Characterization of settlement cues used by the rhizocephalan barnacle Loxothylacus texanus

Abstract

Populations of the greater blue crab Callinectes sapidus throughout the Gulf of Mexico, as far north as South Carolina, USA, are infected by the rhizocephalan barnacle Loxothylacus texanus. Larvae are non-feeding and have approximately 3 d from the onset of metamorphosis from their naupliar stage to successfully encounter and recognize a host before their nutrient stores are depleted. The female cypris and kentrogon stages are the initial infective agents. Chemical cues, like those used by free-living barnacles to identify settlement sites, appear to be important in the identi- fication of potential hosts by this parasitic barnacle. The cypris larvae of L. texanus settle in response to carbohydrate or glycoprotein cues found in the epicuticle layer of C. sapidus exoskeletons. These cues are associated with the epicuticle layer only, not the biofilm associated with the carapace. In fact, the carapace biofilm and lipid-based compounds found in the outer layer of the epicuticle appear to afford crabs some protection against settlement by L. texanus.