Seasonal and nyctemeral variations of the phytoplankton and hydrological parameters were studied at a fixed station (00º46'37.2"S-046º43'24.5"W) situated in Canela Island (Bragança-Pará) in September and December, 2004 and in March and June, 2005. Subsurface water samples were taken for qualitative and quantitative phytoplankton studies and to determine chlorophyll a concentrations. Simultaneously physical and chemical parameters were measured: salinity, temperature, pH, dissolved oxygen and percent of oxygen saturation. A total of 64 taxa belonging to Cyanophyta (one taxon), Bacillariophyta (54 taxa) and Dinophyta (nine taxa) were identified. Chlorophyll a concentrations ranged from 4.67 mg m-3 (dry season), to 5.44 mg m-3 (rainy season) and follow phytoplankton densities, which were higher during the rainy period (mean values of 1,870 x 10³ cell L-1). Phytoflagellates quantitatively dominated the local phytoplanktonic community followed by diatoms. Dimeregramma minor and Skeletonema sp. were abundant and very frequent species over the studied period. Resuspension processes originated by the strong winds and waves in the surf zone favored the dominance of D. minor during the dry period. In the rainy period, high rainfall, moderate winds as well as the influence of estuarine waters from Taperaçu and Caeté propitiated the decrease of salinity and the development of other phytoplankton species.
Plankton; composition; biomass; density; Amazon coast
