Jellyfish: The Next King of the Sea

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

Jellyfish such as these Northeast Pacific sea nettles in Monterey Bay Aquarium, are brainless, bloodless and mostly aimless. (John Lee / Aurora Select)
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Widmer’s lab at the Monterey Aquarium is dominated by bubbling lime-green columns of algae, which he feeds to brine shrimp, which he then feeds to jellyfish. The algae come in six other “flavors,” but he says he prefers the green type for its mad scientist aesthetic. The room is full of jellyfish tanks ranging in size from salad bowls to wading pools. The containers rotate slowly, creating a current. “Let’s feed!” Widmer cries. He scrambles up and down stepladders, squirting a turkey baster of pink krill into this tank and that.

Toward the back of the lab, haggard orange sea nettles stumble along the bottom of their tank, their bells brownish and transparent, their tentacles torn. These, Widmer says, have been taken out of the public display and retired. “Retired” is Widmer’s euphemism for “about to be snipped up with fabric scissors and fed to other jellies.”

He calls his prize specimens “golden children.” He speaks to them in cooing tones usually reserved for kittens. One tank holds the petite but striking purple-lipped cross jellies, which Widmer retrieved from Monterey Bay. The species has never been bred in captivity before. “Oh, aren’t you cute!” he trills. The other golden child is a small brown smudge on a pane of glass. This, he explains, dabbing artistically at the smudge’s edges with a paintbrush, is a colony of lion’s mane jellyfish polyps.

When jellyfish sperm and egg meet, the fertilized egg forms a free-swimming larva, what Widmer describes as “a fuzzy ciliated tic tac.” It whizzes around before landing on a sponge or other seafloor fixture. There it morphs into a weedy little polyp, an intermediate form that can reproduce asexually. And then—well, sometimes nothing happens for a good long while. A jellyfish polyp can sit dormant for a decade or more, biding its time.

When ocean conditions become ideal, however, the polyp starts to “strobilate,” or bud off new jellyfish, a process Widmer shows me under a microscope. One polyp looks as if it is balancing a stack of Frisbees on its head. The tower of tiny discs pulses slightly. Eventually, Widmer explains, the top one will fly off, like a clay pigeon at a shooting range, then the next one, and the next. Sometimes dozens of discs launch, each disc a baby jellyfish.

To test the impact of warming oceans on polyp productivity, Widmer assembled a series of incubators and seawater baths. If he heated each a few degrees warmer than the last, what would the jellyfish do? At 39 degrees Fahrenheit, the polyps generated, on average, about 20 teeny jellyfish. At 46 degrees, roughly 40. The polyps in 54-degree seawater birthed some 50 jellies each, and one made 69. “A new record,” Widmer says, awed.

To be sure, Widmer has also found that some polyps can’t produce young at all if placed in waters significantly warmer than their native range. But his experiments, which confirm research on other jellies done by Purcell, also lend some credence to anxieties that global warming may induce jelly extravaganzas.

Two events ultimately stalled the Mnemiopsis invasion in the Black Sea. One was the fall of the Soviet Union: in the ensuing chaos, some farmers ceased fertilizing their fields and water quality improved. The other was the accidental introduction of a second exotic jellyfish that happened to have a taste for Mnemiopsis.

In lieu of dismantling superpowers or importing invasive species, countries have adopted jelly-proofing strategies. South Korea recently released 280,000 native, jelly-eating filefish along the coast of Busan. Spain dispatched indigenous loggerhead sea turtles off Cabo de Gata. Japanese fishermen hack at the giant Nomura’s with barbed poles. Mediterranean beaches have organized jellyfish hot lines, spotter boat armadas and airplane flyovers; the slimy troublemakers are sometimes sucked up by garbage scows, carted off by backhoes or used for fertilizer. Bathers in the worst areas are advised to wear full-body Lycra “stinger suits” or pantyhose or to smear themselves with petroleum jelly. Most sting-treatment products feature vinegar, the best remedy for jelly venom.

When, nearly two decades ago, Daniel Pauly, a fisheries biologist at the University of British Columbia, started warning of the dangers of overfishing, he liked to alarm people and say we would end up eating jellyfish. “It’s not a metaphor anymore,” he says today, pointing out that not only China and Japan but also the U.S. state of Georgia have commercial jellyfish operations, and there’s talk of one starting in Newfoundland, among other places. Pauly himself has been known to nibble jellyfish sushi.


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