The influence of parasitism on producers and nutrients in mesocosm ecosystems

Abstract

Pathogens and parasites are increasingly recognized as important components within host populations, communities, and ecosystems. Both density-mediated and trait-mediated impacts of parasites on ecosystems are known and likely operate together to influence ecosystem processes. Despite the assertion that trait-mediated impacts of parasites are pervasive, empirical evidence of these effects is lacking. Our aim is to fill this gap and test whether parasitism can influence ecosystem processes within controlled mesocosm ecosystems. In the host-parasite (snail-trematode) system used, parasites form cysts in second intermediate host tissue and cause minimal direct mortality (minimizing density-mediated parasite impacts). We created mesocosms across a gradient of parasitism and measured water column nutrient concentrations, producer biomass, and invertebrate community composition. We demonstrate that trematode parasitism is correlated with an increase in periphyton dry mass and percent ash-free dry mass. Additionally, water column carbon and phosphorus concentrations were influenced by producers but not parasites. We demonstrate that parasites in the metacercarial stage have limited impact as “ecosystem engineers”, but some data suggest parasites may have a subtle influence on ecosystem processes.