Unusual population explosion of the giant jellyfish Nemopilema nomurai (Scyphozoa: Rhizostomeae) in East Asian waters

摘要: A population explosion of the giant jellyfish Nemopilema nomurai (Scyphozoa: Rhizo- stomeae) occurred in Sea Japan 2002 and 2003, causing severe damage to fisheries. There was a further 2004, but on much smaller scale. In both years, young medusae began appear Tsushima Korea Strait July August, followed by north- ward expatriation Current northern Japan. We obtained scyphistomae this species artificial fertilization, reared them medusa stage laboratory. Asexual reproduction means podocyst formation. thermal increase from 13 23°C induced strobilation, liberation 3 7 ephyrae strobila. The developed metephyrae having complex canal system characteristically possessing long reddish purple filiform appendages. By 40 d post-liberation, had grown which central mouth closed been replaced numerous mouthlets oral wings scapulets. results laboratory-rearing experiments field investiga- tions were combined construct seasonal life cycle geographical distribution N. eastern Asian waters. Possible causes for mass occurrence nomurai, has tended be more frequent last decade, are discussed.