Morphological and Geographical Features of Two Alien Barnacles that were Recently Introduced into Northern Japan

Abstract

Balanus grandula and Perforatus perforatus, two alien barnacles, have very recently extended their geographical ranges into northern Japan, part of the Far East. B. glandula is a cold water species inhabiting Alaska and Baja California, and P. perforatus is a warm water species living in coastal areas in the Mediterranean and the eastern Atlantic ranging from south-west Wales through West Africa. At the time of their discovery, the two species were already in high densities and dominant species in littoral and infralittoral zones in northern Japan. B. glandula and P. perforatus have extended their geographical distribution into north-eastern Hokkaido and the Pacific side of north-eastern Honshu respectively. Although barnacles are one of the most important marine fouling organisms, only little public attention is being given to these creatures. Therefore, this paper intends to provide morphological and geographical information about the two new alien species so that it will lead to a greater understanding of the present state of their invasions in Japan.