Temporal Succession of Phytoplankton Assemblages in a Tidal Creek System of the Sundarbans Mangroves: An Integrated Approach

Sundarbans, the world's largest mangrove ecosystem, is unique and biologically diverse. A study was undertaken to track temporal succession of phytoplankton assemblages at the generic level (≥10 µm) encompassing 31 weeks of sampling (June 2010–May 2011) in Sundarbans based on microscopy and hydrological measurements. As part of this study, amplification and sequencing of type ID rbcL subunit of RuBisCO enzyme were also applied to infer chromophytic algal groups (≤10 µm size) from one of the study points. We report the presence of 43 genera of Bacillariophyta, in addition to other phytoplankton groups, based on microscopy. Phytoplankton cell abundance, which was highest in winter and spring, ranged between 300 and 27,500 cells/L during this study. Cell biovolume varied between winter of 2010 (90–35281.04 µm3) and spring-summer of 2011 (52–33962.24 µm3). Winter supported large chain forming diatoms, while spring supported small sized diatoms, followed by other algal groups in summer. The clone library approach showed dominance of Bacillariophyta-like sequences, in addition to Cryptophyta-, Haptophyta-, Pelagophyta-, and Eustigmatophyta-like sequences which were detected for the first time highlighting their importance in mangrove ecosystem. This study clearly shows that a combination of microscopy and molecular tools can improve understanding of phytoplankton assemblages in mangrove environments.