Seasonal effect on the relationship between the photosynthetic capacity of intertidal microphytobenthos and temperature

The response of the photosynthetic capacity (P-max) of microphytobenthos to short-term variations of temperature (in the range 5-35 degrees C) was assessed on a seasonal basis. The relationship is described mathematically, and relevant physiological parameters are identified: P-MAX, the maximum value of P-max achieved at T-opt, the optimum temperature. Estimated values of T-opt do not change significantly throughout the year and remain close to 25 degrees C. It is thus concluded that T-opt is not influenced by seasonal variations in the daily range of mud surface temperature. Identical conclusions hold for T-max (ca. 38 degrees C), the thermal threshold beyond which no photosynthesis occurs. Conversely, P-MAX estimates exhibit substantial variability: P-MAX (mean +/- root mean square error) is highest in April (11.18 +/- 0.42 mu g C.[mu g Chl a](-1).h(-1)) during the beginning of the annual increase in temperature, photoperiod, and maximum irradiance and is lowest in December (3.04 +/- 0.16 mu g C.[mu g Chl a](-1).h(-1)). From an ecological point of view, the short-term and seasonal variations of P-MAX suggest that the microphytobenthic community takes advantage of the abiotic spring environmental conditions, allowing the onset of the bloom. Nevertheless, no ''acclimation strategy'' (i.e. shifts in T-opt and T-max that prevent temperature inhibition in summer or improve photosynthetic rates in winter) is apparent from our results.