Invasive Mussels at Apostle Islands: They're Hardier than You Thought

Locations of zebra and quagga mussels in and near the waters of Apostle Islands National Lakeshore, along with the dates they were discovered.  (Data source: Trebitz et al. 2019)

Image by Leah Carter

by Leah Carter

Apostle Islands National Lakeshore (APIS) needs your help to prevent the spread of invasive zebra and quagga mussels in Lake Superior. These bivalves, native to fresh waters in Eurasia, were initially transported to the Great Lakes via ships’ ballast water, and have spread to waters across the United States via boats and other recreational equipment. These tiny invaders threaten the aquatic ecosystem integrity of the Great Lakes system. They can quickly reproduce and cover lakebeds, suffocating native mussels and changing food webs on which other aquatic species depend. Additionally, according to the Center for Invasive Species Research at the University of California, Riverside, it is estimated that the cost of management and economic damage from zebra mussels in the Great Lakes alone exceeds $500 million per year.

Lake Superior was long thought to be inhospitable for these invasive mussel species due to it’s cold temperatures and low concentrations of the calcium that mussels need for shell growth. However, recent scientific findings from the Apostle Islands show that these invasive mollusks are hardier than previously thought. Live zebra and quagga mussels have been found on shipwrecks, commercial fishing gear, and reef habitats within Apostle Islands National Lakeshore.

How are the mussels getting to Apostle Islands waters? One theory is that some mussels are hitching a ride to APIS by clinging to private and commercial boats, which come from more suitable mussel habitats. Another theory recently investigated by scientists points to another source. Veligers, or invasive mussel larvae, have been found within the waters of Apostle Islands National Lakeshore. Investigators believe that currents from the Saint Louis River estuary, where mussels have established, may carry viable veligers to the Apostle Island region. The zebra and quagga mussel invasion in Lake Superior is still very limited, with established infestations only found in high-traffic harbors. Early action to detect and remove these tiny invaders from other APIS habitats can prevent them from spreading or achieving the large numbers seen in other Great Lakes. A National Park Service project beginning in 2021 aims to prevent invasive mussel establishment and related ecosystem damage to four Upper Midwest parks including Apostle Islands National Lakeshore through targeted prevention, early detection, and rapid response efforts. Each park (APIS, Grand Portage National Monument, Isle Royale National Park, Pictured Rocks National Lakeshore, and Voyageurs National Park) features high resource quality and imminent invasive mussel threats. At each park, boat cleaning stations are being deployed and prevention-based outreach efforts are being implemented or enhanced. NPS divers, cooperators, and volunteers will survey high-risk locations for invasive mussels. Any new infestations will be removed manually.

There are many actions that individuals can take to slow the spread of these aquatic hitchhikers. Live zebra and quagga mussels are still transported through recreational boating. As these mussels can survive for up to five days out of water attached to boats and other equipment, boat owners should make sure to inspect their boat, trailer, and any other recreational equipment, remove all mud, plants, or animals; drain all bilge water at least 100 ft from water; wash all parts of their boats, paddles, and other equipment, and let their equipment dry for at least five days before entering another fresh water body. Don’t forget to stay informed and inform others on the threats invasive species pose to the Great Lakes. Together, we can make a difference in preserving the biodiversity and natural beauty of our national parks.