2003 Fiscal Year Final Research Report Summary
Studies on jellyfish blooming in marine coastal waters : mechanisms for the population increase and technical development for the countermeasures
| Project/Area Number |
13480158
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| Research Category |
Grant-in-Aid for Scientific Research (B)
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| Allocation Type | Single-year Grants |
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| Section | 一般 |
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| Research Field |
Environmental dynamic analysis
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| Research Institution | HIROSHIMA UNIVERSITY |
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Principal Investigator |
UYE Shin-ichi Hiroshima University, Graduate School of Biosphere Sciences, Professor, 大学院・生物圏科学研究科, 教授 (80116540)
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| Co-Investigator(Kenkyū-buntansha) |
ISHII Haruto Tokyo University of Marine Science and Technology, Faculty of Marine Science, Research Associate, 海洋科学部, 助手 (30251680)
NAGANUMA Takeshi Hiroshima University, Graduate School of Biosphere Sciences, Associate, 大学院・生物圏科学研究科, 助教授 (70263738)
TAKEOKA Hidetaka Ehime Univesity, Center for Marine Environmental Studies, Professor, 沿岸環境科学研究センター, 教授 (90116947)
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| Project Period (FY) |
2001 – 2003
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| Keywords | Jellyfish / Mass occurrence / Ecological impact / Marine costal environment / Nuisance of jellyfish / Decomposition of jellyfish / The Inland Sea of Japan / Tokyo Bay |
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| Research Abstract |
The moon jelly Aurelia aurita is one of the most common schyphomedusae in the world's coastal waters, and the population of this species is highly speculated to have been increasing for the last decades. In the Inland Sea of Japan, the increase of this species occurred intensively in the last 10 years, due probably to the combination of the following factors:
1) increase in food supply for the jellyfish owing to eutrophication or the modification of nutrient supply
2) elevation of water temperature in the winter to allow the population overwintering
3) increase in the polyp attachment area owing to the modification of the water front and construction
4) decrease in planktivorous fish stock size owing to overfishing.
The technique to monitor the Aurelia aurita population has been established using composite airphotographs from a Cessna and groundtruthed net surveys. The monitoring in the Uwa Sea for 4 years (2000-2003) reveals that the total jellyfish biomass varies more than one order magnitude year to year, although the causes for such annual difference are not known. According to fishermen, the nuisance of jellyfish aggregation is very severe in the Inland Sea of Japan.
By measuring the respiration, feeding and growth rates of Aurelia aurita, the ecological impact of the jellyfish upon the zooplankton populations has been estimated. The daily feeding pressure ranges from a few % to several hundreds % of the zooplankton biomass, depending on the density of the medusae.
One of the countermeasures is to decompose the medusae using jellyfish decomposing bacteria. Several bacterial strains which are effective to the decomposition have been isolated from the Inland Sea of Japan. A preliminary test plant for the decomposition of Aurelia aurita has been established.
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