Parasitism is increasingly recognized as an important component in ecosystem function, such as nutrient cycling. Despite a number of theoretical reviews on the subject, empirical studies supporting a role for parasites at the ecosystem scale are sparse. Yet, the indirect influence of parasites on host behavior, physiology, and mortality has been known for some time. We explored host-parasite-nutrient interactions using mesocosm “ecosystems”. We seeded 150 liter mesocosms with local sediment, algae, zooplankton and snail communities. After establishment, uninfected and echinostome-infected Helisoma spp. snails were used to create a gradient in parasitism (0%, 40%, and 100% infected Helisoma) across mesocosms.
Results/Conclusions
Increasing infection prevalence was positively correlated with the biomass of Wolffiella gladiata, a regionally rare floating aquatic plant. Additionally, periphyton ash-free dry mass (a measure of periphyton nutrient content) was significantly higher at 40% Helisoma infection prevalence than in 0% control treatments. Interestingly, Helisoma mortality was significantly lower in 40% treatments compared to 0% control treatments. We suggest that greater ash-free dry mass associated with parasitism may increase forage quality, prolonging the host lifespan, and generating a positive feedback on infection. These results suggest that parasitism likely has an underappreciated role in ecosystem functioning and warrants further exploration.