The contribution of marine benthic habitats for maintaining fish biodiversity

Abstract Elucidating how biodiversity is distributed across marine habitats is essential to guide conservation efforts at a time of unprecedented anthropogenic impacts. However, the relative importance of different benthic habitats for maintaining fish biodiversity remains unclear because studies have typically focused on a single marine substrate. This study used a standardized video-based survey to test whether fish gamma diversity, species composition and contribution to beta diversity would differ among benthic habitats with contrasting characteristics off the central coast of Brazil, southwestern Atlantic. Nearshore reefs supported 32–82% higher gamma diversity of typical and dominant species compared to offshore reefs, rhodolith beds and sand bottoms, while gamma diversity of rare species did not significantly differ between habitats. Community composition also varied markedly among the four habitats, with only four species (3.1% of the 127 recorded) shared among them. Species replacement (0.652–0.890) contributed far more to total beta diversity among habitats than nestedness did (0.036–0.126). Despite a large difference in gamma diversity, nearshore reefs and sand bottoms contributed equally to beta diversity. These two habitats presented consistently higher median contributions considering both species’ abundance and presence/absence. Our results reveal a strong taxonomic distinctiveness of fish communities across the continental shelf and highlight the importance of including diverse habitat types in conservation planning, even those depauperated in species.