A hierarchical study of macroinvertebrate recolonization of disturbed patches along a longitudinal gradient in a prairie river

1. Macroinvertebrate densities and community composition were examined at three spatial scales after substratum disturbance; among reaches along a longitudinal gradient, within reaches and within plots. Reaches consisted of sandstone outcrops that were separated by approximately 2 km of highly mobile sandy silt substratum. 2. Substrata were disturbed by scraping sandstone plots (0.3 ± 0.3 m). Body-sized depressions created by Trichoptera in the sandstone were removed along with the upper 5 mm of sandstone, resulting in areas of newly exposed, smooth sandstone. 3. The spatial scale of examination determined whether patterns of macroinvertebrate distribution and densities were discernible. Initially there were no significant differences in community composition or total densities among reaches or among upstream/ downstream locations within reaches. Following substratum disturbance and 30 days recolonizarion, total macroinvertebrate densities did not differ significantly between undisturbed plots and disturbed plots. However, densities of Petrophilia (Pyralidae: Lepidoptera) differed along the longitudinal gradient and the Simuliidae had its highest density in the upstream reach. Significant differences were found in total macroinvertebrate densities between the upstream and the downstream halves of disturbed plots, with higher densities occurring in the downstream portions. 4. Recolonized plots had similar macroinvertebrate densities and community composition to undisturbed plots, suggesting that the stream community was highly resilient.