European Crab Poses Threat to West Coast Sea Life

Capable of wiping out natives, an alien intruder has been discovered as far south as California’s Central Coast, and if it hasn’t already invaded Southern California, it appears to be on its way.

Europe’s green crab--the most notorious invader of coasts around the world--can wreak ecological havoc, eating its way through marshes, harbors and bays where rare native birds and fish feed.

A fairly recent arrival on the West Coast, the green crab until now had not been found farther south than Monterey Bay. Two weeks ago, however, biologist Ted Grosholz of the UC Davis Department of Environmental Science found several of the crabs while collecting animal samples in Morro Bay--a discovery that surprised and dismayed scientists and environmental officials.

“It’s on the move south,” Grosholz said. “We hadn’t expected to find any in Morro Bay. The possibility is that it is already farther south.”

The green crab, originally a native of Europe’s North Atlantic waters, is one of the Nature Conservancy’s 12 least-wanted species in America, joining the zebra mussel and the brown tree snake on the list of foreign animals and plants that are most feared.

The crab “poses a great many risks to Southern California,” because it “can potentially lead to numerous cascading disruptions” of life in marine waters, said James Carlton, a marine scientist at Williams College in Massachusetts who is a leading expert on alien species.

The crab is such a new invader to the West Coast, Carlton added, that no one at this point can estimate the damage it has caused.

In a span of less than a decade, the green crab has migrated hundreds of miles up and down the West Coast, as its eggs are dispersed by ocean currents.

“We’re witnessing now, on the West Coast of North America, the greatest marine-range expansion for any species ever,” said Armand Kuris, a biologist at UC Santa Barbara who is researching biological techniques for controlling the green crab and other alien species.

“Within a few years, we’re seeing an expansion of green crab larvae coming out of the Golden Gate and sweeping north almost a thousand miles,” he said. “As a biologist, I’m very impressed with that.”

The green crab has such a huge appetite--it will eat virtually anything and lots of it--that it can decimate native creatures.

Clams, oysters, mussels and Dungeness crabs are some of its favorite fare. A single green crab can eat 40 small clams in a day and devour crabs its own size. Within three years of its arrival in Bodega Harbor, native clams and shore crabs showed “fivefold to tenfold declines,” according to a study by Grosholz.

“It is larger and more powerful than our shore crabs,” Kuris said. “None of our species has any defenses against that type of shell-cracking. Virtually all of our animals have no basic adaptation to resist being eaten like popcorn.”

So far there has been no documented damage to fisheries along the West Coast. But if the crab becomes as abundant as it has on the East Coast, it could imperil the $20-million annual shellfish harvest in Washington’s Puget Sound, or the oyster, clam and Dungeness crab industries in Northern California and Oregon.

In Southern California, the damage would be ecological, not economic, since the area has no significant shellfish industry.

The greatest danger involves rare coastal marshes at Bolsa Chica and Upper Newport Bay in Orange County, as well as estuaries in Ventura, Santa Barbara and San Diego counties. In those coastal areas, fish and endangered birds such as snowy plovers, terns and clapper rails are already facing great stress from urban development.

Alien species, estimated at about 6,000 in the United States, are considered to be among the leading threats to diversity of wildlife and vegetation, contributing to extinctions and disrupting multimillion-dollar fishing industries.

The fist-sized green crab may already have arrived in Southern California and escaped notice because few people are specifically looking for it. Most of the migration was expected northward, because of the predominant direction of currents in winter, when the crabs lay their eggs.

“I’m not surprised they’re moving south, but we had expected a very slow movement south,” said Kathy Hieb, a crustacean expert at the California Department of Fish and Game.

Although the discovery in Morro Bay is unwelcome news, Southern California may have some natural protection from an invasion because marine animals have difficulty rounding Point Conception, north of Santa Barbara.

“It’s not time to cry out that the wolf is at the door yet,” Kuris said. “But this is an eye-opener.”

Common in the North Atlantic, the crab arrived on the East Coast of the United States in the 1800s, probably as a stowaway in a ship’s ballast water.

It is now found throughout the Eastern Seaboard, and has contributed to the decimation of New England’s soft-shell clams and mussels. Fisheries have also been damaged in South Africa, Australia and Japan.

Along the West Coast, the green crab was first noticed in 1989 in San Francisco Bay, and it quickly moved north to Tomales and Humboldt bays and Coos Bay in Oregon.

When an exotic species takes hold, it is virtually impossible to stop its spread. The crab is especially prolific--a female lays up to 200,000 eggs at a time.

“Once the genie is out of the bottle, there are a limited number of options,” Grosholz said.

Perhaps the most effective, yet controversial, means of battling the crab would be to release a European parasite into California’s marine waters. Kuris’ team at UC Santa Barbara is studying the effect the foreign parasites--barnacles--might have on native crabs.

Unlike the crustaceans it feasts upon, the green crab is not a good source of seafood. Although tasty, it is a spindly creature with little meat.