In December 2024, researchers working with the submersible SuBastian in the Weddell Sea noticed a strange sight: small swarms of Antarctic krill actively moving along mineral fissures on the ocean floor. No one expected to encounter these tiny crustaceans, accustomed to surface waters, at a depth of more than 900 meters at hydrothermal vents.
All the collected individuals turned out to be sexually mature females carrying eggs. Analysis of the contents of their stomachs showed that they fed on chemosynthetic microbes — bacteria that obtain energy not from sunlight but from chemical compounds released by the vents. Such data confirmed studies of the microbiome, isotopic composition and trace-element content in the tissues.
It was previously thought that krill mainly inhabit the upper 300 meters of water and feed on phytoplankton. Now it is becoming clear that reproductive females can descend to considerable depths, where year-round food and important minerals are available — manganese, zinc and iron, which are necessary for the development of embryos. At the same time, toxic metals such as lead and cadmium were also found in the tissues.
The discovery, published in September 2026 in the journal Communications Biology, forces a reconsideration of ideas about the krill life cycle. For decades scientists assumed that spawning occurs in the surface layers; now the possibility of deep-water spawning, or at least preparation for it, must be taken into account.
Antarctic krill are the foundation of the Southern Ocean food web, supporting whales, seals, penguins and fish. In addition, they play a role in carbon sequestration. If females actively use hydrothermal habitats, this changes the understanding of the species' ecology and requires such zones to be taken into account when planning marine protected areas.
Hydrothermal vents, where life exists without photosynthesis, have long amazed biologists. Now another layer has been added: they may serve as a kind of "dining hall" for a key Southern Ocean species during the breeding period. This highlights how little we know about deep-sea ecosystems and their connections to the surface.
The study was conducted as part of the National Geographic and Rolex Perpetual Planet Ocean Expedition with the participation of the Schmidt Ocean Institute. The authors emphasize the need for further observations to understand how widespread this behavior is.
The discovery shows that even well-studied species can spring surprises when scientists descend deeper than usual.
