Invasive zebra mussels found in pet shops nationwide

Zebra mussel
Credit: Unsplash/CC0 Public Domain

Zebra mussels, those invaders that have wreaked havoc on the Great Lakes, have found a new way to further their damaging spread: pet shops.

A citizen's report of an invasive zebra mussel found in an aquarium moss package from a Seattle pet store prompted a U.S. Geological Survey expert on invasive aquatic species to trigger nationwide alerts. That has led to the discovery of the destructive shellfish in pet stores in at least 21 states, from Alaska to Florida and including Michigan.

A Seattle pet shop employee on Feb. 25 reported finding an invasive zebra mussel in an ornamental aquarium moss ball. Moss balls are imported from the Ukraine that are often added to aquariums.

USGS fisheries biologist Wesley Daniel learned about the finding March 2. Daniel coordinates the agency's Nonindigenous Aquatic Species Database, which tracks sightings of about 1,270 nonnative aquatic plants and animals nationwide, including .

Daniel immediately notified the aquatic invasive species coordinator for Washington state and contacted invasive species managers at the USGS and U.S. Fish and Wildlife Service. He then visited a pet store in Gainesville, Florida, and found a zebra mussel in a moss ball there. At that point, he and other experts realized the issue was extensive. Zebra mussels have since been found in moss balls in Alaska, California, Colorado, Florida, Georgia, Iowa, Massachusetts, Michigan, Montana, Nebraska, Nevada, New Mexico, North Dakota, Oklahoma, Oregon, Tennessee, Vermont, Virginia, Wisconsin, Washington and Wyoming.

"The issue is that somebody who purchased the moss ball and then disposed of them could end up introducing zebra mussels into an environment where they weren't present before," he said. "We've been working with many agencies on boat inspections and gear inspections, but this was not a pathway we'd been aware of until now."

Almost three decades after being discovered in Lake St. Clair, likely arriving in the ballast water of freighters that traveled through eastern Europe, zebra and closely related quagga mussels can now be abundantly found in each of the Great Lakes and most major river systems in the eastern U.S. Though only about the size of a dime, the mussels reproduce quickly, eat voraciously and clump together, clinging to almost anything in the water.

Zebra mussel encrusted clams that were pulled from the Huron River near the Portage Lake Dam in Dexter Township, Mich.

They have all but crowded out native clam species and have disrupted the base of the aquatic food chain—vacuuming up the tiniest plants and animals upon which aquatic insects and small fish feed. Those, in turn, are eaten by the large game fish that create a multibillion-dollar fishing tourism industry in Michigan. Zebra and quagga mussels also cost industries, businesses and communities $5 billion between 1993 and 1999 by clogging water intake pipes, according to congressional research, with $3.1 billion of that cost coming from the power industry alone.

Federal agencies, states, and the pet store industry are working together to remove the moss balls from pet store shelves nationwide. They have also drawn up instructions for people who bought the moss balls or have them in aquariums to carefully decontaminate them, destroying any zebra mussels and larvae they contain using one of these methods: freezing them for at least 24 hours, placing them in boiling water for at least 1 minute, placing them in diluted chlorine bleach, or submerging them in undiluted white vinegar for at least 20 minutes. The decontamination instructions were developed by the U.S. Fish and Wildlife Service, the USGS and representatives of the pet industry.

"I think this was a great test of the rapid-response network that we have been building," Daniel said. "In two days, we had a coordinated state, federal and industry response."

The USGS is also studying potential methods to help control zebra that are already established in the environment, such as low-dose copper applications, carbon dioxide and microparticle delivery of toxicants.

To report a suspected sighting of a zebra mussel or another non-indigenous aquatic plant or animal, go to

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