Dynamic model of the short-term variability of microphytobenthic biomass on temperate intertidal mudflats

In the present paper, we list and document the relevant behavioral and phys iological processes controlling primary productivity of epipelic microalgae on intertidal mudflats in order to develop a simplified model. We first pr opose, in an attempt to characterize the 'photosynthetically active biomass ' of the epipelic community, a new approach to describe the photic environm ent at the sediment surface, by substituting a discrete a-layer model in pl ace of continuous vertical light distribution. This concept thus allows us to build a functional representation of the distribution of the photosynthe tically active biomass in the sediment and, by then integrating the light a nd temperature forcing of the latter biomass, to predict the dynamics of th e whole epipelic community on short-term time scales. The model then clearl y reveals an oscillatory behavior of the total biomass at the surface of th e sediment, consistent with field biomass daily measurements performed duri ng a spring-neap tidal cycle. Biomass increases occur during the diurnal em ersion phase, in alternation with decreases during the submersion and noctu rnal emersion phases; the dynamics of intertidal microphytobenthos is thus controlled by the night/day cycle and tidal hydrodynamic forcing, which det ermines the fast changes in environmental conditions (light and nutrient av ailability, temperature) which epipelic microalgae experience. The similari ty between model simulations and field observations leads us to conclude th at the conceptual framework of the model is valid.