Broad scale patterns of genetic structure in coastal communities are strongly affected by both ecological transitions and larval dispersal. Along the Chilean coast, we examined 2 species of co-distributed barnacles, Jehlius cirratus and Notochthamalus scabrosus, which span an ecological transition associated with a sharp increase in larval recruitment. A distinct break in haplotype frequencies in the mitochondrial cytochrome oxidase I (mtCOI) gene was detected in N. scabrosus, with only marginal genetic structure observed in J. cirratus, suggesting significant differences in either selective pressures or dispersal ability between the species. The nuclear gene elongation factor la was also analyzed in N. scabrosus, and similarly suggested limited gene flow. The sharp genetic transition is downstream of the described ecological transition, effectively mirroring a genetic cline described in a different barnacle species along the North American Pacific coast.