Life history strategy of Aurelia aurita (Cnidaria, Scyphomedusae) and its impact on the zooplankton community of Tokyo Bay

Abstract

The life history of the common jellyfish Aurelia aurita in Tokyo Bay was investigated by monthly sampling over a 32-month period from May 1990 to December 1992. Young medusae of 3 cm diameter occur from April. Growth was rapid. Some specimens of this cohort reach 25 cm and spawn by July/August and then decrease in size or die. Others reach a maximal size of >20 cm by October, when spawning takes place. A considerable number of mature individuals remain after spawning the next year and decrease in size. Release of ephyrae seems to be induced by a lowering of environmental temperature to below 15C with peak release occurring in December/ February. A drop in temperature may be the cue for strobilation in the bay. Preliminary analysis of predation rate indicates that in summer A. aurita may lead to a sharp decrease in Acartiu omorii density, but does not markedly affect the smaller copepod Oithona duvisae, which remains abundant throughout the year.