Spatial Distribution of Dinoflagellates Associated with Harmful Algal Blooms (HAB) in Laguimit Bay, Samar, Philippines

Laguimit Bay is among the few areas in the Philippines where green mussels thrive. However, no studies have been conducted on Harmful Algal Bloom (HAB) in the area. This study investigates the spatial distribution of dinoflagellates associated with HAB in the surface water of the bay. Multiparameter water quality testers were used to determine the physicochemical characteristics while a plankton net was used to filter the dinoflagellates and counting was carried out in a compound microscope. Based on the results, the surface water temperature is between 27–31 °C while the pH ranges from 8.1–8.2 and dissolved oxygen is 6.3–6.5mg/L at salinity ranges from 30–31ppt. This indicates that the water quality of the Bay is sustainable for farming mussels. Microscopic examination of the samples showed that the only dinoflagellate associated with HAB is Pyrodinium bahamense var. compressum which causes Paralytic Shellfish Poisoning with an average concentration of 22 cells/L. Other non-HAB species were Protoperidinium depressum with an average of 489 cells/L and the rest are Ceratium macroceros, Ceratium furca, Ceratium trichoceros, Ceratium lunula, Dinophysis caudata, Dinophysis miles. The Shannon-Wiener diversity index was 1.8723 in station 1 and 1.8406 in station 2 and 1.7439 in station 3 which indicates a low diversity index. The presence of P. bahamanse has the potential for recurrence of HAB formation in Laguimit Bay which could affect the economic livelihood of fisherfolk in the country. Continued monitoring and management are recommended to mitigate potential HAB risks and ensure the sustainability of shellfish resources.