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Study Shows Zebra Mussels Can Colonize Sand And Mud

COLUMBUS -- Researchers have found that zebra mussels have built colonies on the sandy and muddy bottom of Lake Erie, a habitat previously thought incapable of supporting the animals.

Since their Great Lakes debut in the mid-1980s, researchers believed that these tiny freshwater bivalves could only colonize hard, underwater surfaces such as rocks, clams and runoff pipes. The new findings are reported this week in the journal Nature.

“In terms of potential zebra mussel habitat, Lake Erie is wide open,” said Paul Berkman, senior research associate at Ohio State University’s Byrd Polar Research Institute. “More than 90 percent of the Lake Erie floor is a soft substrate. This is a wake-up call.

“We found that zebra mussels clearly colonize sand and muddy substrates in the lake,” he said, adding that the densities of some zebra mussel colonies exceed 20,000 animals per square meter.

Berkman and his colleagues studied 200 kilometers of the Lake Erie floor from the New York-Pennsylvania border to the lake’s western basin. They determined that by 1995, zebra mussels covered about 2,000 square kilometers of the lake bed’s soft sediment.

“We do know that mussels colonize soft substrates and that they are doing this over a significant portion of the lake,” Berkman said.

A zebra mussel starts out as a microscopic larva and can attach itself to a single grain of sand or mud. When the animal becomes a juvenile, it starts secreting byssal threads, which serve as anchors to attach the mussel to a stable surface. It continues sending out these threads, picking up more sand grains and creating a mat of cemented sediment.

“This creates a hard substrate,” Berkman said. “By binding sand grains together with their byssal threads, the mussels create a conglomerate, subsequently settled by juveniles, which creates a bed of zebra mussels on the lake bottom.”

Researchers used side scan sonar (SSS), a device that sends out frequencies that can differentiate between hard and soft underwater surfaces.

“Since the side scan sonar signal is strongly reflected by hard substrate and weakly reflected by soft substrate, we could profile the lake bottom to determine where the zebra mussels were located,” Berkman said.

The researchers then used an underwater video camera attached to a submersible remotely operated vehicle to take pictures of the suspect areas and discovered zebra mussels had colonized the soft sediment of the lake bed.

“In studying patches of zebra mussels, we observed small mussels on the order of millimeters attached to individual sand grains,” Berkman said. He says the potential implications for this discovery are great.

“The only clear thing we know for sure is that zebra mussels can grow on soft substrates,” Berkman said. “All you can do is identify problems that haven’t been studied and begin developing the necessary ecological baselines to determine the future impact.”

Other researchers include Melissa Hultuch and Emily Tichich, both of the Byrd Polar Research Institute; David Garton of the Ohio Sea Grant Program; Gregory Kennedy and John Gannon of the United States Geological Survey; and Scudder Mackey, Jonathan Fuller and Dale Liebenthal, all of the Ohio Department of Natural Resources.

This study was funded by the National Sea Grant College Program under the National Oceanic and Atmospheric Administration and administrated through the Ohio Sea Grant Program.

Ohio State University. May 1998.


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