Aquatic creatures are not only found in the sea. This can even happen in bathing lakes – and can be frightening – as an incident in Croatia shows.
Vinkovci – Some of you may have noticed it on your last beach holiday or even in a bathing lake: When swimming, you can come across many sea or lake creatures, and sometimes strange encounters occurTwo water sports enthusiasts in Croatia have now had this experience. In a lake in the east of the country, they found animals that they would not have expected to see there.
Water sports enthusiasts have unexpected encounter in bathing lake – “We were surrounded by about twenty of them”
As they often do, Petra and Antonio Udovčić were recently out on their surfboards on Lake Banja in Vinkovci, about 20 kilometers from the Croatian-Serbian border. After moving a little further away from the shore of the lake, they discovered in the water the strange outline of an animal that they had previously expected to see on the beaches of the Adriatic, hundreds of kilometers away in western Croatia.
“First we met a small one, and then we were surrounded by about twenty of them,” Petra Udovčić told the Croatian online newspaper Day. What the two water sports enthusiasts saw in the lake water around their surfboards were the outlines of numerous small jellyfish. The two managed to catch one of the specimens in a glass jar. They then sent it to the nearby University of Osijek.
The University’s Biology Department confirmed that the animals found in Lake Banja in Vinkovci were definitely freshwater jellyfish of the type Craspedacusta sowerbii And that they must have travelled an enormous distance to reach the lake in western Croatia.
Unusual encounter: Freshwater jellyfish in Croatian lake actually come from East Asia
“The freshwater jellyfish originate from East Asia, from the Yangtze River area. And it is believed that their spread actually occurred through the transfer of ornamental aquatic plants or through the pet market,” said Barbara Vlaićević from the Faculty of Biology in Osijek in an interview with Day.
The small jellyfish are rarely seen. In the polyp stage, they are only about one millimeter in size, so tiny that you wouldn’t see them even from close up. When the two water sports enthusiasts discovered them in Lake Banja, the specimens there were already so big that they had already formed a hat.
The sudden presence of the jellyfish and the fact that the two water sports enthusiasts would never have suspected them in their local lakeeven frightened them at first: “At first we didn’t even expect to see jellyfish in our lake, and then we didn’t know what to expect from jellyfish. So we wondered if they could possibly harm our skin,” said the water sports enthusiast.
All clear for bathers: Freshwater jellyfish are not dangerous for humans
The relatively warm water of the lake suits the jellyfish. It also provides enough food for the animals. The most important thing for humans, however, is that the freshwater jellyfish cannot harm them. Although they do have tentacles, they only serve to catch their food, so-called plankton shrimp.
The tentacles cannot penetrate human skin. Touching nettles would therefore be more painful than coming into contact with the freshwater jellyfish. When the two Croatian surfing fans found out about this, they were sure that they would be able to end the summer season with further visits to the local Banja Lake.
The freshwater jellyfish from East Asia is also spreading in Germany
The freshwater jellyfish, which originate from East Asia, have now not only made it to Croatia, but also to German waters. The animals, which often go unnoticed due to their size, have also been spreading in Germany for several years, as Herwig Stibor from the Ludwig Maximilian University of Munich (LMU) reported on the university’s website. As a professor of aquatic ecology, Stibor researches the ecology of East Asian freshwater jellyfish.
“So far, only the jellyfish have been described because they are easy to see,” says Stibor. “But that is actually only a small part of the jellyfish’s life cycle. If we want to understand their invasion dynamics, we also need to understand this bottom stage, which has hardly ever been studied so far.”
In contrast to the jellyfish with its temperature requirements, polyps are extremely resilient, which makes the jellyfish a highly invasive species: “The polyps survive everything by forming permanent stages. The permanent stages are resistant to drying out, you could even freeze them at -250 degrees or boil them in sulphuric acid and they would survive,” Stibor marvels. (fh)
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