16 March 2015

Ocean Giants: Nomura's jellyfish

If the longest medusozoid is the lion's mane jellyfish, the heaviest would be Nomura's jellyfish. Scientifically known as Nemopilema nomurai, it is found endemic to the East Asian Marginal Seas - Bohai Sea, Yellow Sea and East China Sea [1]. The largest recorded species measured 2 m in bell diameter and weighed 200 kg [2].

Photo by Choi, Jong-Kwan taken in Korea.

Majestic as this species can be, fishers have found them troublesome. Since the early 2000s, jellyfish bloom has threatened the fisheries of Japan; instead of fishes, nets were full of this jellyfish. Studies conducted to determine the cause of the increasing frequency of jellyfish blooms in Japan revealed global warming and overfishing as the main factors [1, 3]. 

  1. Global warming: It appears that podocysts are carried out by the Tsushima Current from the Yellow Sea to the Sea of Japan. Exposure to higher temperatures triggers their development into medusa form. This explains why the bloom occurs only in Japan, not in China nor in Korea
  2. Overfishing: Note that both fish and jellyfish prey on zooplankton. Thus, excess fishing is advantageous to jellyfish because of decreased competition. Since there are fewer fishes, they can easily dominate the area where food is readily available.
Photo by Shin-ichi Uye, Hiroshima University, posted on BBC.

To know more about the biology of Nomura's jellyfish, visit SeaLifeBase.

If you have other information on them, which you wish to include in our information system, please e-mail us at sealifebase@fin.ph or join us as a collaborator.

[1] Uye, S (2008) Blooms of the giant jellyfish Nemopilema nomurai: a threat to the fisheries sustainability of the East Asian Marginal Seas. Plankton Benthos Res 3 (Suppl.):125-131.
[2] McClain, CR, et al (2015) Sizing ocean giants: patterns of intraspecific size variation in marine megafauna. PeerJ 2:e715. Accessed from https://peerj.com/articles/715/
[3] Kawahara, M, Ohtsu, K, Uye, S (2013) Bloom or non-bloom in the giant jellyfish Nemopilema nomurai (Scyphozoa: Rhizostomeae): roles of dormant podocysts. J. Plankton Res. 35(1):213-217.

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