Long-term population dynamics of Littorina obtusata: the spatial structure and impact of trematodes

There are few examples of host population regulation by macroparasites in stable communities; however, strong impact of parasites on the host individual is obvious in many cases (for example increased mortality, a reduction in fecundity up to the complete castration). Associations between the host populations (periwinkle Littorina obtusata ) and prevalence of trematodes was investigated using long-term data (1982–1997) of two L. obtusata populations in the White Sea, northwest Russia. We hypothesized that high prevalence of trematodes will reduce future host population density, and increase mortality. Using a general linear model, we found a significant negative correlation between host population density and the prevalence of the most abundant parasite, Microphallus piriformes in the previous year. We found no correlation between snail reproduction and the prevalence, but observed a significant reduction in middle-aged mollusk abundance which was associated with high prevalence. This indicates the importance of parasite-induced mortality for the dynamics of the host population. There was an association between trematode infection and L. obtusata populations that influence their distribution within littoral zone. The ‘source’ population, located in the lower section of the macrophyte zone, appears to be self-sustaining, controlling the whole population recruitment and dynamics.