Skip to Main Content

Starry Stonewort: An Example of Invasive Aquatic Algae

written by
Ashlee Haviland

Certified Lake Manager, Ashlee Haviland, walks through one of the less known impacts of invasive aquatic algae and plants in waterbodies – the out competition of native plants and the impact on the operating ecosystem – below, using the well-known invasive starry stonewort as an example.

Invasive species can cause havoc on natural and manmade waterbodies – lakes, ponds, rivers and more. Even beyond blatant impediment of recreational use for boats, jet skis, swimmers and fishers, these invasives can be hugely detrimental to water quality, raising nutrient levels, obstructing the introduction of oxygen and leading to the destruction of native plant and wildlife species.

A view of a lake during a sunrise

One such invasive that has been found in lakes across parts of the Midwest is starry stonewort.

Starry stonewort (Nitellopsis obtusa) is a macroalgae that has plant like structures and can grow in dense mats. In addition to a myriad of effects these dense mats can have on the recreational use of water, it also tends to choke out native plants – and reduced native plants can negatively affect native fisheries populations within lake ecosystems.

What are the Impacts of Reduced Native Plants?

When trapped within monocultures of invasive aquatic vegetation, or in this case, invasive algae such as starry stonewort, without access to varied native plants, native wildlife populations face reduced foraging opportunities. These native wildlife populations often struggle to continue thriving, thus reducing species richness within an ecosystem.

Without species richness, ecosystems do not function and often fail to produce vital nutrients and other benefits to local wildlife, which may lead to further species dying off. This modification of ecosystem function could become irreversible and impair the waterbody for generations. Property values, recreational use, economic, and ecological impacts can all be affected without proper management of invasive species, especially starry stonewort.

Identification of Starry Stonewort

Starry Stonewort pulled out of the water: Photo courtesy of Paul Skawinski

The easiest way to identify starry stonewort is by its small star-like bulbils. It has 4-6 whorls around the stem and can grow up to two meters tall. It can grow in marl sediments and in 9 meters or more of water. Starry stonewort can also overwinter in some locations.

Where Did Starry Stonewort Come From?

Starry stonewort originated in Eurasia and was transported to the United States by ballast waters – fresh or saltwater held in ship’s ballast tanks and cargo holds – on cargo ships during the 1970s. Since then, it has spread throughout the Eastern United States, creating established populations throughout Michigan, Indiana, Minnesota, Wisconsin and Illinois.

Today, it still spreads easily, often via pieces attached to waterfowl feathers or small fragments transported via boat and equipment from waterbody to waterbody.

Why is Starry Stonewort Considered Invasive?

Starry stonewort is considered invasive because this algae spreads by fragmentation and creates dense mats that out competes even other invasive species like Eurasian watermilfoil and curly-leaf pondweed. These dense mats block out sunlight from other native plants as well as impede the movement of fish, spawning activities, water flow and recreational pursuits.

Unlike native stonewort, starry stonewort can grow with less light, within deeper and cooler waters, and tolerate salinity fluctuations.

A shallow, rocky area of a lake

Control and Prevention of Starry Stonewort

The best way to protect your waterbody is by community-wide prevention – after all, it only takes one person to introduce starry stonewort-carrying boats or equipment into a waterbody.

Checking boat trailers for any plant, mud or other debris, cleaning water intakes and draining all live wells before you leave a location is the best way to prevent the spread of any invasive species, especially starry stonewort.

A boat being taken out of the water for inspection of starry stonewort or other traces of invasive aquatic plants

Once starry stonewort becomes established in a waterbody, early detection and chemical treatment are the most viable options for reducing the impact of starry stonewort within a waterbody. While the use of chemical control in the form of algaecides can greatly reduce the biomass of macroalgae over time, its bulbils often remain viable for regrowth.

Without treatment or management, an ecosystem can become severely impaired. The financial burden of managing and restoring a lake ecosystem after starry stonewort is established can affect management strategies, property values and recreational use. Management of starry stonewort can cost tens of thousands of dollars annually. Aesthetic and recreational use can become diminished over time as well as ecosystem function.

Monitoring for Starry Stonewort and Other Invasives

Including a strategy for monitoring aquatic algae and vegetation within waterbodies can greatly increase the chances for early detection and management of starry stonewort. Resources for lake residents can also prevent the spread and slow the impact of invasive species at their lake. It is important to educate residents and lake users the negative impacts that invasive species have on a waterbody.

You can learn more about Midwestern aquatic plants – both invasive and native here.