INTRODUCTION, DISPERSAL AND POTENTIAL IMPACTS OF THE GREEN CRAB CARCINUS-MAENAS IN SAN-FRANCISCO BAY, CALIFORNIA

The North Atlantic portunid crab Carcinus maenas (Linnaeus, 1758) has invaded the North Pacific Ocean following more than two centuries of g lobal dispersal due to human activities. C. maenas was first collected in San Francisco Bay, California, in 1989-1990, where its distributio n and prey selectivity were investigated in 1992-1994. It has become a bundant in shallow, warm lagoons (which as favorable and retentive mic rohabitats may have served as invasion incubators) and spread througho ut the north, central and south bays. It may have arrived in ballast w ater, on fouled ships, amongst algae with imported live bait or lobste rs, or by intentional release; genetic comparisons of the Bay populati on with possible source populations may aid in defining the transport mechanism. C. maenas' eurytopic nature, its high breeding potential, a nd its diet and feeding behavior suggest the potential for extensive e cosystem alterations through predator-prey interactions, competition, disturbance, and indirect effects. Although both negative economic imp acts through reduction or disruption of fisheries and positive impacts of providing bait and human-food fisheries have been documented in a few regions, the potential economic impacts in San Francisco Bay remai n largely unknown.