Ontario Zebra Mussels

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“Zebra Mussel” (Dreissena polymorpha )

Zebra mussels, Dreissena polymorpha, are small, fingernail-sized, freshwater mollusks accidentally introduced to North America via ballast water from a transoceanic vessel. Since their introduction in the mid 1980s, they have spread rapidly to all of the Great Lakes and an increasing number of inland waterways in the United States and Canada. Zebra mussels colonize on surfaces, such as docks, boat hulls, commercial fishing nets, water intake pipes and valves, native mollusks and other zebra mussels. Their only known predators, some diving ducks, freshwater drum, carp, and sturgeon, are not numerous enough to have a significant effect on them. Zebra mussels have impacted the Great Lakes ecosystem and economy greatly.

SOURCES: “Zebra Mussels in the Great Lakes” 1992. Great Lakes Sea Grant Network
SLIDE. “Close-up of Zebra Mussel”. Ohio Sea Grant (on NIS site)

Zebra mussels are freshwater mollusks that often attach in large numbers to hard objects in the water. They are normally brown in colour, with yellow or white stripes, and are very small - about the size of a fingernail. In the Great Lakes, zebra mussel colonies have clogged municipal and industrial water intake lines, covered boat hulls, fouled beaches, killed native clams, and disrupted the lake ecosystems.

Zebra mussels have spread rapidly in Ontario. Since their initial discovery in 1988 in Lake St. Clair, they have spread throughout the Great Lakes/St. Lawrence River system, and into some inland lakes. Zebra mussels have invaded the Trent-Severn and Rideau systems, and have been found in some Muskoka Lakes. They probably entered these inland systems through recreational boating traffic. Zebra mussels are invisible to the naked eye in their early life stage (called a veliger), when they can be transferred unknowingly in live wells, bilge water and bait-fish buckets. In their adult stage they can attach to boat hulls.

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