Temporal and Spatial Variations of Heterotrophic Bacteria, Pico- and Nano-phytoplankton along the Bangpakong Estuary of Thailand

Abstract

The densities and distribution of heterotrophic bacteria and pico- and nano-phytoplankton were determined along the Bangpakong River during the dry (February and April) and wet (July and September) seasons of 2004. Heterotrophic bacteria, with average densities ranging from 1.38 x 106 to 1.87 x 108 cells/ml, were 10 to 100 times more abundant than autotrophic picoplankton (picophytoplankton). The communities of nanophytoplankton were dominated by nanoflagellates, with average densities ranging from 2.54 x 106 to 1.33 x 109 cells/l. Other nanophytoplankton included diatoms, dinoflagellates, coccolithophorids and cyanobacteria, with average densities ranging from < 1 to 108 cells/l. The abundances of pico- and nano-plankton were higher in the wet season than in the dry season. Higher densities of both groups were also recorded in the upper estuarine region and the densities tended to decrease towards the sea. Heterotrophic bacteria and nanoflagellates dominated the pico- and nano-plankton communities throughout the study periods, while the densities of the other groups showed an increasing trend from the lower estuarine region of the river (salinity > 25 psu) towards the sea. The densities of the pico- and nanoplankton were statistically related to the temperature, salinity and dissolved inorganic nutrients in the Bangpakong River.