LONGITUDINAL CHANGES OF MACROINVERTEBRATE COMMUNITIES ALONG AN APPALACHIAN STREAM CONTINUUM

Richness and mean annual abundance and biomass of benthic taxa were me asured in prevalent habitats along a first- through seventh-order stre am continuum in the southern Appalachian Mountains (United States). Ri chness was greatest in midorder reaches, and benthic densities were hi ghest in cobble habitats, followed by bedrock, pebble-gravel, and depo sitional areas. Abundance-based estimates of functional feeding-group composition were dominated by collector-gatherers and changed little w ith habitat. In contrast, biomass-based estimates differed greatly amo ng habitats: collector-filterers generally dominated cobble and bedroc k areas; collector-gatherers, in pebble-gravel; and shredders and coll ector-gatherers, in depositional habitats. When functional-group bioma ss estimates were weighted for relative habitat availability along the continuum, patterns of benthic community composition generally matche d predictions of the river continuum concept (RCC), although localized changes in stream geomorphology also influenced community structure. Habitat-weighted abundance estimates did not produce similar trends. B ecause RCC predictions are based on benthic biomass, caution and quali fication must be exercised when using abundance data to test RCC predi ctions.