Biogeographic patterns of coastal fish assemblages in the West Indies

This paper explores the factors influencing or controlling West Indies reef fish assemblages, using an extensive underwater survey (mensurative experiment). The sampling units represented variation in substrate type, depth, and geography. For that, the distribution of coastal species assemblages was examined in different islands, from the Dominican Republic in the north to Bequia (Grenadines) in the south. Visual surveys were made by snorkeling and SCUBA diving in various habitats from the surface to 55 m deep. Presence-absence data from 248 sites and 228 species were analysed by canonical redundancy analyses. Three quantitative variables (depth, latitude, and location of the sites along the Caribbean arch) as well as qualitative descriptors corresponding to 10 habitat types were used as explanatory variables in the canonical analyses. Variation partitioning showed that substrate was the most important factor, accounting for 15.2% of the species variation, while the geographic gradients explained 8.4%; 2.3% was explained jointly by the two groups of variables. Most of the variation explained by depth was also accounted for by the substrate categories. In a canonical analysis of community composition by substrate types, the first canonical axis divided the sites into soft substrates characterized by few species and hard substrates characterized by several other species. The second axis separated the outer reef slopes, with low or high coral cover and sandy areas with coral patches (deep habitats) from shallow non-reef rocky substrates and reef fronts. A second canonical analysis of community composition by geographic gradients produced an ordination of the sites in which the succession of islands along the Caribbean arch is recognizable. The species are positioned in the ordination according to their contributions to the fauna of the various islands. This paper supports the hypothesis that fish community composition in the Caribbean islands is controlled mostly by a latitudinal and a hydrologic gradient, as well as by the type of habitat and, with a lower influence, by depth.