- Prepared for the Aquatic Nuisance Species Project, Pacific States Marine Fisheries Commission.
- The recent invasion of Pacific Northwest estuaries by the European green crab, Carcinus maenas, caused much initial alarm. Following the last El Niño of 1997-98, a strong cohort of young green crabs appeared in estuaries along the coasts of Oregon, Washington, and as far north as Port Eliza on the west coast of Vancouver Island, British Columbia. Unusually strong northward-moving coastal currents (up to 50 km/day from September 1997 to April 1998) must have transported green crab larvae from more established source populations in California to the Northwest. Coastal transport events and recruitment of young green crabs have been much weaker in recent years.
It was hoped that green crabs would go extinct in the Pacific Northwest estuaries once the original colonists reached the end of their life span of 4-6 years and no new larvae arrived from California. This has not happened. Local recruitment has occurred most years since 1998. Recruitment strength is linked to winter temperatures: cold winters (2002) result in poor recruitment while warm winters (2003 and 2005), in good recruitment. As the 1998 year class dropped out of the population, it was replaced by the 2003 year class as the most dominant one. It was found it in the Coquille, Coos, Yaquina, Netarts Tillamook and Willapa Bay estuaries as well as on the northwest coast of Vancouver Island. Even though the 2003 year class was an order of magnitude less abundant than the 1998 one, it produced sufficient recruits in 2005 to maintain the Oregon and Washington satellite population.
There can be a substantial time lag between the discovery of an exotic species and its impact on the native community. For example, green crabs were documented to exist in New England in 1817, but it was not until the 1950’s when this species expanded its range and increased in abundance sufficiently to impact the soft-shelled clam populations in Massachusetts, Maine and Nova Scotia. Even though green crab abundance in the Pacific Northwest is low when compared to Europe, eastern North America, Tasmania and California, it is imperative to continue monitoring efforts for two reasons:
1) to elucidate the process of range expansion and population persistence of this model non-indigenous marine species with planktonic larvae and
2) to understand the role of ocean conditions on recruitment in order to predict the next strong recruitment event of green crabs.
Efforts to educate the general public, including boaters and shellfish growers, not to transport non-native Aquatic Nuisance Species from one area to another should continue to prevent the establishment of the green crab in the inland sea between Vancouver Island and the mainland, including Puget Sound and Hood Canal.
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