SEASONAL EFFECT ON THE RELATIONSHIP BETWEEN THE PHOTOSYNTHETIC CAPACITY OF INTERTIDAL MICROPHYTOBENTHOS AND TEMPERATURE¹

Abstract

ABSTRACT The response of the photosynthetic capacity (P max ) of microphytobenthos to short‐term variations of temperature (in the range 5–35° 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 opl , the optimum temperature. Estimated values of T opt do not change significantly throughout the year and remain close to 25° 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° C), the thermal threshold beyond which no photosynthesis occurs. Conversely, P MA estimates exhibit substantial variability: P MAX (mean ± root mean square error) is highest in April (11.18 ± 0.42 [μg C · [μg 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 μg C · [μg Chl a] −1 · h −l ). 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.