Distribution of phytoplankton in the East China Sea and the southern Yellow Sea in spring in relation to environmental variables and dimethylsulfide compounds

The coastal ecosystems are highly sensitive to climate change and are usually influenced by variations in phytoplankton communities and water physiochemical factors. In the present study, the phytoplankton community, chlorophyll a (Chl a) and their relationships with environmental variables and dimethylsulfide (DMS) and dimethylsulfoniopropionate (DMSP) were investigated in spring 2017 (March 24 to April 16) in the East China Sea (26.0 degrees-33.0 degrees N, 120.0 degrees-128.0 degrees E) and southern Yellow Sea (31.0 degrees-36.0 degrees N, 120.0 degrees-125.0 degrees E). The spatial distributions of phytoplankton species composition and cell density were investigated by qualitative and quantitative methods and were compared with historical data to study phytoplankton species succession in the survey area. The results showed that there were 275 phytoplankton species belonging to 90 genera and 6 phyla in the survey area, of which 208 species belonged to 62 genera of Bacillariophyta and 56 species belonged to 20 genera of Pyrrophyta. The dominant phytoplankton species were Skeletonema dohrnii, Chaetoceros vanheurckii and Prorocentrum donghaiense. The phytoplankton cell densities ranged from 0.06x10(4) cells/L to 418.73x10(4) cells/L, with an average value of 21.46x10(4) cells/L. In spring, the average ratio of Bacillariophyta/Pyrrophyta was 41.13 for the entire study area. The areas with high phytoplankton cell density were mainly distributed in the northern South Yellow Sea and offshore waters of the East China Sea. According to a canonical correspondence analysis among phytoplankton and environmental parameters, the water Chl a concentrations were notably consistent with phytoplankton cell density (P<0.001), and both showed significant negative correlations with salinity and nitrite (P<0.05) and significant positive correlations with dissolved oxygen and pH (P<0.001). There was a significant positive correlation between diatom (both in cell density and in dominant species) and DMS (P<0.05), which indicated that diatoms play a greater role in DMS production in this investigated area.