COROPHIUM-VOLUTATOR (COROPHIIDAE, AMPHIPODA) AS AN INTERMEDIATE HOST OF LARVAL DIGENEA - AN ECOLOGICAL ANALYSIS IN A COASTAL REGION OF THE SOUTHERN BALTIC

Seasonal variations in the infestation of the amphipod Corophium volutator (Pallas, 1766) by trematodes were studied in the shallow Mecklenburg Bight on the south Baltic coast. More than 20 encysted larvae of the digenetic trematodes Levinseniella brachysoma and Maritrema subdolum were found in some C. volutator specimens. The prevalence varies markedly during the year, less than 10% of the individuals being infested in spring compared with almost 100% in late summer and autumn. This increase and the comparatively higher prevalence among juveniles in late summer indicate that cercariae are released into the water during summer. No difference was found between the prevalences of males and females, but infestation was significantly more severe among large females than smaller ones. Indications of increased mortality among infested C. volutator were found: The prevalence was lower among large animals and among overwintering females. Infested females had fewer eggs in their egg pouches than those that were not infested. The impact of parasites as a factor affecting the population dynamics of marine organisms is discussed.