SEASONAL VARIATIONS OF PHYTOPLANKTON IN RELATION TO ENVIRONMENTAL INFLUENCES IN THE SOUTHERN MEDITERRANEAN (TONGA LAKE, NORTHEAST ALGERIA)

The spatial and temporal dynamics of phytoplankton communities were examined in relation to environmental characteristics in Tonga Lake, situated in the Southwestern Mediterranean (Algeria).Monthly samples were collected from November 2021 to October 2022 at two key locations: one near the sluices and another at the centre of the lake.The study assessed the taxonomic composition, abundance, and diversity index of phytoplankton.A total of 43 genera of phytoplankton were identified within the lake.Notably, diatoms were predominant, with 24 genera identified, compared to 12 genera of Cyanobacteria and 7 genera of Dinoflagellates, highlighting seasonal shifts in these taxa.During the summer months, the community was primarily composed of Aphanizomenon sp., Nostoc sp., Asterionella sp., Planktothrix sp., Dinophysis sp., Cyclotella sp., and Tropidoneis sp., correlating with elevated concentrations of ammonium (NH4), chlorophyll-a (Chl-a), and temperature (T).Conversely, the spring season was marked by the prevalence of Stauroneis, Achnanthes, Cymbella, Anomoeneis, Gomphonema, Mastogloia, Navicula, Nitzschia, Peridinium, and Surirella.Additionally, autumn showed a significant presence of Diatoma sp., Gyrodinium sp., Diploneis, Pinnularia, and Lyngbya sp.