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Jellyfish such as these Northeast Pacific sea nettles in Monterey Bay Aquarium, are brainless, bloodless and mostly aimless. (John Lee / Aurora Select)

Jellyfish: The Next King of the Sea

As the world's oceans are degraded, will they be dominated by jellyfish?

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On the night of December 10, 1999, the Philippine island of Luzon, home to the capital, Manila, and some 40 million people, abruptly lost power, sparking fears that a long-rumored military coup d’état was underway. Malls full of Christmas shoppers plunged into darkness. Holiday parties ground to a halt. President Joseph Estrada, meeting with senators at the time, endured a tense ten minutes before a generator restored the lights, while the public remained in the dark until the cause of the crisis was announced, and dealt with, the next day. Disgruntled generals had not engineered the blackout. It was wrought by jellyfish. Some 50 dump trucks’ worth had been sucked into the cooling pipes of a coal-fired power plant, causing a cascading power failure. “Here we are at the dawn of a new millennium, in the age of cyberspace,” fumed an editorial in the Philippine Star, “and we are at the mercy of jellyfish.”

A decade later, the predicament seems only to have worsened. All around the world, jellyfish are behaving badly—reproducing in astonishing numbers and congregating where they’ve supposedly never been seen before. Jellyfish have halted seafloor diamond mining off the coast of Namibia by gumming up sediment-removal systems. Jellies scarf so much food in the Caspian Sea they’re contributing to the commercial extinction of beluga sturgeon—the source of fine caviar. In 2007, mauve stinger jellyfish stung and asphyxiated more than 100,000 farmed salmon off the coast of Ireland as aquaculturists on a boat watched in horror. The jelly swarm reportedly was 35 feet deep and covered ten square miles.

Nightmarish accounts of “Jellyfish Gone Wild,” as a 2008 National Science Foundation report called the phenomenon, stretch from the fjords of Norway to the resorts of Thailand. By clogging cooling equipment, jellies have shut down nuclear power plants in several countries; they partially disabled the aircraft carrier USS Ronald Reagan four years ago. In 2005, jellies struck the Philippines again, this time incapacitating 127 police officers who had waded chest-deep in seawater during a counterterrorism exercise, apparently oblivious to the more imminent threat. (Dozens were hospitalized.) This past fall, a ten-ton fishing trawler off the coast of Japan capsized and sank while hauling in a netful of 450-pound Nomura’s jellies.

The sensation of getting stung ranges from a twinge to tingling to savage agony. Victims include Hudson River triathletes, Ironmen in Australia and kite surfers in Costa Rica. In summertime so many jellies mob the waters of the Mediterranean Sea that it can appear to be blistering, and many bathers’ bodies don’t look much different: in 2006, the Spanish Red Cross treated 19,000 stung swimmers along the Costa Brava. Contact with the deadliest type, a box jellyfish native to northern Australian waters, can stop a person’s heart in three minutes. Jellyfish kill between 20 and 40 people a year in the Philippines alone.

The news media have tried out various names for this new plague: “the jellyfish typhoon,” “the rise of slime,” “the spineless menace.” Nobody knows exactly what’s behind it, but there’s a queasy sense among scientists that jellyfish just might be avengers from the deep, repaying all the insults we’ve heaped on the world’s oceans.

“Jellyfish” is a decidedly unscientific term—the creatures are not fish and are more rubbery than jamlike—but scientists use it all the same (though one I spoke with prefers his own coinage, “gelata”). The word “jellyfish” lumps together two groups of creatures that look similar but are unrelated. The largest group includes the bell-shaped beings that most people envision when they think of jellyfish: the so-called “true jellies” and their kin. The other group consists of comb jellies—ovoid, ghostly creatures that swim by beating their hairlike cilia and attack their prey with gluey appendages instead of stinging tentacles. (Many other gelatinous animals are often referred to as jellyfish, including the Portuguese man-of-war, a colony of stinging animals known as a siphonophore.) All told, there are some 1,500 jellyfish species: blue blubbers, bushy bottoms, fire jellies, jimbles. Cannonballs, sea walnuts. Pink meanies, a.k.a. stinging cauliflowers. Hair jellies, a.k.a. snotties. Purple people eaters.

The bell-shaped jellies—distantly related to corals and anemones—launched their lifestyle long, long ago. Exquisite jellyfish fossils found recently in Utah display reproductive organs, muscle structure and intact tentacles; the jelly fossils, the oldest discovered, date back more than 500 million years, when Utah was a shallow sea. By contrast, fish evolved only about 370 million years ago.

The descendants of those ancient jellies haven’t changed much. They are boneless and bloodless. In their domelike bells, guts are squished beside gonads. The mouth doubles as an anus. (Jellies are also brainless, “so they don’t have to contemplate that,” one jelly specialist says.) Jellies drift at the mercy of the currents, though many also propel themselves by contracting their bells, pushing water out, while others—such as the upside-down jellyfish and the flower hat, with its psychedelic lures—can recline on the seafloor. They absorb oxygen and store it in their jelly. They can sense light and certain chemicals. They can grow quickly when there’s food around and shrink when there isn’t. Their tentacles, which reach up to 100 feet long in some species, are covered with cells called nematocysts that fire tiny poison harpoons, enabling the animals to immobilize krill, larval fish and other prey without risking their mushy bodies in a struggle. Yet if a sea turtle bites off a hunk, the flesh regenerates.

A breeding jellyfish can spit out unfertilized eggs at a prodigious rate: one female sea nettle may spew as many as 45,000 per day. To maximize the chances of sperm meeting egg, millions of moon jellies of both sexes assemble in one place for a gamete-swapping orgy.

Chad Widmer is one of the world’s most accomplished jellyfish cultivators. At the Monterey Bay Aquarium in California, he is lord of the “Drifters” exhibit, a slow-motion realm of soft edges, rippling flute music and sapphire light. His left ankle is crowded with tattoos, including Neptune’s trident and a crystal jellyfish. A senior aquarist, Widmer labors to figure out how jellyfish thrive in captivity—a job that involves untangling tentacles and plucking gonads until his arm is swollen with venom.

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About Abigail Tucker

A frequent contributor to Smithsonian, Abigail Tucker is writing a book about the house cat.

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