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Taking on starry stonewort: Efforts to manage it on Lake Koronis show some success

PAYNESVILLE - Starry stonewort might sound like the name of some obscure, grunge band. Yet the latest aquatic invasive species to reach Minnesota has the potential to be a big time menace and as notorious as other unwanted invaders like eurasian ...

Tom Cherveny | Tribune Kevin Farnum needed only to toss a rake head into Koronis Lake at the Highway 55 access to pull a mass of starry stonewort from the waters.
Tom Cherveny | Tribune Kevin Farnum needed only to toss a rake head into Koronis Lake at the Highway 55 access Tuesday, June13, to pull a mass of starry stonewort from the waters.
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PAYNESVILLE - Starry stonewort might sound like the name of some obscure, grunge band.

Yet the latest aquatic invasive species to reach Minnesota has the potential to be a big time menace and as notorious as other unwanted invaders like eurasian milfoil and curly leaf pondweed.

It all depends on what happens on Lake Koronis.

That's where the invasive green alga was first found in Minnesota waters, and where the Koronis Lake Association just launched the second year of its $800,000 effort to manage it. What happens here will help us learn how we might be able to manage the invader, and what ecological harm it may pose.

Right now, we have many unanswered questions on both accounts, according to Dan Larkin with the University of Minnesota's Aquatic Invasive Species Research Center.


Starry stonewort is a single cell alga that links together like a plant. It grows in thick, tangled masses that make boating and swimming difficult if not impossible.

It covered 53 acres when first identified in the 2,968 acre lake in August 2015. Last year it was known to cover 250 acres, and it almost certainly has expanded beyond that now, according to Kevin Farnum, who is leading the lake association's campaign to manage it.

"I think if we hadn't have gotten on it when we did, I think it would have continued to just move around the lake and take over the lake because it out competes the natives,'' said Farnum.

He spoke Tuesday, June 13, as workers with PLM Lakes and Land Management used an airboat to begin applying a copper-based algaecide to a patch of starry stonewort.

Despite its exotic sounding name, most boaters using Lake Koronis are becoming familiar with it, according to Nick Nichols, a watercraft inspector with the Minnesota Department of Natural Resources. He was on duty at the busy, Highway 55 boat access when this season's first algaecide application got underway.

"It's in plain sight,'' said Nichols when asked if boaters know what to watch for. "Kind of looks like what most people consider to be seaweed.''

The biggest difference between starry stonewort and native plants is the tiny, white star- shaped bulbils found on it. They hold anywhere from five to 50 cells, and each cell can start a new plant. And, any single cell strand broken from the starry stonewort plants- which can reach 10- to 12-feet in height- can also start a new plant.

The effort to manage starry stonewort involves a mix of strategies. A mechanical harvester was used last year to remove an estimated 250,000 pounds of it, said Farnum. Scuba divers also helped in the removal.


On some of the harvested acres, an algaecide was also applied. The algaecide was also applied on other acres of starry stonewort.

"There was definitely a reduction in starry stonewor tbiomass abundance with all of the treatments,'' said Larkin. The combination of mechanical harvesting and algaecide application worked best of all.

It's challenging to treat starry stonewortwith an algaecide since it is not a vascular plant. A vascular plant will absorb an herbicide and the entire plant will die. In the case of starry starwort, only the individual cells exposed to the algaecide die.

Unfortunately, the bulbils proved hard to kill. Most survived, possibly because they are often found in the upper sediment and consequently escaped contact with the algaecide, explained Larkin.

Farnum and Larkin said the application of algaecide also seems to have triggered an increased production of bulbils such as otherwise occurs before the onset of winter. As a result, some of the treated areas had a high density of bulbils ready to sprout new plants this year.

The results are only too obvious. Farnum tossed out the head of a garden rake attached to a rope from the dock at the Highway 55 access. He pulled in a seaweed mass full of starry stonewort, far more than he had anticipated.

The lake association has three objectives in its management strategy. It wants to prevent the spread of starry stonewort to other lakes. It wants to keep other aquatic invasive species from getting into the lake. And, it wants to find the most effective ways to manage the starry stonewort in the lake, according to Farnum.

What its presence means to the fishery in Lake Koronis is a complicated question and one of many yet to be answered about this new invasive, said Larkin.


He holds no hope for eradicating it. That's never been achieved. A native of Europe and Asia, it was found in the St. Lawrence seaway in 1978.

To date, all of the starry stonewort found in North America is believed to be male clones of earlier introductions, said Larkin.

Since its discovery in Koronis and adjoining Mud Lakes, it has been found in nearby Rice Lake as well as West Lake Sylvia in Wright County, Turtle Lake near Bemidji, Lake Winnibigoshish, and Moose Lake in Beltrami County.

Farnum believes that starry stonewort will be found in other Minnesota lakes this season as more people learn to identify it. Like many, he suspects its initial presence in Lake Koronis went undetected for some time because people did not recognize it.

Larkin said 125 people from across the state are completing University of Minnesota extension service training to identify starry stonewort and other aquatic invasive species. The Research Center also intends to host an August 5 "Starry Trek'' in which volunteers will visit lakes across the state to search for starry stonewort.

While many boaters on Lake Koronis are now familiar with starry stonewort, Farnum said he still has his worries. Many of those visiting the lake come from all over, he pointed out. Two years ago, a late season walleye bite attracted anglers from five different states, he said.

Researchers at the Minnesota Aquatic Invasive Species Research Center are working to determine what lakes in the state are most susceptible to starry stonewort, said Larkin. Early work suggests that starry stonewort fares best in lakes that are a little higher in ph; have harder water; and are more alkaline with good amounts of calcium and magnesium.

The researchers are also looking at which of the commercial algaecides now available are most effective on starry stonewort.

Farnum, who is retired from a career in food science, estimates that he devotes roughly 60 hours a week as a volunteer for the lake association's effort. The lake association is absolutely committed to the effort, he said. The funds raised towards the management effort includes $5,000 from Kandiyohi County, he added.

And of course, he hears grumbles. Some question spending money on what they believe is the inevitable spread of an invasive. Some believe wildlife transport it. He answers them by expressing his doubts that wildlife make it their practice to always enter Lake Koronis via the Highway 55 access.

And, he points out what it would mean to do nothing. If not managed, starry stonewort will displace native vegetation throughout the entire lake.

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