Zebra Mussels: Not the Ecological Disaster That Was Expected

Habitat and predators prevented widespread problems for intakes and other underwater structures

WBOY-TV
8 October 2011
By Jim Ross

About 20 years ago, the first zebra mussels were found in the Ohio River.

Based on experience with the aquatic invasive species in the Great Lakes, the expectation was that the mussels would coat water intakes, outfalls and almost every solid surface under the Ohio, Kanawha and other rivers, causing millions of dollars of damage and lost productivity.

Only it didn’t happen.

“While the zebra mussel has been a little bit of a nuisance, it’s not been a problem for us at all from an operational standpoint,” said Chuck Minsker, a spokesman for the Huntington District of the U.S. Army Corps of Engineers.

AEP spokeswoman Melissa McHenry said her company’s installations on the Ohio and Kanawha rivers have not had as many problems with the small mollusks as it has had elsewhere. The company developed ways of using water flow and temperature at its intakes and outfalls to prevent colonization, and it has been able to use biocides to clear out those that have attached themselves to underwater structures, she said.

So what has been a significant problem in the Great Lakes has turned out to be a minor nuisance in the Ohio River and its tributaries.

Jeff Kovatch, an assistant professor of biology at Marshall University, said it’s not clear why zebra mussels didn’t spread as much in the Ohio River basin as they did in the Great Lakes, but there are several theories.

First is the nature of the Ohio River itself, he said. Zebra mussels need to attach themselves to solid objects, but much of the Ohio River bottom is mud, and sedimentation can add to the mud already there, Kovatch said.

“They can’t move. Once they’re buried, they die,” he said.

Then there is the fact that some predators find them tasty and easy to harvest, Kovatch said. Ducks like them. So do freshwater drum and maybe catfish. Muskrats find them tasty, too.

“Muskrats are one of the main predators for freshwater mussels, so they likely developed a taste to these things if they’re abundant,” he said.

Mussels native to the Ohio River tend to have thick shells. Muskrats will drag them out of the water and leave them to die on land. When the mussels die, their shells open, and the muskrats can eat the flesh inside. Zebra mussels, however, have thin shells, so muskrats probably can crack them open with their teeth, he said.

Then there is the fact that zebra mussels and native mussels have different life cycles, Kovatch said. Native mussels grow and reproduce slowly, and they have relatively long lives. Some native species live up to 80 years, he said. Zebra mussels, on the other hand, live fast — perhaps five years max — and reproduce quickly.

One thing researchers have noticed is that most zebra mussels in the Ohio River are small, Kovatch said. In other waters, they can grow to a length of 3 to 4 centimeters. In the Ohio, the majority are the size of the nail in a small finger, he said.