In the present paper, we list and document the relevant behavioral and physiological processes controlling primary productivity of epipelic microalgae on intertidal mudflats in order to develop a simplified model. We first propose, in an attempt to characterize the 'photosynthetically active biomass' of the epipelic community, a new approach to describe the photic environment at the sediment surface, by substituting a discrete a-layer model in place of continuous vertical light distribution. This concept thus allows us to build a functional representation of the distribution of the photosynthetically active biomass in the sediment and, by then integrating the light and temperature forcing of the latter biomass, to predict the dynamics of the whole epipelic community on short-term time scales. The model then clearly reveals an oscillatory behavior of the total biomass at the surface of the sediment, consistent with field biomass daily measurements performed during a spring-neap tidal cycle. Biomass increases occur during the diurnal emersion phase, in alternation with decreases during the submersion and nocturnal emersion phases; the dynamics of intertidal microphytobenthos is thus controlled by the night/day cycle and tidal hydrodynamic forcing, which determines the fast changes in environmental conditions (light and nutrient availability, temperature) which epipelic microalgae experience. The similarity between model simulations and field observations leads us to conclude that the conceptual framework of the model is valid.