Where Invasive Zebra Mussels Came From Amid Warning They Are in 21 U.S. States

An invasive species of mollusk that entered the U.S. via shipments of aquarium moss balls has now been found in pet stores across 21 states.

The shellfish, known as zebra mussels, became the center of a U.S. Geological Survey (USGS) probe this month after a PetCo employee in Seattle, Washington, discovered them stuck to an ornamental product known as the "Betta Buddy Marimo Ball."

Experts seeking to contain the situation fear the moss balls sold to customers may have spread the pests to areas they have never been before.

Zebra mussels are described as a fingernail-sized mollusk native to the Caspian Sea of Asia. They are listed as invasive because they clog the water intakes of power and water plants, block water control systems and damage fishing and boating equipment.

According to the USGS, the moss balls in question are imported from Ukraine, designed to be added to aquariums. Now, stores are working to remove them from shelves.

The U.S. Fish and Wildlife Service has said the species are easily transported when in a microscopic larval stage—before they reach juvenile and adult stages.

"Adult zebra mussels can stay alive for several days outside of water and are common hitchhikers on boats, fishing equipment–and aquarium plants!" a fact sheet said.

"In spite of their small size, zebra mussels clog pipelines used for water filtration, render beaches unusable, and damage boats and infrastructure. They also negatively impact aquatic ecosystems by harming native organisms," the agency added.

The species takes it name from the dark colored stripes on its shell, and likely arrived in the Great Lakes in the 1980s via water discharged by ships from Europe.

In this instance, the Petco staffer filed a report with the USGS's Nonindigenous Aquatic Species Database on February 25, soon catching the attention of experts.

"I work in the aquatics department, and almost every shipment... that I have unpacked for the past two months has had mussels nestled in the moss balls," they wrote.

USGS fisheries biologist Wesley Daniel was made aware of the presence of the zebra mussels in moss balls on March 2. He traveled to a pet store in Gainesville, Florida, and found a zebra mussel in a moss ball there—indicating it was a widespread issue.

As of March 8, the USGS said reports about zebra mussels in moss ball products had now come from Alaska, California, Colorado, Florida, Georgia, Iowa, Massachusetts, Michigan, Montana, Nebraska, Nevada, New Mexico, North Dakota, Oklahoma, Oregon, Tennessee, Vermont, Virginia, Wisconsin, Washington and Wyoming.

Customers who have purchased the aquarium moss balls recently have been urged to safely dispose of them—and not by flushing them down the toilet. The options include freezing, boiling, using chlorine bleach or submersion in undiluted white vinegar.

Full instructions were published online by the Fish and Wildlife Service.

A Petco spokesperson told Newsweek in a statement via email: "We were approached by the Washington Department of Fish and Wildlife regarding an investigation into a potential link between Marimo aquarium moss balls and wild zebra mussels.

"To aid in the investigation and prevent potential spread, we immediately paused the sale of all Marimo aquarium moss balls at Petco locations and on petco.com.

"We are working closely with regulatory authorities, our vendor partners and our own veterinary staff on appropriate next steps, including proper handling and disposal of any affected product and proactively contacting our customers to provide information and resources on how to responsibly collect and dispose of them at home, if necessary."

zebra mussels
Invasive zebra mussels in a Betta Buddy product recently found at a Salem area pet store. Oregon Department of Fish and Wildlife/Supplied