Diversity in coral reef fish communities: the effects of habitat patchiness revisited

Abstract

Explanations for the association between habitat patchiness and diversity in coral reef fish communities are often conflicting among studies, and no consensus has been reached. We inves- tigated patterns in diversity and structure of fish communities associated with large and small coral patch reefs at Glover's Reef, Belize. The abundance of fish was greater on large reefs (mean size 2300 m 2 ) than on small reefs (mean size 740 m 2 ), but species richness was less consistent among the different sizes of reefs. Results from rarefaction analyses indicated that both species richness and spe- cies evenness were similar between a single large reef and 3 smaller reefs of equivalent total area to the large reef. Furthermore, the density of species on standardized sizes of reef habitat was similar or greater on small reefs than species density on large reefs. The nested subsets hypothesis predicts that species assemblages on small isolated habitat patches will constitute only a subset of the assemblage on a large patch. However, reef fish communities in our study did not show any nested patterns when they were ordered by species richness, reef size, or reef isolation. To further evaluate why the fish communities on small reef patches were so diverse, we compared the number of numerically rare species and the spatial segregation of species within large and small reefs. More rare species, includ- ing both transients and resident species, occupied the combined small reefs than the large reefs. A greater number of species occupied reef edge habitats than the reef top and thus contributed to greater species density on small patches with larger perimeter:area ratios. Diversity in coral reef fish communities may be associated with the spatial distribution of species over the physical structure of reef habitat, but these patterns may be highly scale-dependent.