RESPONSES OF GREAT LAKES HAB FORMING ALGAE TO SHIFTS IN NUTRIENTS AND TEMPERATURE

The impact of increased temperature and nutrients on harmful algal blooms (HABs) has been extensively studied in recent decades. However, less is known about how changes in temperature, nitrogen and phosphorus impact the relative abundance of specific bloom forming taxa in the Laurentian Great Lakes. To better understand these shifts we conducted 4 identical 28 day nutrient addition bioassays in Mawikwe Bay Lake Superior and Sandusky Bay Lake Erie during 2022 and 2023. This timeframe was selected to allow for competition to take place. A Fluoroprobe was used to track broad changes in communities every 3 days and microscopy was used to obtain detailed community information on days 14 and 28. Microscopy analyses allowed us to track changes in relative abundance of dominant bloom forming species, shifts in major phytoplankton groups, and changes in dominant functional traits in each treatment. In Lake Superior the dominant bloom forming genera Dolichospermum was significantly more abundant in treatments with lower N:P ratios. In Lake Erie Microcystis was significantly more abundant in treatments with higher N:P ratios and Dolichospermum more abundant in treatments with lower N:P ratios.

Primary Presenter: Reane Loiselle, University of Minnesota (loise031@d.umn.edu)

Authors:

Reane Loiselle, University of Minnesota Duluth - Large Lakes Observatory  (loise031@d.umn.edu)

Robert Sterner, University of Minnesota Duluth - Large Lakes Observatory  (stern007@d.umn.edu)

Ryan Wagner, Bowling Green State University  (ryansw@bgsu.edu)