Starry stonewort Image: State of Michigan, Paul Skawinski
By Eric Freedman
Some aggressively stealthy invaders may be more aggressively stealthy than we thought.
Consider the starry stonewort, a green alga from Eurasia that now thrives in many inland lakes in the Great Lakes region and that can outcompete native plants.
Its first documented discovery in North America was in New York in 1978 — or so scientists believed.
Then through a combination of old-school and new-school technologies they discovered that earlier samples had been collected from the St. Lawrence River in Quebec, possibly in 1974 but maybe even earlier, a new study says.
Starry stonewort — Nitellopsis obtusa to scientists — “prefers slow-moving, developed waterways,” according to the study by researchers at the New York Botanical Garden. It’s found in “numerous inland lakes from Minnesota to Vermont, and from Lake Ontario and inland lakes in southern Ontario.”
In Michigan, for example, “Thick mats of starry stonewort cover lake bottoms that effectively block fish access to suitable spawning habitats,” according to the Department of Environmental Quality (DEQ). It was first detected in the state in Lake St. Clair in 1986, and can “now be found in lakes in the Lower Peninsula, particularly the southern region,” including St. Joseph County’s Lake Templene.
The study said, “There are numerous examples of Eurasian invasive species introduced into North American via St. Lawrence Seaway shipping routes.”
Kenneth Karol Image: New York Botanical Garden
And the new discovery supports the theory that starry stonewort also arrived by way of the St. Lawrence, according to Kenneth Karol, the lead author of the study and an associate curator at the New York Botanical Garden.
How did that discovery come about?
In approximately 1974, an algae scientist at the Université du Québec collected and preserved a specimen that he found during his research into water quality, Karol said. That scientist sent the unidentified specimen to another researcher who “put it on his shelf” and didn’t do anything with it.
When that researcher died, the New York Botanical Garden inherited his collection, which then “sat on our shelf” until the institution began to digitize its collection of 7.8 million plant specimens, including 300,000 algae specimens, Karol said.
And that’s when he and doctoral student Robin Sleith of the City University of New York put it under a microscope and identified it as starry stonewort. Sleith coauthored the new study published in the “Journal of Phycology.”
“It’s really cool that we can use these relatively old natural history collections to understand invasive and native species,” Karol said.
The process is leading to other scientific discoveries as well. For example, he said, “I’m getting very usable DNA from samples in the 1800s, so we can look at the genetics from, say, specimens from the Old World over time and space.”
Noting that starry stonewort is considered “rare and endangered” in the Old World but aggressively invasive in North America, he said scientists are trying to understand why that is. The answer may lie in genetics, in the presence or absence of predators, or somewhere else.
In addition, the research may help scientists learn about hotspots for invasions, he said: “Where these boats are picking it up and moving it around. Hopefully we can curb that movement and control the invasion.
The Michigan DEQ’s Water Resources Division says starry stonewort could have arrived in the state in a ship’s ballast water and then was spread by waterfowl or boats.
The state Department of Natural Resources says, “Control efforts — mechanical or chemical removal — for starry stonewort are currently underway in some areas and have historically been led at the local or regional level. The management responsibility, including financing the effort, usually rests with the owner of the infested property.”
The study calls for further research into the extent of starry stonewort in Quebec.