Thecal plates, toxin content and growth of five clones of Alexandrium tamarense (Dinophyceae) isolated from Jinhae Bay, Korea

Five clonal cultures of Alexandrium tamarense (AT-2, 6, 10, A and B) were isolated during toxic shellfish events in Jinhae Bay, Korea, in 1997. Thecal plate morphology, toxin composition and content, and growth characteristics were determined for each clone under different environmental conditions in order to distinguish potentially toxic A. tamarense and to improve the monitoring and prediction system in Korean coastal waters. Examination using epifluorescence microscopy after calcofluor staining showed that the thecal morphology of the apical pore complex, the first apical plate, and the posterior sulcal plates in the five clones of A. tamarense were similar. However, paralytic shellfish toxins analysed using high-performance liquid chromatography showed a range of 0.04-5.71 pg STXeq cell(-1). Two clones in particular (AT-2 and AT-6) produced higher levels of toxin, at 3.2-5.7 pg STXeq cell(-1). Toxin composition profiles of AT-6 showed neosaxitoxin and C-toxins (C1, C2) as the principal toxins, with gonyautoxins (GTX1, GTX4) as minor components, but no neosaxitoxin could be detected in AT-2. Neither STX, dcSTX, nor GTX5 were detected in any of the five clones of A. tamarense. The most toxic clone, AT-6, showed optimal growth at temperatures of 16-19 degreesC, salinities of 20-30 parts per thousand, and pH 7-8. These results imply that the phytoplankton may contain an abundance of AT-6 and similar clones, rather than AT-A and AT-B, during April and May, whereas in June, it may be dominated more by AT-B.