Giant Venomous Jellyfish Undergoing Population Boom Terrifies the Internet

A striking image of a gargantuan jellyfish next to a woman's foot for scale has gone viral on Reddit. The jellyfish is pictured lying on its side on the sand, and is a dark pink and brown, almost like a brain with tentacles coated in Jell-O.

According to user Alesig, he took the photo on a beach near Incheon in South Korea in 2008, but has never seen anything as big before or since.

"[It was] maybe 1-1.5m [3.2 to 4.9ft] across. Hard to tell. It was dead and squashed up a bit," Alesig told Newsweek. "I've never seen anything like it since."

Commenters reacted in horror, with one saying: "Some countries were just never meant for beaches and swimming."

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The jellyfish photographed by Reddit user Alesig in South Korea in 2008, with a human foot pictured for scale. Thought to be a Nomura’s jellyfish, there are currently huge population blooms off the coast of South Korea. u/Alesig

"I fear no man, but that thing—it scares me," said another.

According to many of the other comments under the Reddit post, the huge creature may be a Nomura's jellyfish. Gill Mapstone, a jellyfish expert and Scientific Associate at London's Natural History Museum, agrees.

"The giant Nemopilema nomurai [Nomura's jellyfish] is a rhizostome jelly, and as such does not have any marginal tentacles around the bell. This, together with the fact that it was imaged in South Korea, does make it seem the most likely species," she told Newsweek.

Nomura's jellyfish is a very large species of rhizostome jellyfish, nearly as big as the lion's mane jellyfish, which is the largest in the world.

"It can have a bell diameter of 2 m [6.6 feet] and weigh up to 200 kg [440 lbs]," Mapstone said.

These behemoths are usually found in the East China Sea and Yellow Sea. Their long tentacles contain venom that can cause itching, swelling, acute pain, and in some cases, even death.

"The sting is generally non-lethal and the pain very intense for about half an hour and then eases off, but a few deaths have been reported from China," said Mapstone.

Unlike many notable species, Nomura's jellyfish numbers are actually growing, with population blooms appearing to be increasing in frequency. The number of Nomura's jellyfish off the coast of South Korea has reached the point where the government has issued a warning advising beach-goers of the dangers of being stung.

As reported by the Korea Times, up to 10 jellyfish per 100 square-meter [around 1,000 square foot] area were spotted in waters off South Gyeongsang Province as of July 19.

The current bloom in Korean waters is expected to be handled using ships that will use nets and pumps to suck jellyfish from the ocean.

These increased population blooms, which historically only occurred once every 40 years and now occur nearly every year, may be a result of climate change.

According to research published in the journal Plankton & Benthos Research in 2007, the year before the viral photo was taken, increased water temperature, eutrophication (the gradual increase in the concentration of phosphorus, nitrogen, and other plant nutrients in an aging aquatic ecosystem), coastal modification and over-fishing in Chinese coastal waters may be responsible for the increased blooms.

As sea temperatures are increasing at an average rate of 0.1 degree Celsius per decade, in the 15 years since that paper was published, it is likely that the effects of increased water temperatures on bloom frequency have only accelerated.