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They're alien-looking, they're stealthy, and they can hurt. Jellyfish are the pests of the sea, coming out in droves every summer to turn a day at the beach into a world of pain. After a three-mile-long armada of jellyfish stung hundreds of vacationers on Spanish beaches earlier this month, the question might seem perverse: Can we ever learn to love the jellies?

Fernando Boero thinks we can. A professor of zoology and marine biology at the University of Salento in Lecce, Italy, Boero is the brains behind JellyWatch, the first attempt to mobilize the public in a wide-scale survey of the Mediterranean Sea's least popular resident. Run under the auspices of the Mediterranean Science Commission (CIESM), the scheme was piloted in Italy in 2008, meeting such success that Israel joined a year later. So have France, Tunisia and Turkey, with other jelly-vexed nations expected to follow. "Nobody was looking at jellies over a vast scale," says Boero. "There are similar initiatives for birds or butterflies, but nothing like it for marine science."

JellyWatch relies on "citizen scientists" — mostly beachgoers — who are encouraged to record their sightings and send photos by e-mail either to Boero or to the website of Italian science magazine Focus. The photos are uploaded onto a map to show which species occur when and where — data that CIESM hopes might one day allow for short-term forecasting of jellyfish swarms or blooms. Some send shots of their blistered skin, others images of rarely or never-before spotted species. In June, a dive-shop operator on Pantelleria, a volcanic speck of an island between Sicily and Tunisia, sent in photos of an Atlantic jelly called Catostylus tagi — its first sighting in the Mediterranean. "Without JellyWatch, we wouldn't know about its presence," says Boero.

Meanwhile, a composite image of JellyWatch sightings for May, June and July shows Italy's 5,000-mile coastline to be fringed with multiple species. Boero says it reveals useful information about where they are and how many are out there. Take Pelagia, the mauve stinger, billions of which famously devoured a huge salmon farm off Northern Ireland's coast in 2007: thanks to JellyWatch, scientists know it's more abundant in the Tyrrhenian and Ligurian seas, and appears all the way from spring through fall. Members of the public are "becoming the eyes of the scientific community," says Boero. They are also becoming jellyfish lovers, sending in their photos with messages of appreciation. "People admire their elegance and beauty," says Boero. "They don't see them just as a nuisance."

JellyWatch received more than 500 reports from Italy in the first half of August alone. But citizen science can't provide all the answers; despite their seeming ubiquity in summer news reports, jellyfish are elusive and mysterious creatures. Mauve stingers, for example, disappear in the winter, and nobody knows where they go. And crucially, scientists still don't understand enough about the impact of jellyfish on marine ecosystems. "It's not easy to observe them," says Boero. "It's impossible to see them from satellites, so standard observation from space is useless." And looking for them by sea isn't easy, either. The Adriatic coast of Apulia — the heel of Italy — is usually thick with tentacle-less Rhizostome, but bad weather can drive them into deeper water. So even when a research vessel chases a major sighting, it might arrive to find a jelly-free sea. "Citizen science is the only option," says Boero.

The charismatic ambassador for matters gelatinous — who once named a jellyfish Phialella zappai, after Frank Zappa — hopes JellyWatch will help change popular perceptions toward the much-maligned creature. Boero wants people to know that while there are species of Mediterranean jelly that sting, none are deadly — unlike those lurking in Australian waters — and some are even edible.

Those involved with JellyWatch — and a similar project, jellywatch.org, launched in February by the Monterey Bay Aquarium Research Institute in Moss Landing, Calif. — hope the project will boost public interest in science in general. "The best way for the public to understand and appreciate science is to participate in it," wrote Jonathan Silvertown, an ecology professor at the Open University, in a 2009 paper called "A New Dawn for Citizen Science." And not before time. The Mediterranean is undergoing a "major convulsion," warns Bella Galil, a senior scientist at the Israel Oceanographic and Limnological Research Centre in Haifa, with one symptom being an increasing number of jellyfish blooms: in June and July, the venomous Rhopilema nomadica, a tropical species thought to have arrived via the Suez Canal in the 1970s, formed two vast swarms of 60-plus miles long off Israel's coast.

The accelerating influx of such alien species piles further pressure on a rich but vulnerable marine ecosystem that must already cope with pollution, 200 million tourists annually and warming water and acidification attributed to climate change. Overfishing has removed species that prey on jellies, which further disrupt the aquatic food chain by feasting on fish larvae. The impact on fish stocks is dire but hard to quantify. "We cannot separate the man-made causes from the jelly effect," says Galil. "We can only calculate the amount of food an individual jelly consumes and sigh."

Vacationers are probably sighing too. "Totally futile" is how Galil describes efforts to protect Mediterranean beaches with anti-jelly booms or nets. These can actually cause jellyfish to break apart and allow the stinging cells on their tentacles to sweep ashore. "People like the sea to be a swimming pool," says Boero. "If they see a living being, they are horrified. But they have to be aware that there is life in the sea, and it has to be respected." Whether we love or loathe jellies, it seems all we can do is learn to live with them.

• Andrew Marshall
• It wouldn't be summer without stories of jellyfish swarms stinging beachgoers. Now the minds behind JellyWatch want members of the public to become 'citizen scientists' and record their sightings