Climate change impacts in freshwater

Climate change is driving significant shifts in biodiversity and ecosystem functioning, yet its impacts on microbial communities in tropical freshwater environments remain underexplored. In this study, we investigated bacterial communities from eight streams located in central Brazil, using a space-for-time substitution (SFTS) approach to simulate warming scenarios. Water and sediment samples were analyzed through 16S rRNA gene amplicon sequencing, followed by community composition profiling, diversity metrics, and co-occurrence network analysis. Alpha diversity (Hill numbers) declined significantly with increasing temperature, indicating a loss of richness with greater and increased dominance of thermotolerant taxa. Beta diversity patterns showed compositional homogenization at higher temperatures. LEfSe analysis identified Cyanobacteria, particularly Fischerella muscicola and Elainella saxicola, as dominant thermophilic taxa, suggesting their role as potential bioindicators of climate change. While co-occurrence network stability (robustness and vulnerability) remained unchanged across the thermal gradient, temperature enhanced network density and decreased modularity, resulting in denser and less compartmentalized microbial associations. These network structural changes were likely driven by the rise of Cyanobacteria, known for strong intra-phylum connectivity. Our findings underscore the value of co-occurrence network topology, alongside taxonomic indicators, as a sensitive ecological tool for monitoring the early impacts of climate change in tropical freshwater ecosystems.