Toxic Dinoflagellates in the Mediterranean Sea.

A review of the distribution of toxic dinoflagellates and related toxic events in the Mediterranean Sea is provided. Diarrhetic shellfish poisoning (DSP) and paralytic shellfish poisoning (PSP) are the main seafood contaminations, that have been reported since 1987. In 1994 four lethal cases for PSP were reported in Morocco. DSP seems to be restricted in the Northern part of the basin, while PSP contamination presents a wider distribution. Potentially DSP species, belonging to the genus Dinophysis, are widely distributed in the Mediterranean Sea, suggesting a wider extension of this contamination. The lack of monitoring programs in the Southern Mediterranean could be responsible of DSP overlooking. The species responsible for PSP are Gymnodinium catenatum in the Alboran Sea and Alexandrium minutum in various parts of the basin. Ichtyotoxic effects, due to Gymnodinium and Gyrodinium species, have been sporadically reported in some Mediterranean areas

PHYTOPLANKTON DETECTION AND DSP TOXICITY - METHODOLOGICAL CONSIDERATIONS

Two different phytoplankton sampling methods (bottle and net sampling) were used to evaluate the concentration of toxic Dinophysis species in seawater and their correlation to mussel toxicity, assessed by mouse bioassay. Dinophysis concentration in net samples revealed the higher correlation to mussel toxicity (r = 0.75, p < 0.01). Net sampling therefore seems more suitable for the detection of low abundance species like Dinophysis characterised by vertical aggregations at different depths in the water column

Phytoplankton selection by mussels, and diarrhetic shellfish poisoning

To better understand the dynamics of diarrhetic shellfish poisoning (DSP) contamination a field study was carried out on the feeding behavior of Mytilus galloprovincialis (Lmk) during an important DSP outbreak. The study was focused on the relationships between phytoplankton in seawater and algal cells, or their remnants, in mussel stomachs. During the period studied, M. galloprovincialis seemed to feed selectively on dinoflagellates rather than diatoms. Further selection was observed among different dinoflagellate genera, a preference for the genus Dinophysis being particularly evident. In addition, mussels seemed to open the thecae of Dinophysis cells and digest them more easily than other dinoflagellates. Due to the high variability of the results of phytoplankton analysis in the mussel stomachs, no correlation was found between the abundance of Dinophysis species in the mussels' stomachs and the content of okadaic acid plus dinophysistoxin-1 in their digestive glands, evaluated with an ELISA assay. Conversely, the presence of Dinophysis fortii (the main DSP-causative agent in the area studied) in integrated net samples of the whole water column and the toxin content of the digestive glands presented similar temporal trends