Bathymetric distribution of brachyuran crabs: Alpha and beta diversity variation in an upwelling area

Biodiversity studies might help to understand the ecological dynamics of regions under the influence of upwelling and serve as a baseline to conservation and management strategies. Here, we evaluated the alpha (species richness and Shannon‐Wienner index – H’) and beta (Bray Curtis index) diversities of a Brachyura assemblage within a depth gradient (5, 10, 15, 25, 35, and 45 m) in the Macaé region, State of Rio de Janeiro, Brazil. A total of 1,221 decapod individuals were sampled, comprising 11 species .The highest diversity index was recorded at 5 m in depth and the lowest at 25 m. The ecological indexes (diversity and evenness indexes) were inversely proportional to the organic matter and phi (sediment texture). This finding suggests that the heterogeneous sediment of shallow areas increases habitat complexity, therefore increasing biodiversity. Since the study area is an upwelling zone, the coastal area is more affected by cold‐water masses, leading to a distinct biodiversity distribution when compared with regions that are not under the influence of upwelling. Considering these peculiarities, the importance of coastal areas to the biodiversity of regions affected by upwelling becomes evident. Such areas must have differential importance when conducting environmental conservation and management projects.