The landmark of diatom microalgae is their 3D siliceous cell wall, the frustule, which shows extremely refined nanostructures with unique optical properties. These nanostructures behave like photonic biocrystals which are similar to the ones used for diverse advanced technologies. Therefore, the nano-scale expertise of diatoms is more and more used in biomimetic nanotechnologies and nanophotonics. The DiatOp project proposes to explore the potential of diatoms, especially of benthic growth forms (i.e. which can form biofilms and which inhabit on/in substrates) as an emerging natural source of photonic material. The central objective of the project is the measurement of the frustule optical properties (absorption, focus, diffraction, etc.) in different growth forms (i.e. subtidal and intertidal) and species (i.e. different morphologies and sizes) of benthic diatoms.