Research Press Release
Nature Ecology & Evolution
July 25, 2023
A paper reporting that distinct deep-sea transition zones at depths greater than 4 km separate deep-sea organisms by body type,Nature Ecology & Evolutionwill be published in Many animals with shells were found shallower than this transition zone, whereas soft-bodied animals dominated deeper.
The deep-sea zone is the most extensive habitat on Earth, covering more than 60% of the Earth’s surface, but it is also the least explored. At a depth of 3-6 kilometers, no sunlight, and a temperature of 0.5-3°C, organisms must adapt to cope with the extreme pressure. Although the deep ocean is thought to be less species rich than shallow-water ecosystems, it is not clear how biodiversity changes within the deep-sea zone.
Erik Simon-Lledó and colleagues collate images from 12 deep-sea expeditions in the Clarion–Clipperton Zone of the Pacific Ocean to analyze data on the presence of more than 50,000 megafauna (animals larger than 10 millimeters in size) that live near the seafloor. As a result, two distinct areas were found in the deep-sea fauna. Soft corals, brittle stars (starfish-related organisms), and shell mollusks dominated shallow-water communities at depths of 3.8-4.3 km, while sea anemones, glass sponges, and sea cucumbers dominated deep-sea communities at depths of 4.8-5.3 km. In the transitional zone between the two areas, these two communities were mixed. In the deep sea, biodiversity is maintained across this boundary, although one might think that the deeper the depth, the lower the biodiversity. Simon-Lledó et al. suggest that such distinct zoning in the deep ocean may be determined by carbonate compensation depth. Carbonate compensation depth is the depth at which calcium carbonate in seawater becomes unsaturated, beyond which the conditions for animal shell formation become unsuitable.
Simon-Lledó and colleagues argue that climate change and ocean acidification could alter this zoning, and combined with the impacts of deep-sea mining, would weaken the ecosystem.
doi:10.1038/s41559-023-02122-9
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