DNA-based monitoring uncovers contrasting salinity-driven diversity patterns of bacterial and protist plankton in the Baltic Sea area.

Protist diversity increases with salinity while bacterial diversity remains stable across the Baltic Sea's salinity gradient, revealing contrasting ecological patterns.

• Why it matters: Understanding how salinity influences microbial communities is crucial for predicting ecosystem responses to environmental changes, yet the effects on protists are poorly understood.
• What they did: DNA metabarcoding was used to analyze bacterial and protist diversity in 398 surface water samples from the Baltic Sea and Kattegat-Skagerrak, focusing on community composition and alpha diversity.
• The result: Protist alpha diversity rose with salinity, dominated by marine taxa, whereas bacterial diversity stayed constant despite community shifts, highlighting different eco-evolutionary dynamics and informing environmental monitoring.