Notes on the population structure of the portunid crab Charybdis longicollis Leene, parasitized by the rhizocephalan Heterosaccus dollfusi Boschma, off the Mediterranean coast of Israel

The Levantine population of Charybdis longicollis, a Lessepsian migrant, ha s been parasitized recently by the sacculinid rhizocephalan, Heterosaccus d ollfusi. Incidence of infestation, its effects on host's size, sex ratio an d multiple infestation are examined. We recorded 77% infection rate with up to 57.6% of infested hosts bearing more than one externa. The rapid spread and the high prevalence of H. dollfusi can be ascribed to the dense popula tion of the host and the year-round reproduction of the parasite promoting recurrent re-infection. As heavily-infested populations are presumably main tained by immigration, it is likely that the Levantine population of C. lon gicollis will suffer drastic perturbations, as it is doubtful whether immig ration of non-infested crabs through the Suez Canal suffices for population renewal.