According to this article from the Statesman Journal, researchers are finding more young European green crabs (Carcinus maenas) this year than ever before off the coast of Washington and Oregon. The crabs have been known in the area since the 1980s, but haven't garnered a lot of attention (translation: funding) because they were not causing significant problems. Now that evidence suggests there are well-established breeding populations, there is concern that a population explosion could be just over the horizon. The article notes that it took the green crab a century to become established on the east coast of the U.S. They certainly make up the majority of crab shells I have seen along Boston Harbor (G-R-E-E-N...G-R-E-E-N...).