Toxicity and ribosomal DNA of the dinoflagellate Dinophysis sacculus (Dinophyta)

High-density blooms of Dinophysis sacculus Stein, a dinoflagellate that pro duces diarrhetic shellfish toxins, are reported from a brackish lagoon in S icily, Italy. The diarrhetic shellfish poisoning (DSP) toxicity of plankton assemblages dominated by this species (less than or equal to 97%) was asse ssed by high-performance liquid chromatography. Spring outbreaks of D. sacc ulus were associated with the production of okadaic acid and, to a lesser e xtent, dinophysistoxin-1 (7-24% of the total DSP toxins), as confirmed unde r controlled conditions, using no nutrient enrichment. Addition of culture medium to the Dinophysis assemblages favoured the simultaneous growth of ot her taxa, not allowing comparative analyses of toxicity under enriched trea tments. The nucleotide sequences of internal transcribed spacers 1 and 2 an d 5.8S rDNA were determined from populations of D. sacculus maintained unde r controlled conditions. Comparison with sequences obtained in our laborato ry from other dinoflagellate genera such as Alexandrium and with those repo rted in the genomic databases suggests that the ITS-5.8S region could be us ed as a molecular marker for detection of D. sacculus. This could be partic ularly useful when toxic populations occur at very low densities or switch to a quiescent phase, since they are then easily overlooked by conventional microscopical analyses.