PAYNESVILLE — Starry stonewort was first discovered in Minnesota waters in Lake Koronis in 2015.
Its toehold in Lake Koronis quickly became the focus of research on how this aquatic invasive species might do in other Minnesota waters.
Researcher Carli Wagner charted its expansion in the lake from 2017 to 2019 and presented her findings to a room filled with scientists eager to learn what she found.
“There was an audible gasp in the room when the data was shown,” said Ranjan Muthukrishnan in a webinar presented Nov. 3 by the University of Minnesota’s Aquatic Invasive Species Research Center.
To everyone’s disappointment, the data showed that the grass-like algae had expanded dramatically throughout the lake. It was not totally unexpected, as aquatic invasive species often proliferate rapidly at the onset of their arrival in new waters.
Muthukrishnan is a scientist with the Environmental Resilience Institute at Indiana University, Bloomington, and holds a doctorate in ecology and evolutionary biology from the University of California, Los Angeles. He was a postdoctoral research assistant at the University of Minnesota from 2013-2018.
Muthukrishnan is now conducting the research to help us understand what’s ahead. His presentation, titled “Understanding Starry Stonewort Invasions in a Changing Climate,” offered a look at how a warming climate may affect its growth in our waters.
Since the 2015 discovery of starry stonewort in Koronis and Mud Lakes, the invasive alga has been found in another 17 waterbodies in the state, including Lake Minnewaska in Pope County and Leech Lake and portions of the Mississippi River. It was originally reported in North America in 1978 when it was found in waters in New York state. It has been moving westward ever since.
Along with the data from Koronis, Muthukrishnan and his team have been monitoring starry stonewort’s growth in other selected lakes in Indiana, Wisconsin and Minnesota. The goal is to learn how the climate is affecting the plant’s productivity in the northern latitudes of the United States, which are roughly comparable to its native range in Europe.
Overall, the research showed year-to-year variability in the total biomass of starry stonewort. There were good years and bad years for it. Warm summers adversely affected its total biomass, while warmer winters appear to have allowed it it to expand its coverage area, according to the research.
Its expansion was not as consistent as it showed in its early years in Lake Koronis. There were some years with reductions, which was contrary to the initial instincts of the researchers, Muthukrishnan noted.
The Minnesota research also monitored the population of starry stonewort in Pike, Winnibigoshish and Moose Lakes. The researchers documented some regression of starry stonewort in those lakes in the past year. It is possibly a reflection of greater resiliency in the ecosystems of these northern lakes, which have diverse native plant communities.
Most surprising, the research showed that warmer temperatures — especially as experienced in this past year — led to decreases in the overall biomass of starry stonewort in most study lakes, according to Muthukrishnan.
“This is not at all what we expected,” he said.
While warmer summer temperatures could reduce the total biomass, the area of a lake bottom covered by starry stonewort tended to increase in the summers that followed warmer winters. In this way, water winter temperatures could be associated with greater spread of starry stonewort, he noted.
The warmer climate is creating a clear shift in the plant’s phenology. Data from the 1980s in North America showed that starry stonewort usually reached its peak in terms of total biomass in late August and early September and its biomass stayed at the plateau late into the calendar year. As the temperatures warm, the plant is reaching its peak biomass earlier, in some cases in early to mid-July, and is dying back sooner, according to Muthukrishnan.
Much more needs to be learned, he said. But the data can help find the most effective methods for controlling the invasive plant, he pointed out. In many of the infected lakes, Koronis included, mechanical harvesting and herbicide applications are being used to manage it.