Organism-Substrate Relationships in the Main Channel of the Lower Hudson River

Benthic invertebrates from 16 stations within the limnetic (freshwater) zone of the Lower Hudson River were sampled four times from June-September 1983 to assess organism-substrate relationships in the main channel of a large river. Overall, the fauna consisted mainly of Tubificidae and Chironomidae. Limnodrilus hoffmeisteri was by far the most abundant species, contributing 54% and 79%, respectively, to total numbers and biomass Chironomids were the most taxonomically diverse group (40 taxa). The structure and composition of the benthic communities appeared to be determined mainly by physical traits of the substrate. Stations with relatively heterogeneous substrates (sands mixed with silts) contained the richest fauna in terms of both standing crop and taxonomic richness. Not surprisingly, the fewest taxa and lowest biomass occurred in fine, well sorted sand. In silt-clay substrates, the presence of at least some sand appeared critical for the occurrence of several taxa and the abundance of others. As su...