MICROPHYTOBENTHOS BIOMASS AND COMMUNITY COMPOSITION STUDIED BY PIGMENT BIOMARKERS - IMPORTANCE AND FATE IN THE CARBON-CYCLE OF A TIDAL FLAT

Microphytobenthos biomass and community composition vi ere studied by the use of pigment biomarkers during one year at a tidal flat located in the Westerschelde (SW Netherlands). Benthic microphytes appeared to be an important carbon source in the Westerschelde, especially in the central part of the flat with a mean biomass as high as 65 mg Chi a m (-2) in the superficial 1 mm of sediment. Diatoms (fucoxanthin, Chl c) dominated the population during both spring and autumn blooms. In sum mer microphytobenthic biomass decreased, and diatoms coexisted with Cy anobacteria (zeaxanthin) and Euglenophyceae (Chl b, zeaxanthin and lut ein). The shift in the community composition may possibly be linked wi th the decrease in silicon concentration in the overlying water. The d egradation and recycling of microphytobenthic biomass was assessed by the study of degraded chlorophyll pigments, and pigments in deeper sed iment layers. The fate of microphytobenthos appears to include rapid b acterial degradation in spring, episodic grazing by benthic animals in surface layers of sediments in the centre of the flat, and export by resuspension in sediments more exposed to currents.