Zebra mussels are here to stay

By Christina Campbell
Sun staff writer
It was only a matter of time. For years, Glen Lake has been the last holdout against the Leelanau County zebra mussel epidemic. But this summer, swimmers are seeing native Glen Lake clams coated with the mussels. These massing molluscs have now infected every main recreational lake in the county. And although we may be able to slow their advance and minimize their scope, zebra mussels are here to stay.

Lake Leelanau, infected in 1996
The adult zebra mussel, or Dreissena polymorpha, is less than two inches long. Its stripes vary in color but never leave the dull end of the spectrum. In the palm of your hand, it’s just another boring bivalve. But give it a spawning season in clean, calm, oxygen-rich water, and the deceptively innocuous zebra mussel will tag-team with others of its kind to mob lake and river bottoms, altering entire ecosystems.
A female zebra mussel produces one million eggs per year. The resulting larvae are the diameter of a human hair and disperse easily through water. Bilges, bait buckets, fishing gear, or scuba equipment — anything that holds even a miniscule amount of water — can be a zebra mussel larvae vector. So you should wash and thoroughly dry boats and water toys inside and out before transporting them into new water bodies.
Adult zebra mussels are less subtle invaders than their larvae. If you find adult mussels clinging to your boat, help to control their spread by scraping them off and disposing of them in a very dry area. (In humid conditions, they can survive several days out of the water.) You might also see zebra mussels attached to buoys, docks, plants and particularly lazy crayfish and turtles. In Leelanau lakes their favorite substrate is our native clams. First a few pioneering zebra mussels find a foothold, and then more mussels pile on top of them; in large lakes, colonies more than a foot thick are not unusual.
Little Traverse Lake, infected in 1998
Native to the Caspian Sea and Ural River, zebra mussels spread across Europe more than a century ago via canal construction. Then came the transatlantic shipping era. Vessels from freshwater European ports arrived in the Great Lakes carrying ballast water full of zebra mussel larvae. When the ships picked up their American cargo, they dumped their ballast into the Great Lakes. The first North American zebra mussels were seen in 1988. They appeared in Lake St. Clair, a small lake connecting Lake Huron and Lake Erie. By 1990, they had spread to all the Great Lakes. In parts of Lake Erie, there are more than one million zebra mussels per square meter.
Cedar Lake, infected in 2000
Zebra mussels have a devastating impact on our native mussels. Clams covered with zebra mussels cannot feed, breathe, move, grow, or reproduce efficiently. Could you? Thousands of zebra mussels might layer up on one native mussel, often quadrupling the clam’s initial weight.
While the native clams’ appetites diminish, zebra mussels continue to feed heartily, sucking up the algae that would normally go to the clams, snails and small fish. Because one mussel can filter food out of up to a gallon of water per day, an infested lake or river becomes very clear very quickly. Extremely dirty lakes like Lake Erie can benefit greatly from the zebra mussels’ purifying powers. But according to Meg Woller, Leelanau Conservancy Stewardship Director, “There’s a flip side to water clarity … The water is clear because there’s no food.” When native invertebrates and small fish starve away, larger lake-dwellers need to look harder for a meal. Zebra mussels are fraying the food web.
As a food source themselves, zebra mussels are the twinkies of the freshwater world — tasty and filling, but devoid of nutrients. Fishermen describe pulling in sickly, starved whitefish with bellies full of zebra mussels.
Zebra mussels directly impact our own species as well. They clog city water-intake lines and other industrial facilities. The pipes at one Michigan power plant were victimized by 700,000 zebra mussels per square meter. Farms and golf courses are vulnerable as well, via irrigation. Boaters suffer increased drag and engine damage from attached mussels. Navigational buoys sink under the colonies’ multi-ton weight. Encrustations damage steel and concrete bridge supports. Shipwrecks, dock pilings and other underwater artifacts deteriorate when covered by the mussels. Tourism suffers when zebra mussel waste creates algal blooms, foaming and fish kills.
We have no good weapons for fighting the zebra mussel war. These adaptable molluscs put up a tough fight. Physical removal is tedious, damages underwater structures, and is seldom permanent, except in very new colonies. Chemical attacks damage innocent organisms. Boater education does slow the spread of the mussels, but only for so long, as seen in the case of Glen Lake.
Glen Lake, infected in 2002
Because the Glen Lake zebra mussel infestation is yet young, physical removal is still a viable way to control the population. If you see a clam or plant with zebra mussels attached to it, scrape off the mussels. They attach to their substrates via byssi, or dark mucous-laden threads. When you pull the zebra mussels off a clam, the byssi usually stretch and break. The ripping of its byssal threads kills the mussel; it’s like you having your guts ripped out. Try to contain the dead mussels in a bag or other enclosed container, just in case a few of the beasts escaped with their byssi unbroken (that is, with their guts intact).