Weird Creatures: Nomura’s Jellyfish (Nemopilema nomurai)

nomuras-jellyfish

“Of all ocean species, jellyfish are among the least studied by scientists, in part because of their lack of obvious utility to humans, and in part because of the specific challenges of working with them,” Kalee Thompson writes in “Attack of the Jellies” in the January 2008 issue of Popular Science. Nomura’s jellyfish (Nemopilema nomurai) may become an exception, but not because of its massive size and hauntingly beautiful appearance. Economics is a more likely prod to curiosity, for from 2002 to 2007 the inexplicably large blooms of this giant jellyfish resulted in such severe damage to Asian fisheries each autumn and winter that the nations of Japan, China, and Korea convened meetings to address the problem. Just as inexplicably, 2008 saw a massive falloff in the number of Nomura’s jellyfish, with less than 200 sightings as of November 2008 versus about 6,300 in 2007.

“Information on the biology and ecology of N. nomurai is extremely scarce due to the difficulties in sampling and rearing this giant jellyfish as well as its restricted distribution area,” write Hye Eun Lee, Won Duk Yoon, and Donghyun Lim in their article “Description of Feeding Apparatus and Mechanism in Nemopilema nomurai Kishinouye (Scyphozoa: Rhizostomeae)” in the March 2008 issue of Ocean Science Journal. However, several N. nomurai studies have been published in the past three years, and what is known about this gigantic cnidarian is enough to make it more than worthy of inclusion in the Weird Creatures category of this cabinet of curiosities.

The first recorded appearance of Nemopilema nomurai was in Korea in 1814. It resides primarily in the northern East China Sea, Yellow Sea, and Bohai Sea, but as mentioned above it has been moving northward in large numbers into the Sea of Japan. It’s a truly massive creature, capable of growing to a bell diameter or body width of 6’6” (2 meters) and a weight of nearly 450 pounds (200 kilograms), making it one of the largest jellyfish in the world.

Despite its size, N. nomurai’s sting is very rarely lethal. Symptoms are cutaneous (red skin, small blisters), but do include “very intense pain” and a “strong burning sensation,” as described by “Stings of Edible Jellyfish (Rhopilema hispidum, Rhopilema esculentum and Nemopilema nomurai) in Japanese Waters” by Masato Kawahara et al. It’s also edible, but though Japanese fishermen have tried to make a sushi of necessity, N. nomurai hasn’t really caught on, primarily because, as Kawahara writes, “it does not have the preferred crunchy texture.”

As for N. nomurai’s own diet, it may appear large enough to eat a human or jellyfish whole, but it actually eats only small-sized zooplankton, mostly small crustaceans called copepods. As Lee et al. write, an adult N. nomurai, or medusa, has eight oral arms and lacks a central mouth. To eat, it has “developed complicated canal systems connecting the tip of the tentacle and oral arm to the gut cavity… The prey is gathered by paralyzing nematocyst at the tentacles and by adhering cirri at the oral arms and scapulets. They are engulfed into the terminal pore located at the oral arms and scapulets, and entered into the gut cavity via the canal system. The estimated digestion time is 1 hour and 20 min. The diameter of terminal pore is always about 1 mm, implying that they could not eat prey larger than that pore size.” However, young medusae, or ephyrae, do have central mouths, and “could swallow prey as large as adults could.” During the ephyra stage, N. nomurai’s daily growth rate is as high as 15% of its own weight, according to research conducted by Shin-ichi Uye.

Several speculative causes have been given for the 2002 to 2007 Nomura’s jellyfish scourge which resulted in poisoned fish, broken fishing nets, and stung fishermen, and reduced incomes by as much as 80% in some fishing-dependent communities. Potential causes include global warming, overfishing and a resultant niche for invasive jellyfish, and eutrophic or nutrient-rich water flowing into Chinese seas. But last year’s disappearing act—and the lack of Nemopilema nomurai-related research—makes any such speculation difficult. Will Fall 2009 see The Return of the Giant Jellyfish? Only N. nomurai knows for sure…

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