COMPOSIÇÃO DE MICROFITOPLÂNCTON DE UM ESTUÁRIO DO RIO AMAZONAS, PARÁ, BRASIL

This work aims to describe the composition, relative abundance and frequency of occurrence of microphytoplankton in the Arienga River, determined from the analysis of ten samples collected in the rainy and dry seasons (May and September 2009 respectively), during five stations, using a plankton net with a mesh size of 20mm. In the period studied, the rainfall showed an atypical behavior, compared to the average of the last ten years for the region, as pH and temperature did not undergone changes. A total of 128 species were identified, belonging to divisions: Dinophyta (0.78%), Chrysophyta (0.78%), Cyanobacterium (12.50%), Chlorophyta (26.56%), and Bacillariophyta (59.38%). Of Genres found, 17 had 100% of representativeness at in both fenods. It was possible to confirm two large groups, suggesting that the rainfall regime was the main controller factor of phytoplankton composition and spatial variation of species along the Arienga River. The phytoplankton diversity was considered characteristic of the Amazon region; therefore, it is considered that the human action did not affect the phytoplankton community of the Arienga River to date. Keywords: phytoplankton; estuary; Amazon; Bacillariophyta; Polymyxus coronalis .