For 10 relentless days and nights in September, workers at eastern China’s largest coal-fired power plant battled an invader unlike any they had faced before: a tidal surge of jellyfish.

At the Zheneng Jiaxing Power Plant in Zhejiang province, teams worked in rotating shifts, frantically clearing millions of jellyfish that had swarmed the plant’s cooling systems, threatening to bring operations to a standstill.

Even after more than 150 tons of jellyfish had been cleared from the plant — an overwhelming load for the local sanitation department — the influx showed no signs of slowing.

Bags of jellyfish continued to pile up, releasing a pungent stench. Workers, meanwhile, had to remove the jellyfish from filter screens by hand, one at a time, making the task slow and arduous.

“In the plant’s 30-year history, we have never encountered anything like this,” Xi Chao, deputy director of the plant’s maintenance department, told state broadcaster CCTV on Sept. 29.

The invading jellyfish, a species known as Rhopilema esculentum, have been enjoyed as a delicacy in China dating back to the Tang dynasty (618–907). This year, the species saw what domestic media described as an “unprecedented harvest in decades” along China’s coastal regions, prompting excitement and attention.

For the Zheneng Jiaxing Power Plant, however, this surge was anything but good news.

On Sept. 18, a massive influx of jellyfish overwhelmed the plant’s circulation pump station, which pulls in seawater to cool its generators. The jellyfish latched tightly onto the rotating filters, clogging the intake and straining the system until the filters overloaded and tripped — ultimately shutting down the generator.

In the days that followed, over 100 emergency repairs were rushed in to address jellyfish-related malfunctions, Xi told domestic media outlet Southern Metropolis Daily.

However, the problem wasn’t limited to this plant. In August, two power stations in neighboring Shanghai faced similar jellyfish invasions. And even around the globe, coastal nations like Japan, South Korea, and the UK have contended with comparable disruptions over the past three decades.

Experts assert that recurrent jellyfish blooms are symptomatic of broader global environmental shifts. Factors like seawater eutrophication — an excess of nutrients causing algal blooms and low-oxygen conditions that favor jellyfish — and overfishing, which reduces interspecies competition, have allowed these resilient creatures to thrive and spread, wreaking havoc worldwide.

Just eat them?

News of the jellyfish crisis at the Zheneng Jiaxing Power Plant quickly made waves on social media, amassing over 41.69 million views on the microblogging platform Weibo and sparking a flurry of reactions.

“Why not just eat them?” many curious netizens quipped, referencing the long history of R. esculentum jellyfish as a cherished delicacy in China.

Traditionally prepared as jellyfish salad, the species has been a staple in Chinese households for over a thousand years. Ironically, the haul cleared from the power plant could, in theory, yield at least 300,000 servings — if only it weren’t piling up in emergency bags to keep the lights on.

Once celebrated as a symbol of abundance, this jellyfish species has now become a symbol of disruption.

“In the past, if we saw an increase in the R. esculentum jellyfish, it wouldn’t have been called a disaster, but a bumper harvest,” Sun Song, former director of the Institute of Oceanology at the Chinese Academy of Sciences, told Sixth Tone. “This time, however, they clogged up the power station, causing a crisis.”

Jellyfish have long been valued in China for their purported detoxifying, pain-relieving, and anti-inflammatory effects. In 1984, faced with declining jellyfish populations due to overfishing, China even took steps to replenish stocks and boost harvests by releasing cultured juveniles.

However, Xi, the plant’s deputy director, explained to Southern Metropolis Daily that they were uncertain whether the jellyfish clogging the plant were entirely edible, preventing any potential sale to the public.

According to Sun, alongside the edible variety, China’s coasts often see blooms of two other species — Aurelia aurita and Cyanea. Unlike the sought-after jellyfish, these species hold no culinary value and are typically regarded as invasive or accidental nuisances.

Global swarm

Over the last few decades, jellyfish blooms have emerged as a global challenge, posing serious threats to power plants worldwide.

“In fact, every power plant around the world has been plagued by jellyfish at some point; it’s a worldwide problem,” explained Sun, who has studied the species since 2005.

He underscored that nuclear power plants are particularly vulnerable. Unlike coal-fired plants, which can stop operations quickly, nuclear reactors require a gradual shutdown process. If jellyfish clog intake pipes and cooling water is lost, reactors face a dangerous risk of overheating, potentially leading to catastrophic explosions.

And since power plants are frequently built near coastal waters to access cooling water, they are especially susceptible to marine intrusions. This vulnerability has played out on multiple occasions.

In June 2011, Japan’s Shimane Nuclear Power Plant was forced to deal with a jellyfish blockage, followed the same month by Scotland’s Torness Nuclear Power Station, which experienced another major incident in October 2021.

In 2013, one of the world’s largest nuclear reactors, Sweden’s Oskarshamn Nuclear Power Plant, had to shut down due to jellyfish clogging its cooling systems, as did a power plant in Israel in 2019.

Beyond power plants, jellyfish blooms can also significantly disrupt tourism, often souring idyllic coastlines. Along the famed French Riviera, jellyfish stings have become a recurring summer concern, even with the installation of an €80,000 ($84,500) anti-jellyfish net. This past summer alone, South Korea recorded around 2,900 jellyfish sting cases.

A 2023 study shows that jellyfish risks have steadily expanded over the past six decades, from the 1960s to the 2010s. It found that jellyfish typically thrive in bays and semi-enclosed seas, with major hotspots including the Sea of Japan, the Mediterranean Sea, and the Yellow Sea.

Other research suggests that jellyfish populations may not be consistently increasing but could follow a roughly 20-year cyclical pattern — a theory that requires further data for confirmation.

Stemming the tide

Jellyfish have thrived where other marine species falter due to their unmatched resilience in harsh environments. “The jellyfish’s greatest competitive edge lies in its resilience to harsh environments — essentially, it’s an opportunist,” says Sun, formerly of the Institute of Oceanology at the Chinese Academy of Sciences, adding that the Craspedacusta sowerbii, or peach blossom jellyfish — a species that has endured for 550 million years and survived multiple mass extinctions — exemplifies their adaptability.

Such resilience allows jellyfish to benefit from overfishing and excess nutrients from fertilizers and sewage, according to a 2009 study that first drew global attention to the rise of jellyfish blooms.

Sun tells Sixth Tone that both jellyfish and fish rely on plankton for food, but overfishing depletes fish stocks, giving jellyfish a chance to dominate ecosystems. Rising nitrogen and phosphorus levels from eutrophication can lead to algal blooms and oxygen depletion — conditions that hinder fish survival but favor the more resilient jellyfish.

“Jellyfish can even consume fish eggs and juveniles,” says Sun. “When large blooms occur, they take over fishing grounds, making it hard for other organisms to recover.” In 2015, a surge of Nomura’s jellyfish in Japan, each weighing up to 200 kilograms, caused a 60% decline in flatfish catches.

Jellyfish also possess a unique lifecycle. Before becoming the free-floating medusas seen in blooms, they exist as polyps attached to the seafloor. These polyps can remain dormant for years, reproducing asexually until favorable water conditions trigger sudden population booms, Sun adds.

Sun underscores that jellyfish blooms often remain undetected until they strike, leaving limited options for intervention once the problem emerges. “It’s similar to wildfire prevention,” he explains. “Scientists can tell you why it occurs — maybe due to dry conditions or a stray spark. But once the fire ignites, experts can do little; you need firefighters on the scene.”

Pointing out that awareness of measures to prevent jellyfish clogs in power plant pipelines remains insufficient in China, Sun says that both domestic and international efforts to manage and mitigate jellyfish hazards are steadily evolving.

In 2018, the Chinese Academy of Sciences proposed using zooplankton as bait to locate and scrape away the polyp zones of A. aurita jellyfish. In South Korea, researchers have developed the “jellyfish terminator” — a robot capable of detecting and destroying the creatures.

In the UK, drone technology has become part of a proactive early-warning system, using medium-altitude drones to monitor and signal jellyfish movements toward power plants. And a power plant in Japan has adopted a novel approach, installing additional air pipes to create bubbles that lift and divert jellyfish away from water intake pipes.

For long-term prediction, monitoring jellyfish polyps attached to the seafloor remains a key strategy, as their presence indicates the potential scale of future blooms, says Sun.

However, he admits that much work remains to be done in seafloor observation, adding: “We actually know less about the seafloor than we do about the surface of the moon.”

Editor: Apurva.

(Header image: 500px/VCG)