SPATIOTEMPORAL DISTRIBUTION OF THE MICROPHYTOBENTHIC BIOMASS IN INTERTIDAL FLATS OF TAGUS ESTUARY (PORTUGAL)

A study on spatio-temporal distribution of microphytobenthos in intert idal zones of Tagus Estuary was carried out from 1990 to 1992. Near Li sbon, Portugal, Tagus Estuary is a shallow mesotidal estuary, covering an area of 320 km(2). The intertidal area ranges from 20 to 40% of th e total area and it is constituted mainly by mudflats. Intertidal flat s are richly populated by microalgae, diatoms being the most important and ubiquitous group. Spatial variation of microphytobenthos was stud ied in spring 1990, 21 different sites were sampled. Microphytobenthos biomass was evaluated as chlorophyll a content of the surface centime ter, ranging from 10 to 240 mg m(-2). A Principal Component Analysis s howed that 62% of the total variability found in intertidal flats of T agus estuary could be attributed to two major factors: sediment type a nd tidal height. A hierarchical grouping defined 3 major groups of sim ilar stations, each one representing a different strata of the ecosyst em. One station from each group was chosen for the study of the tempor al variation. A sampling program took place from April 1991 to April 1 992, with fortnightly sampling, the Chl a ranged from 20-300 mg m(-2). No clear seasonal variation was found, and our results indicated that tidal height of sampled site played an essential role in temporal bio mass evolution, thus upper littoral sites were influenced by climatic parameters, whereas in lower sites action of tides mainly controlled m icrophytic biomass.