Possible relation between a bloom of Distephanus speculum (Silicoflagellata) and anoxia in bottom waters in the Northern Adriatic, 1983

Silicoflagellates, rare planktonic algae, were registered inbloom-like conditions in the 20-m-deep bottom layer of the Gulfof Trieste, Northern Adriatic. The confusing taxonomy and ecologyof these phytoflagellates, as well as their possible contributionto the oxygen depletion of the bottom layer, is discussed.     

Occurrence ofDinophysis spp. and toxic shellfish in the Northern Adriatic

The dynamics of the toxicity of the musselMytilus 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 of 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 ofDinophysis in the area of both shellfish farms. During the period of the DSP outbreak in Slovenia (autumn and winter 1989).D. fortii andD. acuminata were the most frequentDinophysis species. There was a high positive correlation between the onset of mussel toxicity and the appearance ofDinophysis spp.