MEPS 151:123-134 (1997)  -  doi:10.3354/meps151123

Circumstantial evidence has suggested that marine microphallid trematodes using gastropods Hydrobia spp. as first intermediate hosts, amphipods Corophium spp. as second intermediate hosts, and various waterbirds as final hosts, may cause temperature-dependent epizootics and eventually local extinction of intermediate host populations. Therefore, we examined experimentally the impact of the microphallid trematode Maritrema subdolum on Corophium volutator with special reference to the influence of temperature, during the parasites' transmission from snail to amphipod. Trematode infected snails and amphipods were established together in experimental aquaria at temperatures of 15, 22 and 24°C for 9 d. Amphipod surface activity, survival rate, parasite prevalence, infection rate, and parasite distribution both within and between amphipod individuals were recorded during, or at the end of, the experiment. The snails' shedding rate of larval trematodes as a function of temperature was also examined. Increasing temperature resulted in higher infection levels and parasite-induced mortality in the amphipods, most likely governed by a similar temperature-dependent emergence of larval trematodes from the snails. No transmission occurred at 15°C, whereas at 24°C the parasite prevalence approached 100% and the parasite-induced mortality exceeded 50% in relation to controls. As assessed by the transparency of the amphipods' gills, infestation inflicted anaemia was the likely mechanism behind the increased surface activity observed among infected specimens. This parasite-induced behavioural change may facilitate transmission of infective stages to shorebird hosts feeding on C. volutator. The results demonstrate that microphallid trematodes are able to induce a significant additive mortality in C. volutator populations. The temperature mediated mortality emphasizes the potential significance of a density-independent process in controlling the impact of parasites on host organisms and thereby host population dynamics.

Corophiumvolutator · Parasitism · Mortality · Temperature · Population dynamics · Behavioural change · Microphallids · Trematodes · Tidal flat · Hydrobia ulvae