Marimo moss balls sold at pet stores have been found to be contaminated with Zebra mussels.

AGFC: Aquarium moss balls may contain invasive zebra mussels

B.C. Conservation seizes thousand of moss balls due to hidden invasive species

Pest Alert: Zebra Mussels Found in “Moss” Balls — Oregon Invasive Species Council

BC works to eradicate invasive zebra mussel infested moss balls

Avoid moss balls from Ukraine - OATA - The Ornamental Aquatic Trade Association

Invasive zebra mussels found in aquarium moss products (some in Kalamazoo) prompt national response

UPDATE to Consumer Alert: Aquarium Moss Balls May Contain Invasive Zebra Mussels - N.C. Wildlife Resources Commission

Invasive zebra mussels found on pet store moss balls for sale

Pest alert: Invasive zebra mussels arrive in Oregon in moss balls sold for aquariums

Moss balls could pose serious issue for water systems if discarded improperly, DEQ says

Keep your moss balls out of Yukon, N.W.T. waterways

Zebra mussels found in moss balls shipped to pet stores in several states, including North Dakota