Role of cyst germination in the bloom initiation of Alexandrium tamarense (Dinophyceae) in Masan Bay, Korea

The role of cyst germination in the bloom initiation of the toxic dinoflagellate Alexandrium tamarense was examined in Masan Bay, Korea. Germination success was measured by the incubation of cysts isolated monthly from natural sediments and compared with vegetative cells and environmental factors (temperature, salinity and dissolved oxygen) in the water column. Germination maxima (80 to 90 %) were observed during the period of decreasing water temperature in December 1996 and November 1997, while little or no germination occurred in summer. The seasonal germination exhibited an opposing pattern with temperature and similar seasonalities with salinity and dissolved oxygen, respectively. The bimodal nature of A. tamarense blooms, a large bloom in spring and a much smaller bloom in fall, was observed. Excysted cells in early spring can initiate the spring bloom and then proliferate to the bloom peak in increasing temperatures. Massive germination in fall contributes directly to the small bloom in fall. A temporal discrepancy between the peak of germination success and of vegetative population was found in A. tamarense dynamics from Korean coastal waters.