Zebra mussels first appeared in Lake Champlain almost a decade ago, catching rides into North American waters in the ballast of transoceanic vessels. Since then, researchers have been frantically searching for ways to prevent their spread. In Burlington this summer, Kathleen Coons, a 20-year-old biology major at St. Michaels College, is teaming up with Declan McCabe, an ecology instructor at St. Mikes, and University of Vermont lake biologist Ellen Marsden to find out whether obnoxiously flashing lights effectively repel the nasty striped mollusks.
The project began with Tennessee-based Flash Technology, a leading U.S. manufacturer of strobe lights for the aviation industry. Years ago, they were contacted by a Boston hydropower consulting firm looking to install strobes deep underwater to scare fish away from turbine engines in dams. Last September, after using that opportunity to refine its technology, Flash got in touch with the National Sea Grant Foundation, an organization that puts private industry in touch with universities doing environmental research. McCabe was one of the researchers to respond.
Ive done much more theoretical stuff on organisms that nobody cares about, to be honest, says McCabe. It was fun for me to try something that might actually be useful beyond science.
McCabe, along with Coons and Marsden, set up the field part of their project under the boathouse on the Burlington waterfront an area with a large settlement of juvenile zebra mussels in early June. Three eight-inch, 400-watt strobes are attached to wooden pilings and flash four times a second 24 hours a day. Once a week, Marsden goes diving with an underwater video camera to monitor the density and movement of the adult mussels.
The project isnt an attempt to control zebra mussels in the wild. You cant put strobe lights all over Lake Champlain, Marsden points out. But you can try to control them in particularly worrisome areas such as water intake pipes and boat hulls. Every situation is going to be different, the UVM professor says.
If zebra mussels gather in a power plant intake pipe, recirculated heat can kill off the clingy little buggers. At a water treatment plant, they might be eradicated with chlorine injections. Strobes are just another tool, Marsden says, and it would be nice to know is this a useful tool in the toolbox, or not? Thats essentially where well end up at the end of this.
Exactly how much havoc can zebra mussels wreak? Consider the case of Monroe, Michigan, where an intake pipe became so congested that only one-third of its original diameter was clear. The city shut down because the water plant basically called them and said, Sorry, guys, we dont have any water, Marsden recounts. McCabe likens the inside of that pipe to a hardening of human arteries.
Zebra mussels tend to avoid light, but the pending question is whether light will have an effect on adult colonies that are already established. Will a strobe be so unpleasant to them that they will rip up their byssus threads and go wandering off to get into the shade again? asks Marsden, referring to the fibers by which mollusks cling to a surface.
To help answer this question, the investigators have also installed control plates in the field, some in direct view of the strobes and others in dark areas. The amount of larvae detected on the control plates will be a good indicator of whether strobe lights deter young zebra mussels from settling. The plates will also gauge the density and movement of the adult population. Because dim light and murky water under the boathouse have made it difficult to get good images, the re-searchers subsequently installed more strobes at Chipmans Point Marina, near Orwell, where the water is clearer. The marina strobes will only flash 12 hours a day, however, because boaters have found them disorienting at night.
In addition, Coons has set up six indoor aquariums filled at the bottom with sand and covered on top with aluminum foil. In some of the tanks she installed a strobe light. She placed young zebra mussels inside all the tanks. After an hours test, she can examine the trails the mussels leave in the sand to evaluate how much the animals move and where they go in response to the flashing light. So far, in the six trials that Ive done, theyve all moved away from the light, she reports.
There are dozens of species that dont belong in the lake, but certain of them cause particularly bad problems, says Marsden. Zebra mussels are among the worst. And their crimes dont stop at damaging hard surfaces and cutting beachgoers feet. They have also learned to colonize soft surfaces, such as sand and mud, causing a substantial biological threat to other aquatic species. Billions of them can thickly carpet the bottom of the lake, suffocating native mussels and preventing fish from getting to their food.
To make matters worse, zebra mussels reproduce at a ferocious rate: A single female can lay up to a million eggs per year. Since they moved into the neighborhood, zebra mussels wanton activities have caused seven native organisms to be put onto the threatened and endangered species list.
There is a light at the end of the (clogged) tunnel, though. After increasing exponentially for five to 10 years, a zebra mussel population tends to plateau for about as long. When carrying capacity in the lake has been reached and there are no more resources to sustain their overwhelming numbers, predators yellow perch, crayfish, carp, etc. will begin to take a noticeable bite out of the overall zebra mussel community. At that point, the population will crash to about a third of its peak level.
At the end of their experiment, McCabe and Coons will return to St. Michaels for the fall semester. McCabe will teach aquatic and invertebrate ecology in labs that will probably contain some strobe lights. Coons will complete the last year of her studies as a biology major.
Marsden, meanwhile, is looking forward to continuing her sabbatical, which shes devoting to a major lake-trout-population restoration project. Im technically a fisheries biologist, she says, laughing. Zebra mussels just keep getting in the way. Its one of those things: They foul everything, including the careers of fisheries biologists.