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Sediment-inhabiting microphytobenthos (MPB) is dominated by raphid pennate diatoms that use vertical migration (VM) and the xanthophyll cycle (XC) as main photoprotective mechanisms against excess light. This study compares the short-term kinetics of activation of the two processes upon exposure to high light. The light response of VM was studied with temporal resolution of minutes, by using a new experimental approach (a ‘multi-actinic imaging’ system) based on the combination of (1) simultaneous application of multiple levels of incident light (50–1350 µmol m⁻² s⁻¹) to replicated samples, through the projection of spatially separated beams of actinic light, and (2) reflectance-based imaging of MPB surface biomass, using a modified chlorophyll fluorescence imaging system with red and infrared bandpass filters. The induction kinetics of the XC was inferred by measuring the activation of non …