Long-term trends in Great Lakes shallow zooplankton communities

Zooplankton abundance and community structure are commonly used as indicators of ecosystem state in aquatic systems, and zooplankton data provide insights into differences in ecosystem function across lakes and over time. The EPA Great Lakes National Program Office (GLNPO) has monitored zooplankton communities in all five Great Lakes during spring and summer for more than two decades using both deep net tows (0-100 m or 2 meters off the bottom,153 µm mesh) and shallow net tows (0-20 m, 63 µm mesh). While all samples are analyzed for crustacean zooplankton community, the shallow net tows are also analyzed to assess microzooplankton, including nauplii, rotifers, and dreissenid mussel veligers. We present results from shallow tow monitoring data for 2001-2022 from 72 GLNPO routine monitoring sites and evaluate variation in surface layer zooplankton community structure across lakes, years, and seasons. We present trends in shallow zooplankton community structure, discuss how they compare to previously reported patterns for whole water column zooplankton, and highlight the contributions of microzooplankton to total zooplankton biomass across the lakes.

Primary Presenter: Julie Lietz, GDIT (julie.lietz@gdit.com)

Authors:

Anne Scofield, Environmental Protection Agency  (Scofield.Anne@epa.gov)

Stephanie Figary, Cornell University  (sef92@cornell.edu)

Julie Lietz, GDIT  (julie.lietz@gdit.com)

Joseph Connolly, Cornell University  (jkc238@cornell.edu)

Christopher Marshall, Cornell University  (ccm243@cornell.edu)

Lars Rudstam, Cornell University  (rudstam@cornell.edu)

James Watkins, Cornell University  (jmw237@cornell.edu)