The Indiana Department of Natural Resources is warning aquariums owners of an invasive species that has been found in moss balls sold at pet supply stores and aquarium stores.

Marimo moss balls are sold through a number of retailers both brick and mortar and online. They are literal living balls of marine life. Marimo is a not actually a moss at all but rather a variety of algae that grows in the form of a ball. Some people use them in their aquariums or terrariums - others use them as a stand alone, living piece of decor often displayed in glass bowls on tabletops.

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So what do these little green balls of algae have to do with the Indiana Department of Natural Resources and why are they warning consumers to be cautious with them? Some of the Marimo moss balls purchased in aquarium and pet supply stores have been reportedly found to contain a very invasive species of Zebra Mussel. The United States Fish and Wildlife Services actually calls the Zebra Mussel, "one of the most destructive invasive species in North America."  Apparently these miniscule mollusks (they're the size of a fingernail!) are detrimental to the food chain and can even change the chemistry of the water.

Zebra mussels can quickly take over once they get established in a waterbody and cause significant damage including disrupting the food chain, changing the chemistry of the water (which can cause more blue green algae outbreaks or offensive taste), and clogging water intake and delivery systems. The concern is that live mussels released into a storm drain or flushed could be introduced into a waterway.

You may remember that blue green algae was a problem in a number of natural bodies of water resulting in warnings for pet owners across the country as blue green algae releases a toxin that is deadly to dogs if they ingest it. Even if they don't drink the water, the toxin from blue green algae sticks to their fur and can be ingested when they groom themselves.

So what do you do if you have one of these marimo moss balls and you find a zebra mussel? Do not flush it or throw it outside! The United States Fish and Wildlife Services advise that because "Zebra mussel larva can live in the water, in the aquarium substrate, on decorative elements, and in the filter systems," the Zebra Mussels should be destroyed in one of the following ways:

  • Freeze - Place the 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 1 full minute.
  • Bleach / Vinegar - Submerge the moss ball in chlorine bleach or undiluted white vinegar for 20 minutes.

Once the Zebra Mussels have been destroyed, they must then be properly disposed. The offending moss balls, and their packaging should be sealed inside a plastic bag and thrown in the trash. As for your aquarium and your fish, the United States Fish and Wildlife Services recommends that any fish or other living organisms in the aquarium be moved to another tank with uncontaminated water. The water that remains in the original tank should be purified with one quarter teaspoon of bleach per gallon of water and allowed to sit for ten minutes before disposing of the water down a household drain. To learn more about disposal and remediation after exposure to Zebra Mussels, visit They ask that if you have purchased a moss ball contaminated with these creatures that you submit a non-indigenous aquatic species report to the USGS.

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