Besides the direct impact on the general performance of individual organisms, the ecological consequences of climate change in terrestrial and marine ecosystems are expected to be determined by complex cascading effects arising from modified trophic interactions and competitive relationships. Recently, the synergistic effect of parasitism and climate change has been emphasised as potentially important to host population dynamics and community structure, but robust empirical evidence is generally lacking. The amphipod Corophium volutator is an ecologically important species in coastal soft-bottom habitats of the temperate North Atlantic, and commonly serves as host to microphallid trematodes that cause intensity-dependent and temperature-dependent mortality in the amphipod population. Using a simulation model parameterised with experimental and field data, we demonstrate that a 3.8 degrees C increase in ambient temperature will likely result in a parasite-induced collapse of the amphipod population. This temperature increase is well within the range predicted to prevail by the year 2075 in the International Wadden Sea region from where the model data are obtained. Due to the amphipods' ecological importance, their population decline may impact the coastal ecosystem as a whole.