Invasive European Green Crab Threatens West Coast Ecosystems

The European green crab, a small but vicious predator, has been making its presence known on the West Coast of North America and wreaking havoc on native ecosystems. Native to the coastlines of Europe and northern Africa, the green crab has spread to coastlines around the world, from Australia to South Africa, and now to the western United States. With alarming impact, these predators have been nicknamed “cockroaches of the sea”. Having reached Alaska, they may pose a new threat to salmon populations.

“I worry about the salmonids,” says Tammy Davis, Invasive Species Program coordinator at the Alaska Dept. of Fish & Game (ADF&G). “I don’t have any evidence that they are competing for food at certain life stages, but the green crabs tear up the eelgrass that provides vital habitat for juvenile salmon and their prey, and in an already stressed ecosystem, having another stressor can affect the whole food web.”

“In Southeast Alaska, we have an estimated 19,000 miles of coastline and much of it is suitable habitat for green crabs.” She adds that many of the islands and passages of the Southeast archipelago have estuaries with eelgrass meadows protected from heavy surf, providing food and protection for green crabs.

The European green crab is believed to have arrived in North America in the mid-1800s, transported in the ballast water of ships or clinging to the hulls of boats. It took decades for the species to make its way up the coast from the Atlantic to the Pacific, where it was first documented in California in the 1980s. Since then, it has steadily spread northward, reaching Oregon, Washington, and now Alaska.

The crab’s ability to thrive in diverse environments has enabled rapid expansion. Green crab tolerate a wide range of briny waters and temperatures, allowing them to colonize new habitats. Their prolific reproduction rate (each female crab can produce up to 200,000 eggs per year) further accelerates the spread.

Linda Shaw, a wildlife biologist with the National Oceanic and Atmospheric Administration in Alaska, reported that the Metlakatla Indian Community identified three invasive green crab shells on July 19, 2022. The discovery occurred during a survey of the Annette Islands Reserve, raising concerns about the presence of this non-native species in the region. “We did some immediate trapping,” said Shaw. “Based on the carapace sizes, we estimate that they had been there for at least two years.”

In August 2024, following the discovery of invasive green crabs in Bostwick Inlet, the Alaska Department of Fish and Game (ADF&G) launched an extensive trapping operation as part of its Early Detection and Rapid Response Plan. Multiple ADF&G teams deployed over 100 traps throughout the inlet to contain the invasive species. After eight days of intensive efforts, the teams successfully removed 33 green crabs of varying age classes, marking a significant step in managing the potential ecological threat.

“In Alaska, we’re at the leading edge of green crab spread,” says Davis. “We have large remote areas to try to monitor, with limited capacity. Thankfully, we have lots of partners who care and are engaged. Collectively, we operate under the umbrella of the Alaska Invasive Species Partnership (AKISP). Key partners are Kachemak Bay National Estuarine Research Reserve, Metlakatla Indian Community and numerous Alaska Native tribal entities, Prince William Sound Regional Citizens’ Advisory Council, local communities, and others.”

Davis reported that the AKISP European green crab monitoring network is actively overseeing nearly 60 sites across Alaska, stretching from Southeast Alaska to the Aleutian Islands. With limited monitoring resources, Davis and her team are analyzing currents and habitat types to anticipate where the green crab may next try to colonize.

European green crabs are not just adaptable; they’re aggressive. They can feed on a wide variety of prey, including clams, mussels, small fish, and young crustaceans. This diet allows them to quickly adapt and exploit new ecosystems, which makes their presence such a risk.

One of the biggest threats posed by the green crab is their destruction of eelgrass beds and other critical marine habitats. Eelgrass provides a nursery habitat for many marine species, including salmon and Dungeness crab. Green crab uproot eelgrass as they search for food, which leads to erosion and poor water quality. As they spread, the green crab disrupt sensitive habitats, impacting species that rely on them for shelter and breeding grounds.

In Alaska, there is growing concern over the potential impact on the state’s fragile salmon industry. Young salmon use coastal habitats as nurseries, and the introduction of green crab could threaten juvenile salmon by reducing available food sources or by directly preying on them. This could potentially lead to a decline in salmon populations, impacting both the ecosystem and the vital fishing industry in Alaska.

Efforts to manage and control green crab populations are costly and challenging. Trapping, which is often labor-intensive and expensive, is one of the most common methods for reducing green crab numbers. However, without consistent management, green crab populations quickly bounce back, making long-term eradication difficult. Washington state has invested millions of dollars in trapping efforts, but the crabs’ ability to reproduce quickly and adapt creates a challenge.

West Coast states have ramped up efforts to monitor and manage this invasive species. Partnerships between state and federal agencies, Native American tribes, and local communities are essential. Programs like Washington’s Crab Team, a citizen science and student initiative, work with local communities to monitor and detect green crabs early and limit their spread.

The European green crab invasion highlights the vulnerability of coastal ecosystems to invasive species and the complex challenges of managing them. For the West Coast, proactive efforts to curb the spread of the green crab are crucial to protect native species, local fisheries, and the balance of the ecosystem.