Assessment of Benthic Habitat Quality in Lower Green Bay, Lake Michigan with Special Regard to Potential Hexagenia Recolonization

Abstract

With environmental remediation in the Great Lakes, Hexagenia have recovered or are recovering in systems from which they were once extirpated. An active Hexagenia recovery does not appear to be taking place in lower Green Bay. This study first examines the highly fluidized nature of lower Green Bay sediment as a possible cause for their lack of recovery due to nymphs’ potential inability to construct and maintain burrows essential to the completion of their life cycles. Hexagenia bilineata nymphs collected from the Upper Mississippi River were distributed into oxygenated aquaria containing substrates from lower Green Bay or the Upper Mississippi River collection site. Fluidized lower Green Bay sediment did not appear to hinder H. bilineata survival, growth, production, or biomass turnover in a laboratory setting. These metrics were, in several cases, greater in lower Green Bay substrates compared to control substrates from the nymph collection site. Hexagenia egg hatch and young nymph survival in lower Green Bay, tested in situ by artificially stocking eggs collected from adults emerged from western Lake Erie, were shown to be possible, as nine live nymphs ranging from 2-7 mm were recovered near egg stocking sites within one year of stocking. Additionally, meiobenthos, a group suggested to respond negatively to organic pollution, were sampled at several lower Green Bay sites. Densities of Ostracoda, Copepoda, and total meiobenthos, as well as taxon (order) diversity (Simpson’s Index, Shannon-Wiener Index, richness, and evenness) were compared between sites within and outside the Lower Green Bay and Fox River Area of Concern (AOC). Results showed that densities and diversity were not significantly lower within the AOC (p