At 1,700 meters below the Atlantic, Bathymodiolus azoricus mussels live in darkness beside hydrothermal vents—and their cells can keep a 24-hour rhythm in a laboratory refrigerator. The finding offers a rare way to study how life keeps time in one of Earth’s least explored environments.
These mussels live around vent chimneys on the Mid-Atlantic Ridge, where they face crushing pressure and hot, mineral-rich fluids. The fluids form when seawater moves through the seafloor and then rises back into the ocean. Their flow shifts with the tides. On the deep seafloor, the mussels show rhythms linked to those tides, which last about 12.4 hours. But how an animal without a brain produces such timing has been hard to investigate.
Researchers from the University of Vienna, France’s IFREMER, the University of Oldenburg and Germany’s Alfred Wegener Institute (AWI) have now established cell cultures from the mussels. The cultures have been maintained in the laboratory for more than three years, giving scientists a new way to examine the animals’ biology at the cellular and molecular level.
The technical challenge was keeping the cells alive under conditions that suit a deep-sea species. “While cells in the laboratory usually thrive at 25 to 37 °C, our mussel cells grow in the fridge, at deep-sea temperatures,” said Audrey Mat, the study’s first author and the researcher who began the experiments. The team describes the cultures as a world first.
In the lab, the mussels’ timing shifted from the tidal pattern seen on the seafloor to a mainly 24-hour, or circadian, rhythm. That daily rhythm also appeared in the cell cultures on their own. This suggests that the mussels’ internal timing system can adjust to different cycles, even when studied outside the whole animal.
The team found that the mussels have core circadian clock genes also found in animals from flies to humans, though the mussel genes have some differences. The researchers think those changes may help the clock switch between a 12.4-hour tidal rhythm and a 24-hour daily one. One possible part of that switch is a change in the activity of the clock gene period; the study presents this as a likely explanation, not a settled answer. The research was published in EMBO Reports in 2026.
The work also adds to the case for protecting deep-sea habitats as pressure grows from human activity, including proposed deep-sea mining. Kristin Tessmar-Raible and Marjolaine Matabos, the study’s joint coordinators, said the clocks of deep-sea organisms may be vulnerable to disturbances just as clocks on land can be affected by light or vibrations. With mussel cell cultures now available for study, researchers can begin testing how these remarkable timing systems work—and what might put them at risk.