UNDERSTANDING HARMFUL ALGAL BLOOM (HAB) OCCURRENCES IN MANILA BAY PHILIPPINES

Abstract

Harmful algal bloom (HAB) has been a yearly event in the waters of Manila Bay. The very first major bloom was caused by a toxic dinoflagellate species, Pyrodinium bahamense var. compressum, which is known to cause Paralytic Shellfish Poisoning (PSP). This study primarily aims to review the records of HABs in the bay from the 1980s to 1990s and compare with the recent events. Trends of the two environmental factors (i.e. sea surface temperature (sst) and rainfall) known to influence algal bloom formations were also investigated to verify the influence of these factors to the recurring bloom events in Manila bay. Pyrodinium blooms lasted for almost a decade from 1988 until 1998 and was succeeded by a non-toxic species, Noctiluca scintillans in the year 2000. No PSP cases were recorded from then on until the year 2010 which was caused by another toxic species, Alexandrium minutum. The numbers of recorded PSP cases were higher in the 1980s and 1990s bloom events compared to the recent toxic blooms. Results of Pearson’s correlation analyses revealed no significant correlation between the annual average sea surface temperature (SST) and rainfall to the recorded PSP cases yearly. This study recommends a more comprehensive approach which would involve both ecological studies and the related climate parameters to gain deeper insights of the bloom dynamics in the bay.