ABSTRACT: Previous studies have shown a genetic interface (MPI, GPI loci) between 2 populations of the barnacle Semibalanus balanoides in the vicinity of the Miramichi Estuary, New Brunswick, in the Gulf of St. Lawrence. We examinedwhether gene flow between these 2 adjacent populations was restricted by larval dispersal. We determined the distribution pattern of Semibalanus balanoides planktonic larvae. Current velocity and direction, larval settlement and genetic structureof recruits were measured. Physical results and genotype distribution for MPI support the larval exchange hypothesis (north to south). The presence of another allele, GPI⁴, suggests a substantial contribution of anotherpopulation, possibly from the subtidal zone, to the larval pool. In accordance with previous studies, our results suggest strong selection on newly settled spat in the intertidal zone.