic composition, the two fish assemblages had similar mean values for most morphological traits and morphological-based centroids from multivariate analyses were remarkably similar. Because members of the same feeding guild tended to have similar morphologies, some degree of diet specialization has accompanied morphological diversification in the taxa comprising these communities.