Infestation patterns of microphallid trematodes in Corophium volutator (Amphipoda)

Infestation patterns of digenetic trematodes in Corophium volutator (Pallas, 1766) were studied in a shallow-water area of the southern Baltic Sea. The amphipod C. volutator is the most common second intermediate host of microphallid trematodes, in particular Maritrema subdolum, in this area. Seasonal and interannual alterations in infestation among the amphipod population are described. The general trend of infestation followed a relatively invariable seasonal pattern. Lowest prevalences were generally observed in spring and early summer, when juvenile amphipods predominated. Increasing prevalences and relative infestation intensities were recorded over the summer, with the highest values in late summer and autumn. These observations are mainly explained by the population dynamics of C. volutator and the infection dynamics of the first intermediate hosts, mudsnails of the genus Hydrobia. Exceptionally high infestation rates in summer 1997 may have been triggered by the earlier appearance of high cercaria densities in the field compared to 1996. The coincidence of the infection dynamics of the first intermediate host with the population dynamics of C. volutator was apparently important. Parasite infestation, in turn, obviously induced mortality of the crustacean host, but conclusive evidence could not be provided based on the analysis of the parasite dispersion patterns in C. volutator.