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Hidden world discovered off the Maldives

2/11/2022

Translation: machine translated

The Maldives are known for their rich coral reefs. A few hundred metres deeper in the sea, divers now came across an equally rich ecosystem.

"Trapping Zone" is the name scientists have given to a hitherto completely unknown ecosystem in the island kingdom of the Maldives: At a depth of 500 metres, participants in the Nekton Maldives Mission discovered oases of life in the otherwise lifeless expanse of the Indian Ocean here, Alex Rogers of the University of Oxford and co report in a news release. Here, large fish gather to eat the immense amounts of zooplankton that gather here every day at an underwater mountain.

These micronekton are smaller fish, crustaceans and other organisms between 2 and 20 centimetres in size that move daily between deeper water and the surface: a phenomenon that can even be detected acoustically. The micronekton rises at night and swims back down with the dawn.

At an underwater mountain called Satho Rahaa, cliffs and shallow terraces of former coral reefs prevent the animals from diving deeper than 500 metres and dispersing. The topography causes them to gather as if in a trap, which in turn attracts predators. Schools of tuna, sharks, John Dory, angelfish and other species gather in large numbers and prey on the micronekton, according to the divers' observations. Above all, the great diversity of different shark species amazed the researchers: in addition to hammerheads and tiger sharks, they discovered gulper sharks, gillnet sharks, silky sharks and nail sharks.

The discovery, however, raises some questions: Why, for example, do the animals of the micronekton not migrate further across the terraces into the deep sea, where they would be safer? Do other underwater mountains also form similar traps? After all, these submerged mountains are in principle considered to be species-rich ecosystems in the sea; until now, it was assumed that this could be mainly due to the upwelling of nutrient-rich deep water, which is forced upwards at the obstacles.

The upwelling of nutrient-rich deep water, which is forced upwards at the obstacles, could be the main reason for this.

The ascent and descent of nekton, in turn, represents arguably the largest animal migration on Earth. The total weight of the organisms involved is estimated to be at least ten billion tonnes. The phenomenon, however, is largely unexplored.

Spectrum of Science

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Originalartikel auf Spektrum.de
Titelbild: © Nekton Maldives Mission, Nekton 2022 (Ausschnitt) Mit der Hilfe von Tauchrobotern und U-Booten stießen Wissenschaftler auf eine bislang völlig unbekannte Welt vor den Malediven.

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