Trophic role of the juvenile southern king crabs (Lithodes santolla) in San Jorge Gulf, Southern Atlantic Ocean

VINUESA JULIO, ; BALZI PAMELA ; VARISCO MARTIN

Quingdao

Congreso; Seventh International Crustaceans Congress; 2011

Chinese Crustacean Society

The southern king crab Lithodes santolla (Molina, 1782) is a common lithodid crab in the southern tip of South America. The species is of great commercial interest in the San Jorge Gulf area and its surroundings, and is the largest population inhabiting the Atlantic waters. The juveniles develop in rocky coastal areas with abundant vegetation and a high diverse sessile fauna. The objective of this study was to analyze the relationship of juveniles with these coastal benthic communities. We studied the gut contents of 314 juvenile southern king crab of both sexes, with carapace lengths (CL) between 8.04 and 49.04 mm, between Punta del Marques and Caleta del Fondo, in the central area of the San Jorge gulf. Samplings were held between 2006 and 2007 by SCUBA divers at depths between 1 and 15m. Capture of crabs smaller than 10 mm CL was difficult by diving due to small size and cryptic habitats they select. We calculated prevalence rates of prey consumed, repletion index of their stomachs and quantity of food consumed in relation to sex, size and season. 14% of crabs analyzed showed their stomachs empty. The remaining 55.4% was less than 50% of filling, while 30.6 % had fillings greater than 50%. Crabs did not feed in the period before and after molt. During intermolt all crabs had food in their stomachs. The diet of juveniles consists of 22 groups of organisms. More than 50 different species of algae and invertebrates have been identified in their stomachs. In terms of frequency of occurrence major taxa were: brittle stars (57.9%), red algae (43.2%), isopods (36.8%), sea urchins (29.5%), bivalve mollusks (28.4%) and polychaet annelids (25.3%). At lower frequencies: brown algae, sponges, hydrozoans, bryozoans, gastropods, chitons, amphipods, holothurians, pycnogonids and other undetermined crustaceans. There were no significant differences in the amount of food consumed by sexes. The diet of crabs with CL smaller than 15 mm (age 0+) differed significantly from that of larger size.These differences were due to the higher abundance in smaller crabs of isopods and bryozoans. The great diversity of prey found in juvenile king crabs indicates that they are opportunistic omnivorous predators and take advantage of rocky sublittoral for food and for shelter. Juveniles are preyed upon by two inhabitants of the rocky subtidal, Enteroctopus megalocyathus and the rockcod Notothenia angustata