OREGON STATE UNIVERSITY

Invading crabs pose serious concern, not chaos

05/08/1997

CORVALLIS - The European green crab that has arrived in Coos Bay has the potential to spread fairly rapidly up and down the Pacific Coast, experts say, but may not totally decimate marine ecosystems as some reports have suggested.

This unwanted crab species breeds and spreads rapidly, grows fast, eats almost anything, and has an unusually wide tolerance for variation in both water temperature and salinity, says Sylvia Yamada, an instructor of zoology at Oregon State University and expert on crab predation.

"There's little doubt this crab will spread and cause some problems, and there's not much we can do to stop that," Yamada said. "In some local cases the problems may be severe. But it's also true that other marine species will adapt and survive. Our native marine fauna will not be wiped out."

Yamada just completed a literature review of research on this invasive crab species, which is native to Europe and has been causing problems on the West Coast since showing up in San Francisco Bay in 1989.

Among the findings:

 

  • A female green crab can produce up to 200,000 eggs per year, and its planktonic larvae, in theory, can travel up to 400 miles in one generation on Pacific Ocean currents.

     

  • All bays, estuaries and inland seas from Baja California to Alaska may be habitat for the green crab - including Puget Sound - but it won't become abundant on wave-exposed portions of the coast.

     

  • The green crab is voracious, eating barnacles, clams, oysters, mussels, worms, urchins, young Dungeness or red rock crabs, some plants and small fish.

     

  • These crabs are smaller than native Dungeness and red rock crabs, but larger than other native crab species that can tolerate low salinity, such as the purple shore crab and hairy Oregon shore crab.

     

  • Because of its size, fast growth and low-salinity tolerance, the green crab will pose a special problem to commercial shellfish growers as it feeds on young oysters and clams. It may also disturb the ecosystem through its burrowing habits in soft sediments.

A picky eater? No. In lean times the green crab will make dinner out of 104 biological families, 18 genera, five plant and 14 animal phyla. If it's alive, it's lunch.

But in spite of this list of predatory accomplishments, Yamada said the green crab will probably become just another predatory crab species within the marine ecosystem.

"For one thing, it's important to remember that the European green crab will not only be a predator, it will also be a prey," she said. "Especially when young, it will be eaten by other native crabs, fish, otters, seals, the great blue heron, ducks, gulls and other birds. And maybe humans."

The green crab also can't take waves very well - it will confine itself largely to inland waters of one type or another.

"It's very difficult to predict exactly how a new species will establish itself in a given situation," Yamada said. "It will take time for the green crab to build up breeding populations as it spreads, and it will be preyed upon by many other marine species."

If the green crab does form dense enough populations, Yamada said, we can expect some reduction in clam harvests, decrease in the survival of young oysters, an evolutionary "natural selection" for shellfish with thicker shells, a displacement of native species such as the hairy Oregon shore crab from some of their habitats, and a decrease in the survival of young Dungeness crabs.

Silver linings are hard to come by with this crab species. It might make decent fish bait, and in theory it can be eaten - the green crab is harvested and eaten by people in Portugal, Spain, France and England. But due to its small size it won't compare favorably to a succulent Dungeness crab.

"It's very unfortunate this species has arrived," Yamada said. "In all likelihood we'll just have to learn to live with it. And that's exactly what the other marine species will do."