SPATIAL AND TEMPORAL PATTERNS OF MICROPHYTOBENTHIC TAXA OF ESTUARINE TIDAL FLATS IN THE TAGUS ESTUARY (PORTUGAL) USING PIGMENT ANALYSIS BY HPLC

Measurements of natural estuarine microphytobenthos communities were c arried out in samples of intertidal sediments of the Tagus Estuary (Po rtugal) by means of pigment analysis by HPLC in order to identify micr ophytobenthos composition. The relative abundance of taxa was determin ed by microscopic observations. During spring 16 sites were sampled an d 3 of them, differing in sediment grain size and tidal level, were vi sited fortnightly for 1 yr. At all sites throughout the year, diatoms were the dominant algal group, evidenced by the relatively high concen trations of chlorophylls c(1)+c(2), fucoxanthin, neofucoxanthin, diadi noxanthin, diatoxanthin and beta-carotene, chi b and diatoxanthin were related with observed euglenophyte populations, zeaxanthin with cyano bacteria, lutein with macrophyte debris and alloxanthin with falling p hytoplanktonic cells of cryptophytes. The spatial study allowed a dist inction between sites regarding the presence of macrophyte debris, eug lenophytes or only diatoms. The temporal survey showed the seasonal tr ends of diatoms and cyanobacteria and the main periods of plant debris deposition. Pheophytin a and chlorophyllide a concentrations were qui te low. Degraded chloropigments were constituted mainly of pheophorbid es a, 9 of which were quanti fled. The most abundant among them indica ted intensive grazing by macrozoobenthos at the muddy stations.