Program

Dormant resting cyst of harmful dinoflagellates plays a crucial role in bloom development, dispersion and depopulation in a new area. Under unfavorable conditions, many toxic marine dinoflagellates produce resting cysts in their life cycle, and the cyst germination is one of the factors controlling Harmful Algal Bloom (HAB). Alexandrium minutum, paralytic shellfish toxin (PST) producer, is distributed worldwide and its impact towards public health is tremendous. While many studies had revealed the factors of encystment-excystment of A. minutum, these studies focus on temperate regions and might not reflect the same scenario of the tropical A. minutum. Therefore, this study aims to investigate the cyst formation and germination of a tropical A. minutum. Intercross-mating experiments in a pairwise combination of 15 clonal strains that yielded 105 pairwise combinations were conducted. Total of 53 combinations were successfully formed resting cysts. The cyst displayed general cyst morphology, with a red body in its granular content and two layers of transparent cyst walls. In the compatible cross-mating cultures, a unique sexual induction was observed. Cysts germination experiments were undertaken using both laboratory-produced and natural cysts. Under normal incubation of tropical climate (12:12 light:dark photoperiod at 25 °C), cysts germinated within three to five days. The tropical A. minutum cysts have a relatively short dormancy period, thus it is speculated that outbreak could happen any time when ambient conditions are favarable. Routine monitoring and early warning system are essential to evade from further public health problem, environment damages and economic losses. Keywords: Alexandrium minutum; encystment-excystment; mating; cell dancing; hypnozygote; Malaysia