NATIVE PREDATORS CONTRIBUTE TO INVASION RESISTANCE TO THE NON-INDIGENOUS BIVALVE MUSCULISTA-SENHOUSIA IN SOUTHERN CALIFORNIA, USA

As one component of invasion resistance, native predators may consume non-indigenous species in the invaded habitat. I studied the contribut ion of predation to mortality in populations of a potentially dominant , habitat-modifying mussel (Musculista senhousia) which has been intro duced from Asia to California. In short-term (2 to 4 wk) experiments p erformed in San Diego Bay, a muricid snail (Pteropurpura festiva) deci mated transplanted mussel populations by up to 65% within 2 wk. Crusta cean predators were responsible for mortality rates of <4 %. The exper imental removal of byssal cocoons in M, senhousia did not increase the susceptibility of the mussel to predation compared to unmanipulated i ndividuals. In all experiments, predation was more intense inside an e elgrass (Zostera marina) bed compared to either unvegetated clearings or to sand flats adjacent to the eelgrass bed. In a 4 mo predator excl usion experiment, mussel numbers were reduced by 95 % in the eelgrass compared to a decimation of only 36 and 50 % on the unvegetated sand f lat above and below the Z, marina bed, respectively. An aquarium exper iment revealed that P, festiva favored M. senhousia over an abundant n ative clam in San Diego Bay, Chione undatella. In southern California, predation contributes significantly to the resistance of the recipien t community to invasion and may locally prevent M. senhousia from esta blishing dense, habitat-modifying beds with potential effects on nativ e infauna and eelgrass.