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

High-density blooms of Dinophysis sacculus Stein, a dinoflagellate that produces diarrhetic shellfish toxins, are reported from a brackish lagoon in Sicily, Italy. The diarrhetic shellfish poisoning (DSP) toxicity of plankton assemblages dominated by this species (≥ 97%) was assessed by high-performance liquid chromatography. Spring outbreaks of D. sacculus were associated with the production of okadaic acid and, to a lesser extent, dinophysistoxin-1 (7–24% of the total DSP toxins), as confirmed under controlled conditions, using no nutrient enrichment. Addition of culture medium to the Dinophysis assemblages favoured the simultaneous growth of other taxa, not allowing comparative analyses of toxicity under enriched treatments. The nucleotide sequences of internal transcribed spacers 1 and 2 and 5.8S rDNA were determined from populations of D. sacculus maintained under controlled conditions. Comparison with sequences obtained in our laboratory from other dinoflagellate genera such as Alexandrium and with those reported in the genomic databases suggests that the ITS–5.8S region could be used as a molecular marker for detection of D. sacculus. This could be particularly 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.