Scientists discovered egg-laden Antarctic krill thriving nearly 3,600 feet below the surface at hydrothermal vents, a finding that upends long-held assumptions about one of the ocean's most important creatures.
A research team operating a remotely piloted submarine off the Antarctic Peninsula in late 2024 spotted the tiny crustaceans drifting through superheated water near a volcanic vent on the seafloor, a place no one expected to find them. The four krill collected were all reproductive females, packed with eggs and apparently feeding on microbes unique to the vent site. The discovery, published in the journal Communications Biology, marks the first confirmed observation of Antarctic krill at a deep-sea hydrothermal vent.
The finding matters because Antarctic krill sit at the base of one of the planet's most consequential food chains. Penguins, seals, and whales all depend on them. Krill also recycle nutrients that allow phytoplankton to grow, and they are commercially harvested for aquaculture feed and omega-3 supplements. Any shift in where krill live and breed could ripple through the entire Southern Ocean ecosystem, and through the industries that depend on it.
Kim Bernard, a biological oceanographer at Oregon State University and a National Geographic explorer, was not at her station when the krill appeared. She was upstairs in the ship's galley, watching the live ROV feed on a monitor over tea. Her colleague Andrew Thurber, a benthic ecologist from UC Santa Barbara, was piloting the remotely operated vehicle SuBastian roughly 3,600 feet below the surface in the Bransfield Strait.
Bernard told NPR what happened next:
"It's like underwater ballet. 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!'"
The team had only 15 minutes to collect specimens at the vent. Using a suction sampler, Bernard described it as "essentially a vacuum that slurps whatever you want to slurp up", they captured four individual krill. Every one was a reproductive female. Bernard described them as "very heavily laden with eggs. Should be releasing them any moment."
That detail stunned her. Krill are surface creatures. They form massive swarms visible from aircraft. Finding egg-bearing females nearly three-quarters of a mile below the ocean surface, at a volcanic vent, ran counter to decades of scientific understanding.
"And to see something like that at a hydrothermal vent, is completely opposite to what we would have normally expected," Bernard said.
Bernard and her colleagues set out to answer a straightforward question: why would krill travel to such an extreme environment? The analysis pointed to three possible answers, all still classified as hypotheses rather than confirmed conclusions.
First, the stomach contents of the four vent krill showed they had been feeding on microbes at the site, organisms that grow year-round near hydrothermal vents, unlike the seasonal phytoplankton that krill normally eat near the surface. A reliable food source available in every season could draw krill downward.
Second, tissue analysis revealed elevated levels of manganese. Bernard explained the significance: manganese is an important mineral for embryo development in crustaceans, and it is very scarce in the broader Southern Ocean. "So potentially that's a reason for them to go down there," she said.
Third, the warmer water near the vent may speed up embryo development, a hypothesis the team has not yet confirmed but considers plausible given what is known about crustacean biology.
The vent environment is not without risk. Heavy metals including cadmium, barium, and lead are present at the site, posing a potential hazard to any organism that lingers there. Bernard dried the remaining krill tissue and carried it home in her backpack rather than risk losing it to checked luggage or shipping delays.
"I didn't want to put it anywhere out of my sight because it was so important," she said.
Roughly two months after the original cruise, the same vessel visited a second Antarctic hydrothermal vent approximately 1,000 miles from the first. Researchers found egg-laden female krill there as well. The discovery at a second, distant site suggested the behavior is not a fluke confined to one location.
Bernard was direct about the implication: "I am sure that this is something that is not just a once-off, and there's more to this than we ever expected."
The expedition was a joint effort of the National Geographic and Rolex Perpetual Planet Southern Ocean Expedition in collaboration with the Schmidt Ocean Institute. Bernard's findings and those of her co-authors were published in Communications Biology.
Not everyone is ready to declare the vents a critical krill habitat. Simeon Hill, a marine ecologist with the British Antarctic Survey who did not participate in the research, offered a measured assessment.
"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's caution is worth noting, but so is what he said next. He recommended that policymakers develop "a marine protected area process that allows new vulnerable habitats to be added as they're discovered." In other words, even the skeptic thinks the finding is significant enough to warrant a policy response.
Bernard framed the stakes in plain terms. Antarctic krill are the linchpin of the Southern Ocean food web. Penguins eat them. Seals eat them. Whales eat them. And the animals that don't eat krill directly eat something that does.
"Most of them feed on Antarctic krill. 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."
The Southern Ocean is also, by Bernard's account, "one of the most rapidly warming areas on the planet." That warming is cascading through the food web and affecting krill populations. If reproductive female krill are using deep-sea vents as nurseries, for the food, the manganese, the warmth, or some combination, then those vents may play a role in krill survival that no one previously accounted for.
"It's really critical that we put our efforts into trying to understand the role of the deep sea environment for reproductive krill," Bernard said.
Several questions remain unanswered. How many krill visit these vents in total? Are other vent sites across the Southern Ocean serving the same function? What are the precise metal levels in vent krill compared to their surface-dwelling counterparts? And does the commercial krill fishing industry, which harvests krill for aquaculture feed and omega-3 supplements, need to factor deep-sea habitats into its management plans?
Nature has a way of operating on its own terms, indifferent to the assumptions scientists and regulators bring to the table. The lesson from 3,600 feet below the Antarctic is an old one: before you write the rules, make sure you understand what you're managing.
