MICROPHYTOPLANKTON IN THE STRAIT OF OTRANTO (EASTERN MEDITERRANEAN)

The Strait of Otranto is the connection between the Adriatic and Ionia n Seas. Low nutrient concentrations, high transparency, and low phytop lankton cell density and biomass reflect the oligotrophic character of the area. Enrichment of the euphotic layer with nutrients is mainly d ue to discharge of Albanian and Creek rivers, as well as mixing and up welling in winter/early spring. Following phytoplankton bloom in April , a progressive decrease of phytoplankton cell density is due to the c onsumption of nutrients throughout the proceeding summer and autumn. N itrogen was a strong limiting factor for phytoplankton growth in summe r. Deep biomass maxima were detected in the 50 to 100 m layer and corr esponded mostly to cells smaller than 20 mu m. The eastern part of the strait is mostly influenced by the northerly inflowing current from t he Ionian Sea, and the western part by the southerly outflowing curren t from the Adriatic Sea. This typical circulation could be disturbed b y inertial oscillations in the current field, generated by the strong oscillating winds and cyclonic eddies. The type of circulation determi ned the distribution of thermohaline characteristics, abundance, bioma ss, as well as taxonomic composition of phytoplankton, across the stra it. Ecological characteristics of the water masses on two sides of the strait were significantly different during the formation of a longitu dinal thermohaline front in May 1990.