The European Green Crab, already blamed for wiping out the soft-shell clam industry on the U.S. East Coast in the early 1900s, was first detected on the West Coast in 1989 in San Francisco Bay.

November 6, 1998
Web posted at: 7:15 PM EDT

By Environmental News Network staff

(ENN) -- One invasive species benefiting from recent climate changes is the infamous green crab, according to Oregon State University biologist John Chapman.

The European Green Crab, already blamed for wiping out the soft-shell clam industry on the U.S. East Coast in the early 1900s, was first detected on the West Coast in 1989 in San Francisco Bay. Earlier this year it was disco vered in Willapa Bay -- to date more than 300 have been found in Willapa Bay and Grays Harbor. It poses a threat to clam, Dungeness crab and possibly even oyster populations.

But local and state governments have developed a plan to prevent the burgeoning green crab population from reaching reproductive levels, which the crab has yet to achieve, according to Scott Smith of the Washington State Department of Fish and Wildlife.

"It is safe to say this is not a large population at present, although if left unchecked it could become a viable population," said Smith. "We are trying to take a pro-active, preventative approach to control the population while it is at a low level."

Smith leads the recently formed zebra mussel and green crab task force, a group comprised of various government and private interests. The task force has divided into subcommittees to come up with recommendations for action, which will then be presented in a meeting scheduled for Nov. 20 in Olympia. A final preventative action plan will be given to the state legislature by Dec. 1.

In the meantime, Washington Gov. Gary Locke has allocated a $100,000 grant from the state's emergency fund to implement a monitoring and trapping program to keep the green crab population in check, a move Smith called a "great statement."

"The governor recognized this is an immediate need that couldn't wait until the task force reached it findings," he said.

Identifying the green crab is not difficult, thanks to its differences in appearance from native crabs. The small crab, not always green in color and identifiable by its V-shaped body and characteristic five spines behind the eyes, has qualities making it a perfect invasive species:

• high reproductive rate (female can lay up to 200,000 eggs per year)
• high dispersal potential
• rapid growth rate
• extremely broad habitat, temperature and salinity tolerances
• extremely broad diet

The green crab is omnivorous and opportunistic, able to survive on a wide range of foods: plants, insects, clams, oysters, worms, snails, mussels, citons, urchins, sea stars, other crabs and fish.

Yamada, in studying the dispersal of the green crab, has noted an unprecedented rate of distribution northward from San Francisco Bay, where it was likely introduced due to ballast water from an incoming ship.

Typical non-native species are able to expand their West Coast range by a maximum of 50 miles in 40 years. The green crab, sighted this past spring in Willapa Bay and Grays Harbor, covered some 700 miles in nine years. This startling northward march included a jump from Coos Bay in Oregon to Willapa Bay in one year.

Non-native species have numerous routes to aid in dispersal, among them ballast water on sea vessels, commercial shellfish transportation and ocean currents.

At present, government regulators have no mechanism in place to measure the success of laws that call for voluntary ballast water exchange by ships before they reach port to avoid chances of transporting non-native species. Smith cited the fact that the shipping industry has shown concern with the problem of biological pollution, but hopes that the industry will come up with its own standardized regulations to comply with state laws, rather than waiting until the state imposes regulations. "It is in the industry's best interest not to have different ports around the country having different regulations in place," he said.

But ocean currents and not commercial transport, according to Yamada, most likely caused the green crab's rapid northern expansion. Along the West Coast, ocean currents normally flow north in winter and south in summer. Last year, El Ni&241;o caused currents to flow north in September, culminating in seven to eight months of northward currents.

Yamada said the typical winter currents travel at a rate of 15 miles per day. Green crab larvae can remain ocean-bound in algae and plankton up to 80 days, giving them excellent chances to travel up to 1,200 miles during the larval stage.

"The crabs we have found in Willapa Bay and Grays Harbor are all from the same age class, suggesting they came here on the past winter's ocean currents," noted Smith.

Upon its arrival in estuaries in Washington State, the green crab has been shown to favor marshlands over traditional crab habitats such as rocky intertidal areas. Marshes with non-native grasses, such as spartina, are good indicators that green crabs may be present.

Studies on the East Coast in Maine and in Bodega Bay, Calif., have shown that native crabs are sometimes able to fight off the encroaching green crab. In Maine, green crab populations flourish, but to the south the crab has limited success, due to the competing native blue crab. In Bodega Bay, red rock crabs compete with green crab, forcing it out of traditional crab habitat.

But Smith says these studies have limited applicability in Washington, due to the green crab's adaptability and unique ecosystems. "Our area is too unique, with small, dynamic niches, to compare directly with other, out-of-state green crab habitats," said Smith. "Green crab has shown the ability to adapt differently to each new environment to which it is introduced. We have to come up with our own preventative measures to deal with green crab and other non-native species."

Reprinted with permission from Tidepool, News Source for the Rainforest Coast. Tidepool's mission is to provide regional news and information to the northwest coast to promote conservation-based decision making.

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