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AQUATICS

Starry Stonewort the Basics

Starry stonewort is an alga – and an invasive species in inland lakes and ponds that can dramatically alter aquatic ecosystems.

Its growth and expansion since the 1990’s throughout New England and Minnesota has served to destabilize critical ecosystem functions and impair recreational and utilitarian values. Invasive species, like starry stonewort, can reduce property values for the property owners in these riparian areas.

Name: Starry stonewort

Scientific Name: Nitellopsis obtusa

Family: Chara family

Native: Europe and Asia

History: It is believed that starry stonewort first inhabited North American inland lakes in the late 1990’s after being introduced to Michigan’s Great Lakes and St. Lawrence Seaway. Observers identified it in New York in the early 2000’s, but it was not positively identified in Great Lakes region inland lakes until 2006.

Starry stonewort reproduces rapidly, and is one of the most aggressive aquatic invasive species. It is able to out-compete other aquatic plant species, including all other non-native, noxious and invasive plants. However, there are several plant species that seem to thrive cohabitating in the presence of starry stonewort, such as rootless bladderworts, coontail and sometimes water lilies.

The visual impact starry stonewort has on water clarity is profound and water clarity is often excellent in lakes where it is dominant (See Figure 1). However, it can also indirectly and adversely influence the plant and animal life beneath the water surface.

Starry stonewort can spread quickly from lake to lake by producing specialized fragment and structures known as bulbils (See Figure 2) that are easily transferable on the fur of animals and on bird feathers. Plants and plant parts can get caught on boat trailers and are transferred by humans. It is an opportunistic species that can make a substantial and damaging impact on the surrounding ecosystems with its unforeseeable bloom and crash cycles that can happen at what seems to be random times throughout the year. Blooms extirpate desirable plants and compromise critical aquatic habitats. Crash events leave voids in in the plant community that can be rapidly filled by other weeds or trigger cyanobacteria blooms depending on the size of the crash event.

“The most significant characteristic of

this species is that it is predictably

unpredictable. It will bloom and decline without warning.”

- Dr. Douglas Pullman

Figure 2. Specialized fragments (top) that aid in dispersal of starry stonewort bulbils “stars” (bottom).

Figure 1. Effect of starry stonewort on water clarity. Also note the smooth appearance of the mounds of starry stonewort, approximately 2’ below the water surface.

Ecosystem Impacts

The charoid algae look like higher plants because they seem to have stems and branches, but they are indeed algae and members of the characea.

There are dozens of charoid algae species in the Northern US, Chara being the most common genus.

EmpireEukaryota

KingdomPlantae

SubkingdomViridiplantae

InfrakingdomStreptophyta infrakingdom

PhylumCharaphyta

ClassCharophyceae

OrderCharales

FamilyCharaceae

GenusNitellopsis

SpeciesNitellopsis

obtusa

The charoid algae look like higher plants because they seem to have stems and branches, but they are indeed algae and members of the characea. There are 6 extant (living – there are many fossil genera) genera in this family. They include:

• Chara: Chara Linnaeus, 1753: 1156,• Nitella: Nitella C.Agardh, 1824: xxvii• Nitellopsis: Nitellopsis Hy, 1889: 397, 398• Lamprothamnium: Lamprothamnium J.Groves, 1916: 336.• Lychnothamnus: Lychnothamnus (Ruprecht) A.Braun, 1856: 338• Tolypella: Tolypella (A.Braun) A.Braun, 1857: 338

Classification

Starry stonewort can be difficult to identify because it may grow inconspicuously and intermingled with other similar charoid species.

How does it differ from other charoids?• Irregular branching pattern giving it a characteristic “disheveled appearance”. • Often observed to grow at such aggressive levels that it will extirpate even the most noxious invasive species. (Its ability to

grow to inconceivable heights and depths for a non-vascular plant appears related to water flow and convectional currents.)

White, star-shaped bulbils. A definitive identifier, present at random times during the year, usually at the base of the mats.

Identification

Typically light green when actively growing. Translucent “stems and branchlets” that resemble those found in Nitella and Tolypella. Asymmetrical and irregular branching - looks disheveled on close inspection.

Appearance

Scanning sonar systems can be used to delineate starry stonewort beds because of its unique signature. Cross check with rake toss or underwater video.

Remote Sensing

Clear or translucent stems called rhizoids. “Tube-like” cell wall “thallus” can be several inches long, even though it is a single cell. Produces popping noise when compressed.

Stems

No distinct odor.

Smell

Not crusty or crunchy as are most chara species. Single celled “stems and branchlets” are easy to “pop”, similar to bubble wrap. Cellular contents are not vicious or sticky as are some Nitella. More liquid and less like hand lotion.

FeelStars

Commonly found growing to 3’ tall. Can grow as tall as 17’. May grow intermingled with other charoid species making discovery difficult. Can form “mounds” that present a smooth surface at a distance despite how irregular a singular plant might appear.

GrowthProduces red-ish/orange-ish reproductive structures (gametangia). Only the male antheridia have been observed to date.

Visually similar to other charoid algae, but can be useful for microscopic id.

Seeds

A mysterious form of “chara” seemed to have appeared for near shore property owners in an increasing number of southeastern Michigan lakes during the late 1990’s. Numerous reports of three-foot-tall “chara” that made dock access nearly impossible began to surface. During most of the 1990’s, these reports were largely ignored because the charoid algae were always considered to be a highly desirable part of typical Michigan inland lake floras. It was rarely targeted for treatment and its growth was usually encouraged. However, it had become such a significant problem that a charoid algae treatment was planned for a small portion of a SE Michigan inland lake in the mid-summer of 1999.

The objective of the treatment was to merely “burn the charoid algae back” to an acceptable height and provide reasonable access to the lake for the homeowners on that bay. Since the goal of any reasonably managed lake is always to protect or improve plant community diversity, it was also hoped that this treatment would relieve some of the excessive competitive pressure that the “mysterious” charoid algae were having on the few remaining desirable plants that were still present in the bay.

The applicator, only wanting to reduce the height of the algae, applied a “lower than normal” dose of algaecide to the areas in that bay where docks were located. The treatment was limited in scope despite the observation that the mysterious charoid algae had blanketed the bottom of all but the deepest parts of the bay.

To the applicator’s surprise, all of the charoid algae died and collapsed throughout the entire bay within 48 hours of the treatment. Particularly unexpected since chara algae can be difficult to control.

Later, they discovered that the algae was not your typical Chara, but starry stonewort. An algae that appeared extremely sensitive to aquatic pesticides. The discovery of starry stonewort and positive identification of the plant in 2006 should serve as an important lesson to everyone who shares a concern with the spread of invasive species in all lakes, that it is critically important to pay attention to the reports of lay persons and lake management practitioners, even when the reports seem to contradict long held beliefs.

A Historical Account - and Lessons Learned

Aquatic vegetation management programs should plan to preserve, protect and possibly improve the diversity of macrophytes communities. A well planned program serves to preserve and improve the recreational and aesthetic qualities of managed lakes. Choosing lake management tools that provide the most species specific control should be a focus.

Starry stonewort grows to form extremely dense carpets completely covering the bottom of lakes, making control difficult. Mechanical methods are used extensively for the attempted control of starry stonewort, but the outcome of these operations have not been satisfactory. They are generally not able to keep up with the rapid growth of starry stonewort when it is in bloom phase. Desirable plants are also damaged when areas are mechanically harvested. Starry stonewort, being an opportunistic weed, can capitalize on this mechanical disturbance and dominate at even higher levels. Mechanical harvesting can also serve to spread propagules to other parts of the lake that are not already infested.

Hand harvesting is dependent upon visual location of the plant. It also creates a mechanical disturbance of surrounding areas that will favor starry stonewort production over more desirable and ecologically conservative species. Because starry stonewort can grow undetected amongst other charoid algae, it would seem unwise to depend on this strategy as a viable method to protect the biological diversity of submersed plant communities.

Starry stonewort is sensitive to chemical control. It can be selectively targeted with algaecides, and biological diversity of infected water bodies can be preserved and in some cases, improved.

Figure 4. Starry stonewort reproductive structure called an antheridia.

Figure 5. Starry stonewort bulbils (stars).

Figure 6. Starry stonewort thallus (stem) that has been partially emptied of cellular contents. Note the appearance of the empty cell parts.

Figure 3. Starry stonewort grows to form extremely dense mats making mechanical control difficult.

Control Methods

Treat early when first observing active growth. Algaecide application timing can improve the outcomes of starry stonewort management programs. However, the growth of this plant is so unpredictable, that the logistics involved with “treating before it gets too thick or tall” strategy cannot be determined by calendar date.

Watch for Early Growth

Apply algaecides when water flows and convective currents are advantageous, and with agents that are dense enough to sink into the starry stonewort plant mass. Drop hose applications can provide better outcomes than surface spray methods. Make sure not to stir up the muddy lake bottom.

Get the Product Near the Plant

Because this plant can grow inconspicuously among other plants, the margins of the treatment area should also be treated. Several successive algaecide treatments may be necessary if the treatments succeed in only “burning down” the surface of the plant mass.

Treat the Margins

Commercial aquatic applicators have also developed algaecide combinations that have yielded good results. Rodgers and Wersal (2015) have found variations in the potential impact of different algaecides and herbicide combination in mesocosm testing and these may help to select the best control agent.

Try Combination Treatments

Application Tips

With frequent observation, and proper application methods, lake managers have the tools for a successful management program of starry stonewort.

Figure 8. Cutrine® Ultra has been shown highly successful against Starry stonewort.

Figure 7. Starry stonewort bulbils (stars).

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