Echizen jellyfish (English spelling) Nemopilema nomurai

Japanese: エチゼンクラゲ - えちぜんくらげ（英語表記）Nemopilema nomurai

With an umbrella measuring up to 2 meters and weighing up to 200 kilograms, this is one of the largest jellyfish in the world. It is classified as a member of the Nomura's genus of Echizen's jellyfish, family Rhizomedusa, family Polymorpha. In 1922, Dr. Kishigami Kamakichi, a fisheries biology researcher at Tokyo Imperial University, named a specimen collected in Takahama, Fukui Prefecture, as a new species. Mass outbreaks occurred in 1958 and 1995, but since 2002 they have occurred almost every year, causing serious damage to the fishing industry.
The homeland of the Nomura's jellyfish is the coastal areas of the Bohai Sea, Yellow Sea, and northern East China Sea, which are surrounded by mainland China and the Korean Peninsula. Larvae hatch from fertilized eggs attach to rocks in winter and develop into polyps about 2 mm in size. In early summer the following year, as the water temperature rises, jellyfish emerge from the polyps and are carried by the Tsushima Current to the Sea of Japan. In autumn, some of the jellyfish pass through the Tsugaru Strait and escape to the Pacific Ocean, reaching the Boso Peninsula, and die in the winter in the waters near Japan.
In 2009, the jellyfish traveled as far south as the Kii Peninsula, tearing fishing nets, injuring fish caught in them, and causing boats to capsize due to the weight of the nets, causing damage to spread to 20 prefectures. As a result, the National Federation of Fisheries Cooperative Associations requested the national government to provide income compensation for the decline in catches and to increase the financial burden of extermination work.
The extermination method involves two fishing boats dragging a net into the sea to cut up the jellyfish. Other extermination experiments are also being conducted using the black scraper, a natural enemy of the jellyfish.
The causes of the increase in the number of Nomura's jellyfish are thought to be the rise in seawater temperature due to global warming, which makes it easier for jellyfish to grow, the increase in zooplankton, which is the food of Nomura's jellyfish, due to the eutrophication of seawater caused by industrialization of the coastal areas of China, and the decrease in the number of small and large juvenile fish due to overfishing, which reduces the number of competitors to eat the same food. In October 2005, the Enoshima Aquarium in Kanagawa Prefecture became the first in the world to successfully breed Nomura's jellyfish in an aquarium. Professor Shinichi Ue of the Graduate School of Biosphere Science, Hiroshima University, has also begun development of new technology to predict and control the occurrence of jellyfish. Attempts are also underway to make effective use of Nomura's jellyfish as a "fishery resource," such as for food such as dried jellyfish and ice cream, medicine for arthritis, and fertilizer for desert greening.

(Yuka Shimamura, columnist / 2009)

Source : "Chiezo" published by Asahi Shimbun Publications Co., Ltd. About Chiezo

Japanese:

傘が2メートル、重さが200キロにも及ぶ世界最大級のクラゲ。分類は根口クラゲ目ビゼンクラゲ科エチゼンクラゲ属エチゼンクラゲ。1922年、東京帝国大学の水産生物研究者、岸上鎌吉博士が福井県高浜町で採集された標本を新種として命名した。58年、95年にも大量発生したが、2002年からはほぼ毎年大量発生し、漁業に深刻な被害を与えている。
エチゼンクラゲの故郷は、中国本土と朝鮮半島に囲まれた渤海、黄海、北部東シナ海沿岸部。受精卵からかえった幼生が冬に岩場につき、2ミリほどのポリプになる。翌年初夏、水温上昇でポリプからクラゲが発生、対馬海流に乗って日本海に運ばれる。秋に一部のクラゲが津軽海峡を通過して太平洋側へ抜け、房総半島に達し、冬に日本近海で死滅する。
09年には、クラゲが紀伊半島まで南下して、魚網を破る、網の中の魚を傷つける、網にかかった重みで船が転覆するなど、20道府県に被害が拡大したため、全国漁業協同組合連合会は、水揚げ高減少への所得補償や駆除作業の費用負担の拡大などを国へ要望した。
駆除方法は2隻の漁船が網を海中に入れて引き回し、クラゲを切断するなど。他にも天敵のウマヅラハギを使った駆除実験が行われている。
エチゼンクラゲ増加の原因としては、地球温暖化の影響で海水温が上がり、クラゲが育ちやすくなったことや、中国沿岸部の工業化で、海水が富栄養化して餌の動物プランクトンが増えたこと、乱獲による小魚や大型魚の稚魚の減少で同じ餌を食べる競争相手が減ったことなどが推測されている。05年10月、神奈川県にある新江ノ島水族館が、世界初のエチゼンクラゲの水槽内での繁殖に成功。広島大学大学院生物圏科学研究科の上真一教授を中心に、クラゲの発生予測や制御の新技術開発も始まった。なお、干しクラゲやアイスクリームなどの食料、関節症の治療薬、砂漠緑化のための肥料など、エチゼンクラゲを「水産資源」として有効活用する試みも進んでいる。

(島村由花　コラムニスト／ 2009年)

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