- The European green crab (Carcinus maenas) has a six-year life span and has persisted at
low densities in Oregon and Washington coastal estuaries since the late 1990’s. After the arrival
of a strong year class in 1998, significant recruitment to the Oregon and Washington
populations occurred only in 2003, 2005, 2006, 2010 and 2015. Warm winter water
temperatures, high Pacific Decadal Oscillation and Multivariate ENSO (El Niño Southern
Oscillation) Indices, weak southward shelf currents in March and April and a high abundance of
southern copepods are all correlated with strong year classes and vice versa (Behrens Yamada
Peterson and Kosro 2015). Right now, green crabs are still too rare to exert measurable effects
on the native benthic community and on shellfish culture in Oregon and Washington. However,
this could change if a high PDO and strong El Niño patterns were to persist. For example, green
crabs were first documented in New England in 1817, but it took warm ocean conditions during
the 1950’s for their numbers to build to a level at which they decimated the soft-shelled clam
industry in Maine.
The Department of Fisheries and Oceans, Canada found green crabs in all the major
inlets on the west coast of Vancouver Island and around Bella Bella on the Central Coast, but so
far none have been discovered in the inland sea between Vancouver Island and the mainland.
Therefore, outreach efforts should continue to prevent the establishment of this invader in these
inland waters via ballast water, shellfish transport or other human-mediated vectors.
Even though green crab abundance in Oregon and Washington is still low when
compared to Europe, eastern North America, Tasmania, California and the west coast of
Vancouver Island, it is imperative to continue monitoring efforts for two reasons:
1) to elucidate the process of range expansion and population persistence of this model nonindigenous
marine species with planktonic larvae, and
2) to predict the arrival of strong year classes from ocean conditions and alert managers and
shellfish growers of possible increases in predation pressure from this invader.