Brachyuran crab (Crustacea, Decapoda) assemblage associated with Sargassum cymosum in southeastern Brazil

This study describes the structure and temporal dynamics of brachyuran crab assemblages established in association with seaweed beds of two localities on the southeastern Brazilian coast. Collections were conducted each month over the course of 1 year from algal beds of Sargassum cymosum in a rocky intertidal zone on Grande (GR) and Domingas Dias (DD) beaches at low tide. A total of 1948 specimens (1115 in GR and 833 in DD) were obtained, which were distributed in six superfamilies, nine families, 13 genera, and 23 species. Epialtus bituberculatus was observed with highest density in GR (d = 5.97 ind./L) and DD (d = 12.10 ind./L), where it was observed in 100% and 91.7% of samples, respectively. Cross-correlations were observed between the volume of algae and richness in GR (1 lag time; r = 0.796; p <0.05) and between algae volume and density in DD (0 lag time; r = −0.595; p <0.05). Positive correlations were observed between algae volume at GR and volume at DD (0 lag time; r = 0.868; p <0.05), richness at GR and richness at DD (0 lag time; r = 0.761; p <0.05), and density at GR and density at DD (0 lag time; r = 0.690; p <0.05). Crab assemblages in the beds of Sargassum algae were diverse in both localities, represented by different taxonomic groups characterized by distinct lifestyles and feeding strategies. A temporal variation in the assemblage structure was observed between localities. This study shows that this temporal variation in crab assemblages may be related to seasonality in the structural complexity of algae beds as a result of bottom-up and top-down drivers acting on the algae.