Potentially toxic dinoflagellates in Mediterranean waters (Sicily) and related hydrobiological conditions

The seasonal occurrence of 3 potentially toxic dinoflagellates in different coastal environments of Sicily (Mediterranean Sea) and the associated hydrobiological conditions are reported. Dinophysis sacculus and Alexandrium sp. occurred, in 1993, in shallow inland waters (a brackish lagoon of the Tyrrhenian Sea), characterized by thermo-haline homogeneity. The densities of Dinophysis were maximal in April, when the waters 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 replacement of Dinophysis with Alexandrium. In late summer 1993, Gymnodinium catenatum was also recorded in offshore waters of the Malta Channel, during coastal upwelling associated with thermal stratification of the waters and the cells dispersed shorewards. DSP toxicity of blue mussels was detected in April, at a low level only, in the area affected by D. sacculus. No data is, however, available to date on PSP production by Alexandrium and G. catenatum, which are new records for these areas.