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Goldilocks and invasives

September 04, 2020 by Ted Rulseh

How hospitable is your lake to invasive species? I don’t mean how well is your boat landing protected by Clean Boats Clean Waters volunteers or other methods. I mean how likely would an invasive species be to survive and proliferate once it got into the lake? 

Depending on the species, various factors can come into play. One is water chemistry. For example, rusty crayfish (the invasive species in Birch Lake where I live) are more likely to thrive where the water contains enough of the calcium the crayfish need to build their shells.

Another is bottom characteristics. Some invasive plants do better in a lake with a soft sandy or silty bottom than one where rocks and gravel are more dominant. And, according to recent research, another factor is water temperature. The research is described in an article on the University of Wisconsin Center for Limnology website (https://limnology.wisc.edu).

You might think all lakes in the same general area, such as here in Oneida and Vilas counties, would have pretty similar temperatures through the open-water seasons. But according to Jake Walsh, a program coordinator with the Minnesota Department of Natural Resources, that is not necessarily so. In fact, his work suggests that water temperatures can vary significantly with factors such as lake size, depth, shape, and water clarity.

Walsh was the lead author of a study that has implications for predicting whether a lake has suitable habitat for a give invasive organism. 

“Each individual aquatic species – whether it is a fish, plant or tiny little zooplankton – has a temperature range in which it thrives,” says the Center for Limnology article. If the water is too warm or too cold, “the species struggles and the odds that it will be successful enough to invade a lake are quite low. If the water is ‘just right,’ then it becomes vulnerable to invasion.”

To predict water temperatures on a lake-by-lake basis, Walsh and his colleagues used a complex computer model that combines data on air temperatures with data on lake characteristics. They looked in particular at the effect of temperature on the invasive spiny water flea, a species that does best in cool water. 

To prevent the spread of that species, it’s helpful to know what lakes are the most susceptible. To no surprise, lakes with temperatures similar to those in the spiny water flea’s native range in Europe and Asia are likely to be among the most at risk.

At present, some 42 percent of Upper Midwest lakes are now suitable for spiny water flea, according to the article. But, says Jake Vander Zanden, director of the Center for Limnology, scientists expect fewer lakes to vulnerable as the lakes warm with climate change. Current warming scenarios see the vulnerable lakes declining to 19 percent.  

“While the number of lakes that are potentially suitable for spiny water flea decreases, there are still many suitable lakes in the region that spiny water flea has yet to reach,” says the article. “And that means spiny water flea will continue to spread in the region, even with climate warming.”

Walsh observes that getting a better understanding of individual lakes is a key to seeing the big picture of spiny water flea spread. He hopes his temperature study proves helpful.

Ted Rulseh resides on Birch Lake in Harshaw and is an advocate for lake protection and improvement. His Lakeland Times and Northwoods River News columns are the basis for a book, “A Lakeside Companion,” published by The University of Wisconsin Press.. Ted may be reached at [email protected]

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