Horizontal distribution and growth of jellyfish, Aurelia aurita (Linnaeus 1758) sensu lato, in Mikawa Bay, Japan

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Proceedings of the Horiba International Conference "New Direction of Ocean Research in the Western Pacific" : Past, Present and Future of UNESCO/IOC/WESTPAC Activity for 50 years and the JSPS Project "Coastal Marine Science"Section I: Research Articles/BiodiversityWe investigated the occurrence, growth, and horizontal distribution of the moon jelly, Aurelia aurita sensu lato, in Mikawa Bay from April 2007 to November 2008. In May and August 2007, dense populations of adults occurred in the bay mouth. After August, larger individuals with no planula larvae had involuted bells. In March 2008, adults were highly abundant in the western part of the bay. Small-sized moon jellies were observed from March to June, and dense swarms of adults and semi-adults shifted from the western part to the eastern part of the bay from spring to summer. In August 2008, very few adults were observed, and all were damaged or involuted without planula larvae. After August, no adults were observed. The estimated biomass of the Aurelia medusa in Mikawa Bay was much higher than that of the preceding reports. Therefore, the growth of the Aurelia medusae population in Mikawa Bay was comparable to previous observations. A life cycle model of Aurelia medusae that explains the spatio-temporal distribution of young and adult medusae and the appearance of sessile polyps in Mikawa Bay is discussed.