The researchers studied phytoplankton in the northern South China Sea during summer and winter. They found that different species dominated in each season, with higher cell abundance in summer. Phytoplankton abundance was lower in deep water compared to shallow water. The diversity of species was higher in winter than in summer. The abundance of phytoplankton was negatively correlated with salinity and phosphate concentration. Overall, the study showed how phytoplankton communities vary with seasons and environmental factors in the South China Sea.