At least two Duluth stores have found zebra mussels on decorative aquatic moss balls in their store fish tanks and more infested moss balls may still be on store shelves across the U.S.

Doug Jensen, aquatic invasive species coordinator for the University of Minnesota Sea Grant program, said officials are trying to get the word out to retailers and consumers who may have recently purchased the moss balls.

The goal is to find and kill any zebra mussels that may be hitchhiking on the moss balls before the invasive mussel can get into local lakes or rivers.

Federal authorities earlier this month put out the warning that decorative Marimo moss balls — used as fish habitat in aquariums as well as in decorative terrariums and even as table centerpieces — had been found infested with zebra mussels in stores nationwide.

An imported moss ball, generally used in aquariums as fish habitat, that held multiple invasive zebra mussels. (Photo courtesy of U.S. Fish and Wildlife Service)
An imported moss ball, generally used in aquariums as fish habitat, that held multiple invasive zebra mussels. (Photo courtesy of U.S. Fish and Wildlife Service)

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The moss balls have been sold under several names, including Shrimp Buddies, Betta Buddy, Marimo Balls, Mini Marimo Balls and in betta fish startup kits. (The moss balls are not really moss but a green filamentous algae — aegagropila linnaei — that looks like moss.) As of Monday, infested moss balls had been found in at least 30 states.

Consumers are urged not to purchase new moss balls at this point and, if they have any at home that were purchased in recent months, to dispose of them by freezing or dunking them in hot water, salt water or bleach. Once treated, moss balls can be placed in a sealed plastic bag and thrown in the trash. If balls were placed in an aquarium or terrarium, it is a good idea to treat the tank, pump and accessories after removing fish, animals and plants.

“We don’t know if they (zebra mussels) came from the moss balls' point of origin, or the point of import for the moss balls, or even in storage'' or shipping along the way, Jensen said. “But we know they got to Duluth and other area stores.”

National chain stores such as Petco and PetSmart, with stores in Duluth, have cooperated with the national effort to destroy the moss balls and any possible zebra mussels and to disinfect their tanks. But Jensen said some national retailers, including Walmart, continue to sell the moss balls.

“PetSmart in Duluth put the moss balls with zebra mussels in the freezer and surrendered them to the U.S. Fish and Wildlife Service and then sterilized their tanks,’’ Jensen said. “We are still trying to identify all of the smaller stores that may be selling them.”

At least some of the moss balls may have originated in Ukraine, the native home of zebra mussels, and many appear to have entered the U.S. in Florida.

“We don’t know where they all are at this point,’’ Jensen said.

Zebra mussels were first found in Minnesota in the Duluth harbor some three decades ago. They have now been confirmed in 214 lakes, rivers and wetlands in the state and are considered likely in 194 other water bodies connected to those lakes, including popular waterways like Mille Lacs Lake and Lake Winnibigoshish.

Still, that’s only 408 out of 11,842 Minnesota lakes, or 3.5%, and officials say the public information campaign and action taken by anglers and boaters have helped slow the spread here.

“Only a few Northland waters are infested with zebra mussels and we want to keep it that way,’’ said Lori Seele, coordinator of the Duluth Cooperative Invasive Species Management Area group. The local group is working to contact smaller stores and get the word out to the public.

Zebra mussels and their larger cousins — quagga mussels — are foreign invaders that filter-feed microorganisms out of the water, removing key food from the native food chain. The remarkably clearer water that occurs after their infestation looks good but can cause major disruptions in the ecosystem, sending some fish deeper and allowing more weeds to grow. The invading mussels kill most all native clams and cover all smooth surfaces underwater, disrupting water supplies and forcing expensive cleaning efforts for underwater equipment.

For more information on the moss ball problem, go to fws.gov/fisheries/ANS/zebra-mussel-disposal.html.

Anyone finding zebra mussels attached to moss balls is asked to report it to the federal Nonindigenous Aquatic Species database at nas.er.usgs.gov/SightingReport.aspx.

This story was edited at 2:24 p.m. March 23 to note that the importation of moss balls into the U.S. has been halted but that infested moss balls could still be on store shelves. The original story was published on March 22.