Deep-sea mussels on an hydrothermal vent edifice at 1,700 m depth on the Mid-Atlantic Ridge.
Photo Credit: © IfremerMomarsat2024
Scientific Frontline: Extended "At a Glance" Summary: Internal Clocks of Deep-Sea Mussels
The Core Concept: Deep-sea mussel (Bathymodiolus azoricus) cells possess an internal 24-hour circadian clock, despite living in deep ocean environments completely devoid of sunlight. This biological timing mechanism relies on the same core genes that regulate circadian rhythms in land-dwelling organisms.
Key Distinction/Mechanism: Unlike surface organisms whose circadian clocks are set by sunlight, these deep-sea mussels adapt their behavior and biology to the tidal shifts of hot, heavy-metal-rich hydrothermal fluids. Their molecular clock demonstrates significant plasticity, allowing it to transition from a 12.4-hour circatidal rhythm in the ocean to a 24-hour circadian rhythm when observed independently in laboratory cell cultures.
Origin/History: The research, published in November 2026 in EMBO Reports, achieved a world first by establishing deep-sea mussel cell cultures. Led by researchers such as Audrey Mat, the team successfully maintained these cells in the laboratory for over three years at deep-sea refrigerator temperatures.
Major Frameworks/Components:
- Hydrothermal Vent Ecology: The mussels colonize seafloor vent chimneys at depths of 1,700 meters, enduring extreme pressure and shifting hydrothermal fluid flows.
- Molecular Clock Machinery: The timing relies on core circadian clock genes, specifically through modifications in the expression of the period gene, which is conserved across organisms from flies to humans.
- Circatidal vs. Circadian Plasticity: The ability of the molecular clock to dynamically shift between a 12.4-hour tidal rhythm and a 24-hour daily rhythm based on the environment.
- Deep-Sea Cell Culture Technology: The unprecedented technical advancement of growing and maintaining marine cells in refrigerated conditions to replicate deep-sea temperatures, rather than standard incubation temperatures of 25 to 37 °C.
Branches of Science: Marine Chronobiology, Cellular Biology, Molecular Genetics, and Deep-Sea Ecology.
Future Application: These novel cell cultures provide a unique model system for studying biological timing plasticity, cellular adaptation to extreme environments, and the fundamental evolution of circadian rhythms in deep-sea ecosystems.
Why It Matters: The research demonstrates that biological timing mechanisms are highly adaptable and conserved across vastly different environments, proving that sunlight is not a strict necessity for a 24-hour clock and revealing how complex life functions in extreme conditions.
Hydrothermal vents lie in perpetual darkness in the depths of the ocean, yet the cells of the vent mussel Bathymodiolus azoricus, which lives 1,700 meters below the surface, follow a 24-hour rhythm in the laboratory. Researchers from the University of Vienna and the partner institutions IFREMER in France, the University of Oldenburg, and the AWI in Germany established cell cultures from these deep-sea mussels, which now allow cellular and molecular insights into the mechanisms of biological timing in the deep sea. The study was published in the journal EMBO Reports. It shows that in the tide-driven environment of the mussels, biological timing can rely on the same genes as the 24-hour clock that regulates land-dwelling organisms.
Living to the Rhythm of the Tides
At a depth of 1,700 meters, the deep-sea mussel Bathymodiolus azoricus shapes the ecosystem at hydrothermal vents. Its living conditions are extreme by human standards: the mussels colonize the seafloor around the vent chimneys and must withstand high pressure as well as the influence of hot, heavy-metal-rich fluid. This fluid forms when seawater permeates into the seafloor, passes through the underlying rocks, and pours back into the ocean as hydrothermal fluid. Its direction of flow shifts with the tides, which is presumably why the mussels at these vents show tidal rhythms in both their behavior and their molecular biology. How organisms without a brain generate such rhythms has so far remained unclear.
A World First: Deep-Sea Cells in the Fridge
For the first time, the team succeeded in establishing cell cultures from mussels, which have now been maintained in the laboratory for over three years. Audrey Mat, first author of the study and initiator of the experiments, explains: "While cells in the laboratory usually thrive at 25 to 37 °C, our mussel cells grow in the fridge, at deep-sea temperatures. This technical advance is unique in the world and allows novel insights into the biology of these animals."
From Tides to a Daily Rhythm
Interestingly, the mussels' rhythm changes from tidal rhythms on the deep seafloor to mainly circadian rhythms in the laboratory. The circadian rhythm can even be observed independently in cell cultures. This suggests significant plasticity in the clock machinery.
Deep-sea mussels possess the core circadian clock genes found in organisms ranging from flies to humans, albeit with specific modifications. These modifications could enable the clock to shift between circatidal (12.4-hour) and circadian (24-hour) timing, presumably through changes in the expression of the clock gene period.
Relevance for Protecting the Deep Sea
The deep sea is one of the least explored ecosystems on Earth and is under considerable pressure from human exploitation, such as pending deep-sea mining. "The fact that these ecosystems are mechanistically highly complex and possess timing systems as sophisticated as those at the surface underlines how worthy of protection they are. On land, we know that human activities such as light or vibrations disrupt circadian clocks. Deep-sea clocks are very likely just as vulnerable, with significant consequences for organisms and ecosystems," say Kristin Tessmar-Raible and Marjolaine Matabos, the joint coordinators of the study.
Reference material:
Published in journal: EMBO Reports
Title: Endogenous rhythms in deep-sea mussel cell culture and molecular clock characterization
Authors: Audrey M Mat, Federico Scaramuzza, Aida Ćorić, Christophe Klopp, Marjolaine Matabos, and Kristin Tessmar-Raible
Source/Credit: Universität Wien
Edited by: Scientific Frontline
Reference Number: mb110226_01
