THE MARINE DINOFLAGELLATE ALEXANDRIUM OSTENFELDII: PARALYTIC SHELLFISH TOXIN CONCENTRATION,COMPOSITION, AND TOXICITY TO A TINTINNID CILIATE1

The composition of paralytic shellfish toxins in the marine dinoflagellate Alexandrium ostenfeldii (Paulsen) Balech et Tangen grown in unialgal culture was determined by high-performance liquid chromatography. The toxin profile revealed that the low-potency sulfamate toxin B₂ was dominant (90 molar % of total toxins), but small amounts of the weakly toxic 21-N-sulfocarbamoyl derivatives C₁₊₂ and trace amounts of the carbamate toxins GTX₂ and GTX₃ were also present. The mammalian toxicity was confirmed by a modification of the conventional AOAC mouse bioassay (0.6–1.4 pg STX_eq· cell^-1). The acute toxicity to a potential predator, the tintinnid ciliate Favella ehrenbergi (Clap, et Lach.) Jörg., was also investigated. The ciliate was able to graze on A. ostenfeldii when the cell concentration of the dinoflagellate was low (<2000 cells · mL^-1). At higher concentrations the ciliate was affected by exudates (presumably PSP toxins) that induced backward swimming followed by swelling and lysis of the cell. Fluorescence microscopy of calcofluor-stained cells was employed as an easy and rapid method to identify this and other thecate dinoflagellates.