Published online by Cambridge University Press: 10 September 2010
Intertidal gastropods and bivalves are important hosts for a wide range of metazoan parasites, which may exert a variety of negative effects on their hosts with consequences for mollusc population dynamics and community structure. Although vital for our understanding of the relative importance of parasites in intertidal ecosystems, quantitative information on macroparasite communities in molluscs is still largely missing. We examined the macroparasite community in Littorina littorea, Nucella lapillus, Patella vulgata and Mytilus edulis/galloprovincialis from rocky shore habitats on the south coast of Ireland. In total, twelve macroparasite taxa belonging to four major parasite groups were found in 3900 examined host individuals from sixteen intertidal localities. Digenean trematodes were the dominant parasite group, occurring in all of the investigated mollusc species and at all sampling sites. The macroparasite community in gastropods was largely similar to the species composition reported from other European shore localities, possibly due to a wide distribution of bird final hosts. In contrast, the parasite community composition observed in mussels showed obvious differences when compared to data on macroparasites in mussels from soft sediment habitats, which is probably related to differences in the species composition of gastropods acting as first intermediate hosts on rocky shores. Comparatively low infection rates in molluscs on the south coast of Ireland indicate differences in the abundance of bird final hosts as well as less suitable conditions for parasite transmission. Thus, effects of parasitism on the molluscan hosts can be assumed to be rather low, which is favourable from an economic point of view, since periwinkles and mussels are commercially exploited in Ireland.