Perched in sunburst chairs at the Memorial Union Terrace, visitors admire the view of Lake Mendota and its expansive shoreline. The surface is smooth as glass on a calm day, but beneath, an invasive species runs rampant.
The spiny water flea, native to Russia and Northern Europe, took hold of Lake Mendota in the summer of 2009, according to Limnology Ph.D student Jake Walsh.
“[Limnology professor] Jake Vander Zanden took a bunch of students out for basic limnological samplings, and when one student pulled up a zooplankton net and put it in a jar, it was like spiny water flea applesauce,” Walsh said. “It was so dense, and it was shocking because he had never seen them in Lake Mendota before.”
Walsh said it is difficult to pinpoint exactly when the spiny water flea invaded Lake Mendota, but he said he is confident boats transported the fleas from Lake Michigan, where they have been present for more than 30 years.
“Studies on spiny water fleas have found that most of spiny water fleas being transported across land is through boats,” Walsh said.
Walsh said the concentration of Daphnia zooplankton dropped more than 90 percent due to the spiny water flea’s invasion.
The spiny water flea is one of several freshwater zooplankton species in Madison area lakes, according to Walsh. However, it differs in that it eats Daphnia pulicaria, a beneficial species that reduces harmful algae.
The reduction in Daphnia pulicaria has led to higher algae concentrations and caused Lake Mendota's water clarity depth to drop from 4.578 meters to 3.441 meters, which is a substantial drop, according to Walsh.
Diminishing water clarity disables sunlight from reaching native plankton, thereby disrupting the natural flow of energy within Lake Mendota’s food chain.
“The main driver of algae in this lake is manure runoff from farms,” Walsh said. “Spiny water fleas are relatively useless in containing the phosphorus levels like other zooplankton, so their presence wastes energy.”
Walsh said the reduction in Daphnia pulicaria puts added pressure on those working to decrease phosphorus loading because without a natural control method in Lake Mendota, phosphorus levels will continue to rise.
Through Walsh's research into the spiny water flea's impact on the local ecosystem, he discovered Lake Mendota has the highest water flea concentration compared to any place the flea has inhabited across the globe.
Tim Campbell, the aquatic invasive species outreach specialist at UW-Madison’s Sea Grant Institute, said Lake Mendota does not have any natural methods to control the water flea, which poses the gravest problem.
“They’re not only eating native zooplankton, they’re also too big for our native fish to eat,” Campbell said. “Once an invasive species gets into a lake or environment, it’s almost impossible to get rid of it.”
Campbell focuses his efforts on containing the spiny water flea population.
Campbell is working alongside the Dane County Land and Water Resources Department to prevent spreading the spiny water flea to surrounding water sources by informing boaters and fishing enthusiasts about the risks, according to Dane County Water Resource Planner Pete Jopke.
Jopke said initiatives such as “Clean Boats, Clean Waters,” place large signs near major docks to educate boaters.
“We don’t want people to introduce invasive species accidentally,” Jopke said. “And that’s our main goal with the educational programs.”
Despite the containment, Jopke is skeptical as to whether the spiny water flea population will ever decline, because there is currently no natural biological method of eradicating the species.
“I don’t think there’s any silver bullet to the problems of [the spiny water flea],” Jopke said.
However, Campbell said he is optimistic the ecological make-up of the lake will resolve itself in the long run, as seen in Lake Erie after pollution nearly decimated the fish population in the 1970s.
“Nature is going to be fine,” Campbell said. “Nature hates to waste energy; it’ll figure out how to use it, just like we’re seeing in the Great Lakes.”
