Seasonal dynamics and environmental drivers of phytoplankton carbon biomass in the southern yellow sea

Phytoplankton carbon biomass serves as a valuable indicator of phytoplankton biomass, playing a crucial role in parameterizing ecosystem models. However, studies on phytoplankton carbon biomass have been quite limited in continental seas, providing limited references for understanding their role in the biogeochemical carbon cycle. In this study, we examined phytoplankton carbon biomass in the SYS during the spring, summer, and fall of 2018, and clarified its characteristics, distribution patterns and controlling factors. Phytoplankton carbon biomass ranged from 2.33 to 84.74 mu g C/L in spring, 1.19-1454.25 mu g C/L in summer, and 0.01-33.20 mu g C/L in fall in the SYS. Diatoms were the most dominant group, contributing 53%, 68%, and 67% to the total phytoplankton carbon in spring, summer, and fall, respectively, followed by dinoflagellates, which contributed 46%, 31%, and 30%. The carbon biomass of diatoms and dinoflagellates exhibited quite distinct correlations with environmental factors. Diatoms exhibited stronger nutrient dependency, whereas no significant correlation was observed between dinoflagellates and nutrients, reflecting the different nutritional strategies of the two groups (strict autotrophy vs. mixotrophy). Compared to cell abundance, carbon biomass revealed a significantly higher proportion of dinoflagellate biomass in the community structure, which is primarily due to the significant interspecies variations in cell volume. Dinoflagellates tend to have larger cell volumes compared to diatoms in the SYS, leading to an underestimation of dinoflagellate proportions when using cell abundance alone. This indicates that simply using cell abundance may lead to cognitive bias in recognizing phytoplankton community structure, and taking carbon biomass into account will provide a more comprehensive understanding.