Natural phenomenon: prehistoric animals at sea – hatching rare mythic crab – science

Schopfheim (dpa) – a little somersault here, a twirl there – and a steady whirlpool of the little legs: there’s a lot going on in this glass of water. A rare species of fairy shrimp, a type of tadpole shrimp estimated to be 400 million years old.

Hartmut Hess, the 76-year-old in charge of nature conservation, just got them out of the Eichener See in southern Baden – with special permission from the authorities, because the animals, which are about two centimeters tall, are strictly protected. When he talks about crabs, Hayes is ecstatic: “They glide wonderfully through the water, like fairies, hence the name,” he says.

Animals can live in this lake is very wonderful. Because most of the time the water body does not exist. It is a temporary lake that only appears when there is heavy rain in the area or when snowmelt occurs due to snowmelt, Hayes explains. Due to the presence of a sealing layer at a depth of 48 meters, the water cannot flow well down. The lake appears over this “basin”.

For years it wasn’t as big as it is now, Hayes says: it’s about 270 meters long and 150 meters wide. After a certain period of time, the “lake collapses again into an underground maze” of caves in a limestone landscape.

So how did animals manage to colonize this fickle body of water? With a special strategy, explains Hans Bellmann, biologist and president of the Museum of Natural History in Magdeburg. In his museum he cares for a collection of all kinds of tadpole shrimp that are found in Germany from different locations.

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Females of “Tanymastix stagnalis” – this is the scientific name for the equine oak shrimp – lay eggs in the water, where a further evolution of so-called cysts takes place, Bellman explains: a permanent form that is highly resistant. These bags tolerate the lake drought without any problems, then persevere on the meadows and even survive a farmer who comes once a year and cuts the meadow. “The permanent form allows animals to colonize such extreme biomes that are rarely filled with water except for a short period,” Bellman says.

If the lake becomes full again – even if it does not happen for several years – the equine crab larvae hatch within a few days. After three to four weeks, the animals are fully developed and can mate. The biologist says that back swimmers are constantly in motion during their short lives. With eleven pairs of legs, they rotate the plankton in the groove of the abdomen, from where the food reaches the mouth opening. There, the food is then chopped up and pressed into the digestive system, Bellman explains.

According to the director of the museum, there are a total of 11 known species of tadpole shrimp in Germany – and it is possible that two of them are already extinct. Incidentally, primitive cancer is not a technical term, he asserts. The fairy oak shrimp can only be found in a few other places except for southern Baden, including the Bavarian water body and in a small area at the edge of the Elbe in Brandenburg. Also at Pellmann, Krebschen seems to have a special affection: “They look really cute,” he says.

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At the Eichener See, Hartmut Hayes, a conservationist, finally releases his subjects to freedom. Because of it, the water is currently a true place of pilgrimage, says the 76-year-old. Crowds of onlookers flocked over the weekend, and in the past few days he has escorted several TV bands to the beach. The magic should continue for another three to four weeks. After that, the lake will be gone again, Hayes says. Who knows when he will appear again – and with him the back, the tadpole shrimp swim.

© dpa-infocom, dpa: 210312-99-789944 / 2

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