Foreign algae could be ‘greatest challenge’ for lake management
Aggressive. Dominant. Threatening. These typically aren’t the words associated with algae found in lakes, and yet they accurately describe starry stonewort — a plant-like algae that has the potential to be the greatest challenge to lake management efforts in recent years.
Starry stonewort (Nitellopsis obtusa) is not native to the United States, and like many aquatic invasive species, it’s believed that starry stonewort earned free passage to America as a stowaway in the ballast water of ships entering the Great Lakes.
The aggressive algae species is originally a native of Europe and is even considered a threatened species in the United Kingdom. Yet, over the past three decades in Michigan, it has proven itself to be a hardy and invasive opportunist.
“It’s the most aggressive aquatic plant ever observed in Michigan and is able to outcompete all other Michigan plant species, including all invasive and current alien species such as watermilfoil, fanwort, and curlyleaf pondweed,” wrote Dr. Doug Pullman in his article “A Decade of Starry Stonewort in Michigan: Observations and Operational Management Considerations,” which he co-authored with Gary Crawford.
Pullman was the first to positively identify starry stonewort in a Michigan inland lake. In February 2006, he identified the species in Lobdell Lake in Genesee County. Since then, starry stonewort has been found in Michigan lakes throughout the Lower Peninsula, spreading from Mason County to Wayne County. At least nine Oakland County lakes have been invaded by starry stonewort since 2008. Those lakes include Indianwood Lake in Orion and Oxford townships, Sears Lake in Milford Township, Softwater Lake in Springfield Township, Lower Straits Lake in Commerce Township, Williams Lake in Waterford Township, Kent Lake in Milford and Lyon townships, Tipsico Lake in Rose Township, Big Lake in Springfield Township, and White Lake in Highland and White Lake townships.
Dick Pinagel, president of the Michigan Aquatic Managers Association (MAMA) and owner of Aqua-Weed Control, Inc., said he believes starry stonewort is spreading even further throughout Oakland County.
Starry stonewort was first discovered in North America in the St. Lawrence River back in 1978. In 1986, it was found in Lake St. Clair. Although it wasn’t positively identified in a Michigan inland lake until 2006, anecdotal evidence suggests that it has been present in inland lakes since the 1990s.
“It may have been present in several southeastern Michigan lakes as early as 1999 but was thought to be a ‘super weedy chara,’” Pullman explains in his article.
A case of mistaken identity is plausible since starry stonewort resembles the native plant-like macro algae called chara — both look like generic green weeds.
“Starry stonewort is also a macro algae. It’s rootless — although sometimes it can be loosely rooted to the bottom,” Pinagel said. “It’s a charoid algae. It’s very similar to chara.”
Both chara and starry stonewort lack roots; however, they have structures called rhizoids that are used for nutrient absorption and to provide support and stability. Both species also resemble terrestrial plants because of their stem-like and leaf-like structures.
Yet, starry stonewort differs from the native chara in several important ways.
First off, the rhizoids of starry stonewort resemble stars — hence the colloquial name of the species. While they have been observed to be present on all parts of the algae at all times of the year, they are usually common on the algae structures closest to the sediment in late fall and early spring, according to Pullman.
“They look like there are little flowers on it. They look like stars,” said Pinagel. “Once you’ve gotten used to the structure of it, it’s easily identifiable.”
Another defining characteristic of the species is the presence of a tan colored “bulbil” at the base of each cluster of branches. The branches themselves are another identifier of starry stonewort because they have a more irregular branching pattern compared to other charoid algae found in Michigan which tends to lend them a more “disheveled” appearance.
Starry stonewort also tends to be a lighter green color than its similar algael counterparts. It also produces orange colored oocytes that can be easily detected with the naked eye.
Another identifying characteristic of starry stonewort may be its ability and even its affinity to grow at great depths.
“Unlike other Michigan charoids, starry stonewort can grow to remarkable heights and depths,” Pullman wrote.
Added Pinagel, “It can grow in deeper water — usually 10 to 12 feet. Chara typically doesn’t do that. Starry stonewort has been seen to grow 8 feet tall in some areas.”
In Waterford Township’s Williams Lake, for example, starry stonewort has been observed growing at a height of 7 feet at a depth of 27 feet. Pullman hypothesizes that it most likely is capable of growing at even greater depths.
However, it’s really starry stonewort’s intangibles that set it apart from other charoid species.
“Starry stonewort is much more aggressive, denser, and hardier. It’s really a beast of a plant,” Pinagel said.
“It may easily represent the greatest challenge to lake management professionals, regulators, recreational users and the biological integrity of inland lakes in the history of lake management in Michigan,” Pullman wrote.
Part of the reason for this challenge is the algae’s ability to outcompete all surrounding species, especially as it forms dense mats of vegetation able to completely cover the bottom of a lake.
“It grows so dense and thick — Brillo pad-type thick,” Pinagel said.
According to Pullman, when the algae grows densely together and dominates all other vegetation, it forms irregularly spaced “pillows” of vegetation at varying heights as opposed to a mat of uniform height. This marks the stage before starry stonewort invasion reaches the pinnacle of its invasion, which Pullman refers to as “packing.”
“‘Packing’ is used to refer to a starry stonewort population that has filled all available habitat and has moved upslope and downslope into areas that do not appear to be ideal but are still adequate for growth,” Pullman wrote in his article.
Although it has been documented both in the United Kingdom and in Michigan that starry stonewort prefers deeper, less turbulent waters, it is able to colonize shallower environments.
Starry stonewort also has the ability to inhabit a wide variety of lake environments. It has been observed thriving in either clear water or dark water systems and so far doesn’t seem to show a preference for full shade or sun.
While it doesn’t really thrive in boat lanes or high energy shorelines, it will grow in these areas “when it has colonized or filled virtually all of the habitable area of the lake,” according to Pullman’s observations.
The ability to colonize in boat lanes may contribute to starry stonewort’s capacity to spread from lake to lake.
Starry stonewort is easily fragmented, and boat traffic could result in significant fragmentation, causing starry stonewort to float to the surface.
“This type of fragmentation has been implicated in the dissemination of other alien species in Michigan such as the invasive milfoils,” Pullman wrote.
Another likely vector for starry stonewort transmission between lakes could be waterfowl since the oocytes of starry stonewort can be easily transported on bird feathers.
Boat trailers may also aid in the spread of this non-native species — the oocytes can be transported on aquatic plant debris, as well, which can get caught on boat trailers.
Public launch sites are typically associated with the spread of alien species, as boats travel from lake to lake. However, while this may have contributed to the spread of starry stonewort, Pullman maintains that waterfowl and other animals may be the main culprit as the non-native algae has become established in lakes that don’t have a public access site.
With its ability to colonize virtually any lake environment, starry stonewort has proven to be a challenge both ecologically and recreationally.
Ecologically, it presents several problems — including a decrease in the biodiversity of plants in lakes infiltrated by starry stonewort.
“It is extremely obvious in all of the infested lakes that the biomass of competing species has declined significantly in every lake where starry stonewort has spread and come to dominate the lake flora,” Pullman states in his article.
“It’s like throwing a thick tarp across the lake bottom. Very few plants will grow through (starry stonewort) when it has become dense like that,” Pinagel said. “There has been a shift among aquatic species seen in lakes with starry stonewort. Most plants in the lakes are seeing diminished growth.”
However, not only is starry stonewort able to outcompete plants and other algae for space and nutrients, the species is able to change the bio-geochemistry of sediment, inhibiting further plants from colonizing the area after it has been eliminated.
By acting like a commercial benthic barrier, starry stonewort allows for the accumulation of phytotoxins which render the sediment inhospitable for plant growth until the conditions change.
Yet, while starry stonewort seems to suppress most rooted plants growth, there are a few certain rootless plant species that seem to thrive in starry stonewort’s presence. These include rootless bladderworts and coontail.
And although it outcompetes most other native species, it also outcompetes other invasive species.
“We have definitely seen a decrease in some of the other aquatic invasive species,” Pinagel said.
David Cornwell, the riparian representative for Pontiac Lake’s improvement board, agrees. He said the lake improvement board has been fighting starry stonewort in Pontiac Lake regularly over the past few years.
“There are both positive and negative consequences to everything you do,” he said. “The positive of treating starry stonewort is that you get rid of what can be a massive Brillo pad under the water. You can be effective killing it off, but in the short run it allows for other weeds to prosper more fully. Both chara and starry stonewort tend to retard other weed growth, but when you remove either one of those two you get all other kinds of weeds.”
Another seemingly silver lining to the starry stonewort invasion is increased water clarity.
“Water clarity definitely improves with the presence of starry stonewort,” Pinagel said. “Since it derives nutrients from the water column as opposed to the soil, it serves as a giant filter.”
Pullman also attributes the increased water clarity to the ability of the upper parts of the dense algae mats to compete effectively with phytoplankton for nutrient resources.
It also appears as if starry stonewort shares a friendly relationship with another invasive species — the zebra mussel. Starry stonewort appears to be the favorite substrate of zebra mussels, which also have proven to have a favorable filtering impact on water clarity.
While starry stonewort seems to have been able to form some positive relationships between other species, the same can’t be said for its impact on fish habitats.
“Many fisheries have concerns with the effect of the growth of starry stonewort on the fish spawning areas,” Pinagel said.
By forming a thick, dense mat, starry stonewort directly impacts the spawning habitat of some fish because the mat acts as a physical barrier to the areas optimal for nest creation. This results is a reduction of the nesting area and consequently a decrease in the number of nests. This leads to the complete elimination of spawning activity in the area of infestation and leaves fish to compete for suboptimal spawning habitats.
Starry stonewort may also pose a threat to lake fauna whose survival depends on their intimate association with the lake bottom — such as logperch, darters, various minnow species, native clams, and other invertebrates. Threats to these creatures could further decrease a lake’s biodiversity and potentially affect the lake’s overall ecological well-being.
However, starry stonewort doesn’t just pose ecological problems but recreational ones, as well.
Anglers have become frustrated because the algae commandeer the necessary spawning and living habitats of game fish.
“Reports of angler frustration such as an inability of being able to locate black crappies because the stumps have disappeared beneath the mat of starry stonewort or that bass are more difficult to catch because of the disappearance of certain weed beds are becoming more commonplace in our lake management practice,” Pullman wrote.
Another recreational issue is the quality of the boating experience since boats can become tangled in starry stonewort mats.
“It can definitely impact boating as when it nears the surface it can make getting through it very difficult,” Pinagel said.
Between the recreational and ecological issues, lake management of the algae is almost a must.
Mechanical harvesting has been used to control starry stonewort but with little success. Because the algae is capable of producing a large amount of biomass in a relatively small area, starry stonewort is able to cause a mechanical harvesting machine to fill to capacity very quickly, slowing down the harvesting process.
Fortunately, starry stonewort has proven to be highly sensitive to common copper- and endothall-based algaecides. In fact, according to Pullman, starry stonewort seems to be even more susceptible than most common Michigan charoid species.
However, that doesn’t mean that there aren’t challenges posed in managing the non-native algae.
“It’s hard to control. As it’s so dense and thick and grows so tall, we normally are only treating the top layer, and while we can impact the top layer, it normally grows back so quickly that in many cases it’s like we did nothing. So it requires a very aggressive treatment regiment,” explained Pinagel, whose company, Aqua-Weed Control, was one of the first companies in the area to recognize the algae and begin treating it.
“We’ve had partial success with treating starry stonewort, but we are still experimenting with the treatment schedule and regimen to fine tune it,” he said.
Other herbicides have also been found to be successful in hindering starry stonewort growth, in particular when coupled with Cultrine Ultra.
While there have been measures discovered to counteract this intimidating foe, it still remains one of the most challenging non-native species facing lake managers — at least until an even more competitive and dominant species comes along.
“It’s another invasive plant to throw into the mix,” Pinagel said. “Unfortunately, there are probably more to follow.”