Estuarine microphytobenthos biofilms, dominated by benthic motile diatoms, are highly productive. The capacity for motility has been hypothesized to be a major factor explaining the ecological success and productivity of benthic diatoms. The aim of SEARCHLIGHT is to generate an integrated understanding of the adaptive value of phototaxis in benthic diatoms, and of how photobehavior enhances photosynthesis at the cellular level, and ultimately supports the high productivity of estuarine intertidal areas. To do so, up-to-date technics (bioimaging at the cell level, microfluidics) will be set up.