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St. Louis River estuary as possible Dreissena veliger source to western Lake Superior
Citation:
Hatzenbuhler, C., J. Barge, A. Cotter, J. Hoffman, C. Meredith, G. Peterson, S. Okum, E. Pilgrim, B. Wiechman, AND A. Trebitz. St. Louis River estuary as possible Dreissena veliger source to western Lake Superior. Presented at St. Louis River Summit, Duluth,MN, March 03 - 04, 2020.
Impact/Purpose:
The early-detection monitoring survey described in this poster was motivated by a request for help from the National Park Service (NPS) in understanding the distribution and potential impacts of Dreissenid (zebra and quagga) mussels in waters surrounding the Apostle Island National Lakeshore. This work was conducted under SSWR research area 3.01A-2.1, and builds on previous EPA/ORD case studies concerning early-detection monitoring strategies. Outcomes from this research will include development of more refined and robust sampling strategies for non-native species in different coastal systems across the Great Lakes, advancement of DNA-based tools for conducting such monitoring, and providing a baseline for future biological assessment in NPS waters.
Description:
Dreissena mussels have been established in the St. Louis River estuary (SLRE) since 1989 and are readily transported via ballast water and boat hull attachment. Their lack of establishment in Lake Superior proper was thought due to inhospitable physiochemical conditions, but that notion has been challenged by recent Dreissena finds in the Apostle Islands (APIS) region. Motivated by National Park Service concerns surrounding these finds, the U.S. EPA in 2017 conducted an intensive sampling campaign of APIS waters (100 sites, multiple sampling gear) aimed at understanding dreissenid prevalence and distribution. This survey did not find any new settled Dreissena, but did find low densities of planktonic veligers in almost half the zooplankton samples. Since these veliger finds were primarily on the western side of APIS and the SLRE (about 100 km further west) is the only substantial Dreissena population in the region, we wondered whether these veligers were spawned within APIS or transported there from the SLRE by long-shore currents. We followed up in 2019 with a study designed to assess this possibility by examining changes in veliger numbers and size as well as general zooplankton composition along the SLRE to APIS gradient. This effort consisted of 8 locations, each sampled three times two weeks apart with plankton tows, mesh colonization banners, and environmental DNA samples. This poster will summarize findings from the 2017 effort and present preliminary results from the 2019 effort.