Starry stonewort has makings of high-impact invader
Recent research confirms that starry stonewort has the potential to be a high-impact invader in Minnesota lakes, and warrants a high prioritization in controlling it. A graduate student assessed the invasive macroalgae in three lakes, including Koronis where it was first discovered in the state in 2015. It's now known to be in 14 Minnesota lakes.
PAYNESVILLE — It’s only found in 14 Minnesota lakes at this point, but starry stonewort has the potential to cause lots of harm, and fast.
Recent research shows that the macroalgae has the potential to be the high-impact invader in Minnesota lakes that many already fear it is. It warrants the high prioritization that public agencies and many in the public are giving it.
Those are the conclusions of Carli Wagner, a graduate student with the Minnesota Aquatic Invasive Species Research Center , an interdisciplinary research center at the University of Minnesota. She recently completed research on how the aquatic invasive species is doing in three Minnesota lakes. Wagner presented her findings in a webinar on Oct. 17 offered by the Center and the University of Minnesota extension.
Starry stonewort was first discovered in Minnesota waters in 2015, when it was identified in Lake Koronis near Paynesville. It has now been confirmed in 14 Minnesota lakes spread about the state.
Wagner pointed out that there has not been a lot of research on the ecological impacts of the macroalgae in Minnesota waters. Little is known about how it is affecting the native aquatic plants or fish and invertebrate populations.
She set up underwater transects to quantify the spread of the algae in areas of three different lakes: Koronis, Winnibigoshish and Moose (in Beltrami County). She assessed its impact on native plants in the transect areas she monitored, and quantified how the invasion progressed over time in those sites.
It proved to have a high capacity to impact the native plants and alter the overall plant communities in the infested areas, she said. Overall, she found that 11 of 30 native plants in the three lakes were negatively affected. Five of six types of growth forms of plants were affected. Floating leaf plants were the only plant types unaffected. Plants that relied on a connection to the lake’s bottom, whether rooted or not, were adversely affected.
Overall, Wagner found that each square meter of area infested by starry stonewort lost 1.5 native species over the three-year study. Consider that type of impact across the full scope of a lake, and it is easy to see just how harmful the invader can be to native plant communities, she said.
Starry stonewort proved to have a bigger impact on Lake Koronis than the other two lakes in the study. Wagner said a greater diversity of native plants, and perhaps better water quality in Moose and Winnibigoshish Lakes, may have given native plants in those lakes more resilience.
All the same, starry stonewort proved itself an aggressive invader in all three lakes. It carpeted the bottom in portions of the lakes to the detriment of native plants.
She found that it adversely affected both the number of native species as well as the amount of native species in the waters.
The findings led her to conclude that early detection of new starry stonewort populations is very important. Once it is established, it grows and expands quite widely in the littoral areas of lakes, she said.
Her adviser, Dan Larkin with the University of Minnesota, said hand-pulling and removal of starry stonewort has been effective in those locations where early detection has found small and isolated infestations.
Since its discovery in Lake Koronis, the lake association has been working to control it. The association has tapped more than $600,000 in grants and contributions as part of that effort. It estimates it will need about $170,000 annually to maintain the current level of control efforts.
The Koronis Lake Association is offering information on its control efforts to researchers to help identify the algaecides most effective at controlling starry stonewort. Wagner said copper-based algaecides have been shown to decrease the nuisance biomass of starry stonewort. Unfortunately, she said there are no effective means for long-term control over its reproduction.
Larkin told the West Central Tribune that, overall, there has been limited research on the efficacy of different control strategies. The Minnesota Aquatic Invasive Species Research Center is working with other partners and looking at control efforts underway in Minnesota as well as Wisconsin and Indiana to learn what might work best.
The webinar can be viewed at: z.umn.edu/WagnerWebinar