Washed ashore, they aren’t much to look at little more than formless blobs of transparent goo. But these are just the torn and shriveled carcasses of some of the most fascinating and graceful creatures a mariner can encounter: the jellies.
These animals possess many extraordinary attributes: elegant bodies, composed largely of water, growing as huge as 12 feet across and 200 feet long; a dance-like style of motion; the tendency of some to glow vividly with blue-green, bioluminescent light. However, they are most renowned for their ability to kill humans. Certain jellies do rank among the world’s deadliest creatures, but appropriate precautions and treatments can reduce their threat.
The fearsome reputation of jellies is, at least for those species that boast truly powerful poisons, well-founded. Take the case of a four-year-old boy who was swimming in the Gulf of Mexico on a June day in 1990. At about 2:00 p.m., he started screaming, and his mother carried him from the water, only to find his left arm wrapped in tentacles.
These were removed, and meat tenderizer, a common folk remedy for jelly stings, was applied. The boy was rushed by ferry to an emergency treatment facility on Galveston Island. However, within 20 minutes of his encounter with the jelly, he was in shock, listless. His heart rate had slowed, and foam emerged from his nostrils. And by the time of the boy’s 2:39 P.M. arrival at the medical center, he was limp, with pupils fixed and dilated. “He had no spontaneous movements or respirations,” said one of the doctors who attended him, “and there was no cardiac activity on his electrocardiogram. Frothy white foam oozed from his mouth. His extremities were cool, and his left arm had erythematous tentacle marks. A chest X-ray showed massive pulmonary edema.”
Resuscitation attempts were unsuccessful. At 3:21 p.m., less than an hour and a half after the sting, the boy was pronounced dead.
The killer, it was later determined, was a small jelly, likely only an inch or two in diameter, known scientifically as Chiropsalmus quadrumanus and commonly called a sea wasp. The species, which bears four clusters of tentacles, is highly transparent, making it eerily difficult to see in the water. Yet despite the animal’s evident perniciousness, few, if any, other fatalities from C. quadrumanus have been reported in the U.S. Indeed, on the whole fatalities from jellies in the U.S. are, in the words of the Texas doctors who treated the boy, “exceedingly rare.”
Even the most notorious jelly, the Portuguese man-of-war, which occurs with unnerving frequency off the coast of the U.S., has been implicated in only a handful of human deaths here. These include, in Florida and North Carolina, a 67-year-old woman, a 73-year-old man, and a 30-year-old scuba diver who bumped into a Portuguese man-of-war while surfacing.
Instead, contact with poisonous jellies often involves a combination of non-fatal symptoms pain, ranging from none at all to a mild prickling sensation to intense burning; muscular cramps; rashes; coughing; or a host of other symptoms, with the severity depending on various factors. Among them are the type of jelly encountered, the amount of poison received, and the victim’s individual sensitivity to the toxin.
Although many jellies are, in fact, entirely nonpoisonous, serious envenomations do happen each year at locations around the world. In northern Australia, for example, the threat of death by jelly is quite real. There lurks the species reputed to be the most dangerous marine animal in the world. Scientists call it Chironex fleckeri, but it is also known as the Australian box jelly because of its shape. This creature can kill a human in less than four agonizing minutes. It is, without question, the deadliest jelly in the sea, having caused more than 63 recorded fatalities in Australia during the last century. One survivor of a comparatively insignificant sting from the Australian box jelly says the sensation was like being branded by red-hot steel. The unsightly scars left by this animal’s sting do look surprisingly like severe burns, or welts from a brutal whipping. Despite development of an antivenom, the Australian box jelly and its relatives maintain an intensely malevolent presence, causing uncounted deaths each year, mainly in Australian, South Pacific, and Indian Ocean waters.
Attack of the jellyfish
How is it that these wispy, physically insubstantial creatures with a water content of some 96% (compared to 65% for humans) muster such lethal power? The Portuguese man-of-war, the Australian box jelly, C. quadrumanus, and other poisonous jellies, all classified as cnidarians, do it with highly specialized structures called nematocyststiny compartments, each with a trap door at one end, that contain coiled, hollow threads. (The name nematocyst means “thread capsule.”) Triggered by physical or chemical stimulation, the trap door pops open, and the thread shoots out like a miniature harpoon (or an evil jack-in-the-box), injecting poison into the target. A single, long tentacle of the Portuguese man-of-war, for example, may brandish some 750,000 nematocysts. Contact with a small prey item, like a copepod, provokes a couple dozen nematocysts to fire. Larger preya fish, for examplemay find itself assaulted by hundreds or thousands of nematocysts, each contributing a dose of poison to paralyze the victim. The toxins wreak havoc with synapses, halting nerve impulses, and the enzymes induce burning pain.
This feeding method ensures that prey won’t struggle and thrash, tearing the jelly’s delicate body while being shoved into its mouth. Yet nematocysts fire automatically whenever triggered, independent of the rest of the jelly’s nervous system, and they don’t differentiate between good targets and other ones, such as people, that are way too big for the jelly to swallow.
Types of jellies
There are hundreds of species of animals in the sea that might commonly be called “jellies,” owing to their squishy, gelatinous bodies, but many are quite unrelated to the nematocyst-bearing cnidarians. Nematocysts, in fact, are unique to the cnidarians, whose name means stinging threads, and all species of cnidarians bear them. Two other common types of gelatinous marine creatures, the salps and ctenophores (pronounced teen-o-fors), don’t bear nematocysts at all, rely on wholly different strategies for catching food, and pose no danger whatsoever to humans.
“One of the things about gelatinous animals that intrigues me is that there are so many unrelated types that have all adopted this gelatinous body plan,” said G. Richard Harbison, senior scientist at the Woods Hole Oceanographic Institution and a jelly expert. Salps are not related to cnidarians, and yet many people would look at them and say, Oh, there’s a jellyfish. And the same way with ctenophores: They’re not related to cnidarians, even though scientists put them together for many, many years.
To experts like Harbison, gelatinous animals in general are called jellies, and only certain cnidarians are known as jellyfish. Of course, even these true jellyfish are not actually fish. Far from it: The cnidarians rank among the most primitive organisms in existence, only slightly more advanced than the sponges.
“They are considered ancestral organisms to many other groups: us, the mollusks, the worms, and so on,” says Harbison.
Generally speaking, a cnidarian jellyfish looks like a mushy disk or bell with tentacles hanging down, a body form called a medusa. There isn’t much to a cnidarianno brain, no heart, no gills, no kidney, no liver. The animal is only two cell layers thick, with the layers separated by a mass of jelly. The mouth is on the bell’s underside, in the center, and it opens into a simple stomach cavity. Within this pocket, the food is partially digested before being distributed within the animal; digestion is finished off inside individual cells, and waste products are spewed back out through the mouth. Rudimentary as it is, the cnidarian stomach represents a major evolutionary advancement beyond the even-more-basic body structure of the stomachless sponges, which do all their digestion inside individual cells.
Ctenophores, in contrast, are often shaped like tiny footballs, just inches long, and don’t bear as many tentacles as the cnidarians, often just two or none. Their bodies are lined with eight lengthwise rows of combs made up of hairlike structures called cilia, giving rise to the ctenophore’s common name: the comb jelly. These combs are used for swimming, like little paddles that stroke the animal along. Some comb jellies can bioluminesce brightly, showing up in the water at night as blue-green blobs of light. Two widely distributed types of ctenophores, ranging from Arctic to Antarctic waters, are the sea gooseberry, Pleurobrachia, which has two tentacles, and the tentacle-less Beroe, shaped like a thimble.
Although neither the cnidarians nor the ctenophores are at all closely related to humans, the salps are. “To look at them, you wouldn’t know that they were related to humans at all,” said Harbison. Superficially they don’t resemble us, but if you examine them closely you realize they have little central nervous systems, they have muscles, and they have a heart. Salps can grow and reproduce at prodigious rates, forming dense aggregations of thousands of individuals per cubic yard that extend for hundreds of miles.
Life as a jelly
The prevalence of jelly-filled animals raises the question: Why be gelatinous, anyway? After all, jelly seems such a fragile, wimpy material from which to make a body. Moreover, with a composition of only some 1% organic matter and 3% salt (the rest being water), the jelly in these animals actually has less gelatin than would be needed to cook up a firm fruit jelly.
Rules of life in the open sea are different from those on land, however. First off, “there are no hard surfaces to run into,” said Harbison, “so there is no need for an animal to develop a sturdy body to withstand the mechanical stresses of daily life to which we are so accustomed.” Harbison also suggests that, by filtering sunlight, ocean water allows marine animals to get away without an opaque skin’s protection from harmful ultraviolet rays. “The transparency of many oceanic animals may simply be due to the fact that there is no need to be opaque,” said Harbison.
Gravity, too, takes hold in a totally different way underwater. “Since most gelatinous animals are nearly neutrally buoyant,” Harbison said, “they have no need to struggle against an overwhelming pull of gravity, or to develop strong skeletons to withstand its effects. Gelatinous animals are free to develop large, elaborate, and delicate feeding structures.”
The scarcity of food in the ocean, in fact, virtually demands this type of adaptation. “There is a premium on maximizing size while using a minimum of protoplasm,” Harbison explained, “since larger animals can exploit the open sea’s dilute resources more efficiently than small ones. Thus, the gelatinous zooplankton, with their large, delicate, watery bodies, are admirably adapted for life where food is scarce.”
And jellies eat just about everything, including each other, according to Harbison. “They eat fish; they eat crustaceans; they eat microscopic plants. You just about name it, and a jelly eats it, except for whales.”
Since jellies have only a limited ability to swim about in the water, they can’t effectively hunt down prey. Rather, food capture largely happens as a matter of chance, though jellies do what they can to up the odds in their favor. One cnidarian, for example, “fishes.” It swims to the surface, flips over, and then sinks gently downward, tentacles extended to snare shrimp, small fish, and worms. Another cnidarian, the common moon jelly, supplements zooplankton caught on its tentacles and mouth lobes by also eating those that collect on the mucus of its bell. Its cilia sweep these zooplankton to the edge of the disc, where they are licked off by the mouth lobes.
Ctenophore tentacles lack nematocysts and are instead equipped with sticky cells that glom onto passing food particleseggs, larvae, tiny crustaceans, and baby fish. And ctenophores do a good job of feeding voraciously, even earning a reputation for depleting fish stocks at times.
Salps employ an entirely different feeding strategy. “They’re sort of like little ram jets, pumping water through their bodies,” Harbison said. “They have a little net inside that’s made out of mucus that they catch plankton on. They can filter a lot of water.”
In turn, it is hard to imagine that any creature would want to eat a jelly, but many do, including numerous species that specialize in them. “About a hundred species of fish eat jellies almost exclusively,” Harbison said. “Best-known of these is the ocean sunfish, which can weigh as much as 1,500 pounds and are sometimes seen lolling around at the surface. Certain salmon and snapper also eat very large numbers of jellies, and even tuna eat them in small quantities. Some of these fish are immune to jellyfish poisons, and others aren’t. Its sort of like eating chili peppers, I suppose, where the digestive system can handle a lot more than the outside of the body can.”
Likewise, 2,000-pound leatherback turtles frequently munch jellies, and loggerhead turtles have been seen feasting blissfully on swarms of Portuguese man-of-war, chomping on their blue floats. Among the smaller predators of jellies is the tiny, bluish nudibranch known as Glaucus. Looking like a cross between a salamander and a sea monster, but only an inch or two long, Glaucus nibbles on the Portuguese man-of-war and other jellies, miraculously avoiding the toxins and even incorporating the jellies nematocysts into its own body for defense against predators.
A major predator of jellies in Southeast Asia is humans. There, for as much as $12, you can buy what looks like a tough, white pancake but tastes, according to one correspondent, like an oyster-flavored rubber band. This is one of the dozen species of jelly in China, Japan, and Korea that have their tentacles removed, are salted and dried, and then sold as a food, bronchitis cure, and high-blood-pressure reducer. Entrepreneurs have tried to capitalize on sizable U.S. jelly populations by introducing this food to Americans but have met with limited success.
Superman meets jellyfish
A medusa soars through the water by slow rhythmic pulsations of its bell, a graceful form of movement made possible by simple networks of muscles and nerves. But cnidarians have another, hidden side, a Clark Kent-turns-into-Superman transformation that takes place earlier in their lives.
Cnidarian medusas are either male or female, not hermaphroditic, and they release eggs or sperm into the water. A fertilized egg develops into a planula, or tiny free-swimming larva, which, after several days, settles down onto a suitable hard surface, like a rock. There it grows tentacles and a mouth, becoming an anemone-like polyp that feeds itself by snagging food with its tentacles. Every so often the polyp undergoes asexual reproduction: part of the body simply buds off, creeps around a bit, and forms a new polyp nearby. Eventually, the polyp (Clark Kent of the jellyfish life cycle) develops into a free-swimming medusa (Superman).
Yet not all cnidarians are most visible as medusas. Some medusas, like those of the fire coral, are tiny and swim free only for hours, making fire corals best-known for their large, branching, reef-dwelling colonies of polyps capable of painful stings. Fire corals are members of a class of cnidarians called hydrozoans (hydralike animals). Other cnidarians, such as sea anemones and stony corals, don’t ever develop into medusas, living life entirely as polyps. These cnidarians belong to the group known as anthozoans, or flower animals. The third class of cnidarians is the scyphozoans, the animals that jelly experts are talking about when they refer to the true jellyfish.
The three classes of cnidarians can be distinguished, more or less, by the amount of time they spend as a medusa, and by the size of their medusas. Anthozoans lack the medusa stage and live attached to the sea bottom, so they aren’t jellyfish at all, in fact. At the other extreme, the scyphozoans tend to have large and long-lasting medusas. The hydrozoans fall somewhere in between, ranging from those that spend their entire lives as polyps to others that live only as medusas. To add to the confusion, some hydrozoans that float around like jellyfish actually do so as colonies of polyps or conglomerates of both polyps and medusas. These difficult-to-classify creatures include some of the most familiar hydrozoans, the Portuguese man-of-war and the by-wind-sailor.
A Portuguese man-of-war is not a single animal but a colony of highly interdependent individual polyps and medusas, all of which dangle ominously below a gas-filled float that can be a foot long. Each polyp and medusa is specialized to perform a particular function, such as reproduction or feeding. The colony doesn’t swim but is blown by the wind. To avoid drying out, the colony tips its float every five to fifteen minutes, dunking it into the water. Found in warm waters around the world and wielding nearly-transparent tentacles that can dangle 65 feet deep, the Portuguese man-of-war poses a real threat to swimmers.
The by-the-wind sailor, a fellow hydrozoan, is downright amiable in comparison. Also known as velella, or little sail, this cute, small jelly has a flat disk that floats on the sea surface and bears an erect, stiff sail. By lying diagonally to the long axis of the oval disk, the sail allows the animal to tack as close as 63 to the wind. Each velella has its sail permanently set on either a port or starboard tack, so individuals with sails set on opposite tacks are propelled in opposing directions by the wind. Experts disagree on whether velellas are complex colonies or individual polyps, but sailors can look for them in the warmer oceans, where they can be extraordinarily abundant: Mariners in the Atlantic once reported a swarm of millions of velellas spanning more than 150 miles.
Types of true jellyfish
Of the 9,000 or more species of cnidarians, only about 200 are scyphozoans, but some of these are the jellies most visible to mariners. Among the largest of all jellies is the lion’s mane, Cyanea capillata, which reportedly grows up to 12 feet across with tentacles hundreds of feet long. But as jellies go, this is not one of the more attractive. One expert describes it as a large, repulsive, slimy jellyfish. Coloration varies geographically from pinkish to yellow to darker brown or red. This and closely related species range across the North Atlantic, North Pacific, and southern hemisphere, living in bays and in the open sea.
The most common scyphozoans, found in all oceans, are the moon jellies, Aurelia. Fortunately, moon jellies are not especially venomous. Usually up to a foot or so across, but sometimes as big as three feet, moon jellies are easily identified by their four horseshoe-shaped gonads, visible within the medusa, white in males and pink in females.
Undoubtedly the best-known jellyfish in the Chesapeake Bay is the sea nettle, Chrysaora. Seemingly thriving in waters polluted with sewage, it can have tremendous population explosions, wreaking havoc for swimmers. Likewise, the mangrove jellyfish, Cassiopeia, abounds at times in polluted Florida Keys canals; the cannonball jelly also can become extraordinarily abundant in Florida waters.
“Offshore of New England in the summer, right at the edge of the continental shelf,” Harbison said, “you see huge numbers of jellyfish called Pelagia, a purple jelly that gets to be six inches to a foot in diameter, usually smaller, and that can form large aggregations.”
The Australian box jellyfish, Chironex fleckeri, the most venomous animal in the world, is a scyphozoan. With a cube-shaped bell as large as a basketball and some 60 tentacles, each extending 15 feet, a good-sized specimen wields venom enough to knock off more than 50 adult humans. Yet despite their imposing size, box jellies are virtually invisible in the water. Along northeastern Australia, fatalities from box jellies outnumber those from sharks two to one. Characteristic of Australian box jelly stings are tentacle prints with a frosted or cross-hatched appearance, and survivors often have nasty scars.
Chironex fleckeri is only the most lethal of the group of jellyfish called the chirodropids. These include the species that killed the boy in Texas in 1990, and all have a square-shaped bell. Chirodropid species are confirmed to inhabit the Indian, Pacific, and Atlantic oceans, along with the Caribbean Sea and Gulf of Mexico. In the Philippines alone, the death rate from jellyfish stings is estimated at 20 to 40 per year, due largely or entirely to chirodropids.
Aside from the Portuguese man-of-war and the chirodropids, reportedly the only other jellies known to have caused human death are large Stomolophus nomurai, a species that occurs in the Yellow Sea between China and South Korea. At least eight deaths have been attributed to this species.
First aid for stings
“First aid treatment for jellyfish stings is species specific,” said Dr. Joseph W. Burnett, original founder of the International Consortium for Jellyfish Stings, co-author of Venomous Marine Stings: A Biological and Medical Handbook, and chairman of the Department of Dermatology at the University of Maryland School of Medicine.
In Caribbean and U.S. waters, the cabbage-head jellies, Stomolophus meleagris, commonly cause minor stings, while serious stings usually result from encounters with the Atlantic or Pacific Portuguese man-of-war, giant lion’s mane jellyfish, Chesapeake Bay sea nettle, or mauve stinger (Pelagia noctiluca).
As a general strategy for treating stings, Burnett said, “the initial move is to maintain the airway and cardiovascular system, and reassure the patient. The second move is to inhibit additional stings from the nematocysts.”
This second step is necessary because often tentacles left on a persons body after the initial sting still have some nematocysts that have not yet fired. Accidental stimulation by a would-be rescuer can cause them to inject more toxin into an already affected person. For most jellies, the preferred way to prevent this trauma is to flood the sting area with vinegar for a minimum of 30 seconds, inactivating the nematocysts.
However, if the sting occurred in the Pacific Ocean and the culprit was a Portuguese man-of-war, says Burnett, vinegar should not be used. One type of Pacific Portuguese man-of-war has nematocysts that seem to be triggered rather than inactivated by vinegar. Yet, he says, vinegar can safely be used on Atlantic Portuguese man-of-war stings.
The other exception is for the Chesapeake Bay sea nettle, for which Burnett advises applying a slurry of 50 percent baking soda and 50 percent sea water.
“A simple rule of thumb might be this: On the American East Coast, if you’re north of Norfolk and the sting was not from a blue jellyfish [indicating a Portuguese man-of-war], use a baking soda slurry. If you are south of Norfolk, use vinegar,” Burnett recommended.
After the nematocysts are inactivated, tentacles should be removed, preferably with some sort of implement or with thickly gloved hands. However, if these options are not available, according to Burnett, go ahead and use bare hands to pick them off. “In my experience,” he explains, “it’s acceptable to remove tentacles with the bare finger, because the keratin layer on the palm surface of the hand is thick and less likely to be stung.”
Yet inactivation of nematocysts and the removal of tentacles does not reduce the pain of the initial sting. For this Burnett recommends systemic, not topical, treatment. “Since the sting is administered into the dermis where the nerves are, and pain is instantaneous,” Burnett said, “topical anesthetics are of no value. Topical cortisones and topical antihistamines are also of no value. Systemic analgesics, either in the form of oral doses or injections, depending on the severity of the sting and the time that you want the medication to exert its effect, should be used.”
Cold packs can also be applied to minimize skin pain, but Burnett cautions against overdoing it, to guard against hypothermia.
If a supply of Chironex fleckeri antivenom is at hand, it should be used for all serious chirodropid jellyfish stings. Rapid treatment with antivenom is especially crucial for severe stings from the Australian box jelly. Otherwise, death may come within minutes.
Trained as a marine biologist, Pete Taylor is now an editor at Islands, an international travel magazine based in Santa Barbara, Calif.
