Environmental filtering and management effects on functional and taxonomic reef fish diversity in the Abrolhos Reefs, Brazil.

Environmental conditions play a key role in shaping the functional composition of communities by favouring species with specific trait combinations. Certain habitat characteristics likely select for traits that confer advantages under specific local conditions, highlighting the importance of functional traits in mediating species' responses to environmental variation and in structuring community assembly. The main objective of this study was to identify the relationship of functional and taxonomic diversity, and biological traits against environmental variables across a coastal gradient to offshore reefs. Abundance and biomass data were collected from reef fish assemblages in Abrolhos Bank. Functional diversity (FD) indices were established with biomass data, calculated from fish traits. Differences in biomass, taxonomic diversity (TD), FD and redundancy patterns (RP) were assessed for spatial factors isolation, locality, and site. Also, the response of biological traits to onshore-offshore effects were evaluated with effect size analysis. Finally, RLQ ordination together with fourth-corner analyses were employed to establish significant correlations between environmental variables, biological traits and fish composition. The effect size was higher in offshore reefs for biomass, functional entities, richness species, while all FD, except functional richness, had higher effect in coastal areas. A strong environmental filtering mediated by coastal distance plays a role in community structure and reef fish distribution, with fish trophic group being most affected by the natural gradient. However, other traits' response revealed that protection measures might interact synergistically with environmental filtering, and mitigate the effects of anthropogenic pressure on coastal habitats. Ecological functionality, using functional indices considering specific environmental variables and habitats, can be used to monitor reef fish populations and to guide fisheries regulations and MPA establishment and management.