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| Hamline Magazine, Summer 2007 |
The Newest Threat to Minnesota Lakes
You can clean off your boat, but it might not help. The newest threat to Minnesota lakes is unlike anything we’ve seen yet. Hamline professor Leif Hembre and his student researchers are tracking the spiny water flea and studying its DNA—one water sample at a time.
By Kelly Westhoff
Most Minnesotans know about Eurasian milfoil and zebra muscles. 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 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 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.”
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The spiny water flea, 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 continued, “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 lifecycle. There’re 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.
The remainder of this article can be found in the summer 2007 issue of Hamline: The Magazine of Hamline University.
To learn more about Hamline University visit www.hamline.edu.