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General Session 4: Marine environment, ecosystem & sustainability |
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Point-of-no-return in ephyrae of the moon jellyfish Aurelia aurita s.l.
GS4-46
Zhilu Fu* , School of Marine Science and Biotechology, Guangxi University for Nationalities
Shibata Masashi, Fisheries Research Agency, Japan
Ryosuke Makabe, Ishinomaki Senshu University, Japan
Shin-ichi Uye, Hiroshima University, Japan
Presenter Email: fzl19@163.com
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| The moon jelly Aurelia aurita s.l. is the most common scyphozoan jellyfish in the coastal waters around the world, and the mass occurrences of this species have been reported from various regions. The size of medusa population can be determined by two factors: 1) the initial number of ephyrae and 2) their survivorship before recruitment to the medusa stage. The latter has been reported to be <1% in the natural population in Tokyo Bay. Both food availability and predation have been argued to be responsible for the survival of first-feeding larvae of marine animals such as fish. The point-of-no-return (PNR), at which the animals would die even if they feed, has been investigated to evaluate the starvation resistance. We measured the PNR in A. aurita ephyrae at 3 different temperatures (i.e. 15, 12 and 9oC), which they may experience in the field. The ephyrae were extraordinarily starvation resistant as manifested by their extremely long time in reaching 50% PNR (PNR50), i.e. 33.8, 38.4 and 58.6 days at 15, 12 and 9oC, respectively, almost one order of magnitude longer than that in fish larvae. We also examined the decrease of carbon and nitrogen contents of ephyrae during starvation, and found that an ephyra around PNR50 lost ca. 50% of their initial contents. Our results indicate that starvation may not be the primary factor for ephyral mortality, but other factors such as predation may also be responsible. |
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