Developing the options for managing marine pests: specificity trials on the parasitic castrator, Sacculina carcini, against the European crab, Carcinus maenas, and related species.

The impacts of introduced marine pests are becoming increasingly apparent, prompting interest in the possibility of their biological control. We undertook laboratory and field experiments on host selection of one potential control agent (the endoparasitic barnacle, Sacculina carcini) against its natural host (the widely invasive European shore crab, Carcinus maenas) and several confamilial and more distantly related crustaceans. For comparison, we also tested host specificity in a related parasitic barnacle, Heterosaccus lunatus. The results confirm indistinct behavioral host selection in S. carcini, indicate very different mechanisms for host selection by S. carcini and H. lunatus (which could be related to differences between the two species in attachment points), and suggest host specificity in S. carcini depends on interactions between the parasite and the host's physiology. Development of convincing safety trials for marine parasites like S. carcini, in which the infective stage is a planktonic larva, will be more difficult than for many terrestrial parasites and will require detailed knowledge of the parasite's behavior and physiological interaction with its hosts.