Nested analysis of macroinvertebrate diversity along a river continuum: Identifying relevant spatial scales for stream communities

Benthic macroinvertebrates are important for stream ecosystem function and are considerable food resources for vertebrate consumers such as fish. The diversity, composition, and distribution of stream macroinvertebrate taxa are affected by factors that act at different spatial scales, from microhabitat to watershed-level effects. While comparative studies of watershed-level and between stream influences on benthic diversity are common, the effects of scale are less investigated within individual river segments. Benthic macroinvertebrates were systematically sampled across nested spatial scales along a 2.2-km near-pristine stretch of the Upper Black River (MI, USA), and analyzed in relation to near-bed flow and substrate features. Responses of community diversity metrics to near-bed conditions were quantified, and diversity was modeled to determine the contribution of each spatial scale to total diversity. Near-bed conditions, especially Froude number and substrate size, were positively associated with macroinvertebrate diversity and abundance. Larger (e.g., 100 m stream reach) and finer scales (e.g., individual samples) accounted for a greater proportion of variation in taxon richness and abundance, respectively. Longitudinal variation in environmental conditions was an important driver of macroinvertebrate diversity, with replacement between sites (i.e., turnover) contributing a considerably greater proportion of variation in total diversity than nestedness. Results demonstrate that macroinvertebrate communities were shaped by both local flow and substrate conditions as well as taxa replacement over larger spatial scales. This emphasizes the importance of maintaining the hydro-morphological integrity along stream courses as a requisite condition to further watershed and fisheries conservation and management.