Distribution of barnacle epizoites of the crab Portunus pelagicus in the Moreton Bay region, eastern Australia

Abstract

The parasites of some decapod crustaceans are known to cause sterilisation of their hosts, and can thus have an important impact on the population dynamics of infested species. Blue swimmer crabs (Portunus pelagicus) collected in three areas around Moreton Bay, Australia were examined for the presence of epizoic barnacles in their branchial chambers and on their carapace. Of the 952 crabs inspected 92% were infested with Octolasmis spp. The mean number of barnacles (predominantly Octolasmis warwickii) per carapace and gill chamber (mainly O. angulata) were 2.35 and 71.1, respectively. Barnacle infestation of gills was found to differ significantly by area, season and sex with the deeper offshore areas exhibiting the highest number of barnacles. The distribution within the hosts showed barnacles were more likely to be distributed in areas closer to the inhalant aperture. Highest abundances were found on the proximal surface of the hypobranchial side of gills 3, 4 and 5. Host moult stage and parasitism by Sacculina granifera were also found to affect the abundance of epizoic barnacles in some areas.