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How Foreign Species are Introduced to the Great Lakes
Many of the invasive species in the Great Lakes have been transported in the ballast water of international ships. Ships take on ballast water in holding tanks in foreign ports, and then discharge it, along with non-native plants and aquatic animals, often in the form of seeds or larvae, into the Great Lakes. There was a rapid increase in the number of foreign species with the opening of the Saint Lawrence Seaway in 1959, which enabled large ocean-going vessels to pass through from the Atlantic Ocean to the Great Lakes.
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Some Destructive Invasive Species in the Great Lakes
Sea Lampreys (Petromyzon marinus), native to the Atlantic Ocean, were one of the earliest invasive species, entering the Great Lakes in the 1830s through shipping canals. They are parasitic jawless fish that attach to host fish by their oral disc, which functions like a suction cup. They drove lake trout, their preferred host species, nearly to extinction, and caused the collapse of populations of several other fish species. Concurrently with the decline in lake trout numbers, populations of other invasive species, such as alewives and smelt, exploded due to lack of predators, causing a cascade effect that impacted the entire ecosystem as well as the fishing and tourist industries. Fortunately, measures to control the lampreys with a chemical that is selectively toxic to them have significantly decreased their numbers, allowing lake trout populations to begin to recover.
Eurasian Ruffe (Gymnocephalus cernuus), native to Eurasia, were introduced in the mid-1980s. The rapidly increasing numbers of these small fish have threatened numerous native species including perch, walleye and others.
Zebra mussels (Dreissena polymorpha), native to eastern Europe, were first discovered in the Great Lakes in 1988. Adult zebra mussels range in size from 1/4 inch to 2 inches. They live 4 to 5 years and reproduce remarkably rapidly, with females laying up to a million eggs each year. They are filter feeders, disrupting food chains and causing a decrease in the numbers of native mollusks, fish and birds. Zebra mussels can attach to and completely cover any hard surface, including the shells of aquatic animals such as crayfish, native mussels and turtles. They clog water intake pipes and cause extensive damage to boats, engines, navigational buoys and other underwater structures. Removing and controlling Zebra mussels costs millions of dollars per year.
Round Goby Fish (Neogobius melanstomus), native to central Eurasia, were first noted in 1990. They are small, aggressive, bottom dwelling fish that reproduce quickly and out-compete native fish for food, reducing numbers of native fish and threatening rare species. Gobies also eat Zebra mussels, but since Zebra mussels are filter feeders, they accumulate potentially hazardous contaminants in their bodies. When Goby fish eat the mussels, and are in turn eaten by larger predator fish, these contaminants move up the food chain and become concentrated in sport-fish.
Some invasive plant species include purple loosestrife (Lythrum salicaria), curly pondweed (Potamogeton crispus), and Eurasian milfoil (Myriophyllum spicatum). These and other non-native plants spread by producing copious numbers of seeds or by root division. They replace native plants that provide habitat for other species and control erosion, and interfere with swimming, boating and other recreational water activities.
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US Environmental Protection Agency Great Lakes Invasive Species