Percent Model Affinity: A New Measure of Macroinvertebrate Community Composition

A measure of macroinvertebrate community composition was developed using data from 46 shallow freshwater streams in New York State. It is intended for use in conjunction with other biological indices to assess water quality. Using unpolluted sites selected from 300 kick samples, an ideal community composition was developed and expressed as percent composition of seven major organism groups. The index of percentage similarity, as developed by Whittaker and Fairbanks (1958, "Ecology" 39:46-65), is used to measure the affinity of a community in a sampled riffle to that of the expected model community. Percent model affinity was found to be closely correlated with the Hilsenhoff Biotic Index (HBI) and the species richness of Ephemeroptera, Plecoptera, and Trichoptera, and reflected water quality changes better than HBI did in instances of non-organic pollution. With modification of the model community abundances, this measure has potential for use in other geographic areas.