Evaluation of the effects of urbanization and environmental features on sandy beach macrobenthos highlights the importance of submerged zones.

To assess how sandy beach biodiversity is influenced by the effects of environmental features and urbanization, we sampled the macrofauna in the whole across-shore gradient of 90 beach sites in Southeast Brazil. We found that morphodynamic features were the main drivers of macrobenthos, but urbanization-related variables, such as number of beachgoers and number of constructions on the upper shore, decreased species richness and biomass. We also found that submerged zones sustained the highest number of species and biomass in the across-shore gradient, but were the most impacted by human activities. By demonstrating the ecological importance of submerged zones, our results show that beach management practices, which are mainly focused on the upper shore, are missing important components of beach biodiversity. To secure the sustainability of beach ecosystems, management initiatives should include both their social and ecological components and consider the entire Littoral Active Zone as the proper management unit. • We unravel the effects of urbanization and environment on sandy beach biodiversity. • Morphodynamic variables were the primary drivers of beach macrobenthos. • Submerged zones had the highest biodiversity and were mostly affected by humans. • Number of visitors, buildings and grooming were critical indicators of impact. • The entire littoral active zone should be considered as the management unit. [ABSTRACT FROM AUTHOR]