Prohibited invasive zebra mussels found in aquarium moss balls

FRANKFORT, Ky. (April 13, 2021) — Freshwater mussel expert Monte McGregor held a vial up to the light inside the Department of Fish and Wildlife Resources' Center for Mollusk Conservation, and he didn't need a microscope to know what was in it.

Three small shells in the vial carried the markings of a well-known and unwanted invasive species.

"That's classic zebra mussel with all the stripes there," said McGregor, lead malacologist for Fish and Wildlife.

A subsequent examination under the laboratory microscope confirmed his initial analysis: the zebra mussel has found a new way to hitchhike into Kentucky.

Ornamental moss balls sold for aquarium use are an emerging source of zebra mussels that have fisheries biologists across the U.S. concerned about exacerbating an existing threat to aquatic ecosystems.

"We don't want these animals," McGregor said about zebra mussels. "We've had them here in Kentucky for 30 years and we want to keep them from spreading into other areas."

Many local and national retailers that have become aware of the issue are doing their part by pulling the products off store shelves. The public can help, too. Experts are urging anyone who has bought moss balls recently or has them in their aquariums, to follow specific guidelines for disposing of them and disinfecting aquarium equipment.

The guidelines can be found through the U.S. Fish and Wildlife Service's Aquatic Invasive Species website and the Kentucky Department of Fish and Wildlife website. Options for disposing of the moss balls include freezing or submerging them in boiling water or a bleach solution for specified periods of time. There are additional recommendations for disinfecting aquariums. The Pet Industry Joint Advisory Council also released updated guidance for pet businesses and hobbyists earlier this month.

"You should never, ever dump anything from bait buckets or an aquarium into a native waterway," said Andrew Stump, aquatic nuisance species biologist with Kentucky Fish and Wildlife. "That's going to be one of the main modes of transport for some of these invasive species. They could potentially be introduced into areas where they're not currently established."

In response to discoveries across the nation, fisheries biologists with Fish and Wildlife fanned out across the state last month to search for moss balls on store shelves. They purchased several and those specimens were brought to the Center for Mollusk Conservation for testing by McGregor.

The three shells in the vial were pulled from moss balls. McGregor also saw juvenile zebra mussels (less than 1 millimeter diameter) under the microscope.

Zebra mussel larvae are even smaller and can be present in moss balls, but are not visible to the naked eye. Larvae are tiny - microscopic-sized.

"You might say, 'Well, I don't see any in the container,' but they're there," McGregor said. "It's better to just assume they're there. We want to keep them from spreading."

In Kentucky, zebra mussels were first documented in 1991. More than likely, they arrived in ballast water discharged by shipping traffic and have been distributed unwittingly by recreational boaters and anglers. Zebra mussels are now present in several major waterways connected to the Ohio River and some inland systems such as Kentucky, Barkley and Dewey lakes.

Zebra mussels pose a threat to native aquatic species and ecosystems and can cause costly damage to property and public infrastructure, as well as financial losses to industry.

About a quarter of Kentucky's native mussels are federally listed as threatened or endangered. Zebra mussels compete with native mussels for food and space. They can also smother native mussel species and attach to vegetation, hard substrates and surfaces like boat hulls and motors. In great abundance, zebra mussels can change the diets of bottom-feeding fish.

"If you've ever been around a beach with them, they're also very sharp and cut your fingers and your feet," McGregor said. "They're just an unwanted species. It's a non-native animal that our wildlife aren't adapted to cope with. We don't want anything to do with them in this country."

While the recent discovery in a popular aquarium product is a cause for concern, McGregor said it is not a cause for alarm.

"Let's not panic about it," he said. "At the same time, let's be smart about it and follow the guidelines for proper disposal and decontamination."