Phytoplankton and Zooplankton Composition, Abundance and Distribution and Trophic Interactions: Offshore Region of Lakes Erie, Lake Huron and Lake Michigan, 1985

Abstract

During the spring, summer and autumn of 1985, the structure of the phytoplankton and zooplankton communities in the offshore waters of Lake Michigan, Lake Huron and Lake Erie was monitored. In Lake Michigan, the presence of an oligotrophic rotifer association and the oligotrophic crustacean indicator species Diaptomus sicilis and Limnaealanus macrurus, the predominance of mesotrophic diatom species, and the abundance and biomass of plankton between that of Lake Huron and Lake Erie suggest that the offshore waters are currently in the oligotrophic-mesotrophic range. In Lake Huron, the presence of an oligotrophic rotifer assemblage, the domination of the calanoid copepods, the abundance of the oligotrophic Diaptomus sicilis, and relatively low zooplankton abundance suggest that the offshore waters continue to be oligotrophic. In Lake Erie, phytoplankton and zooplankton species composition and biomass suggest a more productive status than Lake Michigan and Lake Huron. Data support the classification of the Western Basin as meso-eutrophic, the Central Basin as mesotrophic and the Eastern Basin as oligo-mesotrophic. Significant changes in the composition of the zooplankton community with the appearance of the large cladoceran Daphnia pulicaria in Lake Erie are attributed to a change in planktivory. The planktivorous emerald and spottail shiners have dramatically declined in abundance, possibly due to a resurgence of the walleye and the salmonine stocking programs.