MADISON (WKOW) -- Students in a Zoology class at UW-Madison discovered spiny water fleas in a sample of water from Lake Mendota's University Bay.
The students were about one-quarter mile offshore on September 11 when they dipped a small net into the lake and started poking through its contents. The net was intended to catch plankton and when the students asked associate professor Jake Vander Zanden to take a look, he was surprised at what he saw.
"I was struck by what looked to be spiny water fleas," he said.
The carnivorous crustaceans, which are not insects, invaded the Great Lakes about 20 years ago. Since then, biologists have watched them devour the native zooplankton that graze on algae and help clarify the water. Algae and water clarity have always been a concern with over fertilized lakes like Mendota.
Vander Zanden, who works at the Center for Limnology is an expert on invasive species that disturb lakes in the Midwest, including the spiny water flea.
"I did a double-take," he says. "I thought, 'They are not supposed to be here.'"
The sample students took from the lake was teeming with the invading water fleas. It was easy for Vander Zanden to identify them because they are larger in size and have a nasty spine hanging off the tail end. That spine protects the flea by making it inedible to small fish. That is another reason the crustacean is harmful to the lake.
Vander Zanden says this find is the most significant discovery from an undergraduate limnology trip.
"I don't normally go on class field trips expecting to find something like that. It was a beautiful, sunny day, and it was kind of exciting, but definitely not the kind of excitement I want."
The students who harvested the sample included Seth Pelock, a senior biology student, and Joanna Klass, a junior who is double majoring in zoology and biological aspects of conservation.
"It was my first trip on Lake Mendota, and I was pretty excited; we got to do all these experiments," Klass says. "It was pretty funny, Jake took it and did not say anything, just stared at the jar. He walked around, and then said, 'Omigosh, this so weird.' He could not believe what was in there, but it was kind of bittersweet."
"There was shockingly little of the normal zooplankton in the net, but a lot of spiny water fleas," Vander Zanden says.
The high level of invasives and algae, combined with the low level of native, grazing plankton suggested that the spiny water flea could already be damaging the lake. Long term, the invasion of the spiny water flea could be bad for water quality because the crustacean preys on planktonic animals that eat algae and clarify lake water.
It's impossible to really know how the species reached the lake. The most likely route is via boats that were previously in Lake Michigan, where the flea has been an established invasive species for decades.
Experts say this discovery is just another example of why boaters need to clean their crafts whenever they pull their boats from the water.
"It is vital that Wisconsin boaters and anglers take simple prevention steps," says Jeff Bode, the lakes and wetlands section chief at the Wisconsin Department of Natural Resources (DNR). "Invasive species affect things we all care about: water clarity, good fishing, clean beaches. And as this recent finding demonstrates, prevention is always the best option because once they are in a lake, removal is often impossible."
To prevent additional invasions, the DNR requires boaters to remove all plants and animals from boats, trailers and equipment, and to drain all water from boats and equipment before leaving a body of water. The DNR also recommends that people either rinse boats with hot or high-pressure water, or allow them for five days.
The discovery in Lake Mendota's waters reflects the kind of practical reward hands-on science instruction that professors often dream of.
"I was already very interested in conservation, but being out there and actually finding this animal told me, 'I can do research. I can find new things.'" says Klass. "It gave me a sense of what it feels to be out there, doing hands-on research and finding new species."
Despite these rewards, the flea's appearance in Lake Mendota is bad news.
"I knew they were going to spread, but I expected they would show up first in lakes closer to Lake Michigan," says Vander Zanden.
The flea's exact impact on the ecology of Lake Mendota cannot be predicted, but Vander Zanden notes that good pre-invasion data exists for only one other small lake, which is in the province of Ontario.
An enormous database on the conditions in Lake Mendota stretches back further than 100 years to the start of limnology studies at Uw-Madison.
"This invasion provides a great opportunity to understand how this invasion will impact lake ecosystems. We need to see how this will play out, but we have little reason to think the changes will be positive," concludes Vander Zanden.