The summer pattern of phytoplankton pigment assemblages in response to water masses in the Yellow Sea

The property of water mass plays an important role in determining the distribution of phytoplankton in the ocean. In the Yellow Sea, summer stratification constrains water exchange and differentiates the properties of the Yellow Sea Cold Water Mass (YSCWM) and surface water, which in turn affects the spatiotemporal patterns of phytoplankton communities. Here, based on four summer cruises in the Yellow Sea, we examined the response of phytoplankton pigment assemblages to three water masses, including surface water (water mass I, WM-I), thermocline water (WM-II), and the YSCWM (WM-III). Based on the opportunities for group dominance across the four cruises, Cyanophyceae, Haptophyceae, Chlorophyceae, and Cryptophyceae preferred living in WM-I, characterized by relatively higher temperature and light intensity but lower nutrients; Bacillariophyceae, Chlorophyceae, Cyanophyceae, and Dinophyceae dominated in WM-I, with relatively lower temperature and light intensity but higher nutrients. In comparison, the highest diversity of the dominant pigment groups was observed in WM-I with intermediate temperature, light, and nutrient levels. The Dirichlet regression model identified the key environmental factors driving changes in phytoplankton assemblages in WM-I, I, and I as dissolved inorganic phosphate (DIP), DIP and light, and temperature and ammonium, respectively. Under the impact of global environmental change, the fluctuations of key driving forces and their potential ecological implications need further investigation.