Review of geographical distribution of dinoflagellate cysts in Southeast Asian coasts

Dinoflagellate cysts play an important role in the initiation, recurrence and geographical expansion of harmful algal blooms (HABs). The horizontal distribution and abundance of dinoflagellate cysts in marine sediments provide very essential information in giving early warnings of the presence of toxic species and possible continuing recurrence of HABs in a given area. A review of available bio-geographical information on dinoflagellate cyst assemblages and distributions from the surface sediments of the tropics and Southeast Asian (SEA) waters mainly on the context of HAB dynamics is also provided. Results of review on such studies revealed how cyst mapping activities contributed to understand HAB expansion in SEA region. Pyrodinium bahamense var. compressum cysts are the most common in the sediments of SEA region, explaining partly the relative wide occurrence of this PSP causative organism in the area. Cysts of Alexandrium spp. have also been found in some areas of the region, indicating the risk from the bloom of some toxic species of the genus. The factors and mechanisms of algal bloom expansion in the SEA region, involving the resting stage of causative HAB species, remain to be well understood. High priority should be given to continuing cyst mapping research in the entire SEA region, as the knowledge is so essential in comprehending HABs dispersal and occurrence thereby aiding in HABs management in the area.