Hamline News

The newest threat to Minnesota lakes

threat article

You can clean off your boat, but it might not help. The newest threat to Minnesota lakes is unlike anything we’ve seen yet. The spiny water flea is a quarter-inch long with a sharp, jagged tail that cuts the insides of fish that ingest it. We don’t know how it is spreading, but it is threatening northern lakes, including those in the Boundary Waters. To stop the spread of this invasive species, Hamline professor Leif Hembre and his student researchers are tracking the spiny water flea and studying its DNA—one water sample at a time.

Most Minnesotans know about Eurasian milfoil and zebra mussels. They even diligently check their water toys, fishing gear, motor boats and trailers for any sign of these aggressive and invasive species before moving on to a new river or lake. But how many check for spiny water fleas? Unfortunately, a new invasive species has come to town.

The spiny water flea hails from Europe. It was first detected in North American waters in 1982. Samples from Lake Ontario revealed the critter had crossed the sea, probably in the ballast water of trans-Atlantic cargo ships. Soon after, it was detected in all the Great Lakes, including Lake Superior, and then it made its way inland. Lakes in Canada, Michigan and Minnesota have been invaded; the Boundary Waters have been affected as well. The spiny water flea appears to prefer deep, pristine waters.

An innocuous part of the food chain in Europe, the spiny water flea has fewer predators in North American lakes. Therefore, when it invades a lake, its population goes largely unchecked. It is classified as a predatory zooplankton, meaning it eats other zooplankton in order to survive. This has two effects. First, most native zooplankton species feed on algae. When their populations are reduced, algae can more freely grow. This can cause unsightly waters. In addition, decay of the excess algae causes oxygen levels in the water to decrease, resulting in a degradation of habitat quality for fish populations. Second, since native zooplankton serve as a food source for young fish, their disappearance curbs fish populations. If that wasn’t enough, the spiny water flea has a long barbed tail that can damage the linings of the digestive system of fish that choose to eat it.
Even though the spiny water flea is visible to the naked eye, it is a tiny creature. It measures less than half an inch long. Most fishermen wouldn’t notice a spiny water flea if it attached to a bait box or motor.

Yet Leif Hembre, a Hamline biology professor studying the spiny water flea, isn’t convinced the animal transmits itself from lake to lake solely on the back of a boat. “We suspect it’s human driven,” he said, “but it could be natural dispersal as well, like fish migrating through streams or by birds.”

The spiny water fleas, Hembre explained, “…produce resting eggs smaller than the adult that have been shown to be very hardy. They can dry out and be out of water for up to a day, then you put them back in the water and they’ll hatch.

“I suspect,” Hembre said, “the main vector for spread is these resting eggs. They can tolerate all sorts of situations. They can pass through the guts of a fish and still be viable. It could be bait that’s moving the eggs. It could be minnows.”

While these resting eggs certainly complicate matters, the spiny water flea has another trick up its sleeve: it can clone itself. Should a female spiny water flea find herself without a mate, she can reproduce by cloning. However, offspring produced in this manner are genetically uniform. Offspring produced from sexually fertilized eggs contain genetic input from both adults, guaranteeing genetic diversity.

“I am inherently fascinated by biology,” Hembre said. “Here is this organism that has both a sexual and an asexual life cycle. There are all sorts of questions you can ask about this.” One of the questions Hembre is asking is whether or not it is possible to map the spread of the spiny water flea through its DNA. He thinks it is.

By comparing the genetic composition of the populations in the invaded lakes, Hembre hopes he will be able to decipher which spiny water flea populations are older, which are younger, and which are more closely related, therefore retracing the invasion. worked with Professor Donn Branstrator from the University of Minnesota Duluth, who had a team of students researching the spiny water flea. Since the organisms came in through Lake Superior, all of Minnesota’s infected lakes are in the Arrowhead region of the state. Island Lake, just south of Duluth, has been a known host to spiny water fleas since 1990. Hembre, along with this team of Duluth students, collected samples of lake water and sediment. Back in a lab, the samples were inspected for spiny water fleas—an adult, an egg, or fossil evidence in the sediment.

After that first year, Hembre decided to branch out and do his own research. Piggybacking off of the Duluth team’s work, Hembre applied for and won a grant from Minnesota Sea Grant. He also enlisted the help of Jacob Cooner ’06, one of his biology students. For Cooner, the opportunity to get involved in a real-life, hands-on science experiment was redeeming.

“I was at a point of panic,” Cooner said. “It was my junior year and I wasn’t having all that much fun in chemistry. I was thinking about changing my major. I’d taken some religion and global studies classes that were really interesting, but they didn’t interest me in the same way that biology had. I wanted to be a biology major because it challenged me, it gave me a run for my money, but I just wasn’t feeling it anymore.”

With Hembre’s help, Cooner did not turn his back on science. He dug into it. Cooner began a collaborative research project on the spiny water flea under the guidance of Hembre. He traveled to northern Minnesota throughout 2005 to collect water samples, which he brought back to a Hamline laboratory where he and Hembre set about characterizing the genetic makeup of the populations sampled. Cooner became so involved in the experiment that he completed an honors project based on the work and graduated from Hamline with a biology major.

“We were analyzing proteins coded for by the DNA [of the spiny water flea] and trying to figure out where there was variation among individuals and populations,” Cooner said. “We were running these proteins for seven, eight hours a day and at some point it became kind of numbing. It definitely wore on my nerves and tried my sensibilities,” he said.

Yet Cooner stuck with it. “This project, for me personally, was more than just isolating sequences or doing something super-technical. It showed me that there are lots of different fields of study and if you allow yourself to pursue something, even something you might never have thought to pursue, you just might find it’s more intriguing than you would ever have guessed,” he said.

“This was the ultimate lab experience. This was where science meets reality,” Cooner said. “It was intriguing because the answer was unknown. We were trying to determine a pattern of where these invasions were coming from, what they were doing to the natural environment and how they were affecting people. There was a real-life aspect to it and we didn’t know where we were going to end up.”

Cooner didn’t unlock the mystery. Neither he nor Hembre fully understands how the spiny water flea is spreading or which Minnesota lakes are those most recently infected. Yet Cooner is satisfied that his lab work has helped Hembre build a stronger case for new grant applications to fund future studies. Plus, not only did the spiny water flea save Cooner’s major, it also helped him land his first job. Cooner started with Medtronic this spring. “There aren’t that many jobs for someone with an undergraduate biology degree because you don’t have any credibility as a scientist. Your experience is just in the classroom,” he said. “When I went for my interview at Medtronic, they asked me a lot about the work I’d done at Hamline.”

Missy Monson hasn’t graduated from Hamline yet. When classes resume this fall, she will be a junior. However, this summer she is hard at work on the mystery of the spiny water flea. The work Cooner had been doing has passed to her and one other student.
“This is my second summer on the project,” Monson said, “and I’ll probably do it again next summer, too. I’m planning on making it my honors project.”

Because Monson had only one year’s worth of college credits under her belt when she joined the project last spring, she admits that last summer she sometimes felt she was in over her head. “I hadn’t taken genetics yet, so everything was new. I had no idea what anything was,” she said. “Professor Hembre is a great teacher. He gave mini lectures that were really informative and we did lots of literature research.” Monson’s sophomore schedule did include a genetics class. Her spiny water flea research helped her whiz through the genetics labs, yet the lectures and text-book readings remained of interest. “I was able to go back and pick up the basics. More than anything,” Monson said, “now I understand why it all works. Last summer, I didn’t understand the rationale behind what we were doing. Now I do.”

As soon as classes let out in the spring, Monson packed for a trip up north. She journeyed to Duluth where she collected more water samples from area lakes. She brought her samples back to Hamline. This summer, she, Hembre, and another student are busy extracting DNA from these newest spiny water fleas. “We do the work five days a week all day long,” Monson said. Her laboratory research prevents her from taking a summer job, so she will receive a small stipend provided by an assortment of grants and a donation from the collaborative research fund.

Yet Monson knows the chance to participate in genuine field and laboratory research offers her more than any part-time summer gig. “I’m not entirely sure what I want to do when I graduate,” she said, “but it will look really good to have real lab experience on my resume. It will be helpful if I want to apply to graduate school or a professional program. I’ll be able to talk easily about what it’s like to do research and work in a lab.”


By: Kelly Westhoff