Patterns in metazoan parasite communities of some oyster species

Metazoan parasite communities of Crassostrea gigas and Ostrea edulis from G reat Britain, Crassostrea virginica from Mexico, and Saccostrea commerciali s from Australia are described and summarized in terms of species compositi on, species richness, total number of individuals and dominance. Metazoan p arasite communities in all host species were composed of turbellarians and the metacercarial stage of digeneans, with the exception of S. commercialis where only metacercariae were found. Arthropods, including one copepod and one mite species, were present only in British oyster species. All metazoa n parasite communities of oysters had few species and low density of indivi duals. Richest communities were found in C. virginica at both component and infracommunity level. The least diverse component community occurred in S, commercialis. Infracommunities in O. edulis and S. commercialis never exce eded one species per host. The host response against parasites is suggested as the principal factor responsible for depauperate parasite communities o f oysters. Environmental factors characteristic of tropical latitudes are l ikely to have enhanced both the number of species and the densities of para sites per host in the infracommunities of C. virginica.