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A destructive invasive species is spreading from moss balls in California’s home fish tanks

Oregon Dept. of Fish & Wildlife
A zebra mussel on an aquarium moss ball.

There's an aquarium accessory called Marimo moss balls that people like to put in their fish tanks -- but some moss balls are carrying an invasive species called the zebra mussel.

That's why the California Department of Fish and Wildlife is urging people to destroy aquarium moss balls, which are actually a type of algae, not moss.

There are a lot of government agencies involved in preventing the zebra mussel from spreading into the nation’s and state’s waterways. That’s because the U.S. Department of Fish and Wildlife considers it one of the most destructive invasive species in North America.

Currently, many California retailers and suppliers are pulling moss balls from their shelves to curb the spread of zebra mussels.

The U.S. Geological Survey discovered the invasive mussels on moss balls and notified California Fish and Wildlife, who traced them back to a Southern California distributor.

Fish and Wildlife worked with the California Department of Food and Agriculture to stop shipments and prevent international importations of the moss balls into the state.

Martha Volkoff is an environmental program manager with California Fish and Wildlife. She said zebra mussels reproduce rapidly in creeks, rivers and lakes, disrupting ecosystems and causing issues with recreational activities such as boating.

“They can attach to boat docks and the hulls of boats that are left in the water for extended lengths of time, create drag on your boat, create a cleaning [and] maintenance problem,” Volkoff said. “They can also clog up in your motor, such that it can jam up and not operate.”

Volkoff said the mussels can also cover shoreline surfaces and change the water quality by producing excess feces.

Volkoff said pet suppliers and aquarists can take a number of actions to prevent the spread of zebra mussels, including bleaching, freezing, boiling, and disposing of moss balls in a sealed container in the garbage, or disinfecting and quarantining tanks and their contents.

Tropics Aquarium Professionals in San Luis Obispo typically sells moss balls at their store front.

Owner Paul Schuldt said he and his staff destroyed the product out of an abundance of caution.

Schuldt said moss balls are a fun element for aquariums but that other plants can be just as interesting to look at. He said he doesn’t expect his business to take much of a hit with the absence of moss balls.

“Even if California decided ‘You know what? We’re just going to outlaw them,’ the show will go on,” Schuldt said. “California has a very restrictive marketplace when it comes to the sale of fish and plants that could possibly become invasive or get introduced into our local ecosystems.”

California Fish and Wildlife said the agency isn’t sure when moss balls may be available for purchase again in the state. Volkoff said that’s up to the U.S. Customs and Border Protection Agency.

California law prohibits possession, importation, shipment and release of zebra mussels in any waters.

Rachel Showalter first joined KCBX as an intern from Cal Poly in 2017. During her time in college, she anchored and reported for Mustang News at Cal Poly's radio station, KCPR. After graduating, she took her first job as a Producer at KSBY-TV. She returned to the KCBX team in October 2020, reporting daily for KCBX News until she moved to the Pacific Northwest in July of 2022. Rachel spends her off-days climbing rocks, cooking artichokes and fighting crosswords with friends.
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