Trematode parasites exceed aquatic insect biomass in Oregon stream food webs

1) Although parasites are increasingly recognized for their ecosystem roles, it is often assumed that free-living organisms dominate animal biomass in most ecosystems and therefore provide the primary pathways for energy transfer.

2) To examine the contributions of parasites to ecosystem energetics in freshwater streams, we quantified the standing biomass of trematodes and free-living organisms at nine sites in three streams in western Oregon, USA. We then compared rates of biomass flow from snails (Juga plicifera) into trematode parasites relative to aquatic vertebrate predators (sculpin, cutthroat trout, and Pacific giant salamanders).

3) The trematode parasite community had the fifth highest dry biomass density among stream organisms (0.40 g m-2) and exceeded the combined biomass of aquatic insects. Only host snails (3.88 g m-2), sculpin (1.11 g m-2), trout (0.73 g m-2), and crayfish (0.43 g m-2) had a greater biomass. The parasite 'extended phenotype', consisting of trematode ...