Science Inventory

Characterizing potentially expanding Dreissena distribution and composition in Lake Superior

Citation:

Trebitz, A., C. Hatzenbuhler, J. Hoffman, C. Larson, G. Peterson, AND A. Szczepanski. Characterizing potentially expanding Dreissena distribution and composition in Lake Superior. Great Lakes Science for National Parks Symposium, Ashland, WI, March 21 - 23, 2023. https://doi.org/10.23645/epacomptox.22278280

Impact/Purpose:

This presentation, to be given at a National Park Service science symposium, summarizes research on Dreissena that we are conducting in and around NPS waters in Lake Superior.

Description:

Lake Superior stands as an exception to the other Laurentian Great Lakes when it comes to Dreissena mussels, with these invasive species established in the St. Louis River estuary (SLRE) since 1989 but seeming not to colonize the lake proper. In the last few years, however, Dreissena have been appearing on shipwrecks and reefs around the Apostle Islands National Lakeshore (APIS), prompting the National Park Service (NPS) to undertake removal efforts and us to better characterize their distribution. In 2017, we conducted intensive sampling in APIS that found no new settled Dreissena but low-density planktonic veligers in almost half the zooplankton samples, with a spatial distribution suggesting they were not locally spawned but rather transported to APIS from the direction of the SLRE. In 2019 we followed up with sampling the SLRE to APIS gradient, which yielded declining veliger density west to east consistent with SLRE as the source and longshore current as the transport mechanism. Veligers cannot be morphologically identified to species, but our 2019 work employed a new DNA marker that showed veligers to be a mix of D. polymorpha (zebra) and D. bugensis (quagga) mussels. The quagga DNA was unexpected, since previous SLRE data reported almost all Dreissena to be zebras, so in 2022 we revisited the SLRE species distribution using DNA markers to analyze water, zooplankton, and settled mussels. Also in 2022, we extracted DNA from a large set of open-lake zooplankton samples to look for veligers further out into Lake Superior. Finally, in both 2021 and 2022 we deployed veliger settlement traps at APIS reefs -- also analyzed with DNA markers -- to complement NPS monitoring for larger mussels. Collectively, these efforts are advancing understanding of Dreissena sources, abundance, and distribution within Lake Superior generally and APIS in particular.