Similar functional composition of fish assemblages despite contrasting levels of habitat degradation on shallow Caribbean coral reefs

Abstract

Functional trait-based approaches provide an opportunity to assess how changes in habitat affect the structure of associated communities. Global analyses have found a similarity in the composition of reef fish functional traits despite differences in species richness, environmental regimes, and habitat components. These large-scale patterns raised the question of whether this same stability can be observed at smaller spatial scales. Here, we compared the fish trait composition and their functional diversity in two Caribbean shallow coral reefs with contrasting levels of habitat degradation: Limones (>30% cover), constituted mainly by colonies of Acropora palmata and Bonanza, a reef with extensive areas of dead Acropora structures, dominated by algae. To characterize the functional structure of fishes on each reef, we calculated the community-weighted mean trait values (CWM), functional richness, functional evenness, functional dispersion, and functional originality. Despite the differences in habitat quality, reefs exhibited a similar proportion and common structure on fish functional traits. Functional richness and functional evenness differed significantly, but functional dispersion and functional originality did not show differences between reefs. The greater niche complexity driven by the high availability of microhabitats provided by A. palmata may explain the higher functional richness in Limones, whereas the reef degradation in Bonanza may contribute to a higher functional evenness because of a similar distribution of abundance per fish trait combinations. Our results suggest that widespread degradation on Caribbean reefs has limited the type, variety, and range of traits, which could lead to a functional homogenization of fish communities even at local scales.