By Stephanie Boismenue,
Oneida County AIS Coordinator
In 2016, a very pretty non-native species called Starry Stonewort (Nitellopsis obtusa), was discovered in the Sturgeon Bay Channel in Door County. So, what is it and why is it a big deal? Starry Stonewort is a rather new aquatic invasive species (AIS) to Wisconsin. It’s a plant-like macroalga that is loosely rooted to the lake bed, grows rapidly, and spreads easily. In fact, it’s an extremely aggressive and opportunistic AIS that causes a significant ecological threat to our lakes, rivers, streams, reservoirs, and ponds, just as Eurasian water milfoil does, maybe even more so.
Starry stonewort is a macro-algae, meaning it does not have a vascular system like true plants. Each branchlet (stem) is a single cell. It anchors itself to the sediment by colorless filaments (rhizoids). A unique feature of the Starry Stonewort is the pretty white star-shaped bulbils (asexual reproductive structures) the size of a grain of rice that form on clear threads at the base of the plant and may be found at or below the sediment surface. The bulbils can easily dislodge and sprout new plants. Small, orange spheres called antheridia (male reproductive structures) may be visible near the tips of the branchlets. Native populations consist of both males and females, but all known introduced populations in North America are male.
Once introduced, it quickly forms dense mats or “meadows” greater than 6 feet thick, which spread throughout shallow waters up to depths of 30 feet. It entangles around propellers, clogs and damages motors, and impairs navigation. It outcompetes and severely reduces native aquatic plants and the dense mats make it hard for fish and animals to move about. It’s paramount ecological threat is its ability to consume the most sensitive and productive critical spawning habitats, resulting in increased competition within any remaining spawning habitats as well as a loss of vertical and horizontal structures necessary for good nursery and refuge habitats.
It looks similar to many native, beneficial grass-like algae, such as other stoneworts and muskgrasses found in Minnesota lakes and rivers, but can be distinguished based on its production of star-shaped bulbils. Native look-alikes include Muskgrasses, Stoneworts, Sago pondweed, and Narrow-leaf pondweeds.
Originally from western Asia and Europe, it was likely introduced to the Great Lakes via ballast water. It spreads between lakes on boats, trailers, and equipment, especially anchors holding sediment. It was first identified in Little Muskego Lake, Waukesha County, during an aquatic plant survey in 2014. Last year it was confirmed in additional lakes in southeastern Wisconsin and is now in Door County.
Treatment methods for Starry Stonewort are still in the experimental stages. Thus far, an effective biological control agent is not known at this time. Hand pulling is possible, but is tedious work and may be impractical on large infestations. Some chemical herbicides and algaecides have been effective at reducing the plant, but the chemical is quickly absorbed, resulting in a chemical burn of the top of the plant and the lower parts are unharmed. Additionally, chemical treatments damage native plant and alga species which opens up more lake bed for Starry Stonewort to colonize in.
Help Stop its Spread:
With your help, we can get the word out there about Starry Stonewort and help stop it from entering our beautiful waterways. Also, early detection and management is critical to sparing our favorite shorelines and fishing spots from the ecological disaster caused by their invasion. You can also help by: Practice clean boating and set a good example at boat launches – “Inspect, Remove, Drain & Never Move” to help Stop Aquatic Hitchhikers! Become a CBCW volunteer and staff a landing to educate boaters and help them clean their equipment. Become trained on the identification of invasive species and help be on the lookout for new populations.