OCCURRENCES OF POTENTIALLY HARMFUL MICROALGAE (PHM) ASSOCIATED WITH ENVIRONMENTAL VARIABLES IN SONGKHLA LAGOON, THAILAND

The spatial and temporal distributions of potentially harmful microalgae (PHM) within Songkhla Lagoon were investigated in relation to environmental parameters.Samples were collected from three stations over a year-long period from October 2021 to September 2022, encompassing the northeast monsoon, intermediate dry, and southwest monsoon seasons.A total of 20 PHM species, comprising 12 dinoflagellates and 8 diatoms, were identified.While cell densities were significantly higher at stations A and B (p<0.001), seasonal variations were not observed (p>0.05).Five dominant species emerged throughout the year, including three diatoms; Skeletonema sp., Chaetoceros sp., Pleurosigma sp., and two dinoflagellates, Alexandrium sp. and Blixaea quinquecornis.Skeletonema sp., common red tide species, indicated peak abundance (1.37x10 6 cells/L) at site A. Salinity, silicate, phosphate, and water temperature were identified as key factors influencing PHM occurrence.The study suggests that nutrient enrichment from aquaculture activities may contribute to an increased risk of harmful algal blooms in the lagoon ecosystem.