Phytoplankton dynamics and bloom events in oligotrophic Mediterranean lagoons: seasonal patterns but hazardous trends

Detailed seasonal analyses of phytoplankton assemblages’ composition were performed on long-term datasets (20 years) two oligotrophic Mediterranean lagoons (Diana and Urbino), in order to test if community bloom events patterns rely a basis. Our results highlight similar between the lagoons, but different terms abundances, timing, magnitude occurrence Taxonomic Units, occurrence. Dominant diatoms group showed repartition, with highest contribution Skeletonema sp. during winter spring, some other groups emerging warmer seasons (e.g. Chaetoceros spp.), or not showing marked seasonality Pseudo-nitzschia spp.). Dinoflagellates’ abundances higher autumn, besides exhibiting punctual proliferations over year. Salinity was strongest environmental parameter controlling Diana lagoon community, while Urbino mostly controlled by turbidity. A worrying evolution toxic diatom spp., linked salinity temperature changes, detected both lagoons. We further demonstrated changes are ongoing these despite their contrasting human pressure contexts, indicating that serious impacts dynamics blooms triggering shall be foreseen within current forecasted climate change scenarios.