Archive of Spotlight Feature Articles

The Origin of the Great Lakes Zebra Mussels

by Jill E. Jentes, Ohio Sea Grant

Since the zebra mussels first invaded the Great Lakes in 1988, research has centered on understanding the impacts these mussels have had on the Great Lakes' economy and ecology. But the question of where exactly these mussels came from still lingered. New Ohio Sea Grant research by Dr. Carol Stepien of Cleveland State University has begun to answer that by comparing the genetics and divergence patterns among the zebra mussel populations in North America to their native counterparts in Eurasia.

Single zebra mussel showing striping and byssal threads; zebra mussels attached to a native clam; cluster of zebra mussels on a small rock.

Stepien analyzed 106 individual zebra mussels (Dreissena polymorpha) taken from six sites in Eurasia including Lake Ijsselemeer near Amsterdam, Netherlands; the Rhine River at Vuren, Netherlands; Wtoctawek Reservoir, Poland; the Danube River at Budapest, Hungary; the Dnieper River in the Ukraine; and the Volga River in Russia. These individuals were compared with 174 zebra mussel samples from seven locations in North America, including Duluth Harbor, Minnesota, Lake Superior; the Mackinac Straits between Lakes Huron and Michigan; Put-in-Bay, Ohio, western Lake Erie; Cape Vincent, New York, eastern Lake Ontario; the St. Lawrence River at Gentilly, Quebec; the Hudson River at Stuyvesant, New York; and the lower Mississippi River at Baton Rouge, Louisiana.

Stepien found that similar to their Eurasian counterparts, zebra mussels in North American samples had a surprisingly high genetic variability. "Because of their present wide range of genetic differences, the results of this study suggest that there weren't a few zebra mussels, but more than likely, large numbers of different zebra mussels that invaded the Great Lakes," explains Stepien.

The study used its data to construct a zebra mussel "family tree," depicting the genetic relationship between the North American populations and the Eurasian populations (see chart). Stepien discovered that the invasion of the zebra mussels in North America appears to have been founded from many sources in northwestern and northcentral Europe, from which most shipping to the Great Lakes originates. The closest genetic matches were with zebra mussels from the Netherlands, the Rhine River, and Poland. Samples from central, southern, and eastern Europe (encompassing the Danube, Dnieper, and Volga Rivers) were very different from the North American zebra mussels, showing that they did not found the invasive populations. Lake Superior had the closest genetic link to a founding population from the Rhine River while the samples from Lakes Huron and Erie appear to be related to those from the Netherlands and Poland. Samples from Lake Ontario and St. Lawrence River showed a genetic relationship with the sample from Poland and the Mississippi River sample appears to be related to a possible founding source from the vicinity of the Rhine River. Hudson River mussels showed a less clear relationship, appearing most similar to the Rhine River and Netherlands sites and were different from all North American sample except Lake Superior's.

Cross section of a pipe clogged with zebra mussels

Variety of shell colors seen in zebra mussels in North America

Stepien hopes the results of this study will help us better understand how the zebra mussels are spreading in the Great Lakes. Unfortunately, the zebra mussels' diverse genetic variations will make them more difficult to control. To find out more about Stepien's research, contact her at c.stepien@csuohio.edu or visit her web site at www.csuohio.edu/cestp/glegl/glegl.html

[10/22/01]

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