Brachyuran Crabs (Decapoda) Associated with Rhodolith Beds: Spatio-Temporal Variability at Gran Canaria Island

Crustaceans are a key component of the fauna living in rhodoliths, but patterns in their distribution and abundance remain largely unknown. This paper assessed spatio-temporal variability of Brachyura associated with rhodoliths. A seasonal study was conducted at three depth layers (18, 25, and 40 m), throughout two years (December 2015 to October 2017) at Gran Canaria Island (eastern Atlantic Ocean). A total of 765 crabs belonging to 10 species were collected. A larger abundance and richness of crabs at 25 m correlated with a larger biomass of epiphytic algae attached to rhodoliths. A seasonal pattern was also observed, where a higher richness of crabs occurred in the summer. The Xanthid crab, Nanocassiope melanodactylus, dominated the assemblage (83%); juveniles of this species were more abundant in deeper waters (40 m), while adults were more abundant on the shallower depth layers (18 m and 25 m). The species Pilmunus hirtellus was restricted to 25 m. Nevertheless, Pisa carinimana and Achaeus cranchii did not show any spatio-temporal pattern. In summary, this study demonstrated that two conspicuous crabs, N. melanodactylus and P. hirtellus, associated with rhodolith beds are bathymetrically segregated.