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 15°C, 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 Acartia omorii density, but does not markedly affect the smaller copepod Oithona davisae, which remains abundant throughout the year.
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M. Omori (1995) studied this question.