2004 Fiscal Year Final Research Report Summary
Influences of the Jellyfish Bloom of Aurelia aurita upon Plankton Production including Fish Larvae
| Project/Area Number |
14560162
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| Research Category |
Grant-in-Aid for Scientific Research (C)
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| Allocation Type | Single-year Grants |
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| Section | 一般 |
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| Research Field |
General fisheries
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| Research Institution | Nihon University |
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Principal Investigator |
HIROMI Juro Nihon University, College of Bioresource Sciences, Professor, 生物資源科学部, 教授 (30112923)
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| Co-Investigator(Kenkyū-buntansha) |
ARA Koitchi Nihon University, College of Bioresource Sciences, Lecturer, 生物資源科学部, 講師 (40318382)
NISHIDA Shuhei Tokyo University, Ocean Research Institute, 海洋研究所, 教授 (70134658)
INAGAKI Tadashi Tokyo University, Ocean Research Institute, Assistant Professor, 海洋研究所, 助手 (00151572)
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| Project Period (FY) |
2002 – 2004
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| Keywords | Aurelia aurita / Jellyfish bloom / feeding / competition / medusivorous fishes / Oithona davisae / microbial food chain / diatoms |
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| Research Abstract |
Aim of the present study is to quantify the impact of massive occurrence of a jellyfish, Aurelia aurita on plankton community including fish eggs and larvae. In the case of Tokyo Bay, one of the most eutrophicated embayment in Japan, average abundance of A.aurita was 0.32 ind./m3. Estimated feeding rates of the A.aurita population ranged between 0.7 and 7 mg C/m3/day. The feeding impact of the average abundance of A.aurita population on the zooplankton assenmblages is not so significant because the production rates of a copepod, Oithona davisae which was the most dominant zooplankton were estimated to be ca. 100 mg C/m3/day. However, when the abundance of A.aurita exceeds 1 ind./m3, which density was frequently found during spring and summer, the population feeding is calculated to correspond to >10% of the daily production of zooplankton.
Although planktivorous fishes compete with jellyfish for zooplankton, jellyfish may surpass the planktivourous fishes considering that these fishes are day light feeder in a contrast to jellyfish that feeds from morning to night.
The most representative zooplankton, Oithona davisae ingest no diatoms which are usually the most dominant phytoplankton. Microbial food chain is also developed by the increase of bacteria which was caused by abundant DOC released into seawater from dead diatoms, and then the energy that previously went into production of fishes may be switched over to the production of jellyfish via bacteria-HNF-ciliates-micro copepod (Oithona davisae).
When the jellyfish food chain is developed, medusivorous fishes such as filefish and harvest fish are expected to increase, however, eutrophication of embayment will be accelerated by huge regeneration of nutrients via microbes and jellyfish itself.
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