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Breaking down zebra mussels: DNR, PRWD collaborate on study of how invasive species will impact Detroit Lake ecosystem

Nathan Olson of the Minnesota Department of Natural Resources pulls a plankton sample out of the water on Detroit Lake. This year's sampling was completed in September; they plan to start up again in May 2019. (Submitted photo)1 / 2
Brent Alcott of the Pelican River Watershed District puts a net down into the water of Detroit Lake to take a plankton sample. He and Nathan Olson of the DNR completed this year's lake sampling late last month. (Submitted photo)2 / 2

Ever since zebra mussels were first discovered in Detroit Lake in 2016, area residents have been wondering what the ultimate impact of the infestation would be on its plant and animal life — and the Minnesota Department of Natural Resources (DNR) is collaborating with the Pelican River Watershed District (PRWD) on a study to measure exactly that.

"Last year, I was trying to figure out some good projects we could do to measure changes in Detroit Lake, now that we have zebra mussels in there," said PRWD Assistant Administrator Brent Alcott. "When I talked to some of our DNR colleagues, they said Nathan Olson had started sampling for zooplankton (microscopic animals) in Detroit Lake in 2016.

"I wanted to see how the phytoplankton (microscopic plants) population might change as well, so we partnered together," Alcott added.

"What we are trying to measure is how abundant zooplankton and phytoplankton (microscopic plants) are in the lake," said Olson, adding that these microscopic plants and animals "are the base of the food chain."

As an example of that, he said, "when walleye are first born, they need zooplankton to survive."

Though zebra mussels weren't found in Detroit Lake until the fall of 2016, Olson added, he had already started to monitor Big Cormorant (which was declared infested in 2015) that summer, so he decided that since Detroit Lake was so close by, he would start testing water samples there as well — and then zebra mussels were found there too.

Though the impact of zebra mussels on the zooplankton and phytoplankton populations won't become measurable for a few years yet, Alcott noted, the measurements that he and Olson have been doing over the past couple of summers will serve as a baseline comparison for when they do.

"The hope is to answer the question of how zebra mussels are changing the food web in the lake, and how that will ultimately impact the fisheries," Alcott added.

"Then we'll have another piece of the puzzle (to find out) whether zebra mussels are playing a role in the increase, or decrease, of certain fish populations," Olson said.

"We do know from past studies that zebra mussels do change the composition of the phytoplankton and zooplankton populations (in a lake's ecosystem), because they selectively filter out certain types of species," Alcott said. "We're not sure yet how that's going to affect our lake."

"Fish can be resilient," Olson explained. "They may be able to switch to another food source, to adapt, but only time will tell. Every lake is different, so we don't know yet how this lake will respond."

Vicki Gerdes

Staff writer at Detroit Lakes Newspapers for the past 18-plus years, currently editor of the entertainment and community pages as well as covering city council and the Detroit Lakes School Board. 

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