Drifting at any depth in all the world’s oceans, these creatures range from an Arctic species with a bell the size of a car, to a venomous microscopic Australian. Carnivorous predators, jellyfish swarm around our coasts and litter our beaches, yet we know surprisingly little about them. Some of the most recognisable species don’t even qualify as true jellyfish. One such, a Portuguese Man of War (Physalia physalis), its inflated bladder keeping it poised at the surface, is not even a single animal, but a sizeable colony containing four types of minute, highly modified polyps.
Jellyfish keep things simple: no heart, no brain, no circulatory system and no bones. They have a pouch for a stomach that doubles as the reproductive system, a mouth that doubles as an anus, and the rest is mostly water and a bundle of nerves.
During the Renaissance, jellyfish were thought to be plants, and while 18th century naturalists allowed them entry into the animal kingdom, they were initially classified as zoophytes, something between plants and animals.
We don’t generally hold jellyfish in great regard. If we see them in the water, we tend to get out. And while hundreds of people will turn up to rescue a beached whale, few of us would stop to re-float a stranded jellyfish.
And yet humans are probably responsible for what seems to be an international jellyfish explosion. In recent years, there have been reports from all over the world of uncommonly large blooms of jellyfish driving people out of the water, suffocating commercial fish farms and clogging up fishing nets and the intakes of ships and power plants. According to numerous scientists, these blooms suggest that all is not well within the ocean, perhaps something to do with climate change, pollution, overfishing, or a combination of all three.
Evidently something is out of balance, but, as many species suffer, the jellyfish prospers. As larger oceanic creatures are fished out, there is more food for jellyfish. They don’t have many predators, and many of them are better suited to warmer water. It seems that one of the most primitive life forms is poised to inherit the Earth—its watery parts at least.
Some would, and have, argued that we might as well get used to eating them, because if we continue fishing the oceans at the current rate, there won’t be much else left. “It’s pretty scary, actually,” says Dr Lisa Gershwin, curator of natural sciences at Queen Victoria Museum and Art Gallery in Tasmania and the former national marine stinger adviser to Surf Lifesaving Australia. “There are many locations around the world that have flipped to jellyfish-dominated environments.”
Gershwin is concerned about the state of the oceans and the fate of the creatures within it, but she is not inherently averse to jellyfish. In fact, she is one of their greatest fans, one of the world’s few jellyfish experts, and probably its only jellyfish taxonomist. “When there’s an international jellyfish conference, it usually means I’ve gone somewhere,” she says.
Dennis Gordon, editor of The New Zealand Inventory of Biodiversity and a principal scientist at NIWA, recently invited Gershwin to help review and update the taxonomy of jellyfish found in New Zealand waters. The review will be published in the middle of this year, and will include 34 jellyfish, including three new species. It’s the first time anyone has seriously looked at local jellyfish for over a century, and it was not an easy task.
Several of the species have been described in the literature, but many haven’t been seen since they were first described. Jellyfish are poorly represented in museum collections, partly because they are hard to handle and tend to fall apart, and partly because nobody has really given them much attention. Even though this is an island nation where scores of jellyfish wash up on shores every year, there isn’t yet a scientist in the country who has chosen jellyfish as their area of expertise. Little is known about the life cycle, ecology or behaviour of our jellyfish. We’re not even sure if any of them are endemic.
You have to wonder why none of the country’s science graduates have chosen to become a jellyfish expert, given that the species is of such medical and public interest. Possibly because the jellyfish is a brainless, heartless blob occupying a low bough on the evolutionary tree of life?
“Well, they do have a simplistic form,” says Gordon. “But that doesn’t mean they aren’t interesting. I think they are incredibly aesthetic. When you watch them in an aquarium, with backlighting, and you can see them in all their diaphanous beauty, slowly pulsing away, they are quite stunning…and what could be more charismatic than a stinging organism?”
Jellyfish aren’t actually fish, but the word is used to describe a certain kind of Cnidarian with an umbrella-like body structure. This includes Scyphozoans, the true jellyfish; Staurozoans, or stalked jellyfish, which remain in the polyp stage and attach to the ocean floor rather than swim around; Cubozoans, or box jellyfish; and Hydrozoans, a complex class of animals that often produce small medusae resembling simple jellyfish. The Portuguese Man of War—which isn’t actually a jellyfish but a floating colony of individuals—is a Hydrozoan.
Gershwin and Gordon’s list of New Zealand species includes six stalked jellyfish, one box jellyfish and 27 true jellyfish. The most frequently encountered jellyfish in our parts are Aurelia, commonly known as moon jellyfish; Cyanea, commonly known as lion’s mane; and Desmonema, which doesn’t have a common name but could be described as the spotted one.
Lion’s mane and moon jellyfish can both cause havoc in our commercial fish farms. In 1998, an invasion of moon jellyfish resulted in the deaths of thousands of salmon farmed in the waters of Stewart Island. The deaths were probably the result of jellyfish mucus coating the gills of the fish and suffocating them, and their nematocysts irritating the fish’s skin and causing them to hyperventilate. “They basically slimed the salmon to death,” says Gershwin. “They lost 56,000 salmon in 30 minutes. It was horrific.”
The Aurelia is flattish and whitish, with a fringe of hundreds to thousands of short tentacles around its margin, plus four tightly held short oral arms that don’t generally extend beyond the edge of the bell. It has four distinctive horseshoe-shaped gonads near the middle of the body. Desmonema is dome-shaped, whitish, with reddish-brown dots all over the top of the bell. It has four long, pleated oral arms, and eight clumps of long tentacles that extend from the edge of the bell in a straight line.
The lion’s mane is the largest of all known jellyfish. Those found in the Northern Hemisphere can grow up to 2.5 m across, while those found in lower latitudes, such as New Zealand, have bells that typically grow to about 50 cm wide. The species grabbed headlines—“Invasion of the Giant Blobs”—a couple of years ago when abnormally large specimens washed up near Blind Bay on Great Barrier Island, with the largest measuring 1.5 m across and many others at least 1.2 m across. A large bloom also arrived in the Coromandel early last year, many of which were a metre wide.
The lion’s mane has a purple bell surrounded by what look like layers of frilly yellow petticoats (its egg repositories) and metres of long thin tentacles. One of the new species described in Gordon and Gershwin’s review is a type of lion’s mane jelly-fish. It is distinct from other lion’s mane species in numerous structural features, the most obvious being the raised gelatinous warts on the exumbrella (the top of the body), which is smooth in other species.
The sting of a lion’s mane jellyfish won’t kill us—some victims have described the sensation as being pricked by dozens of pins—but small marine arthropods haven’t got a chance. “They have these massive curtain-like oral arms, basically extensions of their lips, and all these large crenulated drapes,” says Gershwin. “It’s impenetrable, and tiny things can’t get away…on top of which they get covered in slime and stung.”
Small marine arthropods that do manage to escape the crenulated drapes of the lion’s mane will undoubtedly get tangled in the sensory tentacles that trail up to four metres behind the bell—although the tentacles of the Arctic species of lion’s mane can be as long as 30 metres.
Tentacles are grouped into eight clusters, each containing 65–150 tentacles. Each of these in turn is equipped with thousands, possibly millions, of nematocysts—stinging darts that fire on contact with the surface of a prey animal. The tentacles scoop up the stunned prey and transfer it to its oral arms, which pop it into the mouth of the jellyfish, located somewhere on the underside of its bell.
Jellyfish move with a form of jet propulsion—taking water into the bell and then squirting it out the back, creating a jet of water that propels the creature forward. They can also move left to right, but otherwise go where the ocean currents take them. Like butterflies and caterpillars, jellyfish have two life stages: the polyp, like a tiny sea anemone, and the medusa stage, which is what we mostly think of as a jellyfish.
Eggs are fertilised internally and then released as free-swimming larvae—some begin their life hanging onto their mother’s skirts, or, more scientifically, their oral arms. They then develop into polyps, which attach themselves to the sea floor, where they feed and grow and produce other polyps, in much the same way as a bromeliad produces offspring. Some polyps remain as polyps their entire life, but others bud off immature
jellyfish known as ephyra larvae that grow into the umbrella-shaped jellyfish we all recognise. As they were all born together and grew up together, jellyfish tend to stick together, growing from a few millimetres to full size in a couple of months—sometimes just to wash up on a beach near you.
Most New Zealand beach-goers know that jellyfish can sting, but generally they get off lightly, compared with, say, Australians. Northern Australia is unfortunate enough to have Chironex fleckeri, a type of box jellyfish regarded as one of the most venomous creatures on Earth, an animal that has developed a toxic capacity that far exceeds its needs.
“They do have huge metabolic demands,” says Gershwin. “But it’s overkill because they could kill a horse.”
Last Christmas an 11-year-old girl was stung while swimming in the Calliope River, 23 km inland in Central Queensland. She will be scarred for life and may need skin grafts—the venom burned both her legs, a forearm and part of her stomach. But given that victims of box jellyfish typically die within four minutes, she is fortunate to be alive.
She probably wouldn’t be if it weren’t for two serendipitous factors. Firstly, her screams attracted the attention of a couple who doused her legs with vinegar—which stops the nematocysts of the box jellyfish releasing more venom. The man, whose brother was killed by a box jellyfish, always carries vinegar with him. And secondly, her father was trained in CPR and knew how to administer first aid before the toxins locked her heart, after which it would have been too late.
Gershwin is very familiar with the destructive powers of the jellyfish. She did her PhD on the Irukandji (Carukia barnesi). This tropical species is only 8 mm in diameter, but its venom causes a gruesome range of symptoms, collectively known as Irukandji syndrome. Along with unbearable back pain (people describe it as like a drill bearing down on the spine), increased blood pressure, muscle cramps, vomiting and diarrhoea, there’s a psychotic effect in which victims have a sense of impending doom, convinced that they are going to die. They frequently beg for the gun. The symptoms usually last about 24 hours, after which the victim recovers. Between 50 and 100 cases of Irukandji syndrome are reported in Australia each year. Early this year, a man from the Philippines was stung in Queensland while fishing from the deck of a vessel 25 m above the surface of the ocean. All it took was a splash of sea spray, and he ended up in hospital for the next three days.
Like most of our fauna, New Zealand jellyfish are more benign. “You’re lucky,” says Gershwin. “Your jellyfish are really beautiful, but they won’t kill you.”
New Zealand does have one box jellyfish, a diminutive species called Carybdea sivickisi, which grows to about a centimeter cube, is transparent with bright orange blobs (the gonads) and has four orange-striped tentacles. While its sting isn’t lethal, it will produce a blister, one that will hurt and itch before disappearing, only to return at a later date. “Just like herpes,” she says. “But it isn’t a virus, it’s an immunological response.” Fortunately, these seem to be rare in New Zealand waters; the last was seen in Cook Strait in 1985.
When Gershwin did her thesis only one species of Irukandji had been described, but she has now identified 14, and 145 other jellyfish species new to science. Who knows how many species of jellyfish are in New Zealand waters just waiting to be discovered?
“We suspect that there are more than we know about,” says Dennis Gordon, who goes on to make a plea for information from amateur jellyfish enthusiasts. Photographs, notes, even specimens collected in jars of ethanol would be extremely helpful in our understanding of Cnidarian biodiversity. Divers in particular should be alert for stalked jellyfish that live on the ocean floor—there are at least six species out there, but nothing is known about their distribution or biology.
According to Lisa Gershwin, there’s a whole planktonic world just waiting to be discovered. “Every time I get the plankton net in the water I don’t know what’s going to come up, so I always have this feeling of Christmas—you’ve got a present, but you don’t know what’s inside.”