Metabarcoding revela a dinâmica espaço-temporal de protistas planctônicos em um estuário do semiárido brasileiro

Abstract

Protists are eukaryotic microorganisms that play key ecological roles in aquatic ecosystems; however, little is known about their diversity in Brazilian semi-arid estuaries. In this context, environmental DNA (eDNA) metabarcoding is a powerful tool for characterizing this diversity. This study investigated the spatiotemporal dynamics of protist communities in a semi-arid tropical estuary throughout 2022, considering three seasonal periods (rainy, transitional, and dry) and two plankton fractions: picoplankton (0.2 µm) and nano-microplankton (3.0 µm), based on sequencing of the V4 region of the 18S rRNA gene. Using Principal Component Analysis (PCA), mean values, and ANOVA and Tukey’s tests, it was observed that the environmental variables exhibited strong spatial heterogeneity, with the lower portion showing higher values for salinity, depth of the euphotic zone, and dissolved oxygen, while the upper portion had higher concentrations of chlorophyll and nutrients. The protist assemblages were highly diverse and dominated by diatoms, varying along spatial and seasonal gradients. Alpha diversity, as indicated by the richness, Shannon, and Simpson indices, was highest during the rainy season and in the lower estuary, while the lowest values were recorded in the upper estuary, especially during the transition period. Analyses using Non-Metric Multidimensional Scaling (NMDS) and Permutational Analysis of Variance (PERMANOVA) indicated that the taxonomic composition was primarily shaped by the interaction between seasonality and estuarine location, with beta diversity being predominantly explained by turnover. The linear regression model identified salinity and inorganic phosphorus as the main environmental factors influencing the larger organisms, whereas no significant environmental factors were identified for the smaller fraction. The results reveal complex spatiotemporal dynamics in the protist community, with a predominance of diatoms in the Pacoti River estuary, highlighting the importance of integrative approaches and long-term monitoring for the conservation of semi-arid estuaries in the face of anthropogenic pressures and climate change.