Andrew Martin: A wounded sea takes its slimy revenge

One entertainment open to me on the beaches of Suffolk is to watch a new arrival encounter the jellyfish. He fights his way into his trunks and, laughing and lurching over sharp stones, heads for the shallows. The first wave laps at his crotch and he gives the time-honoured cry at the coldness of the water, except that the water, rather sinisterly, is not cold at all. And then he sees the jellyfish.

Whether he goes any further will depend on his courage. You see some of the braver souls watching the jellyfish around them while standing shoulder-deep in water. But our man will most likely walk back up the beach and start reading his newspaper, hoping to be mistaken for someone who never even thought of going for a swim.

The jellyfish aren't there all the time. My elder son, who has been stung several times, believes: "They come when the sea's warm and the air's cool." His brother has some other theory, believing, quite possibly, the exact opposite. A phlegmatic lifeguard told me: "Yep, there's quite a lot out there, but most are harmless and a lot are dead. If anyone comes in with a sting we put on Jungle Formula spray but you can just rub on a bit of salt water, and that'll do the job."

"That's handy," I said. He nodded complacently. He appeared determined not to be worried by the jellyfish, whereas I'm determined to be worried by them.

I called Peter Richardson, biodiversity conservation manager at the Marine Conservation Society, which collates reports of jellyfish. The commonest ones off Britain are the compass jellyfish, the blue jellyfish and the moon jellyfish, he told me. "The first two can give you a nettle-type sting. Our waters have always had jellyfish, but a University of Plymouth study last year found the numbers were going up, which correlates very nicely with rising sea temperatures."

And what, exactly, was nice about this? "It's global warming, isn't it?" I demanded. "Most expert opinion would make the connection," he said. And what's to stop our warming seas becoming clogged up with jellyfish, including the more dangerous varieties that are closing resorts in the Med? The gist of Mr Richardson's answer, if I understood it correctly, was "Nothing."

To fear the sea because it is violent and ungodly, as people did before the Romantic movement incorporated the wilder forces of nature into God's creation – a 16th-century cliff top bench might well face inland – is one thing. But to fear its revenge for our having abused it is far worse. Its malevolence seems personal.

In The Kraken Wakes (1953) by John Wyndham, unseen aliens infesting the sea arrange for the melting of the Polar ice caps, their actions reflecting man's meddling with nature in the creation of the nuclear bomb. In It Came From Beneath the Sea (1955) a giant octopus, made radioactive by hydrogen bomb testing, kicks up. The film was remade recently as It Came From Beneath The Sea... Again! which seems to sum it all up. Only this time it's real.

Andrew Martin's novel 'Death on A Branch Line' is published by Faber