Revealing the drivers of taxonomic and functional diversity of nearshore fish assemblages: Implications for conservation priorities

Aim Understanding patterns and drivers of biodiversity are essential towards developing effective conservation strategies for shallow marine habitats broadly. However, little is known about the natural and anthropogenic factors that structure fish biodiversity of sandy beaches, one of the largest and most socio-economically valuable nearshore habitats due to their endemic fauna, economic importance and cultural relevance. Here, we investigated how environmental variables and urbanization affect taxonomic and functional diversity of nearshore fish assemblages to provide general biodiversity patterns that can serve as baseline information for management plans when considering conservation prioritization. Location Southeast Brazil. Methods We surveyed fish communities at 77 sites along 150 km of coastline with different natural features and degrees of human influence using a combination of seine nets and surf-BRUVS. We used generalized additive models (GAMs) to investigate the influence of environmental variables and urbanization on taxonomic and functional diversity of resident fish assemblages. Main results We found that significant breaker wave height was the most important environmental variable in explaining the taxonomic and functional diversity of fish assemblages. The effects of increasing wave height were mostly negative, except for piscivorous fishes, which were most abundant at high energy sites, and for benthic and zoobenthivorous species, which were most abundant at sites with intermediate wave exposure. The latter species were also associated with higher chlorophyll-a contributing to increased taxonomic richness and abundance. Further, anthropogenic impacts generally reduced diversity, with highest diversity only observed at the most pristine sites. Main conclusions Our results demonstrate that both natural environmental variation and human activities structure the fish assemblages of sandy beach surf zones, affecting species that possess specific functional traits differently. These drivers should therefore be considered simultaneously in appointing protected areas in order to preserve a diversity of organisms and functional traits integral to productive beach ecosystems.