Digenetic trematodes in four species oflittorinafrom the West Coast of Sweden

Four species of Littorina (L. littorea, L. obtusata, L. fabalis and L. saxatilis) from the Swedish west coast were examined for infections with digenetic trematodes. Four species of the genus Microphallus, Podocotyle alomon, Renicola roscovita, Himasthla elongata, Cryptocotyle lingua, and Paramonostomum chabaudi were found, in addition to encysted metacercariae of the two genera Himasthla and Renicola. The prevalence of sporocysts and rediae varied substantially among sampled populations (0-44%), as did the prevalence of metacercarial infections (3-100%), and this variation was due both to different microhabitats and to different host species. In L. saxatilis exposed rocky shore populations had lower prevalence than sheltered boulder shore populations. Within the same shores, L. littorea was the host species with highest prevalence of digeneans. The general pattern of distribution of the nine trematode species over host species was similar to what have been reported from other North Atlantic areas. However, prevalence and intensity differed both at a geographic scale (in comparison with other studies) and at a local scale. The temporal variation over years was less significant.