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Jellyfish outbreaks a sign of nature out of sync
18 June 2008
Agence France Presse

The dramatic proliferation of jellyfish in oceans around the world, driven by overfishing and climate change, is a sure sign of ecosystems out of kilter, warn experts.

"Jellyfish are an excellent bellwether for the environment," explains Jacqueline Goy, of the Oceanographic Institute of Paris. "The more jellyfish, the stronger the signal that something has changed."

Brainless creatures composed almost entirely of water, the primitive animals have quietly filled a vacuum created by the voracious human appetite for fish.

Dislodging them will be difficult, marine biologists say.

"Jellyfish have come to occupy the place of many other species," notes Ricardo Aguilar, research director for Oceana, a international conservation organisation.

Nowhere is the sting of these poorly understood invertebrates felt more sharply than the Mediterranean basin, where their exploding numbers have devastated native marine species and threaten seaside tourism.

And while much about the lampshade-like creatures remains unknown, scientists are in agreement: Pelagia noctiluca -- whose tentacles can paralyse prey and cause burning rashes in humans -- will once again besiege Mediterranean coastal waters this summer.

That, in itself, is not unusual. It is the frequency and persistence of these appearances that worry scientists.

Two centuries worth of data shows that jellyfish populations naturally swell every 12 years, remain stable four or six years, and then subside.

2008, however, will be the eighth consecutive year that medusae, as they are also known, will be present in massive numbers.

The over-exploitation of ocean resources by man has helped create a near-perfect environment in which these most primitive of ocean creatures can multiply unchecked, scientists say.

"When vertebrates, such as fish, disappear, then invertebrates -- especially jellyfish -- appear," says Aguilar.

The collapse of fish populations boost this process in two important ways, he added. When predators such as tuna, sharks, and turtles vanish, not only do fewer jellyfish get eaten, they have less competition for food.

Jellyfish feed on small fish and zooplankton that get caught up in their dangling tentacles.

"Jellyfish both compete with fish for plankton food, and predate directly on fish," explains Andrew Brierley from the University of St Andrews in Scotland. "It is hard, therefore, to see a way back for fish once jellyfish have become established, even if commercial fishing is reduced."

Which is why Brierley and other experts were not surprised to find a huge surge in the number of jellyfish off the coast of Namibia in the Atlantic, one of the most intensely fished oceans in the world.

Climate change has also been a boon to these domed gelatinous creatures in so far as warmer waters prolong their reproductive cycles.

But just how many millions, or billions, of jellyfish roam the seas is nearly impossible to know, said scientists.

For one things, the boneless, translucent animals -- even big ones grouped in large swarms -- are hard to spot in satellite images or sonar soundings, unlike schools of fish.

They are also resist study in captivity, which means a relative paucity of academic studies.

"There are only 20 percent of species of jellyfish for which we know the life cycle," said Goy.

And the fact that jellyfish are not commercially exploited, with the exception of a few species eaten by gastronomes in East Asia, has also added to this benign neglect.

But the measurable impact of these stinging beasts on beach-based tourism along the Mediterranean has begun to spur greater interest in these peculiar creatures whose growing presence points to dangerous changes not just in the world's oceans, but on the ground and in the air as well.
 

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Jellyfish gone wild ruin tourist spots, report says
December 13, 2008, 12:16 pm

WASHINGTON (Reuters) - Huge swarms of stinging jellyfish and similar slimy animals are ruining beaches in Hawaii, the Gulf of Mexico , the Mediterranean, Australia and elsewhere, U.S. researchers reported on Friday.

The report says 150 million people are exposed to jellyfish globally every year, with 500,000 people stung in the Chesapeake Bay, off the U.S. Atlantic Coast, alone.

Another 200,000 are stung every year in Florida, and 10,000 are stung in Australia by the deadly Portuguese man-of-war, according to the report, a broad review of jellyfish research.

The report, available on the Internet at http://www.nsf.gov/news/special_reports/jellyfish/index.jsp, says the Black Sea's fishing and tourism industries have lost $350 million because of a proliferation of comb jelly fish.

The report says more than 1,000 fist-sized comb jellies can be found in a cubic yard (meter) of Black Sea water during a bloom.

They eat the eggs of fish and compete with them for food, wiping out the livelihoods of fishermen, according to the report.

And it says a third of the total weight of all life in California's Monterey Bay is made up of jellyfish.

Human activities that could be making things nice for jellyfish include pollution, climate change, introductions of non-native species, overfishing and building artificial structures such as oil and gas rigs.

Creatures called salps cover up to 38,600 square miles (100,000 sq km) of the North Atlantic in a regular phenomenon called the New York Bight, but researchers quoted in the report said this one may be a natural cycle.

"There is clear, clean evidence that certain types of human-caused environmental stresses are triggering jellyfish swarms in some locations," William Hamner of the University of California Los Angeles says in the report.

These include pollution-induced "dead zones", higher water temperatures and the spread of alien jellyfish species by shipping.
 

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Not a surprise. The Med is heavily overfished and jellyfish have to face less competition and predation from finfish. Even worse, jellyfish now heavily predate on plankton and fish larvae and so reduce the capability of finfish populations to recover. There is serious threat that the Med and other seas will change from a finfish dominated state to a stable state where jellyfish are the top predators. Something we had back in the Precambrium.
 

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A Gelatinous Invasion
2 November 2009
Time International

How a species of thumb-size jellyfish is threatening to upset the Mediterranean ecosystem.

The Jellyfish in the photos didn't look like they'd pose a danger to swimmers. Thinly veined and translucent, they didn't have stinging tentacles trailing behind them or dramatic colors signaling danger. But Ferdinando Boero, a professor of zoology at the University of Salento in Italy, knew that they meant trouble nonetheless.

The pictures, sent by a biologist in the northern Italian town of Lerici in July, marked the first time the species Mnemiopsis leidyi, a thumb-size jellyfish known as the sea walnut, had been documented in the western Mediterranean Sea. Native to the Atlantic coast of the U.S., Mnemiopsis was introduced to the Black Sea in the 1980s--most likely from the ballast water of oil tankers--and played an instrumental role in the collapse of the region's fisheries. "Now the question is, Will it do in the Mediterranean the same thing it did in the Black Sea?" Boero says. "It's harmless for [humans], but it can be deadly for the fish."

The ominous discovery--the result of Boero's request that all Italians report their jellyfish sightings--came during a series of unusually prolific jellyfish seasons over the past five years. This summer, jellyfish outbreaks forced numerous resorts along the Mediterranean coast to shut their beaches. In Corsica and Tuscany, several swimmers were wounded by Portuguese man-of-wars, jellyfish-like creatures with a potentially fatal sting. In Tunisia, a swarm of jellyfish engulfed a fish farm, killing the year's production of sea bass and sea bream.

Off the coast of Israel, where tropical species have moved in through the Suez Canal, jellyfish floated in swarms more than 100 km long and 2 km wide. Blooms of Mnemiopsis, first documented off Israel last winter, clogged the filters of a desalination plant that supplies coastal communities with 100 million liters of water a day. At the height of the outbreak, water production at the plant dropped by more than a third as desperate workers tried to clear the filters.

The reasons for the recent explosion in jellyfish numbers are many. The problems in the Black Sea occurred because Mnemiopsis had been introduced to an ecosystem that had already been severely overfished. In a healthy ecosystem, small fish keep the jellyfish population in check by eating their young. But when the fish population plummets, the tables are turned. By preying on the eggs and larvae of the few surviving fish, the jellyfish prevent them from replenishing their numbers and quickly take their place. "We're shifting from a fish to a jellyfish ocean," says Boero. "We're removing most of the fish, and nature doesn't like a vacuum."

But overfishing is not solely to blame. The nutrients from fertilizer runoff and sewage suck oxygen from the lower layers of the ocean, creating an environment in which fish struggle but jellyfish thrive. Since 2000, there's been such an increase in numbers of Australian jellyfish in the oxygen-depleted waters of the Gulf of Mexico that shrimpers have been forced to hang up their nets during the swarm season in the summer. In the nutrient-rich waters off the coast of Japan, where jellyfish can grow to the size of refrigerators, a nuclear power plant was forced to lower production in 2006 when a mass of the creatures clogged its cooling system.

Climate change, too, is likely playing a role. As ocean temperatures rise, jellyfish are reproducing faster, and tropical species are beginning to extend their range. "It could be a big economic problem for countries like Australia," says Anthony Richardson, a marine biologist at the University of Queensland in Australia. If the deadly box jellyfish that plague the country's northern beaches migrate south to the Gold Coast, it could have huge implications for the region's multibillion-dollar tourism industry.

Once a body of water becomes infested with jellyfish, it's not so easy to engineer a recovery. The Black Sea has begun to recuperate, but only after a convergence of several unlikely occurrences: many of the region's fisheries shut down when their stocks fell, the breakup of the Soviet Union sharply cut the amount of fertilizer in the sea, and another alien jellyfish, the Beroe ovata, which preys on the Mnemiopsis, not fish, was accidentally introduced to the water. "It's taken three separate events," Richardson says. "The point is you can't just stop overfishing and expect the fish to come back."

To be sure, the Mediterranean's ecosystem is more diverse--and thus more robust--than the Black Sea's. So only time will tell what kind of effect the Mnemiopsis will have. "What these jellyfish are eating are either the young of the next generation or the food of the next generation," says Bella Galil, a scientist at the National Institute of Oceanography in Israel. "We'll know the impact when what they ate does not appear in the nets next year."
 
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