Spatial and Temporal Variations in Phytoplankton Abundance and Species Diversity in the Sundarbans Mangrove Forest of Bangladesh

Abstract

The study examined taxonomic composition, abundance and spatial distribution of phytoplankton, and water quality of three major river systems of the Sundarbans. A total of 134 phytoplankton species were identified, and diversity and abundance were found to fluctuate with time and space. A total of 97 species were enumerated in Rupsha-Pashur while 122 and 110 in Khalpatua-Arpangachia and Bhola-Baleswar river system respectively. Abundance was lowest (3.709×103 ± 4.257×102 cellsL-1) in monsoon and highest (2.174×105 ± 1.723×105cellsL-1) in summer in Bhola-Baleswar. Species composition was dominated by Bacillariophyta over the area except in summer in Bhola-Baleswar, where Cyanophyta become dominated. Species diversity, richness and evenness index varied between 2.03-4.64, 1.2-2.44, 0.77-1.5 in Rupsha-Pashur; 2.47-3.85, 1.8-5.84, 0.78-0.94 in Khalpatua-Arpangachia; and 0.66-4.27, 1.19-5.12, 0.59-1.29 in Bhola-Baleswar. Water temperature, pH, DO, Transparency and Salinity were determined between 19.92°C-31°C; 6.7-7.87; 3.93 mgL-1-7.37 mgL-1; 7.5 cm-60 cm; 2-23 ppt, respectively. Nutrient elements i.e. NO3 -, PO4 3-, NH4 +, SiO4 4- fluctuated seasonally from 0.0062 to 1.633 mgL-1, 0.005 to 0.772 mgL-1, 0.038 to 2.467 mgL-1, 3.124 to 27.234 mgL-1, respectively. Chlorophyll-a concentrations were fluctuated seasonally within 0.24 to 5.94 μgL-1 and highest phytoplankton biomass was observed in Bhola-Baleswar in summer. Chlorophyll concentration was found to be correlated positively with transparency, salinity and nutrients.