Comunidade fitoplanctônica de igarapés da volta grande do Xingu(Pará, Brasil)

Abstract

The Amazon rainforest streams play a crucial role in the diversity of aquatic ecosystems, providing ecological balance to hydrographic microbasins. Phytoplankton, the base of the food web and an environmental bioindicator, responds to physicochemical factors and habitat structure. Considering this, this study aimed to conduct a checklist of the phytoplankton community and analyze the influence of environmental variables (water physicochemical parameters and the Habitat Integrity Index - HII) on the richness and biovolume of phytoplankton in streams of the Volta Grande do Xingu, Pará, Brazil. A total of 295 taxa were identified, with emphasis on Zygnematophyceae, Bacillariophyceae, and Cyanophyceae. Among the diatoms (Bacillariophyceae), we recorded the occurrence of Terpsinoë musica Ehrenberg, a species predominantly found in brackish waters, although also present in freshwater. The identification of the genera Microcystis Lemmermann and Dolichospermum P. Wacklin, cyanobacteria that produce cyanotoxins, reinforces the importance of environmental monitoring. Quantitative analysis revealed 79 taxa, with Bacillariophyceae being the richest and Zygnematophyceae contributing the most to biovolume. Depth, width, and pH significantly influenced the phytoplankton community. We observed that greater stream depths are associated with a larger phytoplankton biovolume, while stream width showed an inverse effect. Additionally, pH exerted a significant effect on the biovolume of the species, corroborating the hypothesis that this parameter is a determining factor for phytoplankton. The species Desmidium quadratum Nordstedt and Mougeotia sp. showed higher biovolume in streams with more acidic waters, while Hariotina reticulata P. A. Dangeard showed a preference for less acidic environments. Therefore, the monitoring of water physicochemical variables and habitat structure is essential to understand the dynamics of phytoplankton, providing information to help maintain the biodiversity and functionality of these aquatic ecosystems.