Variability in Macroinvertebrate Communities of the Susquehanna River in Central Pennsylvania†

Aquatic habitats vary widely in physical, chemical, and biological factors that can directly influence macroinvertebrate communities. Large rivers are spatially heterogeneous ecosystems with habitats affected by proximity to river banks, channel morphology, tributary confluences and human activities. Yet, large rivers remain largely understudied and are generally sampled in easily accessible near-bank areas, leaving macroinvertebrate communities undocumented from deeper, faster flowing mid-channel habitats. Our goals were to document variability in macroinvertebrate community structure in the Susquehanna River and its two main tributaries, to determine the importance of upstream vs. local conditions, and to assess differences in near-bank vs. mid-channel sampling areas. We collected benthic macroinvertebrate samples in summer 2011 from the West Branch, North Branch, and mainstem Susquehanna River using rock baskets to standardize substrate effects across sites. We documented higher abundances of many genera in mid-channel sampling locations compared to near-bank locations but found no significant differences in taxa richness. Many taxa showed particular distribution patterns among river sites, but little correlation between upstream sampling locations and sites directly downstream. Therefore, our results indicate macroinvertebrate communities are primarily driven by the interaction of local habitat conditions.