The European Green Crab....A New Invader
by Zasha Bassett
For hundreds of years humans have been introducing species from one ecosystem into another. These introductions often have devastating biological and economic effects. Now Oregon is being invaded by a new species, the European Green Crab, Carcinus maenas. SEI's Zasha Bassett has been studying the potential effects that this invasive species may have on the Oregon coast.
A native of Europe, the green crab has been widely introduced and has populations in Australia, South Africa and much of the Atlantic seaboard of the US. It was first introduced to the Pacific coast in San Francisco bay in 1989. Since then it has rapidly expanded northward to Bodega bay, Tomales Bay and Humbolt Bay in northern California. It was discovered in Coos bay, Oregon in 1996. Only a few green crabs have been captured in Coos bay since their discovery although hundreds of man hours have been spent searching for them. The individuals found in Coos bay have ranged in size from approximately 2-3 inches in shell width. At this point, it seems that the population in Coos bay is very low.
We do not know exactly how the crabs are being introduced, however, the ballast water from ships carrying larvae from the Atlantic or Japan seems the most likely. The subsequent spread of the population northward is probably the result of larvae riding along ocean currents or additional ballast water introductions.
The green crab is a highly adaptable invader species. It can tolerate a wide range of temperatures and salinities. They are grow quickly, produce large numbers of offspring and are voracious predators. It's diet includes a variety of animals and plants found in the Oregon intertidal and subtidal zones including: mussels, oysters, other crabs, small fish, insects and just about anything it can get its claws on. The green crab cannot tolerate the strong wave action of the open coast and will probably be confined to bays and estuaries.
The green crab may have substantial negative impacts on local commercial and recreational fisheries by preying on the young of valuable species (such as oysters and Dungeness crab) or competing with them for resources. The green crab preys voraciously on oysters. The green crab may prey on young Dungeness crab. The green crab is edible but picking out the small amount of meat is tedious and so the crab has little commercial value. We do not know yet if the green crab will become established in Oregon bays or whether the populations will become dense enough to present a serious problem, although it seems a strong possibility.
Zasha Bassett has been working with Drs. Sylvia Yamada and Gary Allison at Oregon State University to conduct extensive surveys of bays on the central Oregon coast. These surveys will provide important baseline information on the structure of the communities in the bays before the green crab invades. This will allow us to carefully observe any impacts the green crab invasion may bring and discuss possible solutions to the problem.
Zasha conducted a survey of three species of shore crabs, the Purple Shore Crab, Hemigrapsus nudus, the Mottled Shore Crab, Hemigrapsus oregonensis and the Red Rock Crab, Cancer productus in Siletz bay. She also surveyed other invertebrate species such as barnacles, mussels, snails and algae that might be affected if the green crab invades. Siletz bay is at the south end of Lincoln City, Oregon. The bay is a national wildlife refuge and is used for a variety of recreation purposes including clamming, crabbing, wildlife viewing and fishing. OSU students performed similar surveys on Yaquina bay which is south of Siletz bay.
The green crab is continuing to colonize of the Northwest Coast. For more information see the Federal Invasive Species Page and the Washington Department of Fish and Wildlife Green Crab Page.
© 2000 Sustainable Ecosystems