Climate change: A cnidarian on a long journey – a sailing jellyfish washes up on Sylt

They are like miniature boats: just four centimetres long, sail jellyfish consist of a flat, oval ‘hull’ topped by an almost triangular, transparent ‘sail’. The wind propels them along the water’s surface. The jellyfish can only drift along; the position of the sail – of which there are two in every population, however – cannot be changed.

For the first time on the North Sea coast

Specimens of this unusual species have now washed up on the German North Sea coast for the first time – on the island of Sylt. Rainer Borcherding from the Wadden Sea Conservation Station expressed surprise at their appearance: the expert told Norddeutscher Rundfunk that these jellyfish require a water temperature of at least 14 degrees Celsius, even in winter.

At home in the subtropics

In fact, these exotic marine creatures are usually found only in subtropical waters. They rarely stray into the North Atlantic and its marginal seas; until now, sightings in the north have been limited mainly to the western parts of the British Isles. And the North Sea has another disadvantage: it is too shallow for the Portuguese man-of-war to reproduce. This process takes place at depths of up to 1,000 metres.

Signs of climate change

The expert sees the fact that the species has spread as far as the North Sea despite these constraints as a sign of climate change: The sighting shows “just how warm the North Atlantic has become”, Borcherding told NDR. In fact, with an average temperature of 21.1 degrees Celsius, the world’s oceans reached their highest recorded levels just last weekend.

The sail jellyfish is harmless

That said, compared with similar creatures, such as the highly poisonous Portuguese man-of-war – which recently led to beaches being closed in south-west France – the peaceful sail jellyfish poses no danger to humans or the marine environment. It is completely non-toxic.

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