A spike in the number of Mediterranean jellyfish this summer has many European tourists playing it safe in the sand, rather than in the surf. Scientists say overfishing and climate change are to blame.
Scientists say it is an increasingly typical summertime scene in Mediterranean holiday spots: turquoise waters, white sands and hoards of tourists - but no-one in the water. The reason? Jellyfish.
"There's evidence that this is 'the year of the jellyfish,'" Stefano Piraino, a marine biologist at the University of Salerno in Italy, told DW. Piraino says there's been a steady increase in the number of jellyfish in the Mediterranean Sea for years. There has been a major spike this summer, as temperatures hit high levels early in the holiday season.
Most species of jellyfish in the Mediterranean are harmless. Nevertheless, an estimated 150,000 people are treated for jellyfish stings across the region each year and the trend is rising.
Overfishing by coastal communities is just one reason for the recent rise in jellyfish in the Mediterranean.
One problem, multiple causes
"If we get rid of all the fish, we reduce the jellyfish's competitors," Piraino explains. "It means we leave more food in the environment, and jellyfish are very smart and use these available resources," Piraino said.
Many European tourists are avoiding the water when they go on holiday, concerned about getting stung
Piraino also warns that climate change could be playing a role. As the Mediterranean Sea slowly warms, even by a degree or two over time, jellyfish can reproduce faster, Piraino said. Reproductive rates for jellyfish are normally already higher than for normal fish. An increase in water temperature could create a big problem moving forward.
New warm-water jellyfish species can also now survive in waters that were previously too cold for them. "There are a number of alien species coming from the Red Sea, so tropical and subtropical species have entered the Mediterranean Sea from the Suez Canal," he said.
The biggest jellyfish swarms this year have been sighted in the eastern Mediterranean, closer to the Suez Canal. One species found there is a stinging jellyfish, called Rhopilema nomadica. It is now listed by the European Union as one of the most invasive marine species in European waters.
Painful for all
At the other end of the Mediterranean, at a popular beach on the Spanish island of Formentera, swarms of jellyfish clear the water of swimmers.
"My son, he was swimming in the water, playing with his brother, and then he was stung by a jellyfish," says Gabrielle Amand, whose family was visiting from France.
She rushed to the water upon hearing her son's screams. "We saw nothing. It's very small, a little red thing. But it hurts a lot," she said. "He cried a lot."
On some stretches of Spain's coast, scientists have spotted huge, kilometer-long colonies of jellyfish, sometimes with 30 to 40 animals per square meter of sea.
Britain's foreign office put out a warning to its citizens vacationing along Europe's southern waters this summer to be aware of jellyfish. That, in turn, sparked concerns over damage to the crucial tourism industry in struggling European economies like Spain, Greece and Italy.
Scientists enlist holiday-makers
Stefano Piraino, the Italian marine biologist, recently completed a research flight over 300 kilometers of Mediterranean coast, to monitor growing jellyfish populations. Scientists tracking the migration of such animals hope to also recruit tourists as unwitting research assistants. Piraino and his colleagues have developed a smartphone app with which tourists can report jellyfish outbreaks.
"If you are on the beach and you see some jellyfish, you can even send us a picture. In the last three years, we received around 10,000 records from citizens," Piraino said.
On the front lines of Europe's jellyfish battle are the lifeguards who patrol thousands of miles of Mediterranean beaches every summer. They get to know the migration patterns of their local jellyfish very quickly.
"It all depends on the water currents and the wind," Paul, a lifeguard on the Spanish island of Formentera, told DW. "When the wind comes from over there, it's not long before the jellyfish start to appear," he says, gesturing toward the west.
Lifeguards are also on the front lines of managing the public's reaction to jellyfish.
"I deal with a lot of crying children who've been stung, but I don't see it affecting tourism here," Paul says. "People just need to be cautious when they swim, and they'll be fine."
But, as Mediterranean waters warm up slightly towards the end of summer, the next swarm of jellyfish will likely be washing ashore soon.