The researchers studied phytoplankton communities in the Luanhe-Beidaihe estuary in summer 2008 and 2012. They found that the species composition of phytoplankton changed significantly between the two years, with fewer species identified in 2012. The abundance of phytoplankton decreased from 2008 to 2012, and the community structure remained relatively stable. Different environmental factors, such as dissolved oxygen and chlorophyll levels, influenced the phytoplankton communities in each year.