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“The Blob” Brings Invasive Crab to Puget Sound

Scientists think they know what brought invasive green crab into Washington’s inland waters last year.

May 5, 2017

Scientists think they know what brought invasive green crab into Washington’s inland waters last year.

In short: “the blob.” That was the temporary expanse of abnormally warm water off the West Coast from 2013 to late 2015.

Green crab have lived for years on the outer West Coast, particularly on western Vancouver Island. They never made it inland, however, past the cold water in the Strait of Juan de Fuca.

Scientists set traps out anyway, in case the invasive crab migrated.

A couple years ago the blob, on top of El Nino conditions, made way for warmer water that allowed green crab to thrive in the traditionally cold waters.

Emily Grason and Sean McDonald of the Washington Sea Grant Crab Team set traps on San Juan Island for invasive green crabs. Credit: Greg Davis/KCTS 9

Then, strong winds blew the water inland. That likely carried crab larvae, according to the study by researchers from Oregon State University and the Canadian government.

Now, volunteers are searching for green crab to stop the population from growing.

“When it gets very abundant that’s when we see impacts on native habitats. On the East Coast of the United States, the crab is blamed for damaging the softshell clam industry,” said Emily Grason, the program coordinator for Washington Sea Grant’s crab monitoring program.

They have found 26 green crab in the Salish Sea since August 2016. Most of them were by Dungeness Spit on the Olympic Peninsula.

“Fun fact is we do grow the largest green crabs in the world in our part of the country,” Grason said. “They still don’t get bigger than about the size of your fist, but they do get big enough to be predators of some of our smaller species of native crab.”

Green crab can damage local ecosystems by eating native oysters, clams, and tearing up eelgrass beds while searching for food.

Grason said the study sheds more light on crab behaviors. She said they can be tricky to find.

Green crabs in Freeport, Maine destroyed local salt marshes and eelgrass beds. Credit: Gabe Souza/Portland Press Herald.

“It is a green crab, but we also have a number of native crabs that are green, so color can be confusing more than helpful,” she said.

That’s why she said if people think they have found a green crab, snap a picture and send it to her — don’t pick it up.

With the blob gone, researcher Sylvia Behrens Yamada said she doesn’t predict more green crab will enter the Salish Sea any time soon.

The study was published in the Journal of Shellfish Research.


The first invasive European green crab that was found in Puget Sound was trapped on San Juan Island.

Greg Davis