The use of parasites as indicators of ecosystem health as compared to insects in freshwater lakes of the Inland Northwest

Trematode parasites have complex life cycles, requiring multiple hosts. If these parasites are present in an ecosystem, then one can infer that their respective hosts must also be present. Thus, these parasites may serve as reliable indicators of species diversity in an ecosystem. To test this, we sampled larval trematodes and aquatic insects from three freshwater lakes in Idaho that varied in heavy metal pollution and three lakes in Washington that varied in agricultural use. We hypothesized that if parasites do serve as reliable indicators of ecosystem health, then parasite diversity should be higher at the least disturbed sites and should positively correlate with insect diversity. We found that the Shannon diversity index for parasites was highest at the WA reference lake (1.36) compared to the two WA lakes (0.54 and 0) exposed to cattle grazing. The ID lake with the highest levels of heavy metals experienced the highest insect diversity, but a low trematode diversity. We conclude that parasite diversity indices work as well as insect diversity indices as indicators of ecosystem health, especially in instances of heavy metal pollution.