AbstractThe coastline of the Korean Peninsula is influenced by three major oceanographic ecoregions, including the estuarine Yellow Sea ecoregion on the west coast, the warmer and saline East China Sea ecoregion on the south coast, and the cold East Sea ecoregion on the east coast. The influence of these marine ecoregions on the distribution of intertidal barnacles has not been extensively studied. The present study examines the biogeography of thoracican barnacles from intertidal and shallow subtidal zones, along the coasts of Korea. Twenty-one species in seven families were identified, including three species of coral-associated barnacles. Species composition varied significantly in the three marine ecoregions. Multivariate analysis showed barnacle assemblages were significant among the three ecoregions, although there are large overlaps of clusters between the Yellow Sea and East China Sea ecoregions. The estuarine species,Fistulobalanus albicostatus, occurred mainly in the Yellow Sea ecoregion; warm-water species,Tetraclita japonica, and sponge inhabiting barnaclesEuacasta dofleiniwere observed in the East China Sea ecoregion; and cold-water species,Balanus rostratusandPerforatus perforatus, were found in the East Sea ecoregion. Four invasive barnacle species were recorded and the European barnaclePerforatus perforatusexpanded its range northward from its recorded distribution nine years earlier. The cold-water species,Chthamalus dalliandSemibalanus cariosus, previously recorded in the East Sea ecoregion, were absent in the present survey. A trend of increasing seawater temperatures in Korean waters may have a significant impact on the distribution of cold-water species and enhance the northward invasion ofP.perforatus.