Starry Stonewort: Up-And-Coming AIS of Wisconsin

Post by Bradley Steckart, Waukesha and Washington County AIS Coordinator; adapted by Sara Fox, UW-Extension

Starry Stonewort (Nitellopsis obtusa) has made a name for itself in Wisconsin as a well-known invasive species. Questions surrounding its unknown impacts and the viability of its reproductive bulbils have researchers, scientists, and volunteers interested in this relatively new invader. N. obtusa is a prohibited aquatic invasive species currently present in four Wisconsin counties. Here’s what you need to know about starry stonewort: 

What is it?

Starry stonewort is a freshwater macroalgae native to Europe and western Asia. While it is classified as invasive in the Midwest, it is listed as endangered in its native habitat. You might confuse starry stonewort with native stonewort (Chara spp.) or muskgrass (Nitella spp.) and pondweeds such as sago pondweed. 

You can identify starry stonewort by it’s bright green branches that grow in whorls of 4-6 around the stem. It is named after its small, white, star-shaped reproductive structures called bulbils. These bulbils reside 1-3 inches deep in the sediment and act as an anchor for the alga. Starry stonewort is dioecious, meaning that male and female reproductive structures grow on seperate algal stalks. Currently, only males are present in the United States indicating that reproduction is only occurring asexually by bulbil production.

The star-shaped reproductive structure of starry stonewort is called a bulbil. Credit – Paul Skawinski

How might it affect me?

Like many other invasive species, starry stonewort holds potential to outcompete native vegetation and alter the ecosystem of the waterbody where it is introduced. Starry stonewort grows into dense vegetative mats that can interfere with recreational water activities like tubing or water skiing. Large patches of starry stonewort may also threaten fish spawning habitat. However, those impacts are inferred from the impacts of other invasive aquatic plants. The specific effects of starry stonewort on fisheries is largely unknown and is currently under investigation by leading scientists.

As always, it is beneficial to take preventative measures to avoid spreading starry stonewort and other aquatic invasive species to and from your lake.

Starry stonewort can outcompete native plant species in a waterbody. Credit – Paul Skawinski

What does this mean for Wisconsin Lakes?

Manual and chemical control methods have been used to treat starry stonewort with varying success. However, boaters and anglers can take individual action to prevent the spread by following Wisconsin DNR AIS prevention steps:

INSPECT your watercraft vehicles and trailers for plant fragments upon exit and entrance to a waterbody. Pay special attention to anchors and footwear where bulbils might reside. Hunters should make sure to inspect duck decoys and blinds.

DRAIN water from your boat. This includes livewells, motors, and bait containers filled with water from the waterbody you’re exiting.

REMOVE all attached plants from your watercraft vehicles and trailers.

NEVER MOVE plants or water among waterbodies. Not only is this effective, but enforced by Wisconsin law.

For more information on starry stonewort, check out WDNR or UWEX Lakes resources.

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