59 巻 (2004) p. 45-57
There is an increasing public concern about the introduction of marine organisms, and shipping is perceived to be responsible for many unwanted introductions into Japanese waters. A total of 25 unintentionally introduced marine species has been reported in Japanese waters, comprising Annelida (two spp.), Mollusca (10 spp.), Arthropoda (nine spp.), and Chordata (two spp.) among animal taxa, and Phaeophyta (one sp.) and Chlorophyta (one sp.) among marine algae. It is estimated that 68% of these introduced species were introduced via visiting ships. Two main mechanisms, ballast water and hull fouling, are considered responsible for the dispersal of marine organisms worldwide via shipping. The relative importance of these mechanisms for the dispersal of marine organisms differs among nations and regions as a consequence of their trading patterns. Since large amounts of ballast water are discharged at ports exporting dry bulk commodities, ballast water can be considered a relatively important mechanism for introductions in such places (e.g., Australia or San Francisco Bay), whereas hull fouling might be more important in regions that import bulk commodities (e.g., Hawaii or Japan). This study estimates that hull fouling is responsible for 44% of the introduced marine species in Japan. The importance of sea chests as an alternative mechanism for transporting marine organisms around the world has only recently been recognized, and a mechanism may have been responsible for introducing the clam Mercenaria mercenaria, spider crab Pyromaia tuberculata, green crab Carcinus aestuarii, and blue crab Callinectes sapidus to Japan. To prevent the introduction of unwanted marine organisms into Japan by hull fouling, not only are advances in effective and nontoxic anti-fouling paint technology required, but also increases in the frequency of vessel dockings to inspect and clean the hulls. Furthermore, since large volumes of ballast water are exported from the Japanese coasts to many overseas regions, the Japanese government should establish regulations and develon treetment technology to minimize the unintentional export of marine organisms via ballast water.