Beta diversity analysis reveals high turnover in benthic assemblages between tropical coral and subtropical rocky reefs

Understanding species distributions and biodiversity patterns is an old challenge in ecology and biogeography. This approach is especially important because of the current increase in anthropogenic pressure on coastal ecosystems. The Brazilian coastline is a mosaic of complex marine habitats, including extensive rocky shores and the largest coral reef formation in the Atlantic. By decomposing beta diversity into nestedness and turnover components, we investigated how benthic assemblages are structured and how species composition changes along the transitional zone between rocky and coral reefs. To assess the spatial components of alpha diversity, we also analyzed how species richness varies between neighboring habitats. The pairwise comparison of beta diversity revealed the highest turnover rates between the southern and northern assemblages, suggesting differentiation between the two bioprovinces. Southern provinces were characterized by suspension feeders, whereas northern provinces were dominated by stony corals along a north‒south diversity gradient. Redundancy analysis indicated that temperature was the most important environmental driver shaping benthic composition and distribution. Based on these results, we recognize different diversity patterns among two provinces and detect different levels of vulnerability should a stochastic event occur. Considering that human interference tends to increase in this area, the use of beta diversity partitioning can be a useful analytical tool to recognize communities with different levels of priority for monitoring and establishing conservation efforts.