In my mid-20s, I spent three months living in Broome, a coastal township in Western Australia famous for its moonrises, pink beaches, and pearl farms. Each morning during what is known locally as “the buildup” (the hot, muggy weeks heralding the wet season), I would stuff a towel in a bag and trudge out to where the red pindan soil—distinctive to the Kimberley region—marbles powdery dunes, longing to dunk my body in the postcard sea. Often, I could go no farther than the water’s edge. Signs pitched by lifeguards along the beach showed a stick figure lashed by a mass of tentacles: Irukandji jellyfish.

By midday, the mercury might have drifted above 100 degrees Fahrenheit, and still no one would dare to even dabble in the shallows of the jade ocean—corduroyed by waves—knowing that Irukandji had been detected. Back from the shoreline, a few tourists resolutely sweated their silhouettes onto beach chairs. If the notices were plucked from the sand in the afternoon, a tense choreography would ensue. Each heat-strained person would approach the surf and make an elaborate pantomime of applying sunscreen or stretching out hamstrings, hoping not to have to be the first to get in.

The most common Irukandji, Carukia barnesi, are the size of a chickpea, and because they’re colorless, in the ocean they’re more or less invisible. The smaller ones might appear to you as the residue of a sneeze. The Irukandji’s translucent bell, shaped like a tiny boxing glove, trails four tentacles, delicate as cotton thread and about three feet long. The jellyfish’s sting doesn’t hurt overmuch. The pain is perhaps equivalent to a mild static zap from a metal doorknob—hardly even enough to make you want to suck your finger. The C. barnesi does not leave red welts, as other jellyfish do. You might miss the prick of its microscopic, stinging darts. You might think it’s just the start of sunburn.

Worst-case scenario: You’re dead by the following sunset. There are thought to be 25 species of Irukandji. One species, Malo kingi, is commonly known as “the king slayer.” After the initial sting comes a procession of ever more dreadful symptoms: back pain, agitation, the sensation of crawling skin, vomiting. The heart can become arrhythmic. Fluid may build up in and around the lungs. Patients “beg their doctors to kill them, just to get it over with,” the marine biologist Lisa-ann Gershwin told ABC Radio National in 2007.

That desperation is often accompanied by one of the more striking indications of contact with an Irukandji jellyfish: a sense of impending doom. To the afflicted person, nothing seems likely to alleviate distress, no medical professional offers hope. The swimmer might not have seen or felt the sting, but if a touch point can be identified, the treatment is to splash the area with vinegar to neutralize any nematocyst cells on the skin’s surface. Then, if the malady progresses, morphine and antihypertensive drugs are administered. Very few people stung by an Irukandji will be so unlucky as to die, but at least one victim has compared the latter phases of envenomation to childbirth.

There may be as many as 4,800 different species of jellyfish. Not every kind possesses a sting that is perceptible to humans. Individual jellyfish are fragile creatures. Being composed largely of soft collagen, they easily tear. In a net or bunted along a reef by a storm surge, jellyfish are soon shredded. Washed ashore, they evaporate, leaving only a remnant halo of mesoglea (the jellyfish’s gluey core). Organized water: That was one 19th-century naturalist’s minifying description of the jellyfish. The creature’s wispy anatomy confers on it the specific beauty of the readily destroyed, a quality that elicits comparisons to things that are empty and lambent—light bulbs, dropped lingerie, a nebular constellation, the cellophane wrappers from hotel soaps, dribbles of wax.

How appealing it is to fashion metaphors out of a jellyfish. The animal is all stimulus, sensuousness without consciousness. Such evanescent creatures pose none of the anthropomorphizing complications of, say, octopuses. An octopus will regard you with features that resemble a face, and an intelligence that we’ve been advised is akin to that of dogs and dolphins. Most jellyfish are see-through, so we can tell they don’t have minds of their own to speak of. Eyeless, bloodless, brainless—jellyfish are more than alien enough to comfortably objectify.

Their delicacy notwithstanding, in recent decades jellyfish species have come to be thought of as the durable and opportunistic inheritors of our imperiled seas. Jellyfish blooms—the intermittent, and now widely reported, flourishing of vast swarms—are held by many to augur the depletion of marine biomes; they are seen as a signal that the oceans have been overwarmed, overfished, acidified, and befouled. These invasions are sometimes discussed as if they had the potential to culminate in ecophagy, the devouring of an ecosystem in gross. (Phage derives from the ancient Greek word meaning “to eat up.”) The vision—hat tipped to science fiction—is of the planet’s oceans transformed into something like an aspic terrine. In waters thickened by the gummy mucus of living and dead jellyfish, other sea life will be smothered. Because jellyfish recall the capsules of single-celled protozoa, this eventuality invites portrayal as a devolution of the marine world—a reversion to the “primordial soup.”

The unraveling back into the past is a theme that proves common to the apocalyptic arc of how we imagine environmental change. A jellyfish-dominated sea is conceived of as the sea of prehistory, the preserve of simple animals—slimes, diatoms, pulsing dabs—and a reminder of a time when anything motile moved as a squiggle, scuttle, or ooze. Jellyfish have been around for at least 500 million years, probably longer. We know that they’re older than trees, older than leaves. Paleontologists are quick to point out that because jellyfish are soft-bodied, they don’t fossilize the way animals with skeletons or cartilage do, so it’s harder to find their imprints or to know how ubiquitous they may have been in ancient seas.

The lesson we’re meant to take from all this is that ecological collapse will spawn nothing new. No Boschian hellscape of strange and shuddering hybrids will emerge. Environmental disaster is fundamentally uncreative.

Jellyfish have served as excellent protagonists for this narrative, perhaps because they are as close to automatons as anything in the animal kingdom. The insidiousness of a jellyfish bloom lies in its amassed torpor—a monster more monstrous for lacking a center, each animal stewarded by no more than a basic set of compulsions (light, gravity, food, reproduction). Jellyfish species being widespread, people can also recognize them anywhere. Jellies are found in every sea at nearly every depth, and in many brackish rivers. One type in Antarctica looks like a raw mince patty. The Arctic and other frigid waters are home to the lion’s mane, a headless wig of a creature with tentacles that have been measured at about 120 feet. Jellyfish might be primitive animals, but they have an immense carrying capacity for a story that is planetary in scale.

Do jellyfish, in fact, deserve their reputation as an oceanic menace? Should we view blooms with anticipatory dread? In her memoir, Spineless: The Science of Jellyfish and the Art of Growing a Backbone, Juli Berwald embarks on a mission that leads her to challenge the way blooms are popularly characterized. Inspired by a yearning to return to marine science (a professional ambition abandoned after graduate school, and her relocation to Texas), Berwald proceeds to take apart the evidence underpinning depictions of jellyfish as both passive indicators of sickening seas and drivers of environmental atrophy. The ubiquity of jellyfish, she finds, masks a plurality of stories—some well substantiated, others only speculative. 
The demonization of jellyfish, as Berwald frames it, correlates with the new visibility of the creatures. As underwater technologies have become more fine-tuned (as well as rugged, functional in the open ocean and the deep sea), jellyfish have swerved into focus. Are their numbers increasing, or are contemporary scientists now capable of observing profusions that once went under the radar? Jellyfish blooms may occur at intervals that pre-date their surveillance—spreading, say, in 20-year cycles. What looks to us like an aberrance could, viewed in a longer time frame, prove natural.

We see many more jellyfish, Berwald points out, not simply because their numbers are greater but because our population is. The proliferation of coastal and subsurface infrastructure for resource extraction, maritime trade, and power generation has provided ample hardscape for jellyfish-polyp nurseries to graft onto. Human industry is in more frequent and sustained contact with many types of sea life. That we see more jellyfish says one thing; that they see more of us is a different matter.

Riverhead

Perhaps the most complex issue Berwald takes on is jellyfish blackouts. Sweden, Scotland, the Philippines, Tokyo, California, and Israel have all suffered intermittent electrical outages caused by jellyfish sucked into the intake pipes and cooling systems of coal-fired and nuclear power stations. (On Luzon, the largest of the Philippine Islands, the crashing grid was mistaken by some for the start of a coup.) Desalination plants likewise have had to go offline when jellyfish have clogged their conduits and filters. The significance of such damage will only increase as on-land freshwater resources degrade and electricity demand grows. In cities experiencing greater temperature extremes, blackouts expose particularly consequential frailties—refrigeration, air-conditioning and heating, and transportation all matter more in hard weather. These jellyfish–human interactions, Berwald suggests, may say less about their encroachment than about ours.

Jellyfish are not universal adapters, and the world’s oceans are not all subject to the same set of problems. In Spineless, Berwald travels to Spain’s Murcia region and takes us to the Mar Menor lagoon, which had become so jellified in 2002 that “you couldn’t drive a boat through the water.” Here barrel and fried-egg jellyfish are pernicious—so much so that they’re removed from the sea by the bargeload and dumped into ditches near the airport. But elsewhere, as Berwald shows, jellyfish are key to the life cycles of dependent organisms: Open-ocean jellies can host larvae, fish, and small crustaceans “like shrubs with birds nesting in their boughs.”

Some jellyfish thrive in low-oxygen water and can tolerate a wide pH bandwidth. Others so efficiently stir up heavy metals that scientists have proposed using them as mops in contaminated waters. Still other jellyfish appear to be disoriented by upticks in acidity and have no resistance to toxins.

Berwald doesn’t rebut the dark jellyfish narrative, but she usefully qualifies it, exploring a diversity of jellyfish responses to harms unevenly distributed throughout the sea. There is no global jellyfish ecophagy. The real bloom, Berwald argues, is in jellyfish science, where the interplay of jellyfish and their ecosystems is only now beginning to be pieced together.

On a cloudy afternoon in London after finishing Spineless, I caught the train to the Sea Life Aquarium to see Britain’s feted “largest jellyfish experience,” in the “Ocean Invaders” exhibit that opened this past spring. With an hour left before closing, kids were elbowing one another aside for the chance to plunge their hands into a wall cavity emitting purple light and draped with plastic tentacles—an opportunity to experience a pretend jellyfish sting. A motion sensor set off the sounds of electric shock, zzz, zzz, and then the kids fell all over the floor, beating their fists on their ribs. One boy snapped his incisors with such force I thought he might throw sparks. “No teeth!” he screamed. “No teeth! How does it eat?!”

A map of the range of jellyfish species on the wall read global domination. As the crowd thinned out, I saw blue blubber jellies from Australia—studded balls like spaniels’ chew toys—in an underlit tank that went from red to green to red. I saw the Pacific sea nettle, Vaseline- and cola-colored; I saw jellyfish that looked like the crushed Kleenex swept out of a house of mourners. A plaque boasted that “up to 5,000 jellyfish were bred behind the scenes as Ocean Invaders got ready to open.” How strange to think of this swarm, cosseted and captive in so many glass tanks, when beyond the aquarium such a prodigious bloom would be eyed with trepidation, as a jittery forecast for the future of oceans.