Composição do microfitoplâncton do Rio Arienga (Barcarena-Pará)

Abstract

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 geo-referenced stations, using a conical plankton net with a mesh size of 20μm. In the period studied, the rainfall showed an atypical behavior, compared to the average of the last ten years for the region of Barcarena, as pH and temperature did not undergone great 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%). Genres Microcystis Kützing ex Lemmermann, Staurastrum Meyen ex Ralfs, Ulothrix Kützing, Eudorina Ehrenberg ex Ralfs, Volvox Linnaeus, Hydrodictyon Roth, Pediastrum Meyen, Aulacoseira Thwaites, Coscinodiscus Kützing, Pinnularia Ehrenberg, Polymyxus Bailey, Rhizosolenia Brightwell, Actinoptychus Ehrenberg, Thalassiosira Ehrenberg, Tabellaria Ehrenberg ex Kützing, Fragilaria Lyngbye e Navicula Bory de St. Vincent 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.