They are a slimy nuisance that spoil the bathing fun on popular holiday beaches – but jellyfish in the Danube: is that possible? The Cnidarians rush through the Kuchelau in northern Vienna on social media. Fake news or not? And does everyone have to get out of the water now? The “crown” explained.
“I have been rowing in the Kuchelau in Vienna for 17 years. We have never seen jellyfish there. What does that mean?” asks ORF presenter Nadja Hahn in her tweet. And indeed: what clouds the water surface there is very reminiscent of the jellyfish plagues known from the Adriatic Sea as soon as the sea warms up considerably in the summer.
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And it’s true: Craspedacusta sowerbii is the name of the freshwater jellyfish, which can grow up to 2.5 centimeters in size and has been scurrying around in the Danube for quite some time. Although they are not native to Europe, the first European record dates back to 1880, where they appeared in a water lily tank in London’s Royal Botanic Garden. They are native to Brazil or East Asia, from where they were introduced to Europe. Today, the species is found worldwide, except for Antarctica.
Why so much and so suddenly?
The “Krone” check on Sunday night in the Kuchelau shows: the little cnidarians are everywhere, a pest like the moderator’s tweet cannot be identified. The fact that they are visible to the naked eye at all is due to the long heat period that warmed the Danube. The animals usually live as only approx. 2 mm large polyps, sedentary on the bottom of nutrient-rich waters or on aquatic plants and feed on protozoa and nematodes (roundworms). Only at water temperatures above 25 degrees Celsius can so-called medusae be formed by budding – which can then be seen on the surface while swimming.
And now – everyone out of the water?
So much for the science – but what does that mean for the fun of swimming? If you don’t mind the slippery surface, don’t worry about splashing, swimming and stand up paddling. The freshwater jellyfish is neither poisonous nor dangerous. On the contrary: because it prefers slow-flowing waters with clean water, its appearance is a sign of the high water quality of the Danube, even at high temperatures. And for children and hobby researchers, the cnidarians are also an experience and natural spectacle.
Source: Krone
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