Phytoplankton assemblages and environmental variability in the Mar Piccolo of Taranto (Southern Italy, Ionian Sea)

The Mar Piccolo of Taranto represents a pattern of enclosed coastal marine ecosystem in which the intense activity of mussel culture makes it the most important mussel farming in Italy. This basin is characterized by a scarce hydrodinamism, a high water residence and the continuous energetic input coming from waste-waters and agricultural discharges. These features reflect on the composition and succession of phytoplankton communities. During 1991-1994 and 2002-2003 phytoplankton assemblages were investigated in relation with environmental variables at one station located in the First Inlet of Mar Piccolo. Potentially toxic and bloom forming species were also monitored. Results showed that environmental features and phytoplankton assemblages did not change throughout the years, except for a slight decrease of nitrite concentration and cell density. Phytoplankton composition was characterized by the dominance of diatom and phytoflagellate groups. Algal blooms, caused by the potentially toxic dinoflagellates Dinophysis sp. and Alexandrium minutum and diatoms Pseudo-nitzschia spp., were recorded mainly during spring and summer periods. In conclusion, phytoplankton physiognomy showed a typical seasonal trend closely linked to that of nutrients, similarly to other coastal areas of the Mediterranean Sea. The observed decrease of the phytoplankton abundances throughout the years could be also due to the recent reduction of the nutrient loads by means of depurations plans.