‘Zombie plant’ here to stay in N.B. waterways, eradication is futile, say experts

As with many invasive species, now that Eurasian watermilfoil has established itself in the St. John River system, it's here to stay.

While eradication efforts may be futile, one local watershed group isn't going down without a fight.

The Jemseg Grand Lake Watershed Association launched a pilot project last year to try to keep the Eurasian watermilfoil at bay.

Laura Lavigne, a master's student in environmental management at the University of New Brunswick, was the project co-ordinator for the Eurasian watermilfoil removal pilot project.

Lavigne said the goal of the pilot project isn't eradication. She said it's far too late for that.

"We're not looking for eradication for such a large lake, and for such an open system it is unlikely that it'll ever be eradicated."

The real goal is to slow the spread and reduce the number of plants in some heavily affected areas.

Lavigne said the biggest complaint from water users is that the plants interfere with recreational activities like fishing, swimming and boating.

"Once it creates dense mats, it is not pleasant to swim through and then when you cast your line, it gets all tangled, and then boat motors have a difficult time getting through it and it chops all the weeds up, which then causes it to spread more."

'Dense mats of floating vegetation'

The New Brunswick Invasive Species Council describes the Eurasian watermilfoil as a species native to Europe, Asia, and Northern Africa "that was introduced to North America in the 19th century via ballast water or the aquarium trade."

It's become "widely distributed" across North America, which has resulted in "severe impacts on aquatic ecosystems … including rapidly establishing and forming dense mats of floating vegetation that shade out native aquatic plants and reduce oxygen in the water, impacting fish and other species. Large mats of Eurasian watermilfoil can also limit recreation, boating, and fishing opportunities in local waterbodies."

Even a small broken-off piece can root and grow a whole new plant, which is why it's important "to clean off any plant fragments and parts that could be attached to boats and trailer equipment after leaving the water."

Nicknamed 'zombie plant'

Meghann Bruce, an aquatic botanist and research scientist with the Canadian Rivers Institute, first discovered Eurasian watermilfoil in 2015 while doing a botanical survey in the St. John River for another project.

Since then, it's been discovered in the Washademoak, Belleisle Bay, Grand Lake, and the Kennebecasis and Jemseg rivers, among others.

"It's easier to find a site where it exists and is growing than it is to find a site in the river where it's not growing," said Bruce.

When it arrives in an area, "it tends to dominate," she said. And it's also really hard to kill, which is why it's been given the nickname "zombie plant."

"It doesn't mean it's actually a zombie," explained Bruce. "The plant doesn't actually die and come back to life, but it may appear to."

If you pulled the plant by the roots — as you would with a weed in the garden — and thought that would be the end of it, you'd be mistaken.

"In that same spot, it's only a matter of time before that plant rises again and exhibits more growth. So you think you've killed the plant. But really what's happening is in the sediment, that root base will just put up more shoots. So zombie plant is a common term, just referring to how hard this plant is to kill."

And pieces of the plant that are severed by aquatic recreation — paddles, boat motors — can also produce entirely new plants, similar to cuttings, said Bruce.

Grand Lake pilot project

Lavigne said the first step was to survey the area and record where the plants were. She said there are "a lot of sparse individuals" in Douglas Harbour, Dykeman's Cove and the harbour below Dykeman's Cove, but no confirmed sightings in Whites Cove.

The highest concentration of plants was in Douglas Harbour, where people moor their boats.

In October and November, the project team used two different methods to remove the plants. In one area, they snipped the plants at the bottom of the stem. In the other, they pulled the plants — roots and all — by hand. In both areas, all plants were removed.

They also had a control area where they didn't do anything.

This summer, a team will return to the water to count how many plants are growing in each of the three areas.

"So in the second season, we will be able to tell if the removal methods were successful, or which one worked better than the other, or if none of them work and we have to find another alternative," said Lavigne.

"The more knowledge we have, the more we're able to predict where it's going to grow and predict how we can control its spread."

She said "the way that we're going to get ahead of this" is to educate the public about how to minimize the spread.

Clean, drain, dry

Although it cannot be stopped, Bruce said recreational water users can help slow the spread to other waterways by using the "clean, drain and dry" approach, meaning boat owners ensure they don't have aquatic hitchhikers aboard when they pull their boats out of one waterway before going to another.

"Eradication is not possible at this point and so the worst case scenario now is that it gets into other water bodies," said Bruce.

"Once it's in a system, it's in a system. The only successful case of eradication I've heard of to date was by our colleagues down in Maine who were controlling it in a gravel pit."

She said some waterfront property owners are already affected by the spread of the invasive plant. She said there are swimming areas, for example, that used to be relatively plant-free "and all of a sudden, there's plants growing into a really dense mass forming mats on the surfaces."

It has also been "out-competing" native plants.

"When you have something that comes in and just takes over, that means those changes could affect other things."

Some waterways may become impassable to boats, while some fishing spots may also be negatively affected, said Bruce.

Identified in Belleisle Bay in 2020

Eurasian watermilfoil is also in Belleisle Bay, a tributary of the St. John River south of Grand Lake, and is being monitored by a local group, the Belleisle Watershed Coalition.

The species was first identified in the bay in 2020 and is now established in a number of locations, including Hatfield Point and the nearby marsh in the upper bay, and Tennants Cove and Kingston Creek at the mouth of the bay, said Colin Forsythe, the group's executive director.

"It is certainly established here, no question," said Forsythe. "Interestingly, it doesn't seem to have had a big impact here."

While invasive species can often wreak havoc on an ecosystem, they don't always, said Forsythe.

"There is a lot of Chicken Little around these species and it may not be warranted in all cases."

Forsythe said his group isn't "currently actively monitoring" the species, and because it's so well established, there's been no attempt to remove it.