New invasive mussels thrive in Lake Erie
Written by Erie Times-News   
Friday, 24 April 2009 06:21
Zebra mussels, the invasive mollusks that have wreaked havoc in Lake Erie for almost 20 years, now have competition.

It's the quagga mussel, a slightly bigger relative of the zebra mussel. The quagga has been battling the zebra for living space in the lake since the mid-1990s.

And it's winning.

"We're seeing more quaggas, especially in the deeper water," said Eric Obert, a biologist and extension director for Pennsylvania Sea Grant, a partnership of the state, Pennsylvania State University, and the National Oceanic and Atmospheric Administration. "We still see some zebra mussels, but not as many as we once did."

That might seem like good news to anyone who has battled zebra mussels, which can coat boat hulls and clog water-intake pipes.

But quaggas are just as destructive and seem to thrive better in Lake Erie, said Jim Grazio, Lake Erie biologist with the Pennsylvania Department of Environmental Protection.

"The quaggas do better than zebra mussels do in deeper water," Grazio said. "They are more efficient feeders, so they can survive in plankton-depleted water, like we see in Lake Erie."

It takes an expert to tell the mussels apart, he said. Both are about the size of a thumbnail and have stripes, though white quagga mussels are often found.

"If you put a mussel on its bottom and it stands up, it's a zebra mussel," Grazio said. "If it falls over, it's a quagga. But that's not always the case."

Neither mussel is a native of North America. Zebra mussels come from the Caspian Sea, while quaggas originate from a river in the Ukraine.

They both arrived here in the ballast tanks of ships.

Since then, they have changed Lake Erie's ecosystem in several ways:

-The mussels have eaten so much plankton -- microscopic plant and animal life that floats in the lake -- that more sunlight now reaches the lake bottom.

The sunlight, and the phosphate emitted from the mussels, spur the bottom-dwelling algae cladophora to grow more abundantly.

When cladophora dies, it floats to the lake surface and collects in stinky piles along the shore.

"We've seen a lot more cladophora in recent years," Grazio said.

-Besides plankton, the mussels ingest high amounts of botulism toxin. They aren't affected by the toxin, but concentrate it in their systems and spread it to gobies, small fish that eat the mussels.

The gobies, and the fish and birds that eat them, get sick and die.

"It's believed to be a main reason why we started seeing more die-offs around the Great Lakes," Obert said.

Recent studies have also shown an increase in the amount of contaminants like mercury and PCBs in smallmouth bass, which eat gobies.

The theory is that the mussels consume these contaminants, which were "locked away" on the lake bottom, and pass them along to the gobies.

-The mussels also muscle out other species of their spawning areas by eating most of the plankton.

"We've seen dips in the populations of both emerald shiners and smelt, though the shiners have come back a little," Obert said.

"The problem in any body of water, is that there is only so much food, so much plankton," Grazio said. "You can cut the pie finer, but the pie is only so big."

So, are quagga mussels in Lake Erie to stay?

The total number of zebra and quagga mussels in Lake Erie seems to have declined slightly in recent years as gobies and other predators find them, but the quaggas are thriving in their new habitat, Grazio said.

"They are part of the lake's ecosystem now," Grazio said.
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