MODELING THE MUD SURFACE-TEMPERATURE ON INTERTIDAL FLATS TO INVESTIGATE THE SPATIOTEMPORAL DYNAMICS OF THE BENTHIC MICROALGAL PHOTOSYNTHETIC CAPACITY

The mud surface temperature (MST) of an intertidal mudflat in Marennes -Oleron Bay (France) and the biomass-specific photosynthetic capacity (p(max)(B)) of benthic microalgae were modelled to investigate their s patio-temporal dynamics. Simulations were performed over 2 different p eriods during and after the microphytobenthos spring bloom (April and June, respectively) and under 2 different tidal conditions (spring and neap tides). The deterministic MST model is based on thermodynamic pr ocesses. Comparison at different periods between measured data series and simulations clearly establishes the reliability of the model, thus allowing extrapolations over time and space. The spatio-temporal dyna mics of MST is primarily controlled by the immersion-emersion alternat ion combined with the solar cycle, with a strong influence of the phas e difference in their respective oscillations: the highest MSTs are ac hieved in summer in the highest parts of the mudflat, when spring low tide occurs at midday. Three relevant time scales characterize the MST dynamics: long-term (seasonal cycle), medium-term (lunar cycle) and s hort-term (solar and tidal cycles). Within that framework, the respons e of P-max(B) to changes in MST depends upon T-opt, the optimum temper ature for photosynthesis (T-opt = 25 degrees C all year round). In Apr il, when the MST values are below T-opt, P-max(B) varies exponentially with MST at short lime scales. Conversely, in June, when the range of MST partially exceeds T-opt, P-max(B), is inhibited on most of the mu dflat surface area (up to 75%). This thermo-inhibition is highest in s ummer, when low tide occurs at midday.