Diurnal variation of abundance of bacterioplankton and high and low nucleic acid cells in a mangrove dominated estuary of Indian Sundarbans

Abstract

We investigated diurnal-scale variations in the abundances of bacterioplankton, high and low nucleic acid (HNA, LNA) cells, and associated physico-chemical variables in a mangrove dominated estuary of the Indian Sundarbans, during pre-monsoon and monsoon conditions. Bacterioplankton abundance (BA) varying from 1.83 ± 0.47 to 0.34 ± 0.11 × 109 cells L−1 with lowest abundance during the monsoon, was mainly dominated by LNA cells (74.46 ± 12.79% to 74.36 ± 20.51%). In two time series studies bacterial productivity (BP), total bacterioplankton abundance and HNA cell numbers increased towards high tide (BA; 0.21–0.04 × 109 cells L−1, HNA; 0.11–0.06 × 109 cells L−1) while LNA cell abundance varied. Total bacterioplankton, HNA and LNA cell numbers were also highest during the night (total bacterioplankton; 0.32–0.04 × 109 cells L−1, HNA; 0.31–0.01 × 109 cells L−1, LNA; 0.01–0.03 × 109 cells L−1). Highest dissolved oxygen and pH was at high tide (high salinity), while other carbonate system parameters and dissolved inorganic nutrients (except DIP) were higher at low tide. The overall abundances of bacterioplankton, HNA and LNA cells were controlled by a combination of factors, water temperature and dissolved oxygen being the most important controls on day-night and tidal variation of bacterioplankton.