FACTORS CONTROLLING PRIMARY PRODUCTION AND PHOTOSYNTHETIC CHARACTERISTICS OF INTERTIDAL MICROPHYTOBENTHOS

Microphytobenthic primary production and biomass were studied in an in tertidal flat located in the Westerschelde (SW Netherlands) with a ver tical resolution of 1 mm. Short-term variability of primary production and photosynthetic characteristics were compared during low tide in 2 types of sediment: sandy and muddy sands. The changes observed were c ompared with abiotic factors and the biomass abundance, which was domi nated by benthic diatoms. C-14 uptake values obtained from incubations in a photosynthetron were used for the construction of P-I (photosynt hesis-irradianee) curves. Annual averages indicate that both sediments were equally productive (34.5 +/- 23.6 mg C m(-2) h(-1) and 41.1 +/- 11.6 mg C m(-2) h(-1) for the sands and muddy sands respectively), but production rates were highly variable on monthly time scales and were regulated by different mechanisms. Light and temperature played an im portant role in determining the production rates, especially in the mu ddy sediments, where changes in I-k (light saturation) were correlated with temperature. I-k showed seasonal changes, suggesting that algae adapted to the seasonal light conditions but there was not a significa nt correlation between the I-k and PAR (photosynthetic available radia tion) at any of the stations. Vertical migration of the algae, as foll owed by spectroradiometric measurements, probably accounted for a gene ral absence of photoinhibition. In the sandy sediments, production app eared to be limited by the low biomass of algae, due to resuspension a nd export. The fact that gross oxygen production rates measured on int act cores using microelectrodes were not lower than potential producti on obtained from 14C fixation suggests that short-term limitation of p roduction due to nutrients and/or carbon is not frequent in the microp hytobenthos of the Westerschelde.