From stream to surf zone: Differences in the composition and succession of Lake Superior macroinvertebrate communities

Abstract

The benthic communities in the surf zone of the Laurentian Great Lakes were historically diverse assemblages with typically lotic taxa. Conditions were suitable for these lotic taxa due to wave activity and strong, nearshore currents. Due to anthropogenic stressors, including the introduction of Dreissena mussels, surf zone communities have been all but decimated in the lower Great Lakes. Remaining communities persist along the shorelines of Lake Superior, where they are influenced by lake conditions and tributary inputs. Despite their ecological importance, the relationship between these Great Lakes surf zone communities, nearby tributary communities, and the confluence (i.e., tributary mouth) communities has remained largely unexplored. This study compared the composition and succession of Lake Superior communities at three sites: tributary, confluence, and surf zone. Hester-Dendy multiplate samplers (n = 7 per site) were deployed for ∼ 28-day periods over the course of the ice-free season (May through October) to assess community composition. Although diversity was similar between sites, community composition was distinct between the sites across all sample periods. Overall, compositional shifts were greater along the shoreline community, followed by confluence and tributary communities. The magnitude of compositional shifts, as well as diversity and composition, varied across the sample periods. These results suggest these communities are distinct, exhibiting compositional shifts that appear to correspond with production peaks at each site. As warmer temperatures and intensified storms affect Lake Superior in the coming decades, it is important that further research explore the ecology of tributary, confluence, and surf zone communities to better preserve these fascinating communities.