Jellyfish blooms creating oceans of slime

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In the last decade enormous plagues of jellyfish have been taking over the seas. And it is our fault.

After an entertaining time seeking out octopus and cuttlefish among the rocky architecture at the bottom of the Mediterranean sea, my air ran low and it was time to surface. I noticed my fellow divers rising above me were adopting a strange hunched posture, tucking their hands into their armpits and bowing their heads low.

As I rose to a couple of metres below the surface, I saw the problem too late: the shallow water was carpeted with mauve stinger jellyfish (Pelagia noctiluca). There was no avoiding it, reaching the surface meant I had to swim through the flames of stingers.

Onshore, a diver offered to help soothe the burning lashes across my neck, forehead and hands. "I could pee on them," he suggested. I declined.

Locals told me the carpet of jellyfish, known as a bloom, was not an isolated case. My dive instructor said he had seen massive blooms off the coast of Gozo every year since 2000. But never before then.

Global problem

In fact, huge annual jellyfish blooms have been cropping up not just across the Mediterranean, but also the Black Sea, the Gulf of Mexico, and the Yellow and Japan Seas.  Is this a bizarre blip in the continually changing balance of oceanic life, or the beginnings of a new state change in marine diversity?

Or in other words: in the Anthropocene, will the seas be filled with slime?

If they are, we face some serious problems. Last year alone, nuclear power plants in Scotland, Japan, Israel and Florida, and also a desalination plant in Israel, were forced to shutdown because jellyfish were clogging the water inlets. The entire Irish salmon industry was wiped out in 2007 after a plague of billions of mauve stingers – covering an area of 10 sq miles (26 sq km) and 35ft (11m) deep – attacked the fish cages. Two years later, a fish farm in Tunisia lost a year's production of sea bream and sea bass after jellyfish invasions.

Perhaps the most extraordinary blooms have been those occurring in waters off Japan. There, refrigerator-sized gelatinous monsters called Nomuras, weighing 485lb (220 kg) and measuring 6.5ft (2m) in diameter, have swarmed the Japan Sea annually since 2002, clogging fishing nets, overturning trawlers and devastating coastal livelihoods. These assaults have cost the Japanese fisheries industry billions of yen in losses.

Human factor

Marine ecologists are warning of worse to come, and pointing the tentacle of blame at us. Some researchers fear that human changes to the marine environment may be leading to a tipping point in which jellyfish will rule the oceans, much as they did hundreds of millions of years ago in pre-Cambrian times. In 2009, Australian marine scientist Anthony Richardson and his colleagues published a research paper entitled The jellyfish joyride, in which they warn that if we do not act to curb current blooms, we will experience runaway populations that will cause open oceanic ecosystems to flip from ones dominated by fish biodiversity to ones dominated by jellyfish.

The problem is that no one really knows what causes the blooms. Some believe that population explosions result from overfishing of their dining competitors and predators, which include more than 100 species of fish, and animals such as turtles. However, other researchers point out that overfishing also hits jellyfish by reducing their food availability.

Either way, what is clear is that jellyfish are simply better prepared than other marine life for many of the ways humans are changing the ocean environment, such as warmer temperatures, salinity changes, ocean acidification and pollution. In this sense, humans might be jellyfishes’ best friend.

For instance, pollution can cause algal blooms that reduce the water's oxygen content. This hits muscular swimmers like fish hard, but jellyfish can cope far better with these conditions.

Warmer water encourages jellyfish reproduction, and they can also better tolerate population crashes because their reproductive strategies are complex and adaptable. Some species of jelly can clone themselves, whereas others reproduce sexually but also have a polyp stage – like corals, with which they are related – that allows large populations of immature individuals to multiply while waiting for the right conditions to mature into adulthood. In these ways, they can withstand impacts that devastate other marine species.

Even the coastal infrastructure we build seems to be working to their advantage. Rob Condon, a marine scientist at Dauphin Island Sea Lab in Alabama, says that the pontoons, piers and even drilling platforms help provide anchors for jellyfish polyps, encouraging local population explosions.

Slippery customers

But Condon, who set up a global jellyfish database initiative (the wonderfully named JEDI) to monitor blooms, says that the “jellygeddon” scenario envisioned by Richardson and others is unlikely. Jellyfish blooms are nothing new, says Condon, "4,000 years ago in Ancient Crete, they used to paint jelly blooms on their pottery, and even in the 1920s, media were reporting “unprecedented” numbers of moon jellyfish in Monterey Bay."

The JEDI team of more than 20 scientists has now compiled over half a million reports dating back to 1790, and found "no evidence for a global increase in jellyfish blooms". There are some places that are experiencing a pronounced increase in jellyfish blooms, for example "they went berserk in Japan," Condon says, but the data does not support a global increase.

Gathering data on jellyfish, though, is notoriously difficult. Although 70% of the planet is covered by ocean, we really only have a hazy idea about most of the life outside of coastal or estuarine zones. Jellyfish, which inhabit open oceans and deep waters, are still an enigma in many ways. Monitoring individuals and blooms cannot be done by satellite because they are so transparent, have very low biomass, and often occupy waters below the optical depth for satellite penetration. Even finding polyps and larvae in sea grass is tricky. So, despite JEDI's efforts, no one can say for sure whether blooms are increasing or not.

Extreme measures

Dealing with blooms where they do turn up is tricky. Shin-ichi Uye, professor of biological oceanography at Hiroshima University in Japan, has devised an early-warming system, called Stop Jelly, which can predict blooms of huge Nomura along the Japanese coastline up to three months in advance. It may allow fishermen to plan ahead, and perhaps allow patrols to ward invaders off before they cause trouble. The government is providing specially designed layered nets, which snare the jellyfish in one, while trapping escaping fish in another.

But once you trap blooms, what do you do with them? Japanese fishermen initially tried chopping them up in the waters, only to discover that the Nomura's defence strategy is to release its sperm and eggs, thus propagating the problem. In Spain, special jelly patrols were dispatched to fish up huge netfulls of them for burial in landfill.

Condon thinks this is a shame. "It might be a good quick-fix for socio-economic reasons, but we don't know what environmental effects destroying blooms could have," he says. "Jellyfish are an important food source for apex predators, and if we start tinkering with the natural bloom system, we don't know what the ripple-down effects may be." They may even help mix and fertilise the world's oceans, some researchers think.

Perhaps one solution is to sustainably exploit their abundance. Jellyfish do have their uses: in collagen preparations (to treat rheumatoid arthritis, for example), they are popular attractions in aquaria, and their fluorescent proteins have been instrumental in biomedical discoveries.

And, of course, they are a source of food. In Japan and other parts of Asia, jellyfish are dried and chopped into noodle-like strips to be added to soups, for example. Some entrepreneurial Japanese are even making vanilla-and-jellyfish ice cream. Jellyfish are 80% protein and very low in fat, although the high sodium content probably outweighs their health benefits.

So… jellyfish and chips anyone?