Challenges and successes in managing invasive European frog-bit

(As part of Aquatic Invasive Species Awareness Week, MI Environment features a story on European frog-bit by Sarah LeSage and Kevin Walters, of Michigan Department of Environment, Great Lakes, and Energy’s Water Resources Division, from the State of the Great Lakes report.)

European frog-bit, an invasive aquatic plant on Michigan’s Aquatic Invasive Species (AIS) Watch List, is spreading along Great Lakes’ shorelines, connecting channels and inland waters. Recent Michigan detections include the lower Lincoln River in Mason County in 2021 and the Lower Grand River in Ottawa County and Pentwater Lake in Oceana County in 2019. European frog-bit was also found for the first time in Wisconsin in 2021, growing in an unnamed stream and throughout adjacent drainage ditches on the west shore of Green Bay.

European frog-bit was first detected in southeast Michigan in 1996 and has since spread along the coastal areas of Lakes Erie and Huron up to the eastern Upper Peninsula (U.P.), and now, recently, into multiple locations along Lake Michigan.

European frog-bit can form dense mats on the surface of slow-moving waters like bayous, backwaters and wetlands. These mats can impede boat traffic and alter food and habitat for ducks and fish. Because European frog-bit is free-floating, it can easily spread or be transported to new locations. European frog-bit also produces seeds and other seed-like structures called turions that may remain dormant for multiple seasons.

Addressing the westward spread of European frog-bit is challenging due to how easily it can be spread through a variety of human pathways. Similar to other AIS, people play an important role in preventing the spread of aquatic invasive species in the Great Lakes region. Human activities like boating, waterfowl hunting and fishing can unintentionally spread the invasive plant because plant parts can attach to boats, trailers and gear.

Many of the bodies of water where European frog-bit is being found are popular destinations for angling, hunting and water recreation, which means there is a high potential to spread European frog-bit from these locations to other areas. Given that some of the most recent locations where European frog-bit is being found also have direct hydrologic connections to the Great Lakes, spread through the natural movement of water is also a concern.

Fortunately, there are some simple steps that boaters, anglers and waterfowl hunters can take to help prevent the spread of European frog-bit and other AIS. Signage, print materials and outreach campaigns such as billboards are helping to spread the message to “Clean, Drain, and Dry” any boats, trailers and other gear prior to use in another waterbody. Person-to-person messaging at boating access sites through the growth of Michigan’s AIS Landing Blitz from a statewide event into the regional collaborative one is also focused on changing boater behaviors and preventing introduction and spread of many aquatic invasive species, including European frog-bit.

Michigan Department of Environment, Great Lakes, and Energy (EGLE) staff and partners collaboratively plan and undertake annual survey and response efforts across the state for European frog-bit along the Great Lakes coastal areas and on inland waters. The Upper Peninsula Resource Conservation and Development Council and all five U.P. Cooperative Invasive Species Management Areas (CISMAs) are working together to survey high risk areas across the entire U.P. and control known populations in the eastern U.P. Similarly, EGLE staff, contractors, CISMAs and other partners conduct surveys in the Lower Peninsula and use herbicides and hand pulling to prevent further spread. The Nature Conservancy, in partnership with the U.S. Environmental Protection Agency, U.S. Fish and Wildlife Service (USFWS), University of Toledo, Great Lakes Commission, Wayne State University and the Great Lakes states, created an early detection framework and interactive tool that determines risk of invasion from high-risk species at coastal locations across the Great Lakes Basin. This tool is used to identify locations for monitoring and is being expanded to inland waters.

Research on European frog-bit is also being conducted to improve our understanding of this species and inform control efforts. Lake Superior State University, Central Michigan University, Michigan Natural Features Inventory, Loyola University and Boise State University, in collaboration with EGLE, CISMAs and other partners, are implementing projects to measure the efficacy of different control methods. They are evaluating the impacts of European frog-bit on native plants and animals as well as on water quality, investigating new detection methods, developing habitat suitability and risk models and understanding the life history of European frog-bit.

Outreach, surveillance, control and research efforts working in collaboration are essential to address the challenges presented by European frog-bit and other aquatic invasive species.

For more information about European frog-bit and other invasive species, visit Michigan’s invasive species website.

Caption: EGLE's Tom Alwin removes European frog-bit from a backwater area, where it formed dense mats.