In September, 62-year-old marathon swimmer Diana Nyad attempted to swim from Cuba to Florida without a shark cage, which had never been done before. But after making it roughly halfway there, Nyad had to abandon her goal. It wasn’t sharks that forced her to quit, but jellyfish: she received a number of stings, including to her face. The pain had become unbearable, she said, and made it dangerous for her to continue.
In the Gulf of Mexico, fishermen were complaining about them, too. Just over a year after the BP oil spill, a blanket of milky white moon jellies was clogging the water, slowing down business. This summer, media reports said jellyfish were being spotted on south Florida beaches “in record numbers.” Across the Atlantic, in the U.K. and the Mediterranean, bathers worried about large swarms of jellies (which are called blooms). A nuclear reactor in Scotland was temporarily shut down in June after jellyfish clogged its seawater filters. Off the coast of Japan, reports suggested Nemopilema nomurai, or Nomura’s jellyfish, which are as big as refrigerators, are increasing, but researchers aren’t sure exactly why.
Scientists have been sounding alarms about the “rise of slime” for at least a decade. As fish and other marine species are killed off by threats like overfishing, pollution and climate change, some say jellyfish—which have lived through Earth’s five mass extinctions—are taking over. Increasing jellyfish populations could be disastrous, hurting tourism, impeding shipping routes and crowding out the fish we typically rely on for food. But as dramatic as it sounds, experts are by no means in agreement. Among the small, tight-knit community of jellyfish scientists, the question of whether our oceans really are becoming a jelly-filled ooze is hotly debated.
Several types of jellies live off the Canadian coasts, including a tiny red one of the genus Crossota, which lives deep in the Arctic ocean and has appeared on a Canada Post stamp. They’re remarkable animals. “A jellyfish’s body is unlike any other species,” says Dave Albert, a jellyfish researcher at the Roscoe Bay Marine Biology Lab in Vancouver. Its parts radiate from a central axis, like a flower. Some pack a powerful sting, like the box jellyfish, which is found in tropical waters around Australia and has a deadly venom. Even harmless jellyfish stings can still be quite painful: hot water, meat tenderizer and papaya have all been touted as remedies.
Instead of a brain, jellies have a ring of neurons around the edge of the bell that functions as a nervous system; far from being brainless blobs, they exhibit complex, puzzling behaviours. According to Albert, moon jellies surface in the evenings, especially in the summer, although the reason why isn’t known. They’ll stick together in big groups, sensing each other’s presence through a chemical signal that also isn’t really understood. In Roscoe Bay, all the moon jellies will sometimes clump together in one side of the water, he says. “I’ve searched the empty side to see if I can find some, and there are none,” Albert says, calling this “probably the most ancient form of a social behaviour.”
In some overfished parts of the ocean, jellies have replaced plankton-eating fish as the dominant species, “hinting at a future ‘gelatinous’ ocean,” notes a recent study published in Science. Jellies are blind and slow, so they’d seem to be worse hunters than fish, but “they’re actually very successful as predators,” says Sean Colin, associate professor at Roger Williams University in Rhode Island, who co-authored the Science study. (The box jellyfish is an exception: it has 24 eyes.) Jellies pulse their bells to create a feeding current, pushing water through their tentacles to capture prey. “They’re feeding all day long,” Colin says. Jellyfish have evolved to have bigger bodies, the study notes, which makes them slower swimmers but better feeders.
These voracious predators can have a big impact on the food web. Jellies consume plankton that might otherwise be eaten by fish. “If you’re a fish that eats jellyfish, it’s great,” says Rob Condon, faculty research scientist at Dauphin Island Sea Lab in Alabama. “But most don’t.” (Leatherback turtles eat jellyfish. It’s also cooked in Chinese cuisine.) “Jellies take up a lot of the food sources that fish would eat, and convert it into mucous and slimy material,” says Condon, lead author on a recent study that described this process. The mucous and slime they produce go on to feed tiny ocean microbes, but “the microbes convert it into a form the fish can’t use,” he adds, which could ultimately hurt ﬁsh populations.
The waters off Japan are being plagued by mobs of Nomura’s jellyfish, which can weigh more than 450 lb. and have a bell more than two metres across. According to Hiroshima University’s Shin-ichi Uye, records show that Nomura’s jellyfish blooms happened only three times in the last century. But then the species bloomed every year from 2002 to 2009, with the exception of 2008, he says. Their seeding and nursery ground is in the Yellow and East China seas, and ocean currents carry them to the Japan Sea, so studying them is politically complicated. “It is impossible for us to enter Chinese waters to investigate them,” Uye told Maclean’s in an email from Tokyo. (Young jellyﬁsh en route to Japan are monitored.)
These ocean-going monsters don’t have a powerful sting, but they can cause serious problems for the fishing industry, even capsizing boats unlucky enough to catch them in a net. “I do think that jellyﬁsh populations are increasing globally,” he says. “Particularly in the east Asian seas, no doubt.”
But the notion that jellyfish are increasing around the world is far from certain. Condon is the lead investigator of the Global Jellyfish Group, a band of 25 scientists trying to understand this. Part of the difficulty is that jellyfish research “only really kicked off in the 1990s,” he says. “The perception was they weren’t important.” When fishery surveys were done, he adds, they typically didn’t count all these slimy, seemingly useless blobs.
People are much more aware of jellyfish blooms today, but that’s part of the problem, too. According to the jellyfish group’s calculations, in the last decade media reports have greatly outnumbered academic papers and scientific studies. Jellyfish blooms are nothing new: Condon has studied newspaper reports from the turn of the last century, and the Cambrian period (about 500 million years ago) by studying fossils. Researchers still don’t understand what causes a jellyfish bloom, but he says it must be part of their natural cycle.
Condon believes that jellyfish numbers may be growing in some parts of the world, like Japan. But as for whether populations are increasing globally, he says there isn’t enough evidence yet to say. Scientists are starting to gather better data, partly thanks to citizen groups. Several “Jellywatches” have been set up in different countries, including a website that captures sightings from around the world. “If you tried to mount a scientific expedition to do this, it would be very expensive,” says Steve Haddock of the Monterey Bay Aquarium Research Institute, who launched Jellywatch with Katherine Elliott, his intern at the time, in 2009. “Instead, we’re relying on the fact that people experience the ocean daily, everywhere.” Despite the number of media reports about jelly blooms this summer, Haddock says it was “normal or low” this year on the U.S. East Coast, in the Gulf of Mexico and the Mediterranean.
If public paranoia about jelly blooms has grown, our appreciation has, too. In 2008, research into the jellyfish’s glow won three researchers the Nobel Prize in Chemistry after they discovered how to use a green fluorescent protein to watch invisible processes inside the body, like how cancer cells spread. At public aquariums, in the last decade or so, jellyfish exhibits have exploded in popularity. Watching colourful jellies swirl around inside a tank “hypnotizes you,” says Alex Andon, 27, who runs Jellyfish Art, which markets desktop-sized jellyfish aquariums to the public. They’re frequently compared to nature’s lava lamps, although that doesn’t seem to do justice to such a complex, ancient animal.