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Invasive clam discovered by Sherburne County youth

November 9, 2020

A U of M search for starry stonewort led to a find that poses more questions.

The Guthrie family in a park by a lake.
The Guthrie family of Big Lake, Minn., likes to volunteer together. From left: William, Zack, Becky, Savannah, Korby

Invasive species pose a threat in a state that prides itself on its waters. Trained volunteers — even whole families, such as Becky and Korby Guthrie and their three children — help hunt them down. When William, age 12, made an unexpected find, Becky Guthrie wasn’t too surprised it was her middle child.

“William is a conservationist at heart,” says Guthrie. “He reads science journals and believed it was an Asian clam.”

William found the golden clam, also called Asian clam or Corbicula fluminea, while at an event organized to find an aquatic invasive alga called starry stonewort.

Corbicula have been found in Minnesota, but mainly in rivers where power plants discharge their cooling water so it stays warmer year-round,” says Megan Weber, a University of Minnesota Extension educator who teaches volunteers how to identify and track aquatic invasive species (AIS). “Otherwise they've generally been thought to not survive our winters.” 

County and DNR partners involved

Golden clam next to a finger to indicate its size, which is about a third the size of the top part of a thumb.
Golden clams are small, but their effect could be large, so professionals are monitoring for them in Minnesota waters.

The fourth annual Starry Trek was held on Aug. 15 at 28 training sites across the state. Volunteers, many of whom are Extension Master Naturalists and AIS Detectors, were sent to 238 bodies of water and 292 different public water accesses. At each site, they took samples and used their training to set aside suspicious plants for further identification.

The family took William's clam to Dan Cibulka, Sherburne County Soil and Water Conservation District senior water resource specialist who has hosted Starry Trek in Sherburne County since 2017. He agreed with William’s assessment and sent the specimen to the Minnesota Department of Natural Resources (DNR) to be examined.

Tiled photos of nine individual volunteers outdoors wearing masks.
Volunteers from Lake County participated in the Starry Trek statewide event. Photo: Elizabeth Anderson

Weber has been following up with the DNR to learn more about what this might mean for Briggs Lake and our knowledge of Corbicula in Minnesota. Local programs are considering ways to monitor and better understand where else the clam might be in the county.

“The number of golden clams that were found in Briggs Lake suggests that it could be a breeding population,” says Patrick Mulcahy, Extension AIS educator.

Mulcahy and Weber wonder whether breeding populations of the clam, with more cold tolerance than expected, could indicate that changing climate in Minnesota makes our waterways ripe for invasion in the future. A 2014 study examined the impact of climate change on some invasive species, including golden clam. This new find poses more questions about whether they actually survive over winter, how widespread they are in the lake, and about the behavior of the species in this particular lake.

The DNR is planning to propose it be listed as a prohibited invasive species (it currently is not regulated in Minnesota). The draft classification summary has more information.

Volunteers give and receive

William Guthrie throwing a rake into the water off of the end of a dock.
William Guthrie, 12, is a budding conservationist whose discovery of golden clam intrigued conservation professionals.

“It never ceases to amaze me how much we think we know about our local lakes . . . [still] we discover new interesting things each year,” says Cibulka. “We have really focused on surveillance for zebra mussels and starry stonewort due to these species being found in nearby waters. Despite this, a young man with an inquisitive mind and a strong sense of observation found something different, something extraordinary in Briggs Lake.”

Weber agrees. “I really loved how this family found our event, that a young participant made such a unique find, and then that the event inspired them to keep going on their search and bring along more local homeschooling families.”

University of Minnesota Extension, Minnesota Aquatic Invasive Species Research Center, and their partnerships bring volunteer monitoring to counties throughout the state. “Without the dedication of our volunteers and their attentiveness to detail we would have very limited capacity to monitor our waters,” says Cibulka.

It was an exciting experience for the Guthries and their homeschooling group, too. “Our world feels tight right now, but you can still get out in the world,” says Becky Guthrie. “Any time our kids can get their hands dirty while learning, the knowledge seems to go a little deeper.”

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