Highly invasive and destructive freshwater mussels are threatening to make their way to the Pacific Northwest through decorative aquarium moss balls.
Earlier this month, a wholesale aquarium company in King County, Washington, reported finding zebra mussels in a shipment of decorative moss balls. Washington and Oregon state regulators are recommending people with moss balls take extra precautions to prevent the invasive mollusks from infesting waterways.
Marimo moss balls are fuzzy, orb-shaped algae native to Japan and northern Europe that can grow to the size of a tennis ball. People typically use them as decorations in aquariums. They were once widely available at pet stores until 2021, when they were found to carry invasive zebra mussels.
Washington state regulators tweeze out a tiny zebra mussel from an aquarium moss ball on Aug. 12, 2024.
Photo courtesy of the Washington Department of Fish and Wildlife
Many states, including Oregon, now require commercial retailers to get a quarantine compliance certificate before importing moss balls. According to federal regulators, many online retailers, like Amazon, sell moss balls with misleading and false certification claims.
Zebra mussels and their close relative, quagga mussels, are native to the Caspian and Black seas south of Russia and Ukraine. They started infesting the Great Lakes in the 1980s, likely traveling through ballast water discharged by ships traveling from Europe.
Since entering the Great Lakes, zebra and quagga mussels in the U.S. have decimated native fish and mussel populations, triggered botulism outbreaks among birds, and clogged water treatment plants and hydropower plants. They also tend to encrust docks, anchors and beaches with razor-sharp shells, scaring away tourists and clogging boat motors.
Zebra and quagga mussels have yet to invade waterways in Oregon and Washington. Pacific Northwest regulators are trying desperately to prevent them from entering the Columbia River Basin — a massive water system spanning from British Columbia through Washington, Oregon and Idaho. The basin is a critical source of hydropower, drinking water, irrigation and habitat for struggling fish species, like salmon.
“Just the labor costs are through the roof on taking care and mitigating for zebra and quagga mussels,” Oregon Department of Fish and Wildlife invasive species coordinator Keith DeHart said.
Despite those efforts, DeHart said it’s not a matter of if, but when these mussels enter Pacific Northwest waterways. Regulators have already found quagga mussels in Idaho. They were found in the Snake River last year.
It can be hard to tell if a moss ball is housing zebra or quagga mussel larvae.
“You can see them visually when they’re adults, but they’re microscopic when they’re juveniles,” DeHart said. “If you have acquired a moss ball in the last six months, keep an eye on it and treat it as though it’s infested.”
DeHart says people with moss balls should not dump their aquarium water down the drain. People can sterilize the water by boiling it or adding bleach. Infected moss balls should be destroyed by freezing, boiling or sterilizing with bleach or vinegar. They can be tossed in a sealed plastic bag.