The role of biotic interactions in juvenile mortality of the cockle (Cerastoderma edule L.): Field observations and experiment

Recurrent drastic mortalities of juveniles in a population of the edible cockle, Cerastoderma edule, from Western Brittany, prompted a study of the role of biotic interactions. A predation hypothesis was tested through a field experiment using exclosure cages, in parallel with field observations of the natural population. Over 1 month, the juvenile mortality rate outside of the cages was more than 40%. Selective predation on juveniles below 11 mm in length was responsible for more than 85% of this mortality. Juveniles of the green crab, Carcinus maenas, were recognized as the most important predators of the young cockles. Intraspecific competition did not influence survival or growth of the cockle spat, despite the relatively high density of the experimental population i.e. more than 800 individuals.m(-2).