Harmful Algal Blooms and water discolouration events in the Ionian Sea

Syracuse Bay is located along the SE coast of Sicily (Ionian Sea), inside a wide gulf bounded on the north by the Ortigia island and on the south by the Maddalena peninsula. The bay has a limited water exchange, a high nutrient supply from organic and inorganic sources and is characterised by an evident eutrophy with wide water discolouration events especially in the spring-summer period. A part of this bay is also used for productive activities such as shellfish farming. Studies more than decadal (Giacobbe et al. ) have documented the occurrence of red tides phenomena, related to the massive proliferation of this microalga. The bloom season of Alexandrium minutum generally falls between March and May, with maximum densities reaching a magnitude order of 10^6 cells l-1. During blooms salinity ranged from 30 to 35 ppt, temperature from 17 and 23 ° C. Salinity variations are due to influx of freshwater rich in nutrients. The aim of this study was to describe the hydrological and trophic conditions during the early autumn period, when the vertical mixing causes the breaking of the pycnocline and favors the enrichment in nutrients of the surface waters.