Modulation of the light field related to valve optical properties of raphid diatoms: implications for niche differentiation in the microphytobenthos

Differences in the spectral light absorption of photopigments allow for niche differentiation and coexistence of cyanobacteria and diatoms. Evolution in the microphytobenthos could have further been shaped by the photonic crystal-like structures in the frustule of diatoms interacting with sunlight. We studied the optical properties in water of the valves of 3 pennate diatom species collected from an intertidal estuarine mudflat. We observed forward scattering of blue light in the valve, while the angle of incident white light at which this phenomenon was visible differed between the 3 tested raphid species. A slurry of oxidized frustules enhanced scalar irradiance in the blue spectral range by up to 120% compared to downwelling irradiance. Blue light induced higher relative electron transport rates at photosystem II and non-photochemical quenching compared to red actinic light. We hypothesize that structures in the pennate diatom frustule modulate microalgal light absorption for efficient photosynthesis and thereby contribute to niche differentiation of diatoms in the microphytobenthos.