Variation in photosynthetic activity of phytoplankton during the spring algal blooms in the adjacent area of Changjiang River estuary

Nine cruises were undertaken in the adjacent area of Changjiang River estuary from late March to May in 2011 to investigate the variation in photosynthetic activity (Fv/Fm) of surface water during algal blooms. The time series covered the period from Skeletonema sp. bloom to Prorocentrum donghaiense bloom. The results showed that Fv/Fm ranged from 0.17 to 0.73. Temperature, turbidity and nutrients were the primary influencing factors on Fv/Fm and Fv/Fm showed a strong diel periodicity. Additionally, the change in Fv/Fm during Skeletonema sp. and P. donghaiense bloom was similar. Fv/Fm increased to more than 0.60 before bloom initiation, and then chlorophyll a (Chl a) concentration rocketed and the bloom broke out. Fv/Fm was above 0.6 during bloom development and declined to below 0.6 when bloom dissipated. Fv/Fm increasing to higher level occurred several days prior to significant increases in Chl a and outbreak of bloom, indicating Fv/Fm can be used to predict onset of algal blooms.