外来種と同定の問題

抄録

Numerous alien species have been reported in Japanese waters in recent years, but identifications of these species are difficult in most cases. In the Ariake Inland Sea, two new alien gastropods were found in 2000. One of them is Nassarius (Zeuxis) sinarus (Philippi, 1851) from China. This carnivorous species has recently increased explosively in number and has become a pest, eating fish caught in traps. This problem has spread rapidly over wide regions of the Ariake Inland Sea, with goby fisheries using traps in the central and western parts of Saga Prefecture suffering most. Unfortunately, this species was initially misidentified as the endangered species Mitrella martensi (Lischke, 1871). The other alien gastropod species is Stenothyra sp. from Korea. It is an undescribed species in spite of being an alien and had never before been reported from Korea. This case shows that alien species include not only ones that are abundant in their original distribution range, but also unrecognized ones. Several other taxonomic problems posed by alien species are reviewed. Most alien species in Japan have at first been misidentified and/or confused with other species. One of the most important measures to prevent such confusion is the adequate preparation of specimens. Because alien species often appear suddenly, we can not know their origin immediately. If enough specimens are preserved, exact identification may be made through subsequent study. In this connection, alpha-taxonomy will become ever more significant from now on. Comprehensive revisional works for many taxa will be needed in order to identify the alien species.