In the ocean, sunlight gradually diminishes over the first few hundred metres, before total darkness sets in. In this dark environment, one of the least known biomes on the planet, many organisms emit their own light: this is bioluminescence.
In this review, the authors from the Mediterranean Institute of Oceanology (MIO) have brought together all the current knowledge and put forward a new vision of the role of bioluminescence in the carbon cycle, overturning currently accepted paradigms.
In the ocean, the biological carbon pump is the process that regulates the atmospheric concentration of CO2 by transferring the carbon fixed at the surface by photosynthetic organisms to the sediments. Microorganisms are recognised as the main mineralisers of this particulate flow in the dark water column. Until now, scientists thought that the degradation of particles, which fall gravitationally, by higher organisms (zooplankton, micronekton) was linked to whether or not these organisms had the opportunity to be close to a particle (panel a in the figure). It turns out that bioluminescent bacteria can be attached to these particles. Their light emission then acts as a visual marker, leading to the detection, attraction, ingestion and consumption of the particles by larger organisms. These consumers will therefore ingest more of the "illuminated" particles than the particles that are invisible in the dark.
The two possible indirect effects of this increase in the degradation of "illuminated" particles will have opposite consequences on carbon sequestration (panel b in the figure):
the fragmentation of organic matter into smaller aggregates as it degrades will reduce the rate at which it falls, and therefore carbon sequestration;
the consumption of small particles, which will aggregate in part in the stomachs of organisms, will lead to the production of faecal pellets which will fall more rapidly, leading to an increase in carbon sequestration.
These processes remain to be quantified by future studies.
More information
Tanet L, Martini S, Casalot L, Tamburini C (2020) Reviews and syntheses: Bacterial bioluminescence - ecology and impact in the biological carbon pump. Biogeosciences 17:3757-3778. https://doi.org/10.5194/bg-17-3757-2020
Contact
Séverine Martini
MIO/PYTHÉAS
severine.martini@mio.osupytheas.fr
Christian Tamburini
MIO/PYTHÉAS
04 86 09 05 19
stian.tamburini@mio.osupytheas.fr