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Zooplankton Community Composition in the Nearshore Waters of
Southern Lake Michigan
EPA-905/3-82/001
July 1982
John E. Gannon, F. James Bricker, and Kathryn S. Bricker
Biological Station
The University of Michigan
Pellston, Michigan 44769
Grant R005337 01
Project Officer
David C. Rockwell
Great Lakes National Program Office
536 South Clark Street
Chicago, lllinois 60605
UNITED STATES ENVIRONMENTAL PROTECTION AGENCY
REGION V
CHICAGO, ILLINOIS 60609
Zooplankton samples collected in 1977 in the nearshore waters of
southern Lake Michigan (0.4 km from shore) were analyzed to provide
a bench mark on zooplankton community composition for comparison
with future studies. Species composition, abundance, and
distribution were investigated to determine the apparent response of
the zooplankton community to water quality conditions. It is
difficult to establish long-term trends on changes in zooplankton
community composition commensurate with known changes in water
quality in the nearshore waters of southern Lake Michigan because of
the lack of historical zooplankton data. Instead, the effects of
water quality conditions on zooplankton must be inferred by
comparing community composition in nearshore waters impacted by
pollutive discharges with less affected offshore waters.
Distribution and abundance of zooplankton in the nearshore waters
of southern Lake Michigan is highly influenced by physical mixing of
relatively high quality offshore waters with variously polluted
harbor effluents
nearshore. Rotifers were overwhelmingly abundant, comprising about
95% of total zooplankton. Total rotifers and crustacean plankton
generally were most prevalent in nearshore waters exhibiting highest
alkalinity, specific
conductance, and nutrient chemistry and lowest turbidity and Secchi
disc transparency. The predominant species (i.e., Keratella
cochlearis, K. crassa, Polyarthra vulgaris, Conochilus unicornis,
and Bosmina longirostris)-also were most abundant in nearshore
waters. The distribution of these species often was significantly
correlated with physicochemical variables. The apparent response of
the zooplankton community to nutrient enrichment was an increase in
density of indigenous, eurytopic species rather than species shifts
toward more eutrophic forms. This feature seems to be indicative of
mesotrophy in the Great Lakes. Eutrophic indicator species (e.g.,
Brachionus spp., Euchlanis dilatata, Trichocerca spp., and
Acanthocyclops vernalis) were rare and usually confined to harbor
mouths. Besides Bosmina longirostris, no consistent statistically
significant trends were noted between distribution of crustacean
species and physicochemical variables. However, there still was a
tendency for calanoid copepods to be more prevalent in more
oligotrophic offshore waters.
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