Epibionts and intermoult duration in the crab Bathynectes piperitus

Abstract

Crustacean carapaces act as semipermanent hard substrata and can provide useful information on moulting and other biological characteristics of the host. The patterns of epibiosis on the portunid crab Bathynectes pipentus were stuhed from samples collected by trawling off southern Namibia between September 1987 and December 1988. Four species were identified as epibionts of this crab: the hydroid Stegopoma plicatile, the polychaete Spirorbis patagonicus, the pedunculate cirriped Poecilasma kaempfen and the bryozoan Nolella annectens. The patterns of distribution of the 4 epibionts were studied on the carapaces of 318 adult male crabs. The number of individuals or colonies of each epibiont species was noted within each of 4 carapace areas. The hydroid occurred preferentially on the anterior part (46.9 % ) of the carapace, whereas the cirriped was found most commonly on the posterior (45.7 %) The polychaete was more common on the inferior parts (53.1 %) as was the bryozoan (80.3 %). The relationships between the size of the crab and the number of polyps (hydranths), the number of colonies and the number of gonothecae of S. plicatde were also analyzed, since these parameters could give an estimate of the intermoult period of the host. Based on the identification of 3 cohorts in both the hydroid and cirriped populations, and talung into account their probable age, a minimal time for the intermoult period can be defined. Recruitment and reproduction of the hydroid show that the process of colonization is continuous on all sizes of adult crab.