Second Antarctic vent 1,000 miles away also contained egg-laden females
A team of researchers has documented Antarctic krill inhabiting deep-sea hydrothermal vents for the first time, according to findings published in the journal Communications Biology. The discovery, made in late 2024 off the Antarctic Peninsula, raises questions about where the crustaceans reproduce and could inform conservation efforts in one of the planet’s most rapidly warming ocean regions.
Antarctic krill, shrimp-like crustaceans, serve as a key food source for penguins, seals, and whales across the Southern Ocean, according to Kim Bernard, a biological oceanographer at Oregon State University and National Geographic explorer who led the research. “Most of them feed on Antarctic krill,” Bernard said. “And if they don’t, they feed on something else that feeds directly on Antarctic krill. So they are absolutely fundamental to the functioning and health of that ecosystem.”
Krill also recycle nutrients that allow tiny algae called phytoplankton to grow, and the species is fished in large numbers for aquaculture feed and omega-3 dietary supplements. Bernard said the Southern Ocean is “one of the most rapidly warming areas on the planet” and that warming “is cascading through the food web and affecting the Antarctic krill population.”
The discovery occurred during the National Geographic and Rolex Perpetual Planet Southern Ocean Expedition, conducted in collaboration with the Schmidt Ocean Institute. While UCLA benthic ecologist Andrew Thurber was using a remotely operated vehicle in a trough approximately 3,600 feet below the surface to study and video-record a hydrothermal vent, Bernard was watching the live video feed from the ship’s galley.
Bernard described hydrothermal vents as places where “extremely hot water coming from deep within the Earth’s crust” brings with it “metals and sulfides and all sorts of other chemicals that form almost like a tower.” She spotted what she described as a flicker of movement at the vent. “It’s like underwater ballet,” she said of the krill’s backflips. “It just looks like pirouetting. I pretty much threw the tea in the air and ran down to the control room, screaming, ‘There’s krill, there’s krill!’”
Krill had never previously been observed at a hydrothermal vent, and Bernard was not studying the vents herself. The other researchers had planned to sample the vent’s geology and microbiology but gave Bernard 15 minutes to try to catch a few specimens using a suction sampler. The team collected four individual krill — all reproductive females, “very heavily laden with eggs,” according to Bernard, “should be releasing them any moment.”
Researchers had previously assumed that females release eggs near the surface over deep water, though that behavior had never been directly observed. Bernard said seeing krill at a hydrothermal vent was “completely opposite to what we would have normally expected.” “Why on earth are they down there?” she asked. “I really wanted to just try and understand, what are they getting from that site?”
To investigate, Bernard compared the stomach contents of the captured females to krill collected from shallower, non-vent seafloor areas. The four females had been feeding on microbes living near the vent — a food source available year-round, unlike the seasonal phytoplankton that depend on sunlight and photosynthesis.
Bernard dried the remaining tissue and carried it home in her backpack. “I didn’t want to put it anywhere out of my sight because it was so important,” she said. Subsequent analysis revealed that the krill had accumulated elevated levels of metals released by the vent, including manganese. “That’s an important nutrient or mineral for embryo development in crustaceans,” Bernard said. “And it’s very scarce in the Southern Ocean. So potentially that’s a reason for them to go down there.” The warmer waters near the vent may also speed up embryo development.
The findings do not establish that krill depend on hydrothermal vents, according to Simeon Hill, a marine ecologist at the British Antarctic Survey who did not participate in the research. “The study shows that krill can make use of hydrothermal vent habitats, but it doesn’t provide enough evidence to suggest that they are dependent on these habitats,” Hill said. Still, he said he was “reassured that krill can flexibly use different parts of the ocean to live and feed as it demonstrates their resilience.”
Hill added that while hydrothermal vents are reasonably well protected from destructive human activities, additional conservation measures may be needed. “It makes me think it would be sensible to develop a marine protected area process that allows new vulnerable habitats to be added as they’re discovered,” he said. That kind of protection may be especially necessary if the habitats are critical to the krill’s reproductive cycle.
Two months after the original research cruise, the same vessel visited another Antarctic hydrothermal vent roughly 1,000 miles from the first site. That vent also hosted egg-laden female krill. “It was incredible,” Bernard said. “So I am sure that this is something that is not just a once-off, and there’s more to this than we ever expected.”