Nomura's Jellyfish

Dec 8

Nemopilema nomurai

Nomura's jellyfish is among the largest jellyfish species in the world — measuring up to 2 metres (6.6 ft) in diameter and weighing up to 200 kg (440 lb). Starting out as small as a grain of rice, it can grow this large in less than a year.

The waters between China, Korea, and Japan are shallow and calm. The Yellow and East China Seas, and the Sea of Japan have been fished for decades by human civilizations who've long relied on their bounties to survive. They were once home to swarms of tuna and mackerel, dolphins and sharks, multiple species of sea turtles, squid, shellfish, and sea urchins. But these once-rich fishing waters — exploited close to breaking point, nowadays much diminished — have become clogged with a gelatinous plague.

Below the surface, a legion of brainless behemoths drift placidly, dominating the entire water column. Their translucent, bell-like bodies pulse and ripple with the currents. The largest of them is wider than a human is tall, with a bell measuring 2 metres (6.6 ft) across, and behind each monster streams a tangle of murderous, voracious tentacles that can stretch over 6 metres (20 feet) long. A single titan, soaking wet — indeed, mostly (95%) water — can weigh as much as 200 kg (440 lb). And there are thousands of them.

This parade of animate goop is a bloom of Nomura's jellyfish; a horde of some of the largest jellyfish on the planet and, possibly, an apocalyptic glimpse at the future of our oceans.

Humble Beginnings

Each of these colossi were once a microscopic speck, adrift in the sea. With jellyfish, it's difficult to pinpoint when an individual's life begins or ends, for the stages of its lifecycle are many and varied.

The tiny, free-swimming speck, called a planula, has had enough of open water after about a week, and finds a spot to settle; attaching itself to a surface and becoming a white, dome-shaped thing called a scyphistoma. In this immobile, polyp form, it pumps out what are known as podocysts — small polyps that will develop into genetically identical copies of itself. Essentially, it becomes a cloning factory; able to produce up to 18 versions of itself, that will subsequently settle down, grow, and do the same.

After budding off its clones, it transitions to its next life stage; the strobila. This stage too is devoted to reproduction, but in a different form. Atop the sessile strobila grows a stack of larval jellyfish called ephyra. These ephyra, each about the size of a rice grain, are released into the water column. They disperse with the currents, gorging themselves on microscopic plankton with tiny mouths less than a millimetre (0.03 in) in diameter. After 40 to 50 days, if they survive, they develop into young medusae — what we would call jellyfish.

Jellyfish Giants

This jellyfish's growing process, from grain-of-rice to two-metre-giant, takes less than a year. Its bell bulges, its tentacles elongate — shaped like a grotesque chandelier — but, curiously, its millimetre-mouth has not grown with the rest of its body. Its appetite, however, has. So, to compensate, it simply grows more mouths. Like some Eldritch being, its mass of whirling tentacles are teeming with tiny mouths, all snatching at tiny planktonic particles. Fortunately, minuscule as the mouths are, they cannot eat anything much larger, not even small fish.

Nomura's jellyfish may not be capable of eating anything large, but it can still kill. If anyone knows anything about jellyfish, it's that they sting, and this giant is no exception. Smaller animals, like agile fish, actually fare better against the jellyfish, as they're able to weave and dodge between the lethal barbs — using the jellyfish's tentacles as a deadly hideaway from predators. But for larger creatures, getting tangled in a blanket of stinging tentacles is a painful way to go.

Envenomations from this species can cause an itching, swelling rash, accompanied by acute pain — same as many other jellyfish stings — but, in severe cases, the complex mix of toxins delivered through its barbs can lead to shock or even death. A study found 13 toxin-like proteins in this jellyfish's venom, some similar to those in venomous snakes, spiders and bees, and it seems that these multiple toxins work in concert to deliver a killing stroke. Since 2006, at least 11 deaths from Nomura's jellyfish have been reported in China and Korea. This tally is only likely to increase as seas warm and more jellyfish burst forth in massive blooms.

Suffocating Blooms

Prior to this last century, Nomura's jellyfish have predominantly inhabited the East China and Yellow Seas. They were not abundant in the waters around Japan — every week, fishermen would find one, maybe two, medusae in their nets. Then, in 1920, the fishermen hauled up their nets and found them congested with these giant jellies, catching as many as 1,500 every day. The same thing happened in 1958, 1995, 2002, 2003, 2005, and 2006; with increasing frequency as time passed.

For near-inanimate, brainless blobs, that are made up of 95% water, jellyfish can wreak a lot of havoc. Fishing equipment is damaged, nets are clogged, fish in the nets are made unsellable, and both wild, as well as farmed fish populations are devastated. The last bloom in 2009 caused some $89.6 million in damage to the industry in Japan. A bloom of Nomura's jellyfish even capsized and sank a 10-ton fishing boat off Japan's eastern coast when fishermen tried to haul up a too-heavy net packed full of these giants. When they bloom, these jellyfish all but cripple the fishing industry.

It's tempting to see this as the oceans getting their revenge on humans for our mistreatment of them — for we have mistreated them, overfished them, polluted them, and changed their chemical compositions. It's as if the oceans are saying "No more!"; sending forth this army of endless blobs to overwhelm us, sting us, and sink our boats. But, depressingly, these blooms might just be another symptom of our actions. In a way, jellyfish blooms vividly symbolise our own destructive impact on the planet. They look like so many plastic bags, strewn throughout the water, suffocating the oceans. And their proliferation is, at least in some part, thanks to us.

Jellyfish are extremely adaptable — largely because of their simplicity — and changes in temperature, acidity, salinity, or light levels, don't much bother them.¹ To quote wildlife biologist Juliet Lamb, "They combine plantlike simplicity, animal-like mobility, and an almost bacterial ability to reproduce rapidly under favorable conditions." Even direct persecution by people may only increase jelly populations. For instance, the Nomura's jellyfish is a hermaphrodite, with both male and female reproductive organs, allowing it to produce and self-fertilize thousands of eggs, which it releases into the water column. When one of these giants is killed, it spews forth thousands of its progeny, which turn into larvae that swim away to be fruitful and multiply.

So while other animals struggle to adapt to the changes that we inflict upon them and the oceans — warming due to climate change, acidification due to more CO2 dissolving into the ocean, oxygen depletion due to nutrient dumping from agriculture and industry (creating “dead zones"), as well as overhunting — many jellyfish continue to thrive. In fact, certain conditions, such as warmer waters and eutrophication (an excess of nutrients in the water), actually aid the reproduction, the proliferation, of jellyfish. And the disappearance of other ocean life — such as swordfish, sunfish, and leatherback turtles — only means fewer predators for the jellies.

The jellies themselves, in overabundance, can themselves have a harmful impact on other ocean life. They disrupt entire pelagic foodwebs, with each giant jelly swallowing an Olympic-sized swimming pool of planktonic water daily, leaving little prey for other animals. They change the balance of properties in the water (carbon, nitrogen, phosphorus), thus affecting microbial communities as well. It becomes a grim cycle; we create conditions less favourable for most ocean animals and more favourable for jellyfish, and the jellyfish exacerbate those conditions further.

A Jellyfish Future?

*Chuka kurage*; a Japanese side dish made from jellyfish.

With so many jellyfish swarming the oceans and clogging up our fishing nets, we might as well do something with them. Japan has long included all types of sea life in its cuisine, from toxic pufferfish (fugu) to cod fish testicles (shirako). Jellyfish is also on the menu in a dish known as chuka kurage, or seasoned jellyfish — a kind of side dish and drinking snack. China too has a similar dish of "jellyfish salad". Unfortunately, Nomura's jellyfish isn't the most palatable, and the echizen kurage made from it is considered to be of low quality, inferior to kurage made from smaller jellyfish. And if a crunchy-slimy bowlful of jellyfish isn't to your taste, Japan has also invented an ice cream infused with the exquisite taste of jellyfish. Medical uses for Nomura's jellyfish are currently being investigated — one study found an "aqueous extract" with potential for treating inflammatory disorders. As a last resort, these jellies could theoretically be reconstituted to fertilizer, albeit, probably not the most effective one.

But is this what we have to look forward to? Are our future oceans going to become giant breeding tanks for jelly monocultures? Optimistically, probably not. While it's likely that many human activities contribute to increases in jellyfish populations in coastal waters, there isn't sufficient evidence to declare that we're the main cause behind the blooms. Another quote from Juliet Lamb; "Jellyfish are notoriously difficult to study, blooming unexpectedly in inaccessible corners of the sea. The data that were available suggested a more complicated story, in which jellyfish blooms occur in waves that coincide with natural fluctuations in the environment. While there was a slight upward trend of blooms in recent years, that increase was within the normal range of variability. The group didn’t reject the jellyfish-climate link, but they suggested that there might be other explanations for the increase in jellyfish abundance".

An annual jellyfish bloom in Deep Cove, North Vancouver, Canada.

One potential explanation is that humans are increasingly present throughout the oceans and, as such, encounter more of these jellyfish blooms. This also leads to more coverage in the media, stoking the fear of a man-made "jelly apocalypse". But, with the evidence currently at hand, there doesn't appear to be a clear link between human actions and an increase in jellyfish blooms. In any case, casting all jellyfish in this villainous role, as zombie hoards that degrade ocean ecosystems, is also misleading. There are some ten thousand species of jellyfish ², and only a few of them have been involved in damaging blooms. Most species cause no harm — and so we don't hear about them — while many others are elusive and little known, and other jellies still are actually on the decline, suffering along with much of the rest of ocean life.

¹ Relating to jellyfish resilience, there was a recent study, published in 2020, that found genetic adaptation in jellyfish which "allow them to control their bodily salt concentration at the molecular level, allowing them to move vertically and horizontally to catch food without being affected by changing ocean salinity levels".

Clockwise from top left; a lion's mane jellyfish (Cyanea capillata), an Irukandji box jellyfish (*Malo* spp.), spores of a parasitic myxocoan jellyfish (*Kudoa iwatai*), and a Portuguese man o' war (*Physalia physalis*).

² Jellyfish don't comprise a neat taxonomic grouping. They are instead spread throughout several groups within the phylum Cnidaria (which also includes animals such as sea anemones and corals). And their free-floating medusae forms — the forms we think of when we think of jellyfish — are typically just one life stage of many.

They range from giants like Nomura's jellyfish and the lion's mane jellyfish — the largest in the world, with a record size of 36.5 meters (120 ft) from the top of its bell to the tips of its tentacles. To the Irukandji box jellyfish, with an adult size of 1 cubic centimetre (about the size of a sugar cube), that belies its ability to kill a human with its venom. To microscopic, parasitic myxozoan jellyfish that live inside fish and cause "whirling disease". To strange colonial creatures like the wind-sailing Portuguese man o' war, which may look like singular animals, but are actually bunches of tiny, cooperating, co-dependent organisms.

All of these, we call jellyfish. In a way, jellies are defined by what they lack; they have no fins, no teeth nor bones, no blood and no brains. Everything of substance takes up only 5% of their bodies, the other 95% being water. They are organisms stripped down to the barest essentials of capturing, consuming, and using energy.

**Where Does It Live?**

⛰️ Ocean depths between 0 - 176 metres (0 - 577 ft).
📍 The Yellow and East China Seas, and the Sea of Japan.

Size // Large
Length // Up to 6 metres (20 feet)
Weight // Up to 200 kg (440 lb)
Activity: N/A
Lifestyle: N/A
Lifespan: N/A
Diet: Carnivore
Favorite Food: Plankton 𓇼
Phylum: Cnidaria
Class: Scyphozoa
Order: Rhizostomeae
Family: Rhizostomatidae
Genus: Nemopilema
Species: N. nomurai

Nomura's jellyfish is a plankton eater with a big appetite. Its mouth, however, is only about a millimetre (0.03 in) in diameter — having remained the same size since the jellyfish's rice-sized childhood. To compensate, the jellyfish has grown hundreds of these minuscule mouths along its whirling mass of tentacles. Still, it cannot eat anything large, not even small fish.

Like most other jellyfish, the Nomura's mass — up to 200 kg (440 lb) — is mostly (around 95%) water.

Nomura's jellyfish may grow to be among the largest of all jellyfish (up to 6 metres or 20 feett long), but it doesn't measure up to the lion's mane jellyfish — the largest jellyfish species in the world, with a maximum length of 36.5 meters (120 ft), exceeding that of a blue whale.

As per stereotypes, Nomura's jellyfish can sting — and its stings can be fatal. Small and agile (and ballsy) fish will evade predators by entering the swirling mass of a Nomura's tentacles, where larger creatures can't follow for fear of being stung.

A study found 13 toxin-like proteins in this jellyfish's venom, some similar to those in venomous snakes, spiders and bees. Since 2006, at least 11 human deaths from Nomura's jellyfish have been reported in China and Korea.

Prior to this last century, Nomura's jellyfish have mostly lived in the East China and Yellow Seas. In the Sea of Japan, the weekly haul of these jellyfish was one or two per week. In 1920, Japanese fishermen suddenly began pulling up nets congested with these jellies, catching as many as 1,500 every day — similar jellyfish blooms have occurred in 1958, 1995, 2002, 2003, 2005, and 2006.

Such blooms can cripple the fishing industry; the jellies harm both wild and farmed fish populations, they clog nets and make fish unsellable, and they damage fishing equipment — in one case, sinking a 10-ton fishing boat off Japan's eastern coast.

To add insult to injury, these jellyfish are near-valueless to humans. Japan and China both have "jellyfish salad" dishes, but Nomura's jellyfish is considered generally unpalatable (as compared to the delectable savour of smaller jellies). Potential uses in medicine are being studied. In the worst case, the jellyfish could at least be converted to a less-than-optimal fertiliser.

What causes the jellyfish blooms? The answer is complicated and not fully known.

Man-made climate change likely contributes — warmer waters mean more food for jellyfish and a subsequent boom in numbers — as do our other abuses of the ocean — for instance, eutrophication (the excess of nutrients in the water), often caused by our dumping of waste and irrigation water, aids the reproduction of jellyfish. Meanwhile, factors like acidification and overhunting reduce the number of predators that could control jellyfish populations.

However, observations have shown that jellyfish blooms also occur naturally, often unexpectedly and in inaccessible areas of the oceans. The current consensus stands that; "While there was a slight upward trend of blooms in recent years, that increase was within the normal range of variability. The group didn’t reject the jellyfish-climate link, but they suggested that there might be other explanations for the increase in jellyfish abundance."

The lifecycle of a jellyfish is a complicated odyssey through several very different forms:
1. It begins as a free-swimming, larval speck called a planula.
2. The planula eventually finds a spot to settle, becoming a dome-shaped scyphistoma. In this immobile form, it pumps out several copies of itself known as podocysts (which then also settle down, and proceed to do the same).
3. It then turns into a strobila, growing a stack of larval jellyfish called ephyra, which are released into the water column.
4. These ephyra, each the size of a rice grain, eventually develop into medusae — what most people think of when they think of a jellyfish.