By Greg Barnes
In the 1980s, the water in Lake Michigan was a cloudy, blue-green soup of algae and other living microorganisms.
Fast forward to today. The lake is so clear that bathers standing neck-deep in it can easily see their feet on the bottom.
And that’s not a good thing.
Invasive zebra mussels, first detected in Michigan’s Lake St. Clair in 1988, have multiplied into the billions in the Great Lakes, profoundly changing its ecosystem. While the mussels are masters at filtering algae and pollutants from the water, they threaten the Great Lakes’ fishing industry, clog municipal drinking water intakes, and have reached far inland into rivers, streams and other lakes.
Researchers are now worried that the zebra mussels could be coming to North Carolina.
In late March, the N.C. Department of Environmental Quality sent out a release saying the small zebra mussels — scientifically known as Dreissena polymorpha — had been found in moss balls at pet stores in North Carolina and 20 other states. Moss balls, which are spheres of spongy green algae, are commonly imported from Ukraine and used here by aquarium enthusiasts.
Since the zebra mussels’ discovery in moss balls, wildlife researchers have been scrambling to determine how long they have been getting into this country. They’re also trying to educate people on the best practices to destroy the moss balls, said Todd Ewing, a supervisor of the aquatic wildlife diversity program at the N.C. Wildlife Resources Commission.
“The best thing is to not let the genie out of the bottle and the best way — the only way — to do that is to have the public aware of the risk and to utilize best practices as far as disposing of aquarium water and cleaning your boats,” Ewing said.
Little mussels, huge risks
It is believed that zebra mussels got into the Great Lakes from ballast water that was discharged by large ships from Russia and other European countries. It didn’t take long for the mussels to take root and spread.
According to Michigan State University, zebra mussel cleanup in the United States cost between $1 billion and $1.5 billion between 1989 and 2004, with some reports putting the damage as high as $5 billion.
“The ability of zebra mussels to attach onto a variety of surfaces means that they are able to blanket large portions of the lake floor and also disrupt water intake and outtake pipes at factories, power plants, irrigation systems and boats by inhabiting and eventually restricting the flow or completely blocking water pipes,” MSU Extension/Michigan Sea Grant said in a three-part report in 2015.
There is also a human health factor. Ewing said zebra mussels love to devour algae — just not the blue-green algae called Microcystis aeruginosa, which can produce a family of toxins known as microcystins.
Algal blooms containing microcystins have become almost commonplace in some North Carolina
The zebra mussels “don’t tend to filter out the small blue-green algae as much, which leads to higher concentrations of those blue-green algae, because then they’re not having the competition with some of the other algae,” Ewing said. “So these blue-green algae get more abundant.”
He said zebra mussels attach to anything with a hard surface, including boats, docks, piers and even other mollusks and snails. Another health danger is people getting cut by the zebra mussels’ sharp edges, Ewing said.
Greg Cope, a distinguished professor in N.C. State University’s agromedicine program, has been studying zebra mussels — and native bivalves — for 30 years. In vast areas of the Great Lakes, Cope said, the zebra mussel has essentially wiped out clams and other native mollusks by attaching to them and preventing the native mussels from opening their shells to feed, filter and breathe. The state Wildlife Resources Commission lists 25 species of mollusks in North Carolina that are already endangered.
Zebra mussels thrive on phytoplankton, microscopic marine organisms that sit at the bottom of the food chain. In the Great Lakes, phytoplankton are gobbled up by zooplankton, which are eaten by alewives and other small fish, which are eaten by bigger fish all the way up to the top of the chain — the chinook salmon.
In 2018, the Chicago Tribune reported on research from the U.S. Fish and Wildlife Service that found harvests of chinook in the Great Lakes had fallen from around 10 million pounds in the mid to late 1980s to about 3 million pounds. The zebra mussel was largely to blame.
North Carolina water bodies
The good news is that few of North Carolina’s lakes, rivers and streams appear to be suitable for large infestations of zebra mussels.
In 1997, N.C. State researcher Barbara Doll led a study to determine which of the waterways in North Carolina would be most susceptible to the mussels.
Doll’s research examined 338 of the state’s surface waters. She based her study on five parameters: calcium, pH, salinity, temperature and dissolved oxygen. Zebra mussels need high levels of calcium to grow and build their shells. They are freshwater mussels that don’t like salinity, and they need high levels of dissolved oxygen and pH to thrive. At the time of her report, Doll said, zebra mussels had not invaded hotter climates, such as Louisiana and Texas, so more study is needed on the issue of temperature.
Doll said that if any one of the parameters were not met, it would almost certainly rule out the zebra mussels’ ability to invade on a large scale.
“They would not have the kind of chemical makeup of the water to, you know, really thrive,” she said. “They could show up but their persistence might be a little bit hampered because conditions would not be optimal.”
Doll’s report showed a map with about 44 waterways in the state meeting — or mostly meeting — all of the parameters. The map did not list the waterways. But Doll said most of the water bodies in the western part of the state have low acidity, and those in the far eastern part are high in salinity, so the chances of zebra mussels invading those areas are negligible.
“In some ways, it was a little bit of a relief that a lot of our waters are not overly in the kind of perfect match for zebra mussels,” Doll said.
But the threat remains for those North Carolina lakes and rivers that are a decent match. Zebra mussels have invaded some waterways in neighboring Tennessee and Virginia, Cope said.
“We’ve been kind of uneasy about the possibility of that happening and to our knowledge it has not, so I think that by whatever means we’ve been very fortunate,” he said. “Vigilance, I think, is part of that.”
Responding to the threat
One need only to look at the response by the U.S. Geological Survey to get an understanding of just how big of a threat zebra mussels pose to the country.
On Feb. 25, an employee of a pet store in Seattle, Washington, filed a report to the Geological Survey database saying he had recognized a zebra mussel in a moss ball.
After getting confirming information, including a photograph, USGS fisheries biologist Wesley Daniel immediately notified the aquatic invasive species coordinator for Washington state and contacted invasive species managers at the USGS and the U.S. Fish and Wildlife Service.
According to a release on the USGS website, Daniel then visited a store in Gainesville, Florida, and found a zebra mussel in a moss ball there.
“At that point.” the statement said, “federal non-indigenous species experts realized the issue was extensive.”
The U.S. officials teamed with the Pet Industry Joint Advisory Council, state wildlife agencies and regional aquatic invasive species management groups in an effort to further investigate the threat, educate the masses and control the situation.
“I think this was a great test of the rapid-response network that we have been building,” Daniel said in the release. “In two days, we had a coordinated state, federal and industry response.”
In North Carolina, Ewing said, officers with the N.C. Wildlife Resources Commission fanned out to visit nearly every pet store in the state.
“Most of the pet stores that had moss balls voluntarily pulled them off the shelf and agreed to dispose of them and did dispose of them,” Ewing said.
He said the officers found contaminated moss balls in all nine of the agency’s North Carolina districts.
At this time, no zebra mussels from moss balls have been found to have populated any U.S. waterways.
“I do want to reiterate that education is the most effective thing we can do, by far and away, because once they get into water there’s not a lot you can do, at least at a large scale,” Ewing said.
Cope said he spent the early part of his career in Wisconsin trying to find effective ways to eradicate zebra mussels. He said he’s departed from that field of research, but others have picked up the torch.
While new methods continue to be tried, Cope said, no one has yet to come up with a solution to eliminate or reduce the mussels population without harming indigenous species.