A tale of two habitats: whole-watershed comparison of disturbed and undisturbed river systems in northern Michigan (USA), based on adult Ephemeroptera, Plecoptera, and Trichoptera assemblages and functional feeding group biomass

To test the differences in aquatic insect assemblages between otherwise similar habitats, adult genera of Ephemeroptera, Plecoptera, and Trichoptera (EPT) were sampled using ultraviolet lights during summer and early autumn at 15 sites each throughout the undisturbed Pine River watershed and the agricultural Charlotte River watershed, both of the Upper Peninsula of Michigan (USA). The percentage of intact watershed-scale terrestrial habitat upstream of each sampling site was the best of 32 candidate variables at predicting differences in both EPT taxonomic assemblages and functional feeding group (FFG) biomass. Relative to the Pine, streams of the Charlotte had lower intact habitat, lower genus richness, lower biomass of nearly all individual genera, and lower biomass of all FFGs, with scrapers and shredders decreasing more than filtering collectors. Both watersheds followed general trends of river continuity, although the Pine contained double the relative abundance of shredders than is typically reported. This study demonstrates that watershed-scale habitat disturbance decreases nearly all EPT taxa, regardless of FFG. It also demonstrates the importance of biomass values rather than simple specimen counts when calculating metrics, and the utility of sampling EPT adults with ultraviolet lights relative to sampling benthic specimens.