Invasive Species Highlight: Starry Stonewort

Written by Industry Expert Shannon Junior, Aquatic Ecologist and Senior Business Development Consultant

Starry stonewort (Nitellopsis obtusa) is a species of macroscopic green algae in the Characeae family. It was first discovered in the United States in 1978 in the St. Lawrence River, but has since spread to Michigan, New York, Indiana, Pennsylvania, Wisconsin, Minnesota and Vermont. When the algae were first discovered in new areas, they were often misidentified as less invasive native species of macroscopic algae. However, the growth habit of starry stonewort is much more aggressive and robust, and can reach nuisance abundances. These nuisance plants can reduce the growth of desirable aquatic vegetation, reduce suitable fish habitat and cause fishing frustration. Although the algae are non-vascular and have no true plant structures, they have been found to grow as much as eight feet tall. The blooms have severe negative impacts on the habitats where they occur, and have posed unique challenges for lake managers in these areas.

Now that the presence of starry stonewort has become more familiar to lake managers, it is actually quite easy to identify. The blooms appear more “raggedy” than other macroscopic algae species, and have much greater height and biomass. They are also characterized by distinctive “starry” rhizoids, also known as bulbils, which are the reproductive structures of the pond algae. The blooms are very transient, and are subject to a “boom and bust” phenomenon where large blooms will crash suddenly and unpredictably. This can cause hazardous low dissolved oxygen conditions in the waterbodies where it occurs.

Starry stonewort is highly sensitive to algaecides and is fairly easy to control, although extensive, established blooms can be extremely difficult to treat and eradicate. Because the “meadows” of starry stonewort are so dense and spongy, it is problematic to achieve good contact with all of the biomass. There is also some evidence that there are convection currents caused by temperature gradients that form within the blooms, which produce an upwelling phenomenon that makes it difficult to get algaecide products down into the mats to achieve the necessary contact for successful treatment. Therefore, proactive management before a bloom becomes established is a more practical approach that yields improved efficacy.

Starry stonewort is an aggressive invasive species, and it is continuing to spread to a greater geographic footprint. Even if you live in an area where starry stonewort has not yet been identified, it is important to be familiar with the morphology and characteristics of the species so that you can be aware if it encroaches into your neck of the woods. How serious is the threat of starry stonewort? The Aquatic Plant Management Society along with the Northeast Aquatic Plant Management Society, the Midwest Aquatic Plant Management Society and private partners in 2017 are funding a two year $40,000 research grant on the biology, ecology and management of starry stonewort.

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