Effects of Crustacean Parasitic Castrators (Epicaridean Isopods and Rhizocephalan Barnacles) on Growth of Crustacean Hosts

Abstract

Literature available on the crustacean parasitic castrators of the epicaridean families Entoniscidae and Bopyridae, and the Rhizocephala was surveyed for parasite induced effects on host growth. Because the scarcity of controlled measurements allowed only a few direct comparisons between growth of parasitized and non-parasitized hosts, an indirect parameter, that of parasite prevalence (%) as a function of host size, was used as a possible indicator of differential growth. In this manner, a number of specific parasite-host associations were identified in which the parasite could have inhibited, enhanced or had no effect upon host growth. Although variation in types of size prevalence patterns was observed in almost all surveyed families of parasitic castrators, the variation was greatest within the Bopyridae and lowest among families of the Rhizocephala. Effects of host biology on the size prevalence curve could not be evaluated, although it was thought to be significant. Evidence was examined for two mechanisms, nutritional drain and hormonal action, by which parasitic castrators could influence host growth. The evolutionary significance of parasite induced growth effects was also discussed. Assuming that parasitized hosts undergo the same size-specific mortality as non-parasitized hosts, it was concluded that epicaridean- and rhizocephalan-host associations offer opportunities for field controlled investigations into the interactions among growth, size and reproduction in the Crustacea.