By Nancy and John Wilks, MLSA Vice President
A large crowd of riparians, professional lake managers and state government employees met in Lansing on March 15 to hear expert presentations on the biology and management of invasive starry stonewort (Nitellopsis obtusa). Starry stonewort has the appearance of a rooted aquatic plant, but actually is a macro algae. Although native to northern Europe and Asia where it reproduces both sexually and asexually, the exotic invasive population of starry stonewort in North America contains only male plants and reproduces asexually from fragments or its star-shaped bulbils. Studies on the habitat requirements for starry stonewort in the US indicate cool water, lakes rich in calcium carbonate and good water clarity are necessary; starry stonewort is a “sentinel” species in marl lakes having a water quality classification status of oligo-mesotrophic/ mesotrophic.
Michigan sits at the center of the known geographic distribution for starry stonewort in the US, explaining why our state has more infestations of starry stonewort than other states. Starry stonewort was first found in the Detroit River in 1983, but rapidly spread by boating in the past decade to over 400 lakes in 43 counties in the bottom two-thirds of Michigan’s Lower Peninsula.
Starry stonewort may form dense, impenetrable beds of growth many feet thick in the littoral zone of lakes. These infestations impede boating and other recreational activity requiring control of this macro algae. This heavy growth of starry stonewort also reduces the diversity of native aquatic plant species in the infected lake. Copper-based algaecides inhibit the growth of starry stonewort, and these in combination with an herbicide such as flumioxazin can provide more effective control. Mechanical harvesting and other methods of physical removal are partially effective. The treatment program needs to be tailor-made for each lake depending on the location and extent of the infestation, the presence of native species and the goals of the lake residents.
Examples of successful control were reported for individual lakes with continuing annual treatments. The proportion of the invasive aquatic species funds directed at control of starry stonewort for individual lakes tends to increase up to about 30% with successive years of treatment. The rigor of starry stonewort growth in a lake may vary from year to year depending on changes in the climate.