The competitive and predatory impacts of the nonindigenous crab Carcinus maenas (L.) on early benthic phase Dungeness crab Cancer magister Dana

We evaluate the potential competitive and predatory impacts of nonindigenou s European green crab Carcinus maenas on native Dungeness crab Cancer magis ter in the northeast Pacific. The coastal estuaries of Washington State, US A, provide appropriate habitat fur recently introduced green crab, yet thes e areas are important nursery grounds for Dungeness crab and contribute gre atly to the coastal crab fishery. Juvenile Dungeness crabs are dependent on limited intertidal epibenthic shell for refuge habitat during early benthi c life and experience increased mortality on open sand and mud as a result of predation by fish and birds, Early juveniles throughout the subtidal are similarly at risk due to predation by fish and especially adult conspecifi cs. Laboratory experiments and infrared video observations revealed that ju venile green crab displace Dungeness crab of equal size from shelters durin g one-on-one competition. Green crab also consistently win nocturnal foragi ng trials in which the species compete for fresh, damaged clams. Field and laboratory enclosure experiments show that juvenile Dungeness crab emigrate from oyster shell habitat as a result of competition and predation by adul t green crab, Depending on the extent to which the two species overlap, int eractions with the dominant nonindigenous species could have a negative inf luence on juvenile Dungeness crab survival and could conceivably impact rec ruitment to the fishery. However, current evidence indicates that the distr ibution of green crab in Washington State is far removed from nursery areas of Dungeness crab. (C) 2001 Elsevier Science B.V. All rights reserved.