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A study of microphytoplankton across the longitudinal front in the Strait of Otranto (May 1990)

On May 17, 1990, thermohaline profile across the Otranto Strait reviled longitudinal front, between northerly inflowing current from the Ionian Sea and the southerly outflowing current from the Adriatic sea. The aim of this paper was to determine, phytoplankton cell density and community structure in two water masses of different origin, on both sides of the longitudinal front. Water samples for the analyses of phytoplankton and nutrient concentrations were collected from two stations located across the Strait of Otranto, using 5-liter Niskin bottles. Salinity and temperature were determined using TCD-multisond. The boundary between northerly inflowing Levantine water along the eastern part, and southerly outflowing Adriatic water along the western part of the Strait, was indicated by the abrupt gradient of salinity, about 10 km westward from Station 2 (35 km westward from the Albanian coast). The position of the front in the surface layer was located by the 38.55 isohaline. The difference in salinity and cell density of some diatom species between stations was significant (p<0.05) in the 0-50 m layer. Several neritic dinoflagellates and diatoms (especially Nitzschia sicula) were important constituents of the outflowing and inflowing current, respectively. The May 1990 case study across the longitudinal front in the Strait of Otranto, supported the idea that taxonomic composition, distribution and cell density of phytoplankton, could be regarded as indicators (biomarkers) of water masses of different origin.

Phytoplankton; halocline; front; indicator; Adriatic Sea; Otranto Strait; Mediterranean

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