An ecological study of Aurelia aurila (Cnidaria, Scyphozoa) polyps with special reference to mass occurrence of medusae

Abstract

Recent studies of Aurelia aurita polyps using settling plates are reviewed. In particular, population dynamics of polyps under natural conditions were investigated by observing of the continuous changes in the number of polyps on settling plates in Tokyo Bay for one year. The rapid decrease in the survivorship of newly settled polyps was considered to be the result of the invasion and growth of other benthic organisms such as Mytilus galloprovincialis. The decrease of such competition in autumn enabled the polyps to survive and increase their abundance by budding. We suggest that most liberated ephyrae originate from the polyps that settled in autumn, and the presence of ripe medusae with planula larvae in autumn should contribute to a mass occurrence of meduse in the following year.