A study reveals that some marine micro-algae emit their own light to communicate

An international researchers team has discovered that some marine micro-algae, known as diatoms, not only get advantage of the sun's light to carry out the photosynthesis, but also emit their own light directionally, alterating this way the natural distribution os the lighting under the sea.

The work, recently published in the magazine Proceedings of the National Academy of Sciences (PNAS), revals a phenomena unknwon until now that coul change the way in which we understand optical dynamics in the ocean and the interpretation of the satellyte date about marine productivity. 

The study has been led by Joan Salvador Font-Muñoz, researcher of the Mediterranean Institute for Advanced Studies (IMEDEA, UIB-CSIC), in collaboration with researchers of the French Research Institute for Exploitation of the Sea (IFREMER) and the Balearic Islands' University. 

The team focused the research on the Pseudo-nitzschia fraudulenta species, an enlarged diatom and very common in coastal waters. 

Through experiments with individual cells, researchers saw that these micro-algae emit red fluorescence —a light generated by clorophyll— in an anisotropic, which means, with an intensity that shifts in terms of direction. In some cases, the emission in certain orientations was up to a 35% more intense. This property is due to the enlarged form of the cells as well as the intern disposition of its chloroplasts and the optical effect of the silica wall that covers them. 

“The diatoms do not only capture the sun's light: but also redistribute it. Together, they can modify the lighting landscape of the ocean”, Joan Font explains.

When cells get togetehr and guide themselves similarly —something that happens frenquently in stratified or not very agitated waters—, the effects amplifies. According to models developed by the team, the emitted light by a diatoms group tht can vary up to a 15% o 20% depending on its orientation in the water column, without the present biomass quantity changing. 

These results suggest that the fluorescence of the diatoms is not only a subproduct of the photosynthesism but a mechanism with potential ecological functions, such as communication between organisms or regulation of light in its inmediate environment. In addition, this phenomena could have consequences in the satellyte observation, since ths current models of teledetection assume that marine fluorescense is emmitted in an uniform way, something that this study doubts. 

“Comprehending how marine organisms modify the light that surrounds them will help us improve the interpretation of satellyte data and oceanic productivity models”, points out Joan Font. 

The discovery opend the door to a new research line about how microorganisms can use light as a communication device.  According to the authors, the light signs generated by these micro-alge could have a major reach and be quicker that chemical signs, traditionally considered the main channel of interaction for plancton.