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Keep your eyes out for invasive clams this summer

This time of year, we often hear reminders to watch for zebra mussels, the well-known striped aquatic invasive species (AIS). This summer there’s another, lesser-known bivalve to keep your eyes out for, Corbicula fluminea (freshwater golden clam). A discovery of Corbicula fluminea by a young participant during Starry Trek last year in a Sherburne County lake raised some questions about the potential distribution of this species in Minnesota. 

While Corbicula fluminea is a prolific invasive species across the globe, Minnesota’s winter climate has been thought to be outside of its thermal tolerance range. While Corbicula fluminea has been present in Minnesota since 1978, it has generally been confined to parts of river systems where there is some type of warm water input, such as cooling water from power plants, that keeps the area warmer than surrounding waters during cold winter months. There have been reports of empty shells found in a couple of other Minnesota lakes, but so far the discovery in Briggs Lake in Sherburne County has been the only documented case of live individuals in a Minnesota lake. 

As you spend time enjoying Minnesota’s lakes this summer, keep your eyes out for Corbicula fluminea and report any suspected discoveries to the Minnesota Department of Natural Resources via EDDMapS or by contacting an aquatic invasive species specialist. 

Tips to identify Corbicula fluminea

A freshwater golden clam being held in the palm of a hand.
An individual freshwater golden clam, retrieved from Briggs Lake in Sherburne County.

Corbicula fluminea are small bivalves (mollusks with two shells) that can grow up to about 2 inches across in size. They have a rounded shell shape, are golden to dark brown in color, and have ridged concentric rings radiating outward from the “beak” of the clam to the outer edges.  Corbicula fluminea also typically have fairly robust shells. If what you’ve found seems to have a thinner, fragile shell you may have found a native fingernail or pea clam. Fingernail and pea clams do often have visible concentric rings, however they are not heavily textured or ridged as in Corbicula fluminea. Minnesota is also the home to many native mussels, many of which may have similar coloration to Corbicula fluminea or may have various arrangements of bumps or ridges. If what you’ve found is larger than 2 inches across or more oblong in shape, you may have found one of these native mussels, a critical part of Minnesota’s aquatic ecosystems. You can find identification tips for Corbicula fluminea and common look-alike species in our AIS identification guide.

What’s happening now at Briggs Lake?

The discovery of live Corbicula fluminea at Briggs lake sparked some questions about species' cold tolerance so the Minnesota Aquatic Invasive Species Research Center funded a project on Briggs Lake to evaluate the overwinter survival of the Briggs Lake population. The project is being implemented by the Minnesota Aquatic Invasive Species Research Center, University of Minnesota Extension, and Sherburne Soil and Water Conservation District. Researchers have been out since winter sampling clams through the ice, recording locations, water temperature, and whether or not live clams were found, and will continue this work through early fall. Watch for results from this project sometime in late fall or early winter this year!

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