Pest Alert: Invasive zebra mussels arrive in Oregon in “moss” balls sold for aquariums

The highly invasive zebra mussels have made it into Oregon through Marimo moss balls, popular among aquarium hobbyists and commonly sold in pet stores. Nurseries also sell them as house plants. Unfortunately, Oregon is not alone.

The U.S. Geological Survey issued a nationwide alert about the Marimo moss ball contamination. According to the USGS website, the destructive shellfish has been discovered in pet stores in at least 30 states, from Alaska to Florida. These products are sold in stores under the names Marimo moss balls, moss balls, Marimo, Cladophora balls, or lake balls.

Large national pet store chains, including some local pet shops, have been cooperative in removing the products from their shelves. However, they continue to be sold through the Internet. 

Oregon Sea Grant Statewide Extension Watersheds and Aquatic Invasive Species Specialist, Sam Chan, is working with the Oregon Invasive Species Council (OISC) on an evolving website to inform aquarists and hobbyists on what to do if they have Marimo moss balls and how to dispose of them.

Chan said, “The arrival of the zebra mussels through the aquarium trade is a crucial threat to Oregon's economy and environment.”

Why are zebra mussels a problem?

To date, the Columbia River basin is the only region left in the U.S. that is not infested with zebra mussels, or the closely related quagga mussels.

According to OISC, the most significant concern is that zebra mussels may be unknowingly released and introduced into waterways. This could potentially cost millions of dollars in response efforts, monitoring, and ultimately maintenance costs if the mussels become established.

Once they get established, zebra and quagga mussels quickly take over a body of water and the chance that they will be eradicated is slim. These mussels disrupt the food chain by filter feeding plankton and outcompeting native invertebrates and the fish that feed on them. They also change the chemistry of the water, concentrate toxins, foul boats and marine infrastructure, clog water intake and delivery systems for drinking water, irrigation, cooling systems (e.g. data centers) and hydropower.

What are moss balls?

Ornamental Marimo moss balls are not moss rather a string-type alga that forms tightly packed balls ranging from marble to basketball size. Marimo moss balls are native to Northern Europe, Japan and Iceland. The contaminated shipment of Marimo moss balls was imported from the Ukraine.

The zebra mussels found in the Marimo moss balls are small (around 2mm) and hard to see without a hand lens. 

What can you do?

Consumers are advised to stop buying this product. If you purchased a Marimo moss ball in the last year, follow the specific steps detailed by OISC for proper treatment and disposal. Pet and garden store owners are urged to remove Marimo moss balls and other potentially contaminated moss ball products from their shelves immediately and to follow the OISC guidelines

If you are concerned that your pet, aquarium or garden store is selling infested moss balls or you suspect your aquarium is contaminated with zebra or quagga mussels, report it to the Oregon Invasive Species Hotline. Whatever you do, Don’t Let it Loose! Do not dump your aquarium water outside or down the drain without properly disinfecting it. Finally, the public is urged to spread the word and share this pest alert.

Learn more about zebra and quagga mussels

Zebra & Quagga Species Guide - Oregon Sea Grant

Zebra & Quagga Mussels: Species Guide at a Glance - Oregon Sea Grant

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