Estrutura da comunidade fitoplanctônica da plataforma continental maranhense, norte do Brasil

Abstract

The Continental shelf is a geomorphological feature that constitutes a site of interaction between coastal and oceanic systems, where it receives nutrients, suspended materials, and organic matter from these ecosystems. The Maranhão Continental shelf (PCM) is located in the northern portion of Brazil in the equatorial Atlantic, receiving discharges from large estuarine complexes. Due to the ecological importance of the Maranhense Continental Shelf, the objective of this study was to evaluate the structure of phytoplankton communities in different water masses of the Maranhense Continental shelf. The collection was carried out in an oceanographic expedition (Science of the Sea II ship), in April/2019, during the rainy season in the region, in three transects of the Maranhão Continental shelf: São José transect, São Marcos transect, and Cumã transect, with a total of 22 points. The study considered the analysis of environmental variables on the water surface and their relationship with the phytoplankton community. The thermohaline structure of the Maranhense Continental Platform identified two water masses: river water (AR) and coastal water (AC). The phytoplankton community was represented by 68 taxa, representing the three divisions: Bacillariophyta with 55 taxa (81%), Myozoa with 11 taxa (16%), and Cyanobacteria with two taxa (3%). Cell density and phytoplanktonic biomass were higher in the Cumã AR mass. In PCM the Bacillariophyta division was the most representative in all three transects. The water masses defined the structure of the phytoplanktonic community. The river water mass was related to centric diatom species and the coastal mass with colonial diatom species, dinoflagellates, and cyanobacteria.