Zebra mussels hang on while quagga mussels...( MADISON The zebra mussels that have...)

MADISON The zebra mussels that have wreaked ecological havoc on the Great Lakes are harder to find these days not because they are dying off, but because they are being replaced by a cousin, the quagga mussel. But zebra mussels still dominate in fast-moving streams and rivers.

Research conducted by Suzanne Peyer, a doctoral candidate in the University of Wisconsin-Madison Department of Zoology, shows that physiological differences between the two species might determine which mollusk dominates in either calm or fast-moving waters.

"Zebra mussels quite rapidly colonized rivers close to the Great Lakes right after their introduction, within a year or two," Peyer explains. "Quagga mussels were introduced in the Great Lakes around 20 years ago, but they are still not found in the rivers or tend to be present in low numbers."

The mussels are similar in many ways. Their habitats overlap, and both are suspension feeders that filter water to extract their food. But the cousin species are different in many ways, too. Zebra mussels prefer to attach to a hard surface, while quagga mussels can live on soft bottoms, such as sand or silt. Zebra mussels also prefer warmer water temperatures and do not grow as big as quagga mussels.

Peyer's research focused on the ability of the mussels to attach to underlying material. Both species attach to rocks, sand, silt or each other by producing tiny but strong "byssal" threads, string-like strands of protein. These threads act as an adhesive that enable the mussels to attach to surfaces, regardless of how slippery the surface is. Byssal threads are the reason mussels are so difficult to remove from boats or water intake pipes.

Peyer collected both mussel species from Lake Michigan. In the lab, she subjected the mussels to different water velocities that simulated river flow conditions. Her research results supported her hypothesis that zebra mussels are able to produce more byssal threa
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