Survivorship of Aurelia aurita throughout their life cycle in Tokyo Bay [Japan]
2005
Ishii, H.(Tokyo Univ. of Marine Science and Technology (Japan)) | Ogawa, C.
The present paper describes the survivorship of Aurelia aurita throughout their life cycle, from fertilized egg to adult, in Tokyo Bay. Most of individuals will be dead during planktonic planula stage, however, survival rate during this stage has not been calculated correctly because of the lack of the data for polyp density in natural waters. Researches relating population dynamics during polyp stage were conducted to artificial populations on settling plates, not to natural populations. In polyp stage, asexual reproductions are usually observed, and higher survivorship is observed in polyp settled during autumn, It is considered that decreasing the survivorship in polyp stage is caused by invasion and growth of other sessile organisms, and increasing the survivorship after autumn is caused by decrease of their activity. It suggests that the occurrence of ripe medusae with planula larvae after autumn contributes to the success of growth and asexual reproduction during polyp satage. Survivorship of ephyra metamorphosing into young medusae compared to the number of newly liberated ephyrae by polyp strobilation is under 1%. The present paper emphasizes that studies of population dynamics in natural settling polyps are desired to know the whole survivorship and system for mass occurrence of A. aurita in coastal waters.
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