AbstractParasites may mediate ecosystem functioning through a number of direct and indirect mechanisms, but the importance of parasitism at the ecosystem scale is poorly understood. Measuring the density of free-living and parasitic consumers in units that are directly comparable provides a first step toward understanding the importance of parasitism to ecosystem processes. I sampled 2 streams in the New Jersey Pine Barrens seasonally for 1 y to measure the biomass density of all major consumer groups, including macroparasites infecting fish and macroinvertebrates. Parasites made up a small percentage of consumer biomass in Pine Barrens streams, representing just 0.00643 to 0.00733% of total consumer biomass annually. These low values contrast with higher estimates from other aquatic ecosystems, where parasite biomass exceeds that of some free-living consumers. The mean biomass densities of all consumer groups differed significantly between the 2 streams, perhaps because of stream characteristics, such as...