Short-term dynamics of intertidal microphytobenthic biomass. Mathematical modelling

We formulate a deterministic mathematical model to describe the dynamics of the microphytobenthos of intertidal mudflats. It is 'minimal' because it o nly takes into account the essential processes governing the functioning of the system: the aurotrophic production, the active upward and downward mig rations of epipelic microalgae, the saturation of the mud surface by a biof ilm of diatoms and the global net loss rates of biomass. According to the p hotic environment of the benthic diatoms inhabiting intertidal mudflats, an d to their migration rhythm, the model is composed of two sub-systems of or dinary differential equations; they describe the simultaneous evolution of the biomass 'S' concentrated in the mud surface biofilm - the photic layer - and of the biomass 'F' diluted in the topmost centimetre of the mud - the aphotic layer. Qualitatively, the model solutions agree fairly well with t he in situ observed dynamics of the S + F biomass. The study of the: mathem atical properties of the model, under some simplifying assumptions, shows t he convergence of solutions to a stable cyclic equilibrium, whatever the fr equencies of the physical synchronizers of the production. The sensitivity analysis reveals the necessity of a better knowledge of the processes of bi omass losses, which so far are uncertain, and may further vary in space and time. ((C) Academie des sciences / Elsevier, Paris.)