science environment

Green Crab Invaders Show Up in Puget Sound

By Ashley Ahearn (KUOW/EarthFix)
Seattle Sept. 6, 2016 11:30 p.m.
The first documented green crab in Puget Sound was found in Westcott Bay on San Juan Island just before Labor Day.

The first documented green crab in Puget Sound was found in Westcott Bay on San Juan Island just before Labor Day.

Washington Sea Grant/Sean McDonald

Sean McDonald's heart sank when he got the text last week.

"I was shocked and dismayed," said the University of Washington shellfish and crab expert, "I was really hoping that we'd have more time."

Citizen scientists volunteering with the Washington Sea Grant had found an adult male green crab on a routine sampling trip to San Juan Island's Westcott Bay.

The crabs were first documented on the west coast in the late 1980s but this is their first appearance in Puget Sound. Their populations have been rising on the East Coast for decades, "wreaking havoc" on the ecosystem, McDonald said. The crabs eat pretty much everything they encounter — clams, snails, worms, seaweeds, grasses — and they burrow into the marsh, eroding banks and destroying habitat.

The problem got so bad that managers on the East Coast put a bounty on the green crab to encourage people to catch them and kill them.

Volunteers have been on the look out for the crab at 27 sites in Washington. It's taken ten years for the invaders to make their way from Washington's outer coast to Puget Sound. The population of green crabs in California and Oregon has been growing steadily since the first one was spotted in San Francisco in 1989.

Shellfish growers have devised ways to put nets around growing mollusks to protect them from the invaders but the rest of the ecosystem is not so lucky.

"Many of the species haven't had a chance to evolve defenses to this predator," McDonald said. "You may not be concerned about snails or worms but they're prey for birds, salmon and other aspects of the ecosystem we care about."

Green crabs are smaller than the Dungeness and rock crabs that are common to the Northwest, but they are hardy creatures that can endure a broader range of water temperatures.

Another difference: green crabs don't taste particularly good. There have been some attempts to market them as a delicacy in Europe and on the East Coast but with little success.


Green crabs have been established on the East Coast for more than 100 years. They had plenty of time for the population to aggressively expand before anyone took notice. McDonald says the good news is that if managers in the Northwest continue monitoring and put trapping programs in place they may be able to get out in front of the problem and prevent the population from booming.

For more information check out the crab team website and if you think you've found a green crab take a photo and send it to:

The team will be hosting an informational meeting at UW Friday Harbor Labs on San Juan Island Tues. Sept. 13, 7 p.m.