Physico-Chemical Factors Influencing Blooms of Chaetoceros spp. and Ceratium furca in the Inner Gulf of Thailand

Abstract

Physico-chemical factors influencing the blooms of two common phytoplankton—Chaetoceros and Ceratium—in the Inner Gulf of Thailand (IGoT), were investigated during the northeast (NE) and the southwest (SW) monsoons from a fixed station near Si Chang Island, on the east coast of the IGoT. The results showed that the dominance of each phytoplankton occurred under different ecological conditions. The density (mean ± SD) of Chaetoceros spp. was about 0.13 ± 0.13 × 105 cells.L-1 in the NE monsoon period but increased to 2.27 ± 3.11 × 105 cells.L-1 during the bloom in the early months of the southwest monsoon. This density increase was significantly related to values of the ratio of dissolved inorganic nitrogen to dissolved silicate (DIN:DSi molar ratio), dissolved inorganic nitrogen (DIN), dissolved inorganic phosphorus (DIP) and temperature. The density of Ceratium furca increased from 0.08 ± 0.04 × 103 cells.L-1 during the NE monsoon period to 7.14 ± 3.17 × 105 cells.L-1 during the red tide at the end of the SW monsoon under conditions of low salinity, high DIN and DIP.