Epilimnetic Phytoplankton and Zooplankton Biomass
and Species Composition in Lake Michigan,1983 to 1992

Introduction

Evidence of appreciable change in the biota of Lake Michigan (e.g. Jude and Tesar 1985, Evans and Jude 1986, Scavia et. al. 1986, Fahnenstiel and Scavia 1987, Stewart and Ibarra 1991, Evans 1992) has directed attention to the long-term data sets of phytoplankton and zooplankton collected by the Great Lakes National Program Office of the U.S. Environmental Protection Agency.  Phytoplankton, which have short carbon turnover rates, are sensitive to water quality conditions and grazing by zooplankton, and thus respond rapidly to perturbations of the lake ecosystem.  The determination of phytoplankton abundance and species composition is one method to trace long-term changes in lakes (Munawar and Munawar 1982, Makarewicz 1993, Makarewicz and Bertram 1991).  Similarly, whether aquatic ecosystems are perturbed by changes in the top predator fish cascade down the food web or by nutrients or other stressors that are expressed from the first trophic level upward, the zooplankton are sensitive integrators of such changes (McNaught and Buzzard 1973).  They have also proved useful for complementing phytoplankton data to assess the effects of water quality (Gannon and Stemberger 1978) and fish populations on biota (e.g. Brooks and Dodson 1965).  the large interannual variability in abundance of zooplankton requires long-term data sets to detect trends in zooplankton abundance (Evans 1992).  Thus zooplankton have value as indicators of water quality and the structure of the biotic community.  Specifically, has there been a reduction of other change in the phytoplankton community concomitant with the top-down mediated changes observed in the fish and zooplankton community during the 1980s?  In this study, the 1983 - 92 spring and summer phytoplankton and zooplankton data assemblages presented make it possible to examine the historical, geographic, and seasonal relationships prevailing in Lake Michigan and to compare them, where possible, to previous studies.

Table of Contents
This full report is available as Adobe portable document files: 

• Part 1: Table of Contents, Methods, Results and Discussion - Phytoplankton
• Part 2: Results and Discussion - Zooplankton, Literature Cited
• Part 3: Tables
• Part 4: Figures
• Part 5: Appendices
• Part 6: Appendices, Species Lists