Light as an information carrier underwater

Light is a source of both energy and information for the biota. The spatial, temporal and spectral variability of light experienced by marine phytoplankton differs significantly from that experienced by terrestrial plants, due to the selective attenuation of solar irradiance in the aquatic medium. In the present study we analysed such variability and focused, in particular, on those bands within the spectrum that may act as potential signals for physiological responses. Our results demonstrate that the spectral variation of the light field carries information on the time of day, the vertical position and the presence of very close neighbours, also underwater. This is consistent with the recent findings of a widespread occurrence of photoreceptors in marine algae. We show also that red photoreceptors, whose presence in marine algae was difficult to reconcile with the strong attenuation of long wavelengths by water, may be triggered at depth by the red light generated by transpectral processes.