Forecast possible for Irukandji box jellyfish blooms

By Rebecca Morelle Science correspondent, BBC News

Irukandji box jellyfish may be small, but their stings can pack a deadly punch

The sudden arrival of huge blooms of box jellyfish can now be predicted, a study suggests.

Researchers from Australia say that monitoring changes in ocean winds can help to establish where and when Irukandji jellyfish will strike.

The study is published in the Journal of the Royal Society Interface.

Lead author Lisa-Ann Gershwin said: "They travel in very, very large numbers. It's not uncommon to have dozens of stings on a beach in a day.

"The jellyfish bodies and tentacles are invisible in water - it's like a diamond dropped into a glass of water - you just can't see them."

The box jellyfish can arrive in vast numbers, causing havoc on beaches

 

Though no bigger than thimbles, Irukandji box jellyfish are a menace to swimmers.

Brushing past one of their super-fine tentacles is excruciatingly painful, and can lead to hospitalisation. In the very worst cases, an encounter can even prove fatal.

They are found throughout the oceans: They have been spotted as far north as Wales and as far south as Melbourne in Australia. But they are most common in tropical waters, where they can suddenly appear in vast numbers.

"They can be life threatening," said Dr Gershwin, from CSIRO's Wealth from Oceans Flagship institute in Hobart, Tasmania.
"And until now, they've never been predictable."

To find out more, the researchers focussed on the Great Barrier Reef, where jellyfish blooms can have a major impact on tourism.

They compared a sting database containing records collected between 1985 and 2012 with medium-range weather forecasts.

They found that a drop in the strong south-east trade winds, which blow across the ocean, coincided with the arrival of the jellyfish.

The jellyfish prefer the calm waters that a drop in trade winds bring

 

"Normally, the trade winds are the dominant winds, and they make really turbulent waters - it's cloudy, it's rough, it's not real pleasant," said Dr Gershwin.

"And Irukandji are really delicate little guys. They are like the orchids of the jellyfish family - delicate souls. They don't like turbulence, they don't like cloudy water. They like it as flat and calm and clear as possible."

And these improved conditions occur when the trade winds drop, allowing the stingers to rise from the depths and drift to shore.

Scientists say monitoring these offshore winds could give at least a day's warning of their appearance - time enough to warn bathers or even to close beaches.

Although the study focussed on Australia, the researchers believe similar conditions around the world could lead to the arrival of blooms.

"You will probably need a bit of tweaking from place to place, but the general principle will hold true," added Dr Gershwin.