Periwinkle's progress: The Atlantic snail Littorina saxatilis (Mollusca: Gastropoda) establishes a colony on a Pacific shore

The common ovoviviparous and eurytopic Atlantic Ocean periwinkle Littorina (Neritrema) saxatilis (Olivi, 1792) has established reproducing populations in San Francisco Bay, California, USA. The first population was discovered in 1993. The probable mechanism of introduction into the Bay is the disposal of seaweeds (the brown algae Ascophyllum nodosum and Fucus vesiculosus) used as transport packing with polychaete worms used for fish bait. These worms, seaweed, and associated periwinkles originate from Maine. An alternative mechanism may be the similar disposal of seaweeds used as packing for imported Atlantic lobsters (Homarus americanus) for the restaurant trade. Littorina saxatilis could occupy a range on the Pacific American coast from Baja California to western Alaska, and as such it would come into direct contact with the consubgeneric Littorina (Neritrema) subrotundata (Carpenter, 1864) (synonym: Littorina newcombiana Hemphill, 1877) and Littorina (Neritrema) sitkana Philippi, 1846, which occur from southern Oregon and north. These latter two species occur in a range of morphological-physiological ecotypes that are closely analogous to those of Littorina saxatilis. Eradication of this snail invasion may be possible because the populations are easily accessed and relatively small. However, no tested eradication methods are known, nor are jurisdictional authority or regulatory issues clear relative to initiating potential removal of this species.