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Last updated on April 17, 2014 at 21:23 EDT

Jellyfish are Taking Over the Mediterranean

February 16, 2008

For years, Mediterranean beaches have been plagued by jellyfish. Now scientists are reporting that the problem is far worse than they had feared – and that a new generation of the poisonous creatures is poised to overwhelm the sea.

A deadly sea change

Perhaps you thought that jellyfish were a summer hazard of Mediterranean beaches, freak invaders that spoil your enjoyment of your favourite southern holiday resorts – but only momentarily, and only if you are unlucky. Well, if so, be warned.

Jellyfish are now active throughout the winter too, building up strength for their annual assault upon the Mediterranean’s northern shore. What’s more, they won’t be going away. Jellyfish, says Spain’s top scientist who specialises in these glutinous stinging creatures from the deep, are here to stay.

“We think of jellyfish as a worrying summer problem, particularly here in Spain, where we are so dependent on the tourist industry, says Josep Maria Gili, research professor at Barcelona’s Institute of Marine Sciences. “But we have found that they come ashore just as frequently in the winter months, although no one notices. We’ve established that they proliferate off our shores all year round. It means the situation is much more serious than we thought.”

Last November, the institute launched for the first time a pioneering research programme to monitor jellyfish movements off the Costa Brava all year round. Scientists were alarmed to discover that large groups (“blooms”) of Pelagia noctiluca – the ubiquitous mauve stinger familiar to many holidaymakers who have been brushed by its poisonous tentacles – were assembling in large numbers throughout the winter months.

Between last November and January, 30 separate colonies of mauve stinger were detected in concentrations of between four and 10 creatures per cubic metre of water. One day last January, thousands of jellyfish were detected off the coast near Girona, north of Barcelona. A few days later, a similar sighting was reported near the Balearic island of Ibiza and, within a week, hundreds more jellyfish were spotted around the popular Mediterranean port of Valencia.

This generation was formed last autumn; they will themselves reproduce in the spring in readiness for what Professor Gili predicts will be another massive summer invasion.

“They mostly live 10 miles or more off shore. Conditions in recent years have been ideal: very mild and with little rain, with none of the winter rainstorms and icy blasts we usually experience, and with unusually warm sea temperatures. People have been really enjoying it,” he adds with a laugh, swiftly curtailed. “But these are ideal conditions for jellyfish, and they’ve become a continuously present phenomenon, not just a seasonal one.”

Alarmed by the intensity of and frequency of jellyfish invasions over the past three years, Spain’s environmental authorities financed the study. Now they need to put money into preventative measures, Professor Gili says.

Last summer, amateur mariners were mobilised for the first time the length of Spain’s southern coast as jellyfish scouts, to operate as an informal early warning system to alert authorities on shore when an invasion was imminent.

This year, Professor Gili wants the initiative put on a much more professional footing. “We must take measures, and the government must provide the finance, for a flotilla of small boats to patrol the shoreline, ready to scoop up the jellyfish as they head for land, when they are about 100m from the shore.”

There’s no point pursuing jellyfish when they are out to sea, he says. They sink beneath the surface, and you risk netting fish and other marine life, and breaking the tentacles. Those that are swept into shore are usually dead or dying, although their sting remains intact.

“Those floating on the surface can be easily caught in small nets called “pelicanes” if spotted in time. Removed from the sea and dropped into fresh water, their poison drains away within 48 hours. “They no longer pose a health risk and can then be recycled as protein-rich fertiliser,” says Professor Gili.

“The important thing is to catch them whole without causing them damage, because the tentacles remain poisonous even if broken off, and even if the creature is dead.”

But these are short-term measures and they offer no solution to the wider problem of why jellyfish have become so prevalent. Last year, jellyfish were frequently found in concentrations as high as 100 per cubic metre.

Millions of jellyfish washed up on Spanish beaches last year, and tens of thousands of holidaymakers were treated for painful allergic reactions to their stings.

Overfishing is the main cause, the scientist insists. And the only solution is to change the fishing practices of countries that have stripped the world’s seas of big fish such as swordfish and red tuna which feast upon jellyfish.

The other traditional predator of jellyfish – the leatherback turtle, Caretta caretta – has been driven to the point of extinction. The beaches where it lays its eggs have been lost to tourism. It’s not just a Mediterranean problem. Increases in the populations of jellyfish have been “spectacular” from Japan to Africa, from Alaska to Australia, Professor Gili says. “Every time we are swamped with jellyfish, the sea is sending us the message that it is sick and we are mistreating it. We face a huge problem of ecological imbalance.”

Overfishing on a global scale has left jellyfish without the big fish and crustaceans that are their natural predators, and without small fish, such as sardines and whitebait, that compete with them for minute marine creatures and plankton. “Jellyfish are left with all the food they want, so they can reproduce without limit,” says Professor Gili.

To make matters worse, jellyfish gorge voraciously on fish eggs and larvae. The common Aurelia species, for example, whose variant Aurelia Aurita or “moon jellyfish” is common in the Mediterranean, can hoover up to 10 young herrings an hour. Jellyfish, as a result, are taking the place of fish in the global ecosystem.

Apart from the ubiquitous mauve stinger, various other species thrive in the Mediterranean. One regular visitor is Cortylorhiza tuberculata, known as “fried egg”, which luxuriates in the warm, salty lagoons of the Mar Menor, near the fashionable Murcian resort of La Manga. These lagoons are rich in nutrients from fertilisers drained from the region’s intensive plastic-greenhouse agriculture. The fried egg’s sting is mild, but its sheer numbers transform the water into a milky gloop.The Mar Menor is so infested that latterly 1,000 tonnes of “fried egg” have been cleared from it every year.

The Rhizostoma pulpo, or octopus jellyfish, named for its eight long tentacles, is also on the increase.

The fearsome Portuguese Man o’ War (Physalia physalis), whose sting can be fatal, is increasingly swept towards Europe’s Atlantic coasts, in “blooms” resembling a sea of plastic bags. Isolated examples sometimes reach the British Isles, but currents have yet to drag them through the Gibraltar Strait into the Mediterranean.

For all their undulant mobility, jellyfish have little control of their movements. They are not actually fish, but a kind of giant plankton that cannot swim, driven this way and that by winds and currents. In an extreme demonstration of imminent ecological breakdown, they come ashore to die. “Jellyfish are a natural part of the marine environment, but the scale of what’s happening now is a warning that something’s going very wrong,” says Dr David Santilo, a marine biologist for the Greenpeace research laboratories at Exeter University.

Do we then face a return to primeval slime? “A lot of pressures are pushing in that direction,” says Dr Santilo. “The mechanisms are there to make that happen. Ecosystems are flexible up to a point, but no one knows when elasticity breaks into a different sort of ecosystem and you get an irreversible shift. This plague of jellyfish is a like hazard warning light. It’s a wake-up call.”

Jellyfish plagues have happened before, in cycles of seven to 10 years. But recent cycles are shorter, and every year for the last two decades, the blooms have become bigger, denser and longer lasting.

Until three years ago, no one thought to take special measures other than to provide first-aid to bathers suffering painfully swollen limbs, and to close infested beaches. Now that the glaucous visitors arrive en masse every year alarm bells are ringing amid hard evidence suggesting they will be with us for the foreseeable future.

The Mediterranean’s temperature is now two to three degrees warmer than its usual winter minimum, in a clear symptom of global warming, while lack of rainfall has caused a drop in the volume of cooler fresh water entering it from the sky, and from rivers. As a result, the Mediterranean is turning into a warmer, saltier soup that puts off larger creatures, but in which jellyfish thrive

Prodded by Spain’s mighty tourist industry, the environmental authorities are expected to support scientists’ anti-jellyfish recommendations.

The Environment minister, Cristina Narbona, admits more effort is needed. Even with preventive measures in place, “we cannot guarantee in any way the complete absence of these organisms in bathing areas,” she says.

Professor Gili insists that the year-round programme of monitoring jellyfish movements must be continued. He proposes a list of specific measures: to station jellyfish-hunting boats in beaches under threat; provide locals and holidaymakers with information on how to protect themselves; and to close beaches to bathers when necessary.

But far more essential, he says, is to face up to the global ecological crisis highlighted by the uncontrolled proliferation of this spineless, brainless creature, and change the way we manage fish stocks worldwide.