The « lungs » of the Earth have their own « eyes »! Producing half of the oxygen on our planet through photosynthesis—more than all of the forests combined—phytoplankton is distributed across the ocean by mechanisms that scientists are still trying to fully understand. One such mechanism has just been identified: light.
Scientists from CNRS and Sorbonne University made this discovery while studying the sensory abilities of diatoms. These tiny brown algae are « craftsmen in glassmaking at room temperature, » as evidenced by their translucent external skeletons, which feature incredibly varied shapes and patterns (Muséum National d’Histoire Naturelle).
Published in Nature on December 18, 2024, the study conducted by this French team reveals that these marine organisms possess light-sensitive receptors known as phytochromes (press release).
Perceiving Light Where Day Length Varies
Encoded in their genome, these organs allow diatoms to detect changes in the light spectrum within the water column, thus « informing them of their position within this column, » the researchers explain. However, this is not the case everywhere!
By analyzing genomic data collected from water samples taken during Tara Ocean expeditions, the study’s authors noticed that only diatoms from areas beyond the Tropics of Cancer and Capricorn seem to possess phytochromes.
These regions are characterized by « marked seasons » and « significant variations in day length, » leading scientists to deduce that this organ likely helps diatoms « measure the passage of time. »
This light perception would thus be « particularly important » for adjusting their biological activity—especially the intensity of their photosynthesis—in « changing aquatic environments » subject to significant water mixing (high latitudes, temperate, and polar regions).
Oxygen, Nitrogen, Carbon… The Diatom Revolution
By shedding « new light » on how algae navigate using light, the study underscores the need for « integrated research, » both in laboratories and in natural environments, to « better understand the complex dynamics of ocean ecosystems » and the « ability of marine organisms to respond to environmental changes » (press release).
Thanks to data collected during Tara Ocean expeditions, scientists also recently discovered that the diatom Cylindrotheca closterium consumes organic matter in addition to producing it—an unexpected finding that the authors say requires « rewriting the oceanic carbon cycle » (July 2024).
Last spring, a team led by the Max Planck Institute for Marine Microbiology uncovered a symbiosis between a marine diatom and a Rhizobium bacterium. This partnership may help explain much of the nitrogen fixation in the ocean, a crucial process. Who knows what other surprises the « craftsman of the ocean » has in store for us?
Source: GEO
