California Sea Grant College Program

Marine species invasions pose serious ecological and economic threats to coastal areas throughout the world. The mechanisms by which invasive species are introduced to a new habitat are generally well understood, and frequently involve release of invasive larvae or adults in ballast water. However, we currently have little knowledge concerning the physiological characteristics of an invasive species that allow it to succeed, following its introduction. What characteristics of an invader enable it to succeed and, in some cases, to out-compete and replace a closely related native species? We examined the physiological basis of invasive success by comparing two congeneric bay mussels found along the coast of Central California. Mytilus trossulus is a native bay mussel that formerly occurred along the Pacific Coast of the United States from Mexico to Canada. At some point in the early to middle decades of the past century, a second species of bay mussel, M. galloprovincialis, was introduced into Southern California waters. Since its introduction, this invasive species has replaced the native species from the Mexican border to the approximate latitude of Monterey Bay. Between Monterey Bay and areas just to the north of San Francisco Bay, the two species coexist in what is termed a “mosaic hybrid zone.” In this zone, one can find the native and the invasive species and their hybrids.