In summer 2004, scientists studied phytoplankton in the northern South China Sea. They found 161 different types of phytoplankton, with diatoms being the most common. The amount of phytoplankton was highest near the coast and in the Pearl River Estuary. The number of phytoplankton cells in 2004 was double that of 1999, but the distribution pattern was similar. Phytoplankton abundance was linked to factors like ammonia, chlorophyll a, and oxygen levels, while it decreased with higher salinity. Overall, the diversity and evenness of the phytoplankton community in the area were low.