Phytoplankton samples were collected monthly during a tide cycle between April 1986 and March 1987 at 4 fixed stations (Fig. 1). A plankton net of mesh size 65m mand Van Dorn bottlewere used for qualitative and quantitative analysis, respectively. After sampling, the material was fixed in 4% neutral formaldehyde and lugol solution, respectively. Taxa identification was carried out under a standard microscope while the cells density was counted under an inverted microscope WILD-M40 according to Utermöhl (Hasle, 1978) with magnificances of 450X. The relative abundance and frequency of occurrence of each identified taxon were expressed in percentage; density expressed as number of cel.l-1 and the specific diversity was calculated using the Shannon index (1948).
The multivariate analysis was performed using a matrix of species/samples, containing the relative abundance. Each matrix was submitted to cluster analysis, applying Pearson's moment-product correlation coefficient. The classification method used was the hierarchical agglomerate of "Proportional weight" (Weighted Pair Group Method - WPGM). For the species and environmental data were considered those species with more than 35% of frequency of occurrence. It was used the NTSYS (Numerical Taxonomy and Multivariate Analysis System) computer program of the Metagraphics Software Corporation, California - USA.