Prevalences of parasitized and hyperparasitized crabs near South Georgia

Abstract

This study identifies sources of variation in the prevalences of parasitized and hyperparasitized Paralomis spinosissima, a lithodid found around South Georgia. The parasite is Bziarosaccus callosus, a rhizocephalan; the hyperparasite is an undescribed liriopsinine. Generalized additive models were used to model data collected during 1992 and 1995. Parasites were less prevalent on female crabs and most prevalent in submarine canyons. The former effect may be due to sex-specific differences in gill cleaning behavior, and the latter effect may result from reduced gill cleaning efficiency in areas where the seafloor is covered with fine sediment. The size-prevalence curve was dome-shaped; this probably indicates that B. callosus reduces the growth rate and increases the mortality rate of P. spinosissima. Parasite prevalence decreased with increasing crab density but increased with increasing parasitized crab density. These results suggest that parasitized crabs do not aggregate with unparasitized males. Habitat was a significant source of variation in hyperparasite prevalence during 1992 but not 1995. Between-year comparisons of parasite and hyperparasite prevalences were equivocal and failed to provide convincing evidence against parameter stationarity and stability in the P. spinosissima-B. callosus-liriopsinine system.