It took less than ten years. Non-native zebra mussels from Europe first
appeared in the Mississippi River in 1991, and today the exploding zebra
mussel population has carpeted some parts of the Mississippi River bed
with 10,000 to 20,000 mussels per square yard.
Spread largely in bilge water of commercial Mississippi River barge traffic, the mussels' hard shells can cut humans, dogs, and other animals that come in contact with them. Zebra mussels are the only freshwater mollusks that can attach themselves to solid objects such as submerged rocks, dock pilings, and boat hulls. They can clog intake pipes at power plants and require expensive treatments to remove them.
Native mussel species are the losers in this war. Almost 70 percent of the nation's 297 native mussel species are endangered, threatened, or potentially warrant federal protection. Zebra mussels have decimated native mussel species along the Mississippi and pushed the Higgins' eye pearly mussel to the brink of extinction.
Not only do the zebra mussels compete with the native mussels for food, they attach to their shells, preventing their reproduction and smothering them, according to Ron Benjamin, who works with the Wisconsin Department of Natural Resources as fisheries supervisor for the Mississippi River.
Recently crews from Wisconsin, Iowa, and the federal government fanned out along a 500-mile (800-kilometer) stretch of the Mississippi River to look for zebra mussels and clues about how to fight this exotic invasive species and save the native species.
They used bilge pumps and buckets to collect water samples that will be analyzed at an Illinois laboratory for veligers, the microscopic, larval form of zebra mussels. One cup of river water can contain as many as 100 of these young invaders.
"We're trying to study how veligers are distributed in the river, where they settle, how they fare from year to year, and what they do to an ecosystem over time," said John Sullivan, a Wisconsin Department of Natural Resources water-quality specialist for the Mississippi River. "We're in the infancy of studying zebra mussels and how they affect our ecosystems."
This is the fourth year crews have looked for the veligers. They are part of a larger effort to understand and cope with the invading mollusks that includes the U.S. Army Corps of Engineers, the U.S. Fish & Wildlife Service, and other state agencies.
A native of eastern Europe and western Asia, the thumbnail-size zebra mussels were first discovered in U.S. waters in 1988. They likely arrived in the ballast of ocean-going vessels that emptied their tanks in Great Lakes ports.
Today zebra mussels have spread to all of the Great Lakes and major river systems in the Midwest, moving through waterways by attaching to boats and barges.
This spring, biologists with the U.S. Fish and Wildlife Service and the Minnesota and Wisconsin Natural Resource Departments began working to bring the federally endangered Higgins' eye pearly mussel back from extinction.
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