A new mechanism of host colonization: pedunculate barnacles of the genus Octolasmis on the mangrove crab Scylla serrata

Abstract

Aquaculture of marine animals is increasing in importance as a means of producing a steady and reliable source of protein throughout tropical Asia. The mangrove crab, Scylla serrata, is commonly cultured in tidal ponds and sometimes held in cages suspended in the sea until marketable. As is the case with many edible crab species, its respiratory chambers are inhabited by stalked barnacles which occupy space on the gills normally available for exchange of oxygen and carbon dioxide. Previously biologists have assumed that the cyprids of epizoic stalked barnacles colonize potential hosts at all stages of the crab growth cycle in a manner analogous to the way in which acorn barnacle cyprids colonize inanimate substrata. However, the present discoveries demonstrate a new mechanism of colonization: the infective octolasmid cypris larvae collect on the host just prior to its molt and transfer from the old exoskeleton to the newly molted crab at the time of molt. Fortyone premolt crabs had an average of 196.5 cyprids while 20 intermolt crabs averaged only 2.7 cyprids per crab. Forty-one crabs were individually monitored through molt under controlled conditions and 87% of the cyprids on the crabs prior to molt were found to transfer from exuviae to the newly molted crabs.