How conservationists are pushing back against a West Coast invader

On a sunny afternoon in July, Matthew Christensen and Richard Topp walk through the long, coarse grass and spongy sediment of a marsh in B.C.’s Boundary Bay wildlife management area. To the untrained eye, all the plants they walk among may look like they belong, but one is an invader.

A non-native species of Spartina — a perennial cordgrass — is invading the marsh and tidal mudflats along the Fraser River delta in Boundary Bay and Roberts Bank, threatening the surrounding ecosystem. Christensen and Topp are part of the BC Spartina Working Group, led by Ducks Unlimited Canada (DUC) and staffed by teams from the BC Conservation Foundation, that is working to control its spread in the area.

Invasive Spartina is rapidly spreading along the west coast of the U.S. and into the Strait of Georgia. There are currently three species of invasive Spartina found in B.C. Their spread decreases and disrupts intertidal habitat for shorebirds, waterfowl, fish and shellfish; destroys nursery grounds for juvenile fish, clams, mussels and Dungeness crabs; and increases the risk of coastal flooding.

Throughout the Boundary Bay wildlife management area, pink flags mark the location of Spartina plants that have been identified by members of the BC Spartina Working Group. Members use a custom app developed by DUC to input the size of the plant they’ve identified and the app automatically attaches a geographic location to it.

After marking the plants on the app and with a pink flag on the ground, teams return to the location armed with personal protective equipment and a special backpack filled with a bright blue liquid. The backpacks contain an active herbicide known as Habitat that is mixed with a blue dye so the teams can easily see when it has been applied.

Once sprayed, the herbicide moves through the plant down to the roots, disrupting its protein synthesis. This prevents the roots from growing further and gradually kills the plant, explained Christensen, head of conservation programs with DUC. Spartina plants have thick mats of reproductive roots, which is why herbicides that target the roots are most effective, said Christensen. The commonly used herbicide Roundup, which targets the leaves of a plant, would not effectively eradicate Spartina, he said.

Though there are risks associated with using herbicides, this method has thus far proved to be least harmful to native plants in the area, according to Christensen and Topp. Prior to 2013, the group removed Spartina plants from the ground by digging or using a machine to control their spread. However, this method often involved removing native plants near the invaders. Since switching to a targeted application of herbicide, the group has managed to decrease the number of Spartina plants in B.C. from 23,000 in 2016 to 2,000 in 2022 without causing a significant disturbance to native plants.

“It's a very targeted, isolated treatment with very strict conditions around wind and timing,” said Christensen. “There can't be rain or tidal inundation within four hours to allow for drying time. As long as we apply it to the plants directly, it is absorbed by the plants and anything remaining is going to be broken down naturally in the ecosystem.”

The cost of not doing anything as Spartina spreads in B.C.’s intertidal zones is far greater than the impacts of eradicating it. It is possible ocean currents could carry Spartina seeds along the entire B.C. coastline, which includes 59,300 hectares of tidal flats and marsh and more than 440 estuaries. The Fraser River delta has approximately 25,000 hectares of tidal mudflats that are important habitat for fish and migratory birds and support the highest density of wintering waterfowl, shorebirds and raptors in Canada.

Back in Boundary Bay, Christensen and Topp come to a stop at a monitoring site where Topp, a conservation program specialist with DUC, will examine Spartina plants that have been recently treated with herbicide. Team members return to examine the sites at regular intervals up to a year after the plants have been sprayed to determine the efficacy of the herbicide and to monitor the condition of native plants within the site. If the herbicide is working, the Spartina plants will turn from green to brown.

Each year, the working group returns to the site to identify, map and apply more herbicide to the remaining Spartina plants or new ones that have grown since the last herbicide application. By taking note of the size of each plant, Christensen says the team has been able to track the decline in size and abundance of Spartina in the area since they began using the herbicide.

As a result of the team’s efforts, Spartina plants have been prevented from colonizing the tidal mudflats adjacent to the waters of Boundary Bay. Had the team not intervened, Christensen and Topp believe Spartina would have overtaken much of the tidal mudflats by now. The mudflats are home to many important invertebrate species, like amphipods, molluscs, crustaceans and worms that are an important source of food for migratory birds, like the western sandpiper, said Christensen.

Christensen attributes the success of the program to communication between stakeholders, such as the government, NGOs and First Nations. “Having those diverse stakeholders and the interests being represented at the table has been really integral to getting this program to be successful. It's not just for going on spraying the plant — we track and report back to each agency, and they have different resources or expertise to bring to the project.”

He believes lessons from eradicating Spartina plants can be applied to fighting other invasive species in the province, such as the European green crab that has been wreaking havoc on B.C.’s coast, preying on and outcompeting native species for habitat.

“I see parallels between how the Spartina program started and how that species is being managed,” said Christensen. “I think one of the biggest lessons is the complexity of working with chronic invasive species and the effort that goes into co-ordinating all of the different stakeholders.”