Light on the biological pump: impact of bioluminescence
In the ocean, sunlight gradually decreases in the first few hundred meters, then darkness becomes total. In this dark environment, one of the least known biomes on the planet, many organisms emit their own light: bioluminescence.
In this review, the authors of the Mediterranean Institute of Oceanology (MIO) have brought together all current knowledge and put forward a new vision of the role of bioluminescence in the carbon cycle, shaking up currently accepted paradigms.
In the ocean, the biological carbon pump is the process that regulates the atmospheric concentration of CO2 by transferring carbon fixed at the surface by photosynthetic organisms to the sediments. Microorganisms are recognized as the main mineralizers of this particle flux in the dark water column. Until now, scientists thought that the degradation of particles, which fall gravitationally, by higher organisms (zooplankton, micronecton) was linked to whether or not they were able to get close to a particle (panel a of the figure). However, 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. As a result, these consumers will ingest more of the "illuminated" particles than those invisible in the dark.
The two possible indirect effects of this increased degradation of "illuminated" particles will have opposite consequences on carbon sequestration (panel b of the figure):
the fragmentation of organic matter into smaller aggregates during its degradation will reduce their rate of fall and thus carbon sequestration;
the consumption of small particles, which will partly aggregate 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.
For 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