Invasive zebra mussels discovered in commercially sold moss balls

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JEFFERSON CITY, Mo. – Zebra mussels, an invasive species that can cause habitat and economic harm if they get established in reservoirs and streams, have recently been found in a type of algae – known as “moss balls” – that are popular with aquarium owners. Because of this, the Missouri Department of Conservation (MDC), as well as fisheries experts across the country, are asking aquarium owners and pet store staff to examine moss balls for these troublesome mollusks. Moss balls that contain zebra mussels have been found in Missouri.

Marimo is a filamentous algae that grows into green velvety balls – hence the name “moss balls.” In the wild, marimo is found mainly in Europe and Asia (primarily Japan). In recent years, their aesthetic appeal has made these plant-like organisms popular in the aquarium trade.

Recently, it has been discovered that some moss balls being commercially sold for aquariums in several states, including Missouri, contained zebra mussels. Experts don’t know how zebra mussels got inside the moss balls, but this discovery reveals a new way these non-native invasive pests can spread.

Any aquarium containing moss balls infected with zebra mussels also has the potential of having zebra mussel larvae (called veligers) in its water. When aquarium water is switched out or if the contents get dumped into a nearby creek or lake, this could introduce zebra mussels into a new body of water.

This further emphasizes what fisheries biologists in Missouri and other states say often: Never dispose of aquarium contents in a nearby body of water because of the harmful non-native organisms this could introduce into local ecosystems. In the case of zebra mussels, the problems can be both biological and economical. The huge clusters these fingernail-sized mussels can form (sometimes as thick as a million mussels per square meter) can cause operational problems for pipes and other water-intake equipment. Their clustering activities can also kill native mussels and disrupt aquatic food chains.

The discovery of zebra mussels in moss balls means aquarium owners play an invaluable part in preventing the spread of zebra mussels, too. If you find zebra mussels in your aquarium, remember these three words – destroy, dispose, drain.

Destroy in one of three ways:

  • Freeze: Place moss ball into a sealable plastic bag and freeze for at least 24 hours.
  • Boil: Place the moss ball in boiling water for at least one minute.
  • Bleach/vinegar: Submerge the moss ball in a chlorine bleach solution at a rate of one (1) cup of bleach per gallon of water for 10 minutes or undiluted white vinegar for 20 minutes.

Dispose: Once one of the above-listed “destroy” steps have been taken, dispose of the moss ball and any of its packaging in a sealed plastic bag in the trash. If vinegar, boiling water, or bleach was used, the liquid can be disposed down a household drain. Never pour into a storm drain where it could enter and damage local waterways.

Drain: Drain and clean the aquarium. When draining and cleaning your aquarium, it’s important to follow these steps:

  • Collect any fish or other living organisms and place them in another container, with water from a separate, uncontaminated source.
  • Remove contaminated water from the tank and sterilize the water by adding one (1) cup of salt for each gallon of water.  Let the saltwater solution sit for 10 minutes and then dispose the treated water by pouring down a household drain.
  • Decontaminate the aquarium and accessories using one of the following methods, ensuring that the method you choose is in accordance with the manufacturer’s recommendations:
    • Hot Water Method: Flush and coat the aquarium and all accessories with hot water that is 120 degrees F for at least two minutes.  After two minutes, allow the water to cool and then dispose in household drain.  
    • Saltwater Method:  Add one-half (1/2) cup of salt per gallon of water to tank and soak aquarium, substrate, rocks, décor, and filter media for at least 24 hours.  Dispose of the treated water by pouring down a household drain and rinse all items prior to resetting up your aquarium.
    • Bleach Disinfection Method: Make a disinfection solution using one (1) cup of bleach per gallon of water. Soak the aquarium, substrate, rocks, décor, and filter media in the bleach water solution for at least 10 minutes.  After 10 minutes, treated water can disposed of by pouring down a household drain. Rinse off all items prior to setting up the aquarium. Dispose of the previously used filter media and replace it with new media. 
  • Once the decontamination steps are completed, allow tank and accessories to dry for at least 15 minutes before refilling with water. If the bleach disinfection method (see above) was used, add a dechlorinating product to neutralize any residual chlorine prior to reintroducing aquatic life.
  • It is recommended that aquarium owners do another water change within a week and continue to monitor the tank for any unusual or unexpected aquatic life. If needed repeat the above-listed steps.

This is an evolving situation, the latest information about how to take care of zebra mussel-infected moss balls and aquarium systems can be found at

MDC thanks people and businesses for their help in preventing the spread of this invasive species and for helping to protect Missouri’s natural resources.

More information about how to prevent the spread of zebra mussels in Missouri can be found at