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Invasive zebra mussels, which first hitched a ride to the Great Lakes more than 30 years ago in cargo ships from Europe, have now been found in "moss balls,” which are sold at pet supply stores for use in aquariums. 

Earlier this month the U.S. Fish and Wildlife Service reported that zebra mussels had been found in moss balls in more than 25 states. Moss balls are 2- to 5-inch-wide balls made, not of moss, but of green algae, that are popular fish habitat in aquariums.

Minnesota was not on that original list. But they have now been found in the state, said Doug Jensen, aquatic invasive species program coordinator for the University of Minnesota Sea Grant Program. 

Measuring the impact of invasives in Minnesota lakes is complicated, inconclusive

"I can say that they were found in Petco and PetSmart stores,” Jensen said, adding the retailers “have been very responsive and responded appropriately by removing them from the shelves. And if they did have them in any tanks, they have disinfected those."

State and federal officials are concerned that if live mussels are released into a storm drain or flushed into the sewer, they could eventually be introduced into a nearby waterway. 

While large pet stores have stopped selling the moss balls, Jensen is working with the Duluth Cooperative Invasive Species Management Area to get the word out to smaller retailers and aquarium owners. 

“Only a few Northland waters are infested with zebra mussels and we want to keep it that way,” said coordinator Lori Seele.

Fish and wildlife officials ask people who have recently bought a moss ball to dispose of them by freezing or dunking them in hot water, saltwater or bleach, and then placing them in a sealed plastic bag and throwing them in the trash. 

If the balls were already placed in an aquarium, it’s recommended to 

disinfect the tank, pump, and accessories 

after removing fish, animals and plants.  

Zebra mussels can quickly take over once they get established in a lake or river. They can disrupt the food chain, change the chemistry of the water, and clog water intake and delivery systems. 

Jensen says that in the past aquarium owners in Minnesota have mistakenly released plants and animals into the wild. But that hasn’t been a concern for zebra mussels, which most often spread on boats moved between different lakes. 

“We’ve been educating recreational boaters and anglers for almost 30 years now” to stop the spread of zebra mussels, which have now contaminated more than 200 Minnesota lakes and wetlands, Jensen said.

 “And then this thing pops up as a contaminant on some algae, which we never saw coming. So it kind of caught everybody off guard.”

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Dan Kraker

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Invasive zebra mussels, which were accidentally brought to the Great Lakes more than 30 years ago on cargo ships from Europe, have now been found in aquarium plants sold at pet stores in Minnesota and more than 25 other states. 

An invasive zebra mussel on a "moss ball." 

Zebra mussels discovered on aquarium plants at Minnesota pet stores

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