Diel cycles backscattering and attenuation at 3 wavelengths for: the nano-eukaryotic diatom Thalassiosira pseudonana, the cyanobacterium Synechococcus (WH8102), and the pico-eukaryotic chlorophyte Ostreococcus lucimarinus. These optical properties were related to cell concentration, proxies for cell size, and intracellular pigment composition and concentration. We observed species-specific differences in the diel variability of these optical properties, suggesting that deriving biological products (like carbon) from bio-optical (incl. remote sensing data) must consider both time of day and community composition.