Annual nano-microphytoplankton succession in the meromictic brackish lake Faro (Messina - Sicily) in relation to physical-chemical conditions

A multi-disciplinary study was carried out in the meromictic brackish ”Lake Faro” from May 1998 to April 1999, with the emphasis on correlation between nano-microphytoplankton monthly succession and physical-chemical characteristics of the water column. It has been stated that the seasonal dynamics of the phytoplankton community is strongly influenced by the supply of phreatic waters. A partial spring mixing sustained a summer bloom of Diatoms (Chaetoceros genus) and, in July, Dinoflagellates reached a maximum density at 10 m depth in microaerobic waters. After the autumnal decrease, an input of phreatic waters gradually increases phytoplankton growth at the end of autumn. Afterwards, the winter thermal inversion and a mixing involving the upper layer of the hypolimnion in January sustained the growth, of nanophytoflagellates (6.6 x 106 cells L-1) in February and Diatoms (tiny Centrales 9 x 106 cells L-1) in March. Nano-microzooplanktonic Ciliates, adapted to living in the redox zone, graze an abundant population of photosynthetic bacteria living in the chemocline and the other microorganisms living in the upper layer of the hypolimnion.