ABSTRACT The non native Mediterranean mussel Mytilus galloprovincialis is broadly established in the northeast Pacific. Until recently, the coast north of Humboldt Bay, California, USA, was not considered a major zone of sympatry and hybridization with the native sibling species M. trossulus. However, M. galloprovincialis has been introduced in Washington, USA, and British Columbia, Canada. for aquaculture, has been collected from ballast water in-bound to Oregon, USA, and is now ...