When oceanographer Josep Maria Gili steps onto the terrace from his office, he sees the crowds of people on the beaches of Barcelona at his feet. To the left lies the Port Olímpic, together with a sculpture that Frank Gehry had built there for the 1992 Summer Olympics: a giant fish made of steel, shimmering in the sunshine and gazing majestically out into the Mediterranean.

Unfortunately, it seems evident today that the renowned architect picked the wrong animal. The fish, with its gills and fins, is no longer suited as a trademark of Barcelona. Nowadays fewer and fewer fish swim beneath the glittering blue surface off the coast of Catalonia; instead, these waters are now more frequently filled with massive quantities of jellyfish.

The marine creatures – blind and lacking both a heart and a brain, driven by waves and currents – billow toward the coast, many with poisonous tentacles in tow, not just in Catalonia in northeastern Spain, but virtually everywhere in the world. It has become painfully clear to anyone who has had the bad luck of getting in the way of a poisonous jellyfish that this creature is the new queen of the seas. Such encounters sometimes end fatally – for the human being, that is.

The ‘Jellification of the Seas’

Oceanographer Gili’s interest in jellyfish began at about the same time Gehry created his giant fish. It was an exotic discipline, even for a biologist from the Institut de Ciències del Mar. What no one could have known at the time is that today, more than 20 years later, the jellyfish has become the main topic at international conferences. Entire books are written about the supposed “jellification of the seas,” and scientists argue over whether jellyfish are displacing fish and other ocean creatures, whether they are assuming control over entire ecosystems and whether we will have to eat them in the future to keep them in check, as the Chinese have done for centuries.

The fact that human beings and jellyfish tangle with one another more frequently than in the past is unpleasant for both sides. It also costs many millions each year, although the exact costs are difficult to estimate. For instance, jellyfish often cause power outages and equipment damage when they enter the cooling water systems of power plants and desalination plants.

Jellyfish are also harmful to fishery. They ruin nets and cause chemical burns on the hands of fishermen. If a jellyfish bloom collides with the nets that separate fish farms from the open water, the creatures’ toxins can sometimes kill all of the animals in the enclosures.

And then there is the problem oceanographer Josep Maria Gili can see from his terrace: Jellyfish on the beach, coinciding with the vacation season, are a debacle for tourism. These days it is the reddish, glow-in-the-dark jellyfish Pelagia noctiluca, or mauve stinger, that lurks in the waters off Barcelona. In recent days, Red Cross paramedics have had to treat at least 400 swimmers a day for jellyfish injuries. A yellow warning flag is posted on the beach below, and a voice blaring from loudspeakers warns bathers in Spanish, French and English to be careful around jellyfish.

More and More Jellyfish Blooms

“We are used to jellyfish in the Mediterranean,” says Gili, 60, a short, gray-haired man. “But what we have observed here in the last few years is no longer normal.” Pelagia noctiluca, for example, doesn’t swim from the open sea toward the coast of its own volition. Instead, it is driven by waves and currents, dying where it goes aground. In the Mediterranean, this fate has typically befallen mauve stingers about once every 10 to 15 years. But now the blooms have been happening with much greater frequency, with similar incidents occurring in 2005, 2006, 2007, 2011, 2012 and 2013.

The European Union has also begun to show concern over the frequent jellyfish invasions, which present an additional burden on the already ailing economies of its southern member states. That’s why the EU is now funding an international research project that will gather data on the spread of jellyfish in the Mediterranean region for the first time, as well as develop a coastal management strategy. The scientists involved in the project plan to test such strategies as protective nets along beaches and a smartphone app that would enable beachgoers to report jellyfish sightings.

The impetus from Brussels was overdue. Scientists still know little about jellyfish, because the animals are difficult to study. They appear suddenly and unpredictably, as if out of nowhere but in large numbers. But for scientists hoping to collect the creatures and study them in laboratories, jellyfish are difficult to keep alive. Breeding jellyfish in an aquarium is also a complicated undertaking. These obstacles help to explain why there is only a small community of jellyfish experts worldwide.

Gili no longer knows exactly why he decided, years ago, to study jellyfish. Perhaps he found them interesting because he grew up with them, on the island of Mallorca. “When I was young, my father used to rub olive oil on my body before I went swimming, to protect me from jellyfish injuries,” he recalls with a smile. “Olive oil is the best protection. A lot of sunscreen also helps.”

He and his colleague Verónica Fuentes, 35, are in charge of implementing the EU project in Spain. The most important thing, says Gili, is to educate people. “We tell the tourists that they should come to our country because the Mediterranean is fantastic,” he says, “but we also have to let them know that the sea is not a swimming pool. You can enjoy the sun and the warm water here, and sometimes there happen to be jellyfish in the water. You have to be prepared for that.”

Part 2: A Global Problem

It isn’t just a problem in the Mediterranean, but worldwide. Especially in late summer, swimmers in the North and Baltic Seas often encounter lion’s mane jellyfish, which are known as “fire jellyfish,” and for good reason. Their stringy stinging tentacles are often the color of flames. Far more common in the region are blooms of milky-blue moon jellyfish, which, like the majority of jellyfish species, do not inflict pain on human beings.

Compass and crystal jellyfish now dominate the coastal waters of Namibia, where sardines were once abundant. And since the mid-1990s, fishermen in the East China Sea and the Yellow Sea have complained that their nets are being filled with more and more jellyfish and fewer and fewer fish.

A species prevalent in Japanese waters could provide the material for a horror film: the giant Nemopilema nomurai, or Nomura’s jellyfish, with a bell diameter of up to two meters (6 feet, 6 inches). In the last century, there were only three population blooms of the species, in 1920, 1958 and 1995. But Japanese scientists report that the Nomura’s jellyfish has invaded Asian waters almost every year since 2002, with only two light years in the interim: 2004 and 2010. The species is so heavy that large numbers caught in nets can capsize fishing vessels.

What does all of this signify? Why are the seas becoming jellified?

Gili wrinkles his brow. “The jellyfish are a message in a bottle that the sea is depositing on our beaches,” he says. The ocean’s message to mankind, he adds, is simple: “You are destroying me.”

A Changing Ecosystem

He allows his words to sink in for a moment before returning to the facts. The biggest problem, Gili explains, is overfishing. It’s simple mathematics, he says: “If you reduce the number of fish that eat jellyfish, as well as the number of fish that compete with jellyfish for food, naturally the number of jellyfish is going to increase as a result.”

Jellyfish are normally an important component of marine ecosystems. It is known that 124 fish and 34 other animal species, such as turtles, consume jellyfish. Jellyfish, in turn, primarily eat zooplankton, or smaller organisms, as well as fish eggs, fish larvae and smaller fish.

But when the oceans are overfished, as is now the case almost everywhere in the world, self-reinforcing, fatal mechanisms can occur: Jellyfish compete with fewer fish for zooplankton, which means they eat more and multiply. At the same time, they exert even more pressure on fish populations by eating their young. As a result, jellyfish begin to prevail over collapsing fish populations.

Jellyfish are relatively simple organisms. Their bodies are about 98 percent water, with the remainder consisting of gelatinous tissue, sex organs, a gastrovascular cavity, a primitive nervous system and venom capsules which, when irritated, can eject venom projectiles with the momentum of bullets. There are roughly 1,500 known species of jellyfish, some as tiny as a grain of sand and others as heavy as a wildebeest.

As fragile as the individual animals may seem, jellyfish are incredibly tenacious masterpieces of evolution. For about the last 600 million years, they have survived dramatic changes in the oceans – the development of fish, their biggest enemies and competitors for food, massive heat waves, ice ages, the emergence and disappearance of oceans and meteorite impacts – without changing significantly.

Pollution’s Beneficiaries

They are also more resistant to manmade environmental degradation than most other marine organisms. They are more capable of coping with pollution, algae blooms, murky water and oxygen depletion than fish. Overdeveloped shorelines and structures in the open ocean even serve as nurseries of a sort to jellyfish. The surfaces provide more habitat to the young animals, which attach themselves to fixed structures as polyps. Studies have shown that jellyfish infestations often occur in places where human beings use and pollute the sea with particular intensity.

Shipping also promotes the triumph of the jellyfish. When they are transported into new bodies of water in the ballast water of ships, they often settle successfully and displace local species. They are not picky eaters, consuming whatever enters their mouth opening. And if they can’t find sufficient food, they simply shrink their bodies temporarily.

What is more, jellyfish apparently benefit from climate change. Many species grow more quickly at higher temperatures. And tropical species like the sea wasp, whose venom can kill people within two minutes, are spreading in subtropical waters.

Does this mean that jellyfish are the beneficiaries of man’s over-exploitation of the environment? A toxic reminder that, in the end, everything has its price?

Convincing the Skeptics

Jellyfish researcher Gili says that he isn’t worried about tourism in his country, because there are currently no deadly jellyfish in the Mediterranean, unlike Australia and Asia. But the biologist does find it troubling that jellyfish are changing the ecological balance. What can be done about it? Can we put an end to overfishing of the oceans? Pollution of the environment? Climate change? Gili’s colleague Verónica Fuentes is beginning to have success convincing Catalan fishermen of the importance of her research project. It’s no small task. What fisherman wants to be told not to fish as much, for the sake of the environment?

Fuentes has invited Mario Vizcarro, the fishermen’s attorney and secretary of Catalonia’s official federation of fishermen, to the institute. Vizcarro represents the interest of 1,200 fishermen from the region. They sit in a conference room where the lights are dimmed, the petite scientist and the bull-necked lawyer. Fuentes begins the conversation diplomatically, saying: “There are many reasons why the jellyfish are spreading. Fishery is one reason, but there is also water pollution and warmer temperatures.” Vizcarro looks skeptical.

Ominous Images

The scientist projects a photo onto a screen: a jellyfish with small, silver-colored fish hanging from its tentacles. Some jellyfish eat fish, Fuentes explains in a soft voice. Vizcarro bends forward and stares at the photo. “That sort of thing exists here?” he asks, sounding disgusted. “Not here, not yet,” says Fuentes, “but they’re already in the North Sea.”

Vizcarro examines the photo. His fishermen also have a problem, he says: They are hardly catching any sardines anymore. Could it be that the jellyfish are eating the little sardines? He finds the idea unsettling. He scrutinizes Fuentes with newly awakened interest.

Then she shows him a short film from Japan, which depicts massive numbers of giant jellyfish in bursting fishing nets. “Ah!” Vizcarro exclaims, turning away. Fuentes has been working up to this moment. “We need your help,” she says. “We monitor the coast, but we also need information on how many jellyfish there are out there in the ocean. Only fisherman can give us this information.” Her idea is to use a smartphone app specially developed for fishermen.

Vizcarro nods. “We’re interested,” he says. His fishermen, he adds, are also reporting that they are seeing more jellyfish than in the past, and that there are fewer fish in areas where there are lots of jellyfish. Vizcarro sits up and says: “We too want to know what’s going on.”