The influence of the trematode Microphallus claviformis on two congeneric intermediate host species (Corophium): infection characteristics and host survival

In a laboratory experiment the survival of two amphipod species Corophium volutator and C. arenarium was differentially affected by the digenetic trematode Microphallus claviformis, the former suffering from parasite induced mortality. No clear species specific parasite preference was observed, but there was a difference between the two frequency distributions of parasite number per host, indicating a preference for the competitively superior C. volutator. In both species the parasite metapopulation was overdispersed, but to the highest degree in C. volutator. Formation of a penetration cyst on the Corophium cuticle preceeds the penetration of the M. claviformis cercariae, a common feature of microphallid digeneans, but not earlier reported from this species. Dead individuals of both species carried significantly more penetration cysts than the live ones which suggests that massive invasion of cercariae during a short period of time is the cause of death of Corophium, rather than crude parasite intensity. The potential for M. claviformis to act as a structuring agent in communities of Corophium species is discussed.