Feeding activity and contribution of mussel raft culture in the diet of crabs in the Ria de Arousa (Galicia, Northwest Spain)

Mussel raft culture has brought about an increase in the biomass and production levels of benthic megafauna in the Ria de Arousa. The aim of this study was to determine the diel feeding activity, the effect of feeding activity on trawl catches, and the effect of the mussels and their associated epifauna on the diet of the crabs Necora puber, Carcinus maenas, Liocarcinus depurator, and L. arcuatus (Brachyura, Portunidae). There were differences in the consumption of the main diet components between different species and areas (raft, non-raft, and beach stations): the epifaunal crab (Pisidia longicornis) was the main component of the diet of N. puber, C. maenas, and L. depurator in mussel raft areas; polychaetes were the main component for L. depurator in non-raft areas; and seaweeds predominated in the diet of L. arcuatus in beach areas. Diel feeding activity varied with the species and the area. Feeding activity increased slightly at dusk and at night, although no clear diel differences were found in stomach fullness. Catches fluctuated considerably between successive trawls; there was no clear relationship between crab feeding activity and catch fluctuation.