Occurrence of Dinophysis spp. and toxic shellfish in the Northern Adriatic

The dynamics of the toxicity of the mussel Mytilus galloprovincialis was compared between two different shellfish farms, 5 km apart, but using the same cultivation technique. The main differences concerned the freshwater influx and the open aspect to the Gulf to Trieste. It is suggested that a deep closed bay and abundant fresh water inflow are the two main conditions for the low toxicity levels in mussels and for shorter periods of danger. A detailed study of the phytoplankton samples revealed the presence of eight species of Dinophysis in the area of both shellfish farms. During the period of the DSP outbreak in Slovenia (autumn and winter 1989). D. fortii and D. acuminata were the most frequent Dinophysis species. There was a high positive correlation between the onset of mussel toxicity and the appearance of Dinophysis spp.