Mass mortality of the bivalveCerastoderma eduleon the swedish west coast caused by infestation with the digenean trematodeCercaria cerastodermaeI

The trematode Cercaria cerastadermae I, a parasite of the cockle Cerastaderma edule, is recorded for the first time in Scandinavian waters. More than 20% of the investigated population of C. edule was infested by C. cerastodermae I, and most individuals showed severe tissue damage. Infestation intensity and tissue damage together with field observations strongly indicate that infestation by C. cerastodermae I was responsible for the mass mortality of C. edule during the summer of 1991. Patterns of infestation intensity, damage to the bivalve foot and an experiment on burrowing behaviour suggest that infestation by C. cerastadermae I impairs burrowing ability. The resulting large numbers of C. edule lying on the sediment surface may be misinterpreted as being caused by other factors e.g. oxygen deficiency.