Drivers of reef fish assemblage structure in a mosaic of Brazilian marine habitats

Fishes are conspicuous and threatened components of reef ecosystems. Understanding the role of the variables that shape their assemblages is important to buffer species, fishery stocks, and habitats from anthropogenic threats. So, the influence of depth and topographic complexity on trophic guilds and body size of reef fishes was assessed by underwater visual censuses (UVCs) conducted in biogenic reefs, rocky reefs, and rhodolith beds interspersed with algae, invertebrates, and sand. The study area lies in the southern continental shelf of Espírito Santo state, Brazil, a region that has lacked thorough UVC surveys of biogenic reefs and rhodolith habitats. A total of 105 species belonging to 42 fish families were registered. Among the eight trophic guilds registered, mobile invertebrate feeders and herbivores were the most representative in terms of density and biomass. Biogenic and rocky reefs showed higher biomass, density and richness than rhodolith habitats due to greater topographic complexity, which promotes more food resources and shelter. The five habitats hosted distinct fish assemblages (guilds and taxonomic diversity) probably because of the varying ability of resources they provide. Nevertheless, all habitats were dominated by species of low trophic level. Large fish, especially macrocarnivores, were mostly found in the deepest zones. This pattern is associated with ecological preferences but could also be strengthened by overfishing on shallower sites, decreasing the abundance of top predators and influencing their depth distribution. Our results provide a baseline for future studies, presenting subsidies for the management of human activities and the conservation of marine ecosystems in southeastern Brazil.