Relationships between presence or absence of non-indigenous copepods and ballast water at some international ports in Japan

Abstract

Marine non-indigenous, invasive organisms have been directly or indirectly causing serious problems for human societies. East-Asian planktonic and benthic organisms have been expanding their distributions around the world due to ships. Since Japan has been pointed out to be one of the main exporters of ballast water, it might be a candidate for a major donor of some taxa. In contrast Japan has hitherto received no alien zooplankters via ballast water from other countries. We examined copepod faunae at some international ports in Japan (Kawasaki, Nagoya, Osaka, Kobe, Sakaide, Mizushima, Tamano, Kitakyushu) to confirm if or not alien species have been introduced and become established in consideration of the relationships between export and import volumes in foreign trade unique to each. Take-in of ballast water at these ports in 2005 is estimated to have ranged from 208 to 926 thousand tons, while take-out was much more, ranging from 801, 20,689 thousand tons. In spite of the different structures in international trade at these ports no alien copepod have been discovered from these areas. This finding doesn't necessarily mean that there have been no alien zooplankton invasions, because intensive international trades among East Asian countries may have guaranteed cryptic introduction of copepods having a broad distribution in these waters. Possible factors for non-establishment of alien copepods at these ports are presumed on the basis of the present and previous data.