Ecological time series and integrative taxonomy unveil seasonality and diversity of the toxic diatom Pseudo-nitzschia H. Peragallo in the northern Adriatic Sea

•Eight species identified by combining morphological and molecular analyses.•Seasonal patterns of individual species elucidated on a 14-year long time series.•The genus peaks in spring and autumn with occasional outbreaks during summer.•Evaluation of rbcL as a potential diatom barcode marker.•Applied integrated methodology for monitoring and management at LTER sites