Green crab invaders settle in on Dungeness Spit, Olympic Peninsula

An invasion of the European green crab, which started last summer in northern Puget Sound, appears to be continuing this spring with 16 green crabs caught in traps at one location on Dungeness Spit near Sequim.

European green crab
Photo: Gregory C. Jensen, UW

The new findings are not entirely unexpected, given that invasive green crabs have established a viable population in Sooke Inlet at the southern end of Vancouver Island in Canada. From there, young crab larvae can move with the currents until they settle and grow into adult crabs. Last summer and fall, green crabs were found on San Juan Island and in Padilla Bay.

The big concern now is that a growing population of invasive crabs could spread quickly to other parts of Puget Sound, causing damage to commercial shellfish beds and disrupting the Puget Sound ecosystem.

“It knocks the wind out of your sails for sure,” said Emily Grason when I asked how she felt about the latest discovery. “You feel kind of powerless, and you want to get out there and start doing things.”

European green crabs were found on Graveyard Spit, the small spit that juts off the main Dungeness Spit. Google maps

Emily, a biologist with Washington Sea Grant, coordinates a group of trained volunteers known as the Crab Team. These folks place crab traps in dozens of locations where habitat is suitable for green crab survival. When invasive crabs are found, the volunteers put out many more traps in hopes of reducing the population before it grows out of control.

The hope is that invasions can be found early so that the extensive trapping makes it more difficult for the limited number of crabs to locate suitable mates and continue to expand the population. Each female can lay up to a million eggs at a time, and they are not limited to just one or two broods each year.

Officials with Washington Sea Grant are not only dealing with foreboding feelings about the green crab invasion but also concerns that the Crab Team may be shut down for lack of funding. At the federal level, President Trump has proposed eliminating the entire Sea Grant program nationwide, halting research and various types of assistance for marine projects across the country.

“We don’t like to think about a world where we have to stop this program in midstream,” said Kate Litle, assistant director of programs at Washington Sea Grant, “but that’s what will happen if we don’t get funding.”

At the same time, the state’s Aquatic Invasive Species Program may also have little or no money to battle the green crabs. Program officials requested increased funding from this year’s Legislature to support the Crab Team as well as address invasive zebra and quagga mussels. The budget proposed by the state Senate contains the full funding — including a portion of utility tax revenues that currently go into the state’s general fund. The House budget for the program includes a new fee on nonresident watercraft, but the amount of revenue is relatively small.

“If we lose the Sea Grant early detection program, we are going to be in a world of hurt,” said Allen Pleus, coordinator of the Aquatic Invasive Species Program at the Washington Department of Fish and Wildlife. Allen said it would be hard to get along without the trained Crab Team volunteers, who provide the first line of defense for all of Puget Sound.

Emily said she has about 150 volunteers putting out crab traps in every part of Puget Sound, and the number may grow. After last year’s discovery of green crabs in northern Puget Sound, officials from tribes have stepped up to help along with staff from state and federal agencies.

Trapping begins in April and continues into September if the funding holds up. So far this year, traps placed in Padilla Bay — where four crabs were caught last year — have come up empty, Emily said. That’s a good sign, she said, “but we definitely have a different story at Dungeness Spit.” To review last year’s findings, see Water Ways, Oct. 1, 2016.

Unlike Padilla Bay, where the four crabs were few and far between, the 17 crabs caught at Dungeness Spit were all in the same location. Of the first four crabs caught on April 13, two were caught in the same trap on Graveyard Spit, a small spit that juts out from the main Dungeness Spit.

More traps were placed in that general area — up to 52 traps at one time. Three more crabs were caught on April 18, then five more on April 19, one on April 20, and then three more yesterday, along with a discarded shell.

“If we can trap them down to make it harder for the males and females to find each other, that is the best we can do,” Allen told me.

The trapping at Dungeness Spit is being done with staff and volunteers from the U.S. Fish and Wildlife Service, which oversees the Dungeness National Wildlife Refuge.

Anyone can look for green crabs and help control their spread while visiting salt marshes and shallow pocket estuaries. People are asked to leave all crabs in place and follow the instructions to email a photograph of a suspect crab to the Crab Team. For identifying information, visit the Crab Team website.

7 thoughts on “Green crab invaders settle in on Dungeness Spit, Olympic Peninsula

  1. I hate to say it but trapping Green Crabs cannot possibly affect the spread of the crabs. Consider that one pair of crabs can result in the release of four million eggs a year which are then spread by ocean currents. Even a survival rate of 1% will lead to exponential increase in the crab population until some equilibrium value is reached resulting from water conditions and the interaction with other biological variables; e.g., predators. As far as I know, no aquatic invasive species has ever been eradicated once it shows up. Documenting their spread and effect on marine food webs is worth while, however.

    Remember the big hoo-ha about invasive salps, I think it was? There’s still a small funded team doing some dock cleaning or something of the sort, but the scare at least has disappeared but the overall effects on the ecology of our inshore waters of these and other marine invasives don’t appear to have been investigated.

    San Francisco Bay is a good analog for the increasing number of invasive species in Puget Sound and their possible effects.

    1. Thanks for your thoughts, Herb. You’re absolutely correct that we face an uphill battle, but I disagree that trapping can have no effect. As you point out, the connectedness of marine systems makes control much more difficult than in more isolated freshwater or terrestrial environments, but I would argue that there are examples of successes, and that we currently have the best chance for successful control that we are ever going to get. Previous efforts in California (Sea Drift Lagoon) have demonstrated that when green crab populations are isolated, as this one appears to be, trapping can reduce the population to very low numbers. True, it’s labor intensive, but that’s not the same as saying it’s impossible, only that it’s a matter of how much resources people are willing to devote. The challenge in California is that because control wasn’t done early in the invasion, green crab are everywhere, and even though they could be locally eradicated from a lagoon, the water was awash with larvae from nearby areas, so new crabs just got washed back into the lagoon. Here, we have a different situation. We currently have infrequent larval dispersal and isolated populations. If we can locally eradicate crabs, it’s less likely that they would become immediately reinfested. San Francisco Bay is instructive, particularly in what happens when you don’t intervene until crabs are too abundant to control.

      With respect to successes, I’d argue that the challenges faced with respect to marine invasions are in part because, as mentioned earlier, marine systems are trickier to control, but also because historically, less attention has been paid to marine invasives as a management issue. There are very few examples of any monitoring or eradication efforts period! But there are successes. California’s work with the seaweed Caulerpa demonstrates that the early detection and rapid response model can work even in coastal systems. It’s often not a one shot deal, i.e. the potential of invasion will always be present here, so we will likely always have to be on the lookout for this crab. But early detection and even rapid response costs a whole lot less than trapping crabs when they are extremely abundant. And if, down the line, we were to see the impacts on species like Dungeness crab or eelgrass, our only recourse would be to trap green crab,anyway. Trapping now, when there are fewer, is preferable to trapping later when it will inevitably cost more and have less impact on the population.

      That said, you’re exactly right that we might not be able to keep green crab out entirely and forever. But we definitely will fail to do so if we let our best chance to intervene slip by. Nevertheless, even if we only managed to slow the course of the invasion, we benefit local shoreline economies and native ecological communities by buying them time to adapt.

  2. I don’t understand the last paragraph. Why leave one alone after finding it? Recording where you killed it instead would seem to make more sense.

    1. Bill,

      The basic idea is that green crabs are difficult for the average person to identify, and they are still quite rare, even in infested areas. If people were advised to kill crabs that they think are invasive, it could lead to the waste of a lot of native crabs.

      Experts on this topic may wish to weigh in.

      1. Hi Bill,

        Yes, it’s definitely counterintuitive to have to leave the crab in place, when our goal is to make sure we snuff out populations as soon as the pop up. The concern is based on more than a decade of experience by WDFW and other groups in public outreach on this species. In previous efforts, the public was asked to freeze any suspected green crab and mail them to WDFW. However, it turns out correctly identifying this species is just tricky enough, that misidentification caused the death of many native species. That is, many people mistook native crabs for European green crab, and froze them. Our recent experience in triaging suspected sitings confirms this. No correct identifications of European green crab have been confirmed in this way. We have a number of small native crabs that are green, that are confused with green crab. In an effort to avoid defeating the purpose of eliminating green crab by accidentally killing a lot of native crabs, we’re asking people send photos to and leave the crab in place.

        It’s a good reminder that it’s not legal to “take” (including kill on site) any crab (or other aquatic species) without a permit, either a recreational crabbing permit for Dungies and rock crabs, or a scientific collection permit for any other species. European green crab is a prohibited species in the state of Washington, so “take” without a dedicated Aquatic Invasive Species permit is not legal.

        However if you find a molted shell of a suspected European green crab, you can definitely remove that from the beach, and contact us. Molts are sometimes a way that green crab are found before they are found live, so looking in the wrackline at crab shells can be a great way to help out with early detection, even if you aren’t a Crab Team volunteer.

        We realize that it could feel uncomfortable to walk away from a suspected live green crab, but much of what I do is reassure people who believe they have found green crab that their beach actually has a healthy population of native spider crabs or helmet crabs!

  3. I did a little research. On the east coast they have been trying to deal with the green crab problem for some time. An article that is two years old indicated that when boiled they make a great seafood broth. Instead of requiring a permit to take them, make it open season on them like they did when the Atlantic salmon were released into local waters from the pens. Then tell everyone how delicious they are and how to cook them.

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