Trematode parasite cercariae as food in model freshwater trophic interactions

Free-living parasite stages are important but often overlooked components of ecosystems, especially their role(s) in food webs. Trematode parasites have complex life cycles that include a motile transmission phase, cercariae, that are produced in great quantities within aquatic snail hosts and join the zooplankton community after emerging. Here I examined how cercariae presence affected the population abundance of a common freshwater zooplanktonic animal (Daphnia) when predators were present. I also sought to determine the pathways taken by cercariae-derived carbon within a model freshwater food web by using the stable isotope 13C as a tracer. I found that Daphnia population abundance positively benefitted from cercariae presence when larval dragonfly predators were present, serving as alternate prey. I also found that 13C was an effective tool to track the flow of cercarial carbon, demonstrating high consumption by benthic consumers, as well as the utility of this method for use in future studies.