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 has bred dozens of jellyfish species, including moon jellies, which resemble animated shower caps. His signature jelly is the Northeast Pacific sea nettle, displayed by the score in a 2,250-gallon exhibit tank. They are orange and incandescent, like dollops of lava, and when they swim against the current they look like glowing meteors streaming to Earth.

The waters of Monterey Bay have not been spared from the gelatinous woes said to be sweeping the oceans. “It used to be that everything had a season,” Widmer says. Spring was the time for lobed comb jellies and crystal jellies to arrive. But for the past five years or so, those species seem to be materializing almost at random. The orange spotted comb jelly, which Widmer nicknamed the “Christmas jelly,” no longer peaks in December; it haunts the shoreline practically year-round. Black sea nettles, once seen mostly in Mexican waters, have started appearing off Monterey. Last August, millions of Northeast Pacific sea nettles bloomed in Monterey Bay and clogged the aquarium’s seawater intake screen. The nettles typically retreat by early winter. “Well,” Widmer informs me gravely on my February visit, “they’re still out there.”

It’s hard to tell what may be causing jellyfish to proliferate. The fishing industry has depleted populations of big predators such as red tuna, swordfish and sea turtles that feed on jellyfish. And when small, plankton-eating fish such as anchovies are overharvested, jellies flourish, gorging on plankton and reproducing to their hearts’ content (if they had hearts, that is).

In 1982, when the Black Sea ecosystem was already weakened by anchovy overfishing, the warty comb jelly (Mnemiopsis leidyi) arrived; a species native to the East Coast of the United States, it was most likely carried across the Atlantic in a ship’s ballast water. By 1990, there were some 900 million tons of them in the Black Sea.

Pollution, too, may be fueling the jelly frenzy. Jellyfish succeed in all sorts of fouled conditions, including “dead zones,” where rivers have pumped fertilizer runoff and other materials into the ocean. The fertilizer fuels phytoplankton blooms; after the phytoplankton die, bacteria decompose them, hogging oxygen; the oxygen-depleted water then kills or forces out other marine creatures. The number of coastal dead zones has doubled every decade since the 1960s; there are now roughly 500. (Oil can kill jellyfish, but no one knows how jellyfish populations in the Gulf of Mexico will fare in the long run after the BP oil spill.)

Carbon-based air pollution may be another factor. Since the Industrial Revolution, the amount of carbon in the atmosphere from burning fossil fuels and wood as well as from other enterprises has risen by some 36 percent. That contributes to global warming, which, some researchers speculate, may benefit jellyfish at the expense of other marine animals. Moreover, carbon dioxide dissolves in seawater to form carbonic acid—a major threat to marine life. As the seas become more acidic, scientists say, ocean water will begin to dissolve animal shells, stunt coral reefs and disorient larval fish by skewing their sense of smell. Jellies, meanwhile, may not even be inconvenienced, according to recent studies by Jennifer Purcell of Western Washington University.

Purcell and a graduate student, Amanda Winans, decided to breed moon jellyfish in water with the staggering acid levels that some scientists say will prevail in the years 2100 and 2300. “We took it to very severe acid, using the worst predictions,” Purcell says. The jellyfish reproduced with abandon. She has also conducted experiments that lead her to suspect that many jellies reproduce better in warmer water.

With the world’s human population expected to increase 32 percent by 2050, to 9.1 billion, a number of environmental conditions that favor jellyfish are predicted to become more common. Jellyfish reproduce and move into new niches so rapidly that even within 40 years, some experts predict “regime shifts” in which jellyfish assume dominance in one marine ecosystem after another. Such shifts may have already occurred, including off Namibia, where, after years of overharvesting, the once fecund waters of the Benguela current now contain more jellyfish than fish.

Steven Haddock, a zooplankton scientist at the Monterey Bay Aquarium Research Institute (MBARI), is concerned that researchers and the news media may be overreacting to a few isolated jelly outbreaks. Not enough is known about historical jelly abundances to distinguish between natural fluctuation and long-term change, he says. Are there really more of the creatures, or are people simply more prone to notice and report them? Are the jellyfish changing, or is our perspective? A self-described “jelly hugger,” Haddock worries that jellyfish are taking the blame for messing up the seas when we’re the ones causing the damage. “I just wish that people had the perception that jellyfish are not the enemy here,” Haddock says.

Purcell, who sports jellyfish earrings the day I meet her in Monterey, says she is disgusted by what she sees as humanity’s efforts to exploit the ocean, filling it with fish farms and oil wells and fertilizer. Compared with fish, jellies are “better feeders, better growers, more tolerant of all kinds of things,” she told me, adding of the marine environment: “I think it’s entirely possible we’ve made things better for jellyfish.” Part of her likes the idea of unruly jellies causing a commotion and foiling our plans. She’s cheering for them, almost.


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