Zebra mussels (Dreissena polymorpha) are among the most devastating aquatic invasive species to invade North American fresh waters. Dave Britton/USFWS

The state Wildlife Resources Commission is asking North Carolinians who recently purchased a moss ball from a pet store for an aquarium to destroy it. 

The seemingly harmless aquarium accessory could harbor zebra mussels, a threat the state has been eyeing for more than three decades. The mussels were found in moss balls sold in North Carolina and several other states.

The tiny creatures, which grow to a maximum of 2 inches long, are more threatening than they appear. 

In fact, the U.S. Fish and Wildlife Service calls them “one of the most devastating invasive species in North America.”

According to the National Park Service, zebra mussels originated near Russia and Ukraine but have since been found throughout Europe and the United States. They were first reported in Lake St. Clair in the 1980s and were soon found in the nearby Great Lakes. They spread quickly in other areas of the country after that.

Zebra mussels can cause a wide range of harmful effects.

“The feeding habits of zebra mussels can also have a drastic impact on an infested lake,” according to the National Park Service.

“Zebra mussels are filter feeders that siphon particles of plankton from the water. They are highly efficient at this, and a large population of mussels can quickly clear the water of almost all floating particles.

“This change can cause shifts in local food webs, both by robbing food from native species that feed on plankton and also by increasing water clarity and thus making it easier for visual predators to hunt.”

They can also clog and damage boats and water intake pipes and attach themselves to docks.

In the early 1990s, Barbara Doll, a water protection and restoration specialist with N.C. State University and North Carolina Sea Grant, was part of an effort to educate residents and research the level of threat the mussels posed to North Carolina.

Doll’s research about the threat of zebra mussels to North Carolina was included in a report about the issue in Mid-Atlantic states in the early 1990s.

At the time, Doll said more than half of North Carolina’s 60 species of freshwater mussels were “threatened, endangered or species of special concern,” according to her research.

“The U.S. Fish and Wildlife Service estimates that if North Carolina’s larger rivers are colonized by zebra mussels, 13 species could be extirpated from our … state,” Doll stated in that document.

“Of those, four species could become extinct. … If midsized and smaller rivers are also colonized, the death toll is expected to rise even higher.”

Threat to North Carolina

North Carolina isn’t as high risk as some states, but the mussels could still pose a significant problem, Doll told Carolina Public Press.

Saline levels on the Coastal Plain and comparatively high acidity and low calcium levels make North Carolina less of an ideal habitat than places like the Great Lakes, where zebra mussels have been a significant issue. 

But North Carolina can’t rely on those traits, as there are still waterways that are prime habitats.

“Aquaria release is probably the biggest threat we have for introduction of zebra mussels in our state,” Doll added via email.

“And if they did take hold in certain waterways with native mussels, it could be devastating to their survival.”

When an individual disposes of an aquarium, the process runs a risk of putting zebra mussels into the ecosystem. Tanks must be emptied properly to avoid spreading invasive species.

“This recent thing shows how it could happen,” Doll said.

“So many people have fish die or a fish they don’t want anymore. They tend to dump it in a waterway. They don’t think about what’s in (the fish tank) that might be invasive to a local waterway, especially with fish they don’t want; they think they’re rescuing it. We’ve even had goldfish in the creek on the university campus. Someone’s leaving campus, they don’t want it anymore and they dump it.”

There has never been an alert like this issued for zebra mussels in North Carolina, said Todd Ewing, fisheries biologist and aquatic wildlife diversity program manager for N.C. Wildlife Resources Commission, and Christian Waters, chief of inland fisheries for the commission. 

“We had (a) vaguely similar experience a few years ago when snakeheads were found in Lake Wylie or when a bighead carp was found in the Chowan River, but these were much more localized,” Ewing and Waters said via email.

“Very few other species exhibit the level of potential risk as a zebra mussel. With contaminated moss balls identified in the state, this incident represents a very real risk to multiple waterways across the state, especially if pet stores and aquarists do not take extreme precautions.”

In August 1992, Lake Lure had a zebra mussel scare, according to Doll’s research. As a result, the town briefly did not issue new boating permits, and businesses suffered. 

That incident ended up being a false alarm, but similar action isn’t out of the question if zebra mussels are found now.

“If that were to unfortunately happen, then the Wildlife Commission will evaluate the need and feasibility of closing waterways or quarantining boats in areas with a documented infestation,” Ewing and Waters said via email. 

For some areas, this could result in economic hardship compounded by the coronavirus pandemic.

“The closure of a specific waterway would require a rule revision in North Carolina Administrative Code,” Ewing and Waters said.

“All such changes require an economic analysis by law. Any economic impact of closing a waterway would have to be weighed against the economic and ecological impacts of zebra mussels spreading to other waterways.”

Vigilance and education are key, according to Doll. In other states, professional scientists often weren’t the ones who first reported mussels in their area.

“All the monitoring in the world … most of the time, citizens found them,” Doll said. “The best monitoring network you can have is educating your citizenry and giving them a place to report.”

Preventive measures

To prevent the spread of zebra mussels or other invasive species, the commission recommends cleaning boats or other equipment used in the water and removing all water from inside boats, buckets and anywhere else containing water. All equipment should be dried off after use.

If zebra mussels are introduced now, they may not be found until the problem spreads.

“It could likely be several weeks or months, or even longer, before any introduction into the wild is detected,” Ewing and Waters said.

“The discovery of an infestation would invoke a significant response from the Wildlife Commission. However, the specific actions taken would depend greatly on the type of waterway, the location and how big the infestation was. Of course, the ultimate goal would be to eradicate the infestation, if possible.”

Anyone who recently bought moss balls for an aquarium should take care. The commission recommends two methods to destroy them: “placing them in a plastic bag and freezing them overnight; or boiling them or soaking them overnight in a bleach solution (1 cup bleach per gallon of water.)”

According to the commission, the moss balls should be put in a bag before putting them in the trash.

Aquariums should also be thoroughly cleaned.

“Living moss balls or untreated water should not be disposed of in any location where they could reach sewage systems or streams or lakes,” the commission instructed.

“To treat your aquarium: Remove the fish and apply the bleach solution and let it set for at least one hour before disposing the water down the sink or toilet. Disinfect filters, gravel and structures as described above and dispose of the water down the sink or toilet.”

Aquarium water should be changed again a week later, and aquarium owners should watch their tanks to ensure they see no signs of the invasive mussels.

Marimo Moss Ball Plant Grab & Go and Mini Marimo Moss Balls have been confirmed to have zebra mussels, but the state warned that other brands were probably also infected. The warning applies to any recently purchased moss balls from any brand.

Imari Scarbrough

Imari Scarbrough is a contributing writer to Carolina Public Press. Email her at imari.scarbrough@gmail.com