Forewarned about zebra mussels is forearmed Mollusks threaten water supplies


April 26, 1992|By PETER BAKER

Zebra mussel. Probably by now you have heard the words and -- unless you are a boat fisherman who uses Liberty, Prettyboy or Loch Raven reservoirs and who was hit with a one-year suspension of privileges Friday by the Baltimore Department of Public Works -- you might well have heard those words too often.

Enough with the zebra mussels already, you say. You don't fish reservoirs. You don't fish fresh water. You don't fish anywhere the current is slower than you can walk.

OK, we won't use those words. Instead, we will use veligers (troublesome newborns), juveniles (more troublesome children) and adults (sexually prolific parents).

And no matter where you fish, between areas of Canada where the waters do not warm above 54 degrees in summer or southern states where waters average above 81 degrees in summer, veligers, juveniles and adults can have an impact on your fishery, the operation of your municipal water supply and, indirectly, the taste of the water you drink.

That includes virtually the entire United States, with lesser impact in tidal waters than in fresh.

What is this menace? It is a freshwater mollusk introduced from eastern Europe in 1985 or 1986 by cargo ships that blew their water ballast, and their passenger list of veligers, juveniles and adults, upon arrival in the Great Lakes.

Within a year of their discovery in Lake Erie in 1988, that body of water had been thickly colonized. The menace has become well established in all the Great Lakes and has been determined to be spreading to river systems, including the St. Lawrence, Mississippi, Hudson, Illinois, Tennessee, Ohio and Susquehanna.

Several large lakes in Ontario, Indiana and Kentucky have been contaminated, and, according to a study by the Ohio Sea Grant College Program, "Ultimately, zebra mussels will colonize most lakes and rivers in Canada and the United States."

So, what to do? The best thing is to start with a public awareness program, to learn something about how the veliger becomes a juvenile and how a juvenile becomes a veliger factory.

Once that is understood, people can take part in controlling the spread of this mussel.

According to documents from the Ohio Sea Grant College Program, the average three-year life cycle is as follows: Egg production starts when water temperatures warm to 54 degrees and continues until the water cools below 54 degrees. Spawning peaks when water temperatures reach about 64 degrees, with a fully mature female capable of producing several hundred thousand eggs.

Within a few days, eggs become larvae veligers, which remain suspended and drift with the currents for three to four weeks, after which they will die unless they can settle on any firm, nontoxic object, attach and begin to transform into shelled juveniles.

Within a year, juveniles have reached adulthood, and then the real damage begins.

Juveniles and adults like company, and colonies may number as many 70,000 animals per square meter, but 30,000 mussels up to two inches across is a more reasonable figure. These colonies can accumulate over virtually any type of bottom so long as there is one hard object upon which to build in water 6 to 45 feet deep.

One deterrent seems to be current, which will wash away potential colonizers if it is flowing faster than 6 feet per second (about 2 1/2 paces per second for a 6-foot human).

When these colonies are in place, one can begin to understand their natural impact. The menace is a filter feeder, and an adult processes about a liter of water per day. One rock of 30,000 adults would process 30,000 liters, or roughly 7,900 gallons per day.

The problem is that these mollusks are efficient feeders and their diet is phytoplankton, which is the diet of zooplankton, which is ,, the food of choice for larval and juvenile fish and other foraging fish.

Some biologists believe that the menace can effectively cut off the food chain almost before it gets started, leaving a wasted, nearly sterile environment that will not support recreational or commercial fisheries.

The menace also can cause major problems for water supply facilities by clogging intake pipes and reducing productivity. Chemical treatment of water supplies will kill the menace, but it ,, also will sour the taste of your water.

If you are a tidewater fisherman and have reveled in the resurgence of striped bass, for example, remember that stripers rely on a delicate balance of salinity and water flow for successful reproduction. If an impoundment or slow stretch of fresh water upstream becomes colonized, that balance eventually might be altered and spawning and nursery areas might be diminished as well.

If you are a Maryland trout fisherman, you know too well the

success story that is tailwater fishing in streams that have been virtually recreated by judicious release of water from reservoirs and impoundments across the state. If the menace infests the lakes or reservoirs, then flows will be reduced and the tailwater fisheries will suffer.

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