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Invasive zebra mussels have been found in aquarium moss balls in at least 21 states. Wildlife officials say the balls must be destroyed to prevent the fast-multiplying mollusk from spreading.
Depending on the method you choose, destroying the moss balls some people add to their home aquariums is relatively easy, according to the U.S. Fish and Wildlife Service.
They can be stashed in a plastic bag and frozen for 24 hours, or plopped in boiling water for 60 seconds. They can be submerged in diluted bleach (for 10 minutes) or undiluted white vinegar (for 20). After that, you just throw away the remnants, though you’ll want to place them in a sealed plastic bag beforehand.
That all may seem a bit extreme for an aquarium decoration that closely resembles a fluffy green pom-pom, but it’s not the moss itself that must be killed, federal officials said. It’s the invasive zebra mussels that have taken to stowing away in the fuzz, confirmed in pet stores and aquarium stores in at least 21 states.
“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,” Wesley Daniel, a fisheries biologist with the U.S. Geological Survey, said in a statement. “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.”
At a glance, the zebra mussel doesn’t seem all that threatening. Roughly the size of a fingernail, the striped mollusk is native to freshwaters in Eurasia and first came to the United States in the late 1980s via ballast water that was emptied into the Great Lakes. But the mussels multiply quickly—a single female can lay up to a million eggs in a single season—and mass together in clumps on any submerged, solid surface. Often, that leads to costly clogs in drains and water intakes for power and water plants, and expensive damage to boats and fishing equipment.
The mollusks, which have no natural predators in North America, also hog food sources and crowd out populations of native species, disrupting the ecosystem in watersheds throughout the country.
Federal, state and local officials have worked for years to keep the mussels from spreading, with mixed results. But while the species has taken hold in dozens of states and more than 600 lakes and reservoirs nationwide, there are still parts of the country—including most of the west—where they haven’t been found.
Until the moss balls, that is. On Feb. 25, a pet store employee in Seattle alerted federal officials that a zebra mussel had been found there, nestling on one of the fluffy aquarium plants. Days later, Daniel found a second one snuggled in a moss ball at a pet store in Gainesville, Florida.
“At that point, federal non-indigenous species experts realized the issue was extensive,” FWS said in a news release.
Since then, zebra mussels have been found in moss balls in at least 21 states, including a handful of places—Alaska, Montana, Nevada, New Mexico, Oregon and Wyoming—where they’ve never been spotted before. Federal officials are coordinating a response in conjunction with state wildlife agencies and a pet industry trade group, which includes working to remove the balls from store shelves and encouraging people to report new sightings.
There’s no widely adopted method to control populations of zebra mussels once they’re established, though researchers are studying several options. The best control remains preventing the mollusks from spreading in the first place.
Which, for now, includes the destruction of moss balls.
Kate Elizabeth Queram is a staff correspondent for Route Fifty and is based in Washington, D.C.