Biologist Bobbie Buzzell was aware of the Lummi Nation’s invasive species problem last year, but she didn’t know how to deal with it effectively.

This problem was only really brought to light when she and her Lummi Natural Resources Department colleagues began making weekly trips to the landfill in September with a short-bed pickup truck stuffed full of 10,000 frozen green crabs they had caught in the Lummi Sea Pond near Bellingham.

With so much to do in a short period of time, it was overwhelming and daunting.” Especially in light of the events of the previous year. The Lummi Sea Pond, one of the tribe’s most important seafood growing areas, had about 2,500 of the rapidly multiplying invaders removed by 2020. The following year, they rounded up nearly 86,000 people, including 70,000 in just the months of September and October. In November 2021, the Lummi Indian Business Council issued a state of emergency. Buzzell said, “We couldn’t keep up with it.

However, protecting Washington’s waters and the native fish and shellfish that live there requires constant attention to the threat of invasive species. A key part of this is identifying European green crab populations before they have the opportunity to establish themselves in shoreline ecosystems, as they have in Massachusetts. Since arriving on the East Coast in 18th-century ship ballasts, the crabs and larvae have traveled to the West Coast via El Nino currents.

In Washington’s rural coastal regions, shellfish production and the livelihoods of shellfish farmers and harvesters are at risk if we don’t act now and control existing green crab populations, according to Pacific Shellfish Institute executive director Bobbi Hudson.
Observers of the invasion saw the green crab population grow and spread to new areas, so Gov. Jay Inslee declared a “state of emergency” for the invasion on January 19.
In 1998, the crabs were discovered on the shores of Washington’s Willapa Bay and Grays Harbor, and have since spread slowly inland. The Washington Department of Fish and Wildlife’s spokesperson, Chase Gunnell, said, “There is not an infestation in Puget Sound and we want to keep it that way.”

Trapping is a common tool used by wildlife managers and researchers to keep tabs on crab populations. It takes a lot of time and effort to catch these crabs in the places they prefer to live, such as salt marshes, mud flats, pocket estuaries, and other areas protected from larger crabs.

Environmental DNA analysis, or eDNA, is being used by wildlife managers to detect the presence and population density of the crabs even when they’re in smaller, less noticeable numbers, according to new research from the University of Washington. The research shows that this analysis is just as likely to detect crabs as trapping, increasing the state’s ability to monitor.
According to study co-author Ryan Kelly, an assistant professor in the School of Marine and Environmental Affairs, the findings strengthen faith in a new way of looking at the world. “And we can apply that lesson to green crab, but also to the next invasive species, or endangered species,” Kelly said. I believe our paper is the best example of how eDNA works in a real-world management context out there,” says the author.

It’s possible to detect crabs at low densities and respond before they become a problem, according to marine ecologist Emily Grason of the Washington Sea Grant crab team.

These crabs, which are only a few millimeters long, are formidable predators. Although their reddish-green shells rarely grow larger than 4 inches across, they devour young oysters and clams, and even smaller crabs. In places like California and Oregon, they’ve been known to eat local shore crabs.
For shellfish harvesters in Washington, the green crab fundamentally alters ecosystem dynamics by outcompeting other predator species like Dungeness crabs for food and shelter.
It has been shown that they have damaged eelgrass beds, which support a wide variety of species, including juvenile salmon, while encroaching on species on the East Coast. I don’t think it’s just one type of animal. Buzzell opined that “the entire ecosystem is at risk.”

It’s not necessary for researchers to see these predators in order to detect their existence. It’s possible to detect animals in the environment by analyzing the DNA left behind by living organisms — bits of skin, shell, hair, mucus, poop and urine — in water and soil samples. Using this information, they can even estimate the number of animals in the area.

According to Abigail Keller (the paper’s lead author), she collected three months’ worth of water samples in crab habitats around the state to compare with trapping data from the same locations in 2020. While working on the project, Keller and his team came up with an approach that not only shows how trapping and eDNA analysis can both detect the presence and number of green crabs, but also aids scientists in better understanding how the abundance of a species relates to our detection abilities.

The research also gives managers a reason to trust eDNA as a monitoring tool, and begins to guide them on how and where to use it in conjunction with other monitoring techniques. This could increase the chances of keeping the green crab population low by expanding crab monitoring throughout Washington.

Neither eDNA nor trapping can be relied upon to provide exact results. It’s as if you have two different clocks each telling you a different time, says UW professor Kelly, and you have no way of knowing which one is correct.
“We use two different methods to gauge the state of the world, and both of them are seriously flawed. Even so, when you combine the two streams of data, you get a much clearer view,” he said. Having more of these imperfect tools to compare, Kelly said, the better the chance of finding some truth.

This information will aid scientists in determining how many water samples or how many crab traps they need to set in order to detect different densities of potential crab populations.

As a result of this study, scientists and wildlife managers can monitor more areas than trapping permits, increasing their chances of spotting an impending problem.

It is unlikely that state waters will ever be free from green crabs, but people are working to keep the numbers low enough that they don’t destabilize native ecosystems.

Gunnell noted that current monitoring efforts like trapping at places like Drayton Harbor near Blaine, WA, have proven the value of handling known crab populations.

Washington Sea Grant’s Grason said, “because the landscape really influences how a given site will fare.” How quickly people must be able to detect crab populations in order to prevent the crabs from wrecking ecosystems remains an open question.

At this point, Grason said, “the only real answer we can offer is that we want to find these populations as early in their decline as possible.”