California Sea Grant College Program

Since their first sighting in the San Francisco Bay in 1989, European green crabs (Carcinus maenas) have undergone what can truly be called a population explosion. In 11 years, they have spread south to Morro Bay and north to British Columbia, Canada. Untold millions now live under rocks in mud-bottomed areas of the state’s estuaries. Although they have not yet become established on the outer shoreline--perhaps because they cannot tolerate heavy wave action--some biologists believe it is just a matter of time before they spread to the coast.