Resolving the complex relationship between harmful algal blooms and environmental factors in the coastal waters adjacent to the Changjiang River estuary.

The sea area adjacent to the Changjiang River estuary is the most notable region for harmful algal blooms (HABs) in China as both diatom and dinoflagellate blooms have been recorded in this region. Affected by the Changjiang diluted water (CDW) and currents from the open ocean (i.e., Taiwan warm current, TWC), the environmental conditions in the coastal waters adjacent to the Changjiang River estuary are quite complex. To obtain a better understanding of the mechanisms of HABs in this region, analyses based on field investigation data collected by the National Basic Research Priority Program (CEOHAB I) were performed using principle component analysis (PCA), multiple regression analysis (MRA) and path analysis (PA). The results suggested that phosphate and silicate are the major factors that directly affect the diatom bloom, while dissolved inorganic nitrogen (DIN), temperature and turbidity are the factors that influence the dinoflagellate bloom. CDW and the TWC have different roles in affecting the two types of algal blooms. CDW, which has a high concentration of nitrate and silicate, is essential for the diatom bloom, while the intrusion of the TWC (mainly Kuroshio subsurface water that is rich in phosphate at the bottom) is critical for the maintenance of the dinoflagellate bloom. The results of this study offer a better understanding of the mechanisms of HABs in the East China Sea.