Distribution and Environmental Impact Factors of Phytoplankton in the Bay of Bengal during Autumn

In order to better understand the effects of environmental factors and water mixing on the phytoplankton community structure in the Bay of Bengal, a field investigation was conducted from October to December 2016. A total of 276 species from 68 genera were identified, including Bacillariophyta (81 species), Miozoa (188 species), Cyanobacteria (four species), and Ochrophyta (three species). The abundance and distribution of dominant cyanobacteria gradually decreased along the latitude. This is evidenced in the vertical direction, which shows that cyanobacteria were affected by changes in environmental factors caused by the vertical mixing of seawater. The relationship between stratified N:P and phytoplankton also revealed that the changes in the vertical direction of the water deeply affected the phytoplankton community structure in the Bay of Bengal. The regions with strong vertical stratification were more favorable for the growth of cyanobacteria, while the regions with weak vertical stratification were more favorable for the growth of diatoms and dinoflagellates. According to the canonical correspondence analysis, nitrogen, silicates, phosphates, vertical stratification, and temperature were key control factors for phytoplankton communities. However, changes in these chemical parameters in the study area were also caused by the seawater cycle process.