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A new study from researchers from the Faculty of Science at Charles University in the Czech Republic shows that microscopic communities of phytoplankton鈥攌ey primary producers in aquatic ecosystems鈥攃an undergo dramatic shifts in just a matter of days. These rapid transformations are driven both by predators, such as water fleas (Cladocera), and by environmental factors including silica concentrations and wind speed.

"Imagine a forest where, overnight, all the trees vanish due to a sudden storm. Or a meadow where small birds disappear because predators have multiplied," explains Pavel 艩kaloud, author of the published in the New Phytologist. "That's the scale and speed of change we observed鈥攐nly these shifts occur invisibly, beneath the water's surface, among microscopic organisms."

Unveiling hidden dynamics

Phytoplankton form the foundation of aquatic food webs, but until now, the timescale of their community changes remained poorly understood due to limited high-frequency sampling. To address this gap, the team employed DNA metabarcoding over a 70-day period, sampling every three days in a shallow peat bog lake.

The focus was on Synurales (Chrysophyceae), a phytoplankton lineage with diverse species-specific traits such as cell size, colony formation, and protective bristles. By creating a custom reference database of cultured species, the researchers were able to assign 99.93% of eDNA reads to 74 distinct species-level lineages.

Crucially, the database enabled the translation of eDNA diversity into morphological traits, allowing each sequence to be linked with functional characteristics. This approach provided the basis for testing changes in phytoplankton dynamics at the level of morphological traits rather than solely at the taxonomic resolution.

Key findings

• Abiotic factors (silica concentration, wind speed) strongly influenced community changes in colonial species.
• Biotic pressures from Cladocera predators primarily shaped unicellular species, particularly those with bristles.
• Species composition and trait distributions shifted within days, reflecting environmental variability.

This high-resolution insight would have been nearly impossible using traditional microscopy alone. Environmental DNA (eDNA) enabled the detection of even small or rare taxa, highlighting the crucial role of reference databases in understanding biodiversity.

Implications for ecosystem science

The findings shed light on the remarkable sensitivity and adaptability of microbial communities. Rapid community turnover affects nutrient cycling, food web dynamics, and ecosystem resilience, making these processes essential to monitor in a changing climate.

"This study demonstrates that microbial life is not static鈥攊t responds to ecological pressures on extremely short timescales," the team concludes. "Understanding these dynamics is vital for predicting ecosystem responses to environmental change."