Phytoplankton Community Structure In The Bay Of Bengal During Winter Monsoon In 2016

The Bay of Bengal is one of the most important part of the Indian Ocean.The abundant precipitation during the monsoon period and the freshwater input through the runoff from the nearby area have a great impact on the circulation and stratification of the Bay of Bengal,which results in low salinity and creates a strong barrier in this area.Therefore,the lack of significant upwelling is responsible for the low primary productivity in the Bay of Bengal.But now the study on phytoplankton community structure is poorly studied in the Bay of Bengal.Therefore,during 2016 winter monsoon period,a comprehensive survey of biology,hydrology and chemistry was conducted in the Bay of Bengal(80.00° to 96.00°E.4.50° to 18.00°N).It was mainly divided into four sections.S1,S2,S3 and S4.with a total of 45 sampling stations and 256 water samples.The Utermohl method was used to analyze the species characteristics,cell abundance,dominant species and community diversity of phytoplankton in the surveyed seas,and the distribution pattern of chlorophyll a and phytoplankton carbon were studied.The results showed that 298 species of genus Phytoplankton,65 genera and genus,were mainly identified by diatoms and dinoflagellates,and a few chrysophyceae and cyanobacteria appeared.The phytoplankton we identified were mainly tropical in nature and mostly appeared in warm waters,indicating that the area has tropical climate characteristics.The abundance of phytoplankton cells in the surveyed area ranged from 6 to 2084 cells'1 with an average of 109 cells-1.The cell abundance of diatoms ranged from 8 to 1596 cells-1 with an average of 68.52 cells-1.The cell abundance of dinoflagellates ranged from 2 to 488 cells-1 with an average of 38.08 cells-1.The cell abundance cyanobacteria ranged from 0-144 cells-1 with an average of 4.55 cells-1;the cell abundance of chrysophyceae ranges from 0 to 118 cells-1 with an average of 2.76 cells-1.The abundance of phytoplankton cells was higher in the southwestern part of the survey area which gradually decreased towards the northern and eastern part of the Bay of Bengal.The horizontal distribution was mainly determined by the distribution of diatoms and dinoflagellates.Whereas the vertical distribution from deeper depths to surface water showed an increase in abundance with the water depth.Typical trend which we observed was from bottom depth to surface,abundance increased,and the highest value appeared in the 30 m water layerThe main dominant species of diatoms were Synerdra spp.,Coscinodiscus granii and Thalassionema frauenfeldii.Whereas the main dominant species of dinoflagellates were Ceratum fiirca and Prorocentrum micans;The only dominant species of cyanobacteria which we observed was Trichodesminum hildebrantii whereas the only species of chrysophyceae was observed to be dominant.The Shannon-Wiener diversity index of phytoplankton community ranged from 0.41-3.93 with an average of 2.25;the Pielou evenness index ranged from 0.34-0.89 with an average of 0.65,indicating that the Bay of Bengal has better phytoplankton diversity The corresponding analysis of phytoplankton and environmental factors showed that the most dominant species in the Bay of Bengal are positively correlated with ammonium and silicates.In general,the phytoplankton community structure in the Bay of Bengal was primarily affected by environmental variablesThe average concentration of chlorophyll a in the surface waters of the surveyed area was 0.23 ?g/L whereas the highest and lowest values ranged from 1.07 ?g/L to 0.02 ?g/L,respectively at the S02-09 station and the northern S03-02 station in the central Bay of Bengal.The overall distribution characteristics of Chl a showed higher trend in the southwest and lower in the northeast part of the Bay of Bengal which similarly observed with the abundance distribution of surface phytoplankton.Moreover,the vertical distribution of Chl a show highest values in 30 m depth of the surveyed area Furthermore,we measured the carbon content in phytoplankton.The surface phytoplankton carbon ranged between 0.07-10.06 mgC/m3 with an average of 1.23 mgC/m3.Broadly,the Bay of Bengal was divided into four areas including sBOB(southern BOB).cBOB(central BOB),neBOB(northeastern BOB)and nwBOB(northwestern BOB).Moreover,we studied spatial distribution of environmental parameters,phytoplankton community structure and characteristics including Chl a concentration distribution characteristics were discussed.