Parasite transmission between soft-bottom invertebrates:temperature mediated infection rates and mortality in Corophium volutator

Circumstantial evidence has suggested that marine mlcrophallid ti-ematodes using gastropods Hydrobia spp. as flrst lnterlnedlate hosts, amphipods Corophlum spp. as second intermediate hosts, and various waterblrds as final hosts, may cause temperature-dependent epizootics and eventually local extinction of ~ntel-mediate host populations.Therefore, we examined experirnentally the impact of the microphallid trematode Mar~trenia subdolum on Corophluni volutator wlth special relerence to the influence of temperature, during the parasltes' transmission from s n a ~l to amphipod.Trematode infected snails and amphipods were estabhshed togtlther in experimental aquaria at temperatures of 15, 2 2 and 24°C for 9 d.Amphipod surface activ~ty, survlvdl rate, parasite prevalence, lnfectioil rate, and paraslte dlstnbution both within and between amphlpod ~nti~vlduals were recorded d u n n g , or at the end of, the experiment The snalls' shedding rate of larval ti-clnatodes as a function of temperature was also e x a m ~n e d .Increasing temperature resulted 111 higher Infection levels and parasite-induced mortality in the amphipods, most Ilkely governed by a similar temperature-dependent emergence of larval trc'matodes from the snails.No transmission occurred at Ij'C, whereas at 24°C the paraslte prevalence approached 100",1 and the parasite-induced mortality exceeded 50%) in relation to controlsAs assessed by the transparency of the amphipods' gills, infestation inflicted anaemia was the llkely mechanism behind the Increased surface activity observed among infected specimens.This paraslteinduced behavioural change niay facilitate transmission of infective stages to shorebird hosts feeding on C. volutator The results demonstrate that microphalhd trematodes are able to induce a significant additive mortality in C. volutator populatlons.The temperature mediated mortality emphasizes the potential significance of a density-~ndependent process in controlling the impact of parasltes on host organisms and thereby host population dynamics.KEY WORDS Corophiurn voll~tator .Parasitism .Mortality .Temperature .Population d y n a m ~c s Behavioui-al change Mlci-ophalllds Trematodes .Tidal flat Hydrobia ulvae