Originating from the Caspian region of Russia, the zebra mussel (Dreissena polymorpha) has now spread in Ontario, Quebec, and about twenty of the United States with densities sometimes exceeding 15,000 mussels per square foot! This species appeared in 1986 in Lake Saint Clair (Michigan), brought by shipsΓÇÖ ballasts coming from Europe. Sailors, fishers and bargemen then drastically contributed to this extraordinary expansion without knowing it by transporting zebra mussels on their boats or equipment. Today, the zebra mussel risks eradicating several dozen native freshwater mussels of the Unionidae family.
To add a species to a new environment is called an introduction. We also speak of naturalized species when a species establishes itself and begins reproducing in the wild.
