The Great Lakes - March-October 2001


The Great Lakes

* This exhibit is no longer on display *


Invaders of the Great Lakes

Invasive Species



Invasive Species
Illustrations: Fishhook Flea Cercopagis pengoi, Rusty Crayfish Orconectes rusticus, 3-spined stickleback Gasterosteus melanostomus, Purple loosestrife Lythrum salicaria, Round goby Neogobius aculeatus, Black Swallowort Cynanchum nigrum.

Invasive Species

The Great Lakes have suffered an onslaught of invasive plant and animal species, both aquatic and terrestrial. While the sea lamprey and zebra mussel are best known, there are over 600 other exotic species now present. Since there are few vacancies in the ecological network, the invader typically displaces one or more native species. Since the native system did not develop with the invader present, often there is no native predator or parasite available to control its population. Few invaders, once established have been successfully controlled. Efforts to control purple loosestrife using a parasitic weevil are currently under way.


Round Goby
Round Goby
Eurasian Ruffe
Eurasian Ruffe

Flexing Mussels
Left: Windrows of zebra mussel shells on Lake Erie.
Right: Diporeia

Flexing Mussels

Perhaps the best known invader of the Great Lakes is the zebra mussel, Dreissena polymorpha.

Zebra mussels came to the Great lakes from Europe in the late1980s, probably in the ballast water of a ship. While their tendency to cover surfaces and plug water intakes has had obvious impacts on industry, shipping and public utilities, their explosive growth has profoundly affected the Great Lakes ecosystem.

Zebra mussels stifle native mussels and because of their very high populations, they filter out much of the plankton and suspended organic matter that native mussels and crustacea, such as the shrimp like Diporeia feed upon. Zebra mussels have redirected the nutrient and energy flow in four of the five Great Lakes from the pelagic system (the water column) into the benthic system (the bottom and sediments).

In some areas, populations of the native crustacea such as Diporeia have plummeted from thousands per square meter to a few, or none. Zebra mussels are suspected.

Zebra Mussels
Zebra Mussels

Qugga Mussels
Quagga Mussels

Eels and "Eels"
Top: American Eel, Anguilla rostrata.
Bottem: Sea Lamprey, Petromyzon marinus

Eels and "Eels"

Presented are two very different kinds of eels

The American eel is a fish having tiny embedded scales that give the impression they are scaleless. It preys upon smaller fish, spending most of its life in waters and tributaries of Lake Ontario and the St Lawrence River. After several years in fresh water, it matures and migrates downstream to the Atlantic Ocean to breed in the Sargasso Sea. The young eels migrate back up the St. Lawrence River to grow and mature. The American eel was once extremely abundant and an important food fish to Native Americans. Today American eel populations are dwindling and it is at risk of becoming endangered.

The sea lamprey is an eel-like fish that parasitizes Other fish. Previously able to reach Lake Ontario in small numbers, it invaded the upper Great Lakes once shipping canals and locks were built. This invader played a large role in the decimation of Lake Trout. In a manner opposite that of the American eel, it breeds in tributary streams, it migrates to the ocean at maturity. Chemical controls toxic to lamprey larva have been successful in controlling, but not eliminating this pest.

Sea Lamprey
Sea Lamprey, Petromyzon marinus

American Eel
American Eel, Anguilla rostrata.



Acknowledgments: The exhibit was written and complied by Robert Beltran -USEPA Great Lakes National Program Office.
The exhibit was organized and maintained by Barbara Kern - John Crerar Library, University of Chicago.

For more information about exhibits at the John Crerar Library,
please contact Barbara Kern at 773-702-8717 or

B.Kern, Crerar, 2002
Photographs of the exhibit courtesy: B. Kern

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