POTENTIALLY TOXIC DINOFLAGELLATES IN MEDITERRANEAN WATERS (SICILY) AND RELATED HYDROBIOLOGICAL CONDITIONS

The seasonal occurrence of 3 potentially toxic dinoflagellates in diff erent coastal environments of Sicily (Mediterranean Sea) and the assoc iated hydrobiological conditions are reported. Dinophysis sacculus and Alexandrium sp. occurred, in 1993, in shallow inland waters (a bracki sh lagoon of the Tyrrhenian Sea), characterized by thermo-haline homog eneity. The densities of Dinophysis were maximal in April, when the wa ters were depleted in nutrients, the N:P ratio was 10:1 and the algal population, including synechoccoid cyanobacteria, bloomed. Afterwards, the cell concentrations decreased and in summer there was a total rep lacement of Dinophysis with Alexandrium. In late summer 1993, Gymnodin ium catenatum was also recorded in offshore waters of the Malta Channe l, during coastal upwelling associated with thermal stratification of the waters and the cells dispersed shorewards. DSP toxicity of blue mu ssels was detected in April, at a law level only, in the area affected by D. sacculus. No data is, however, available to date on PSP product ion by Alexandrium and G. catenatum, which are new records for these a reas.