Zooplankton Seasonal Dynamics and Community Structure in Severn Sound, Lake Huron

Abstract

Abstract The limnetic zooplankton of Severn Sound, a eutrophic embayment, were studied between 1978 and 1989. Forty-one species of zooplankton were identified from samples collected in the sound. Total zooplankton biomass ranged seasonally from a minimum of 3.9 mg/m3 at less eutrophic stations to over 1,625 mg/m3 at the most eutrophic sites. Annual means ranged from 38 to 373 mg/m3. At the most eutrophic sites the zooplankton community was dominated by the cladoceran Bosmina longirostris. Cyclopoid and calanoid copepods increased in dominance as conditions approached mesotrophy. Calanoid copepods were insignificant contributors at the eutrophic sites, averaging less than 3% of the total zooplankton biomass. Total zooplankton biomass declined with distance from shore and phosphorus point sources as conditions became less eutrophic. Significant empirical relationships (r>0.79) were measured between zooplankton biomass and total phosphorus and phytoplankton biovolume. Densities of several species, Eubosmina coregoni, Daphnia retrocurva and Diacyclops thomasi declined by over 50% during the 11-year period of study and may be related to a shift in fish community structure.