Antarctic krill, a shrimp-like crustacean that supports the food web at the South Pole, was found in a hydrothermal vent off the Antarctic Peninsula during the National Geographic and Rolex Perpetual Planet Southern Ocean Expedition in collaboration with the Schmidt Ocean Institute. hide caption toggle caption Antarctic krill is the soul of the South Pole. These shrimp-like crustaceans serve as a crucial food source for penguins, seals, and whales. “Most of them feed on Antarctic krill,” says Kim Bernard, a biological oceanographer at Oregon State University and a National Geographic explorer. “And if they don’t, they feed on something else that feeds directly on Antarctic krill. So they are absolutely critical to the functioning and health of that ecosystem.” Krill also recycle nutrients that allow small algae called phytoplankton to grow. In addition, krill is fished in large quantities to produce aquaculture feed and omega-3 fatty acids as dietary supplements. But experts say this rich habitat in the Southern Ocean, at the bottom of the world, is changing rapidly due to climate change. “It is one of the fastest warming areas of the planet,” says Bernard. “And that’s cascading through the food web and affecting the Antarctic krill population.” Now, Bernard and his colleagues report in the journal Communications Biology on the discovery of a surprising habitat for krill: hydrothermal vents, which are basically hot springs on the ocean floor. Characterizing the importance of this habitat, especially for breeding females, can help inform how to safeguard these crucial crustaceans. Feelings of ventilation Antarctic krill tend to settle in the upper layer of the ocean. “They can be found forming swarms and layers on the surface,” says Bernard. “You can photograph them from airplanes.” They can also be found on the sea floor at different depths, but she says these deeper observations have been few and anecdotal. Then, in late 2024, Bernard was in Bransfield Strait off the Antarctic Peninsula while aboard the National Geographic and Rolex Perpetual Planet Southern Ocean Expedition in collaboration with the Schmidt Ocean Institute. One of his colleagues, UCLA benthic ecologist Andrew Thurber, was using a remotely operated vehicle in a depression about 3,600 feet below the surface to study and video a hydrothermal vent. Imagine “extremely hot water coming from deep in the Earth’s crust,” Bernard says, “and it brings with it metals, sulfides and all kinds of other chemicals that form almost like a tower.” Biological oceanographer Kim Bernard and her colleagues examine krill they collected from a hydrothermal vent about 3,600 feet below the surface. hide caption toggle caption It is a seemingly inhospitable place. Bernard wasn’t studying the vent, but she was eager to observe the sampling. “While I was having tea upstairs in the kitchen,” he recalls, “I was looking at the giant screens showing in real time what was happening.” And that’s when he saw a flash of movement in the corner of the screen. It was, without a doubt, krill. “It’s like an underwater ballet,” he says, describing the krill’s backflips. “It just looks like a pirouette. I practically threw my tea in the air and ran towards the control room, shouting, ‘There’s krill, there’s krill!'” Krill had never before been seen at a hydrothermal vent. The other research team had planned to sample the geology and microbiology of the vent, but they gave Bernard a precious 15 minutes to try to capture some specimens. “They have what they call a suction sampler, which is essentially a vacuum cleaner that sucks up whatever you want to suck up,” he explains. The team managed to capture four individual krill, all breeding females, “heavily laden with eggs. We should release them any minute now.” “And to see something like that in a hydrothermal vent,” Bernard continues, “is completely opposite to what we would normally have expected.” Researchers had thought that females probably released their eggs near the surface in deep water, but it had never been observed before. Then Bernard was faced with a single basic question: “Why are they down there?” he says. “I really wanted to try to understand what they get out of that site.” It takes a lot of energy for the little krill to go that deep. Additionally, they are exposed to potentially toxic heavy metals such as cadmium, barium, and lead. So whatever is bringing the krill to the hydrothermal vent, Bernard thought, it must be worth it. “It’s really critical that we put our efforts into trying to understand the role of the deep-sea environment for krill reproduction,” he says. Four small krill, one big question To get a better idea of what was happening, Bernard brought a handful of krill to the surface and compared the contents of its stomach with others he collected in other parts of the seabed, in shallower waters without vents. It was evident that the four females had been feeding on microbes living down there. (And that microbial food source would be available year-round instead of seasonal phytoplankton that rely on sunlight and photosynthesis.) “The rest of the krill tissue,” he says, “I dried and literally carried it in my backpack on the way home. I didn’t want to lose sight of it because it was so important.” That tissue later revealed that the krill had accumulated higher levels of metals released by the vent, such as manganese. “It is an important nutrient or mineral for the embryonic development of crustaceans,” says Bernard. “And it’s very rare in the Southern Ocean. So potentially that’s a reason for them to go down there.” Warmer waters near the vent can also speed up embryo development. All or some combination of these reasons may motivate krill to repeatedly descend to the hydrothermal vent and then remain there for some time. “The study shows that krill can make use of hydrothermal vent habitats, but does not provide sufficient evidence to suggest that they are dependent on these habitats,” says Simeon Hill, a marine ecologist at the British Antarctic Survey who was not involved in the research. Still, it assures him that krill can flexibly use different parts of the ocean to live and feed, demonstrating their resilience. And it says that although hydrothermal vents are reasonably well protected from destructive human activities, additional conservation measures may be needed. “This makes me think it would be sensible to develop a marine protected area process that allows new vulnerable habitats to be added as they are discovered,” says Hill. That type of protection may be especially necessary if those habitats are critical to the krill reproductive cycle. Two months after the original research cruise, the same ship visited another Antarctic hydrothermal vent about 1,000 miles away. Female krill laden with eggs were also abundant in that vent. “It was incredible,” says Bernard. “So I’m sure this is not a one-time thing and there’s more to it than we expected.”
