Scientists Find Egg-Bearing Antarctic Krill at Deep-Sea Hydrothermal Vents

Antarctic krill are shrimp-like crustaceans that serve as a crucial food source for penguins, seals and whales. Bernard, a National Geographic explorer, said most of those animals feed on Antarctic krill or on creatures that feed directly on them, making krill fundamental to the ecosystem. Krill also recycle nutrients that support phytoplankton, and they are fished in large numbers for aquaculture feed and omega-3 dietary supplements.

Experts say the Southern Ocean is changing rapidly because of climate change. Bernard described it as one of the most rapidly warming areas on the planet and said the effects are cascading through the food web and affecting the Antarctic krill population. Antarctic krill usually live in the upper layer of the ocean, where they can form swarms and layers at the surface, though they have also been found at different depths on the sea floor, with those deeper observations described as sparse and anecdotal.

In late 2024, Bernard was in the Bransfield Strait aboard the National Geographic and Rolex Perpetual Planet Southern Ocean Expedition in collaboration with the Schmidt Ocean Institute. A colleague, UCLA benthic ecologist Andrew Thurber, was using a remotely operated vehicle about 3,600 feet below the surface to study and video record a hydrothermal vent. Bernard said the vent looked like a tower formed by extremely hot water from deep within Earth's crust bringing metals, sulfides and other chemicals. She was not studying the vent but watched the real-time video from the galley.

Then she saw movement in the corner of the screen. It was a krill, doing what she described as underwater ballet and pirouetting. She said she threw her tea in the air and ran to the control room, shouting that there was krill. Krill had never been spotted at a hydrothermal vent before. The other research team had planned to sample the vent's geology and microbiology but gave Bernard 15 minutes to try to catch specimens.

Using a suction sampler, the team collected four individual krill. All were reproductive females very heavily laden with eggs and, Bernard said, should have been releasing them at any moment. Researchers had thought females probably released their eggs near the surface over deep water, but that had never been observed. Bernard said she wanted to understand what the krill were getting from the site. Descending so deep takes a lot of energy for small krill, and they are exposed to potentially toxic heavy metals such as cadmium, barium and lead, so she reasoned that whatever brings them to the vent must be worth it. She said it is critical to understand the role of the deep-sea environment for reproductive krill.

To learn more, Bernard brought the krill to the surface and compared their stomach contents with those of krill collected elsewhere on the seafloor in shallower, non-vent waters. The four females had clearly been feeding on microbes living down there. Such a microbial food source would be available year-round, unlike seasonal phytoplankton that rely on sunlight and photosynthesis. Bernard dried the remaining krill tissue and carried it home in her backpack, saying she did not want it out of her sight because it was so important. Characterizing the importance of the hydrothermal vent habitat, especially for reproductive females, may help inform how to safeguard the crustaceans.

Editor's Summary

Antarctic krill had not previously been documented at hydrothermal vents. In late 2024, researchers collected four egg-bearing females at a vent in the Bransfield Strait and found they had been feeding on microbes that are available year-round. The finding raises new questions about the deep-sea habitat's role for reproductive krill as climate change alters the Southern Ocean.