An examination of the biotic and abiotic factors influencing theparasitic relationship of a rhizocephalan barnacle and its host

摘要

In the Gulf of Mexico and adjacent waters, the rhizocephalan barnacle Loxothylacus texanus parasitizes members of the genus Callinectes. However, factors affecting the distribution and prevalence of this parasite are not well understood. A series of studies have been conducted to determine what biological and physical factors influence this host-parasite relationship. L. texanus larvae are non-feeding and have approximately three days from metamorphosis to the cyprid stage for identification of a host, before their nutrient stores are depleted. During this time cypris larvae appear to be particularly sensitive to abiotic variations, including salinity fluctuations. The actual identification of a potential host appears to be mediated by chemical cues associated with the host, similar to those used by free-living barnacles. The female cypris larvae of L. texanus settle in response to carbohydrate or glyco-protein cues in the epicuticle layer of crab exoskeletons. Laboratory studies indicate, however, that successful settlement does not guarantee infection of the host. Results suggest that infection rates may be limited by factors such as host size, carapace content or immune response.