Hierarchizing biological, physical and anthropogenic factors influencing the structure of fish assemblages along tropical rocky shores in Brazil

Understanding the distribution patterns of reef fish and the relationships between those patterns and habitat and anthropogenic factors is important for the development of conservation policies by environmental managers. Fish assemblage structure was studied over 22 rocky shores with different physical complexity and benthic cover in Ilha Grande Bay, Southeastern Brazil. We aimed to test the relative influences on rocky reef fish assemblage descriptors (richness, density and biomass) of three categories of predictors: 1) biological features as dominant benthic cover (in percentage), i.e., fleshy algae, turf algae and soft coral; 2) physical factors, i.e., depth and a physical structure index; and 3) anthropogenic factors, i.e., distance from the coast, population of the nearest city, and influence of a marine protection area. The main explanatory variables determining fish assemblage structure according to the distance based linear model (DistTLM) were depth (explaining 16.7 % of the variation) and distance from the coast (14.0 %), followed by population of the nearest city (3.7 %) and turf algae (2.9 %). Similarly, fish species richness was positively associated with deeper areas and greater distance from the coast, thus being less accessible to human influence. Fish density and biomass increased with distance from the coast, and this relationship is likely linked to the presence of large top predators and herbivores. Moreover, fish richness and density increased with the physical complexity indicated by the physical structure index, suggesting that the presence of a variety of refuges enhances the availability of shelter. We recommend that areas farthest from the urban centres and with higher physical complexity should be prioritised in conservation policies.