The giant jellyfish invasion mystery

But underfoot, the blobs were not nearly as troublesome as underwater and intact. They were pieces of Nemopilema nomurai, the giant jellyfish that in recent years have swarmed Japan’s seas with alarming frequency, decimating fisheries and damaging the country’s marine economy.

In the last century, Nomura “blooms,” as dramatic jellyfish aggregations are called, were recorded just three times: in 1920, 1958 and 1995. Then, starting in 2002, blooms hit six times in eight years. In 2009, the last and worst bloom year, a Japanese fishing trawler capsized trying to pull a net full of Nomura, which can grow to the size of a Smart car.

Japan is not the only nation blighted by jellyfish. A storm of mauve stingers wiped out Ireland’s only organic salmon farm in 2007. In the Gulf of Oman, a species called Crambionella orsini clogged the intake pipes of coastal power plants. The Benguela current off the coast of Namibia was once a rich sardine and anchovy fishery; now, jellyfish exceeds fish biomass more than three to one.

Yet for all the apocalyptic headlines these events have generated, scientists are deeply divided about what is happening. Is there a global jellyfish boom underway? Or are we witnessing a natural cyclical uptick — a jellyfish El Niño, rather than a jellyfish global warming?

That question is a matter of intense debate, and how it is resolved will affect anyone with a stake in the marine world — culinary, economic or environmental.

‘Kingdom of fish’

Individual researchers’ responses to the debate are often coloured by the state of their local seas. So it is no surprise that Shin-ichi Uye, a biological oceanographer at Hiroshima University and Japan’s leading jellyfish scientist, fears the worst. Chatting over barley tea in the mess hall of the Toyoshio-maru, his research vessel, Uye framed his take as a parable.

Jellyfish ruled the ancient seas, he said. Then came the “fish kingdom.”

“And now human beings have removed the fish and destroyed the fish kingdom,” he said. “It’s a reverse of natural history. And who did this? Human beings.”

A day earlier, the Star had boarded the Toyoshio-maru with Uye and a handful of students and researchers. The annual research cruise is an opportunity for them to spend a week tallying up observations that could help solve the larger riddle of what is going on with the world’s jellies.

But, in many ways, our journey only deepened the mystery.

We failed to find any aggregations of Aurelia, the common moon jellyfish, which is the most widely distributed jellyfish in the world and one that has bloomed dramatically for more than a decade in the inland sea we visited.

We met fishermen who earned a comfortable living from harvesting the abundant, edible Rhopilema. We sampled their catch and visited a warehouse packed with jellyfish. Yet we never saw a live Rhopilema at sea.

We travelled to Tsushima to meet Sakumoto, with whom Uye has collaborated in the past, hoping to glimpse the notorious Nomura. All we saw were the ugly blobs on his boat’s deck — a piece of Nomura bell and a piece of its arms, but nothing more. It was the end of a confounding journey.

A day after disembarking, Uye sent an email. Sakumoto had discovered more than 100 Nomura in his nets that morning. His neighbours’ nets were also clogged.

It brought to mind another email Uye had sent.

“Although the jellyfish have no words to speak to humans, they are giving a sign to humans by aggregating themselves grotesquely,” he wrote. “We human beings have to learn the message from them.”

But what is their message?

Ancient creatures

The jelliness of jellyfish means they are terrible at leaving behind fossils. With no bones to fossilize, all we have are body impressions left in ancient sediment beds. As a result, much of the early history of jellyfish is — you guessed it — a mystery.

Based on the tiny handful of sites that do exist, scientists know that jellyfish have been around for at least 500 million years. That’s more than 75 million years before the appearance of land plants and more than 250 million years before the first dinosaurs. Humans began walking upright about six million years ago.

“I think it’s fair to say that something like the jellyfish that we have today probably have been around as long as any multicellular organism,” said Larry Madin, an expert in gelatinous zooplankton and director of research at the Woods Hole Oceanographic Institution in Massachusetts.

Being jelly must be pretty advantageous if the trait is hundreds of millions of years older than, say, being furry. And jellies boast some extraordinary features that help explain why they have persisted for millennia and why they have the ability to form sudden blooms.

Their bodies are more than 95 per cent water. So growing rapidly doesn’t burden jellyfish with the same metabolic demands that it does for more complicated organisms. Observe any Homo sapiens teenager in its habitat, and you will probably find the specimen consuming an absurd number of frozen pizzas and growing at a clip of an inch or two a year. Nomura, meanwhile, can add 3 per cent of their body mass a day, tripling their size in less than two months. (If teenagers had arms that were several times the length of their bodies and capped with “mouthlets,” and if those teenagers spent their days drifting through a sea of tiny pizzas, they would probably triple their size in two months, too.)

Many types of jellyfish have double-pronged reproductive systems: they reproduce both sexually, combining genetic material from two individuals, and asexually, by duplicating a single individual.

A female Nomura, for example, after swimming through a cloud of sperm, can release up to a billion fertilized eggs. Those eggs, which have the advantage of genetic diversity, hatch into tiny swimming larvae, attach themselves to a hard surface and become anemone-like polyps.

If conditions are right, each jellyfish polyp can bud many mini-jellyfish — new individuals that are exact genetic copies of each other — in a matter of days. This secondary sexual process increases the number of offspring from a single individual with very little work.

But when conditions aren’t right, many of the species associated with troublesome blooms have another handy trick: the ability to go dormant until things improve. When the water is too cold, too hot, too salty, or otherwise undesirable, the polyps harden into cuticle-walled cysts. Nomura cysts, Uye discovered in his lab, can survive for at least six years, biding their time.

Jellyfish are often described as simple or primitive. That couldn’t be further from the truth.

Nomura, Uye said more than once, are “like aliens.”

The mystery deepens

Despite their ancient origins and evolutionary success, jellyfish were long ignored as a serious subject of scientific scrutiny. There are still only about 200 devoted scientists in the world, by Uye’s count.

“Jellyfish research is in the infant stage,” he said.

Scientists don’t always mean the same thing when they use the term “jellyfish.” Some use the word to refer to the adult members of a specific group called Scyphozoa, the “true jellyfish.” Nomura, Aurelia, Rhopilema and most other easily recognizable types of jellyfish are scyphozoans.

But other scientists use the term “jellyfish” to describe all gelatinous-bodied zooplankton, which lumps together groups such as scyphozoans, cubozoans (like the deadly Irukandji), hydrozoans (like the Portuguese man o’ war), ctenophores (a totally different phylum also known as comb jellyfish), and some pelagic tunicates (another totally different phylum that includes tiny squidgy things called salps).

Many jellyfish bloom studies subscribe to this wider definition — and this story does too, for the simple reason that gelatinous animals don’t have to belong to the same family to become a pest to humans.

From the terminology on outwards, questions proliferate. No one has ever seen a Nomura polyp in the wild (for his cyst experiment, Uye used polyps grown in a lab). No one has ever seen a Rhopilema polyp in the wild, either. Researchers know only generally where those two jellyfish seed, despite their economic importance, one for better and one for worse.

But the biggest problem hampering our understanding of blooms is the lack of long-term data on jellyfish numbers. Historically, jellyfish were too economically unimportant for fisheries scientists, and too big and weird for plankton scientists: they were a nuisance to all, and often literally cast out of marine studies.

“There are even old papers from the ’50s with instructions on how to study plankton, and step one is remove all the jellyfish,” said Lucas Brotz, a jellyfish researcher at the University of British Columbia.

Because so few scientists bothered to collect and count jellyfish, there is little information about what “normal” jellyfish populations looked like 100 years ago, or even 20 years ago. That makes it hard to say whether “normal” has changed.

Everyone agrees the state of the data is unsatisfactory. The schism is over what to do about it.

Brotz became the de facto spokesperson for one side of the debate thanks to a highly publicized paper he authored last year.

For some context, Brotz is a PhD student at the Sea Around Us Project, a laboratory devoted to figuring out how fisheries are modifying the sea and what to do about it. He told the Star about a recent visit to the Tsukiji market in Tokyo, the largest fish market in the world, where he saw stalls crammed with the ocean’s bounty.

“This happens every single day?” he remembered thinking. “If you take that much out of the ocean, it’s obviously going to change things. There’s no way it can’t.”

As a scientist, Brotz is careful not to let his knowledge of the pressing need for ocean conservation influence his research.

But his work is certainly fuelled by a sense of urgency. Faced with the paucity of long-term data on jellyfish, Brotz didn’t want to wait several decades for better research to emerge. So he designed a study that incorporated non-scientific or “anecdotal” data to provide a clearer picture of what is happening in 45 distinct ocean regions that cover the globe. The sources were rigorously scored based on reliability: a news story quoting a lifeguard would be given very low confidence, surveys of fishers were weighted more heavily, and long-term scientific data sets were scored highest.

The resulting signal was shaky, but unmistakable: Since 1950, Brotz and his co-authors found, jellyfish abundance had increased in 28 of the 45 marine ecosystems. The study was front-page news in Canada and generated headlines across the world.

Then, in January of this year, came a study with a very different conclusion.

Its lead author was Rob Condon, a marine scientist at the Dauphin Island Sea Lab in Alabama, and it was co-authored by a who’s who of jellyfish scientists, including Uye.

Condon is wary of anything but the hardest data. He is adamant that if we are going to funnel resources into the conclusions of science, the method must be rigorous — and beachgoers’ observations in newspapers aren’t that.

“You’ve got to let the science do the talking . . . the numbers, and what the data say,” he said. In science, opinion comes after the data analysis, not before it.

Condon’s group only used jellyfish counts that lasted longer than a decade. That left 37 data sets collected between 1874 and 2011.

Their analysis showed a slight rise in jellyfish abundance since 1970, but too weak of a trend to be called a global increase. The strongest trend was that jellyfish numbers cycled up and down over approximately 20-year periods — a natural oscillation, which was on an upward swing in the 1990s and 2000s.

This data also has shortcomings. Sampling methods varied. Eighty-seven per cent of data sets were collected in the Northern Hemisphere. Only nine began collection before 1960, though Condon maintains the longest-running data sets cover key areas.

Condon doesn’t rule out the idea that there could be an upward shift in the jellyfish baseline on top of the natural cycles, like how recent studies have suggested that global warming has triggered more El Niño years. We just can’t say yet for sure. “We really need about another 30 years’ worth of data to make any conclusive statement about jellyfish blooms.”

Brotz and Condon are both exceptionally polite with regard to each others’ work, and they tend to emphasize the many points on which they agree.

But Condon can’t accept Brotz’ unscientific sources, and Brotz can’t abide by Condon’s wait-and-see approach.

“It’s better to be safe and even say no comment about something than to give a quick and easy sound bite to a reporter. Scientists in general . . . fall into that trap,” said Condon. “There are social and economic consequences.”

Brotz said Condon’s group “would say we have to wait a few more decades. I would say, we don’t really have a few more decades to wait.”

Japan: Ground Zero

One place where the data paints a clear picture is the Sea of Japan: whatever is going on globally, nearly everyone agrees there is something remarkable happening here. While the last true Nomura bloom was in 2009, surveys from this year indicate that Nomura will still be a problematic presence. Aurelia aggregate often, particularly in the Seto Inland Sea and Tokyo Bay, and last year saw a bumper crop of Rhopilema.

Experts have many theories about how human interference might be triggering jellyfish blooms. But the easiest way to absorb the science is to chat with the fishermen who have spent their lives on Japan’s seas, and whose observations sync neatly with the scientific literature.

In Hakata Bay on Kyushu, Japan’s southernmost main island, Uye introduced the Star to Yoshikatsu Mori, who had spent 60 of his 75 years fishing the local waters. Mori told us that this past spring, Aurelia bloomed so heavily that some bottom-trawler fishing boats moving through the bay would find themselves at an abrupt standstill. Their underwater nets had encountered an aggregation so thick it stopped the boat like a wall. Some weeks, fishermen didn’t bother to leave their houses.

“In my younger days, there were many fish in Hakata Bay. Now, there are almost no fish here, but it is full of jellyfish,” Mori said as Uye translated.

In fact, fishery depletion is one of the primary reasons scientists think jellyfish blooms might be happening. Some fish eat jellyfish. Other fish compete with jellyfish for the same resources. Since one study estimated that stocks of large predatory fish are at 10 per cent of pre-industrial levels, it’s safe to assume that both jellyfish predators and competitors have dwindled.

Mori brought up another point. In the small port where he docks his boat, a beach had been paved over. Previously, Aurelia would strand themselves on the beach, dehydrate in the sun and die. Now, there was nowhere to do that.

Scientists don’t think a decline in beaches is one of the ways humans have helped jellyfish. But increased marine substrate is: as more docks, bridges and other built environments are added to the sea, there is a far vaster habitat for polyps.

From Hakata Bay, the Toyoshio-maru churned across the choppy ocean and into the Ariake Sea, a shallow interior sea further to the south and a Rhopilema hot spot. There, we met another wizened fisherman: Katsueda Aramaki, also 75.

Aramaki said that Rhopilema, the edible jellyfish, moved through clear cycles since he began fishing at age 20. In the late ’70s, there was two-year spike. Then the population declined, before starting to climb again 10 years ago. (Aramaki told us this as we snacked on Rhopilema he had processed in his shed, which his wife served with soy sauce, wasabi, grated ginger and mayonnaise. Jellyfish is crunchy, like cartilage, and not unpleasant tasting.

But on top of the natural oscillation there seemed to be a general increase, Aramaki said. The sea had changed: he began his career diving for razor clams and other bivalves. Now, he said, the only way to make money is jellyfish.

“The bivalve stock enormously declined. The fish catch, the shrimp catch, the crab catch decreased also. Only the jellyfish is increasing,” Uye translated.

Aramaki blamed the change on the Ariake Sea’s seaweed aquaculturists, saying they had pumped the water full of harmful nutrients. Again, scientists think that fertilizer and other nutrient runoff, which eventually strips a water body of oxygen, affects jellyfish less than other mammals. In the Gulf of Mexico, fertilizer runoff has created a widening “dead zone,” where jellyfish are common and fish have suffered. Diana Nyad, the 63-year-old who just completed the first unaided swim from Cuba to Florida, called off previous attempts because she was overwhelmed by jellyfish stings.

Sakumoto, the fisherman we visited on Tsushima, hit on the last important theory behind why jellyfish might be increasing: global warming. The Yellow Sea, where Nomura are thought to spawn, has warmed by 1.7 degrees Celsius since 1976. In experiments in Uye’s lab, Nomura asexual reproduction rose 20 per cent with similar temperature increases. Only seven species of jellyfish do not increase in abundance in response to warmer waters, according to one study.

Sakumoto had been the hardest-hit of any fishermen we spoke to. Tsushima is a ragged-shored island halfway between Japan and Korea and directly in the path of the Nomura that migrate north through the Sea of Japan over the course of the summer and fall. Sakumoto is a set-net fisherman: every morning he brings his boat to a permanent net to empty the catch. In 2009, the worst Nomura bloom year, he arrived to find his expensive set net gone. The weight of the jellyfish had destroyed it.

Yet Sakumoto also had the sunniest response of all the fishermen we met. He expressed hope for the future of the oceans. “We fishermen always anticipate a good catch, not a bad catch,” he said. “We tend to be optimistic.”

If jellyfish numbers are increasing as a result of a natural, temporary cycle — if jellyfish booms are like El Niño — Sakumoto’s optimism will be borne out, and the most cautious of the researchers will be vindicated, perhaps saving us from throwing money, effort and time after misleading science.

If jellyfish numbers are increasing globally and permanently as a result of human activities, the future could be scary indeed. Very much like global warming, by the time the data is irrefutable, the ocean may be too degraded to fix.

Just before Uye disembarked from the Toyoshio-maru, I asked him if he shared Sakumoto’s optimism. He told me no, with a sad smile.

But later, he sent me the email: he was ashamed of his pessimistic response and wanted to change it. He sent me the note about jellyfish’s message to humans.

“I admit that it is hard to change the current human behaviour to seek economic development (or money), which is the core factor to deteriorate the healthy . . . marine ecosystems to induce the growth of jellyfish populations.”

But, he continued, “The jellyfish act a messenger to us. I would be optimistic that we human beings are wise enough to listen to their voiceless voice.”