Descritores ambientais da qualidade da água e comunidade fitoplanctônica da Baía de São José, Maranhão - Brasil

Abstract

The Bay of São José is located in the east of the island of Maranhão, it is part of a large and complex estuarine and has margins with an extensive concentration of mangroves that can directly influence the high biological productivity of this environment. The main objective of this study was evaluate the influence of the estuarine dynamics associated with the environmental descriptors on the distribution of the phytoplankton community during the dry (October) and rainy (April) season of the year 2017. Subsurface samples of water were made at 0.5 m in syzygy tides during the “high tides”, on eighteen fixed points, distributed in seven radials. A total of 103 specific and infraspecific taxa were recorded in the two seasonal periods, of which, 70 taxa were observed in the April/2017 and 75 taxa in October/2017. These taxa were framed in seven divisions: Cyanophyta, Bacillariophyta, Charophyta, Chlorophyta, Euglenophyta, Ochrophyta and Miozoa, respectively, with the predominance of Bacillariophyta (75%). In relation to the phytoplankton fractionation, it was observed that the nano/picophytoplankton was the most representative fraction in both the dry and the rainy season. The Trophic Index (TRIX) presented higher trophic levels during the dry period. Statistical analysis showed that the phytoplankton community of Bay of São José responded to the environmental conditions of the region, in special the salinity, by grouping radials dominated by coastal influence (RAD1, RAD2 and RAD3) and radials with greater fluvial influence (RAD4, RAD5 and RAD7). During the dry season, these radials highlighted the high density of the species Thalassiosira rotula that is a typical species of coastal environments, showing the direct influence of the oceanic water on the Bay of São José.