Abstract:Two comprehensive surveys were conducted in the frequent Harmful Algal Bloom (HAB) areas of the East China Sea in spring and summer of 2005. Based on the analysis of the variation of nutrients in typical sections, the supply of nutrients was discussed. The results show that the constant nutrient supply is very important for the occurence of HABs in the surveyed areas. The surface water of these areas were mainly influenced by terrestrial source of nutrients，such as Changjiang diluted water (CDW); while the bottom water were mainly influenced by Taiwan warm current (TWC). Moreover, the influence of terrestrial source is stronger on the northern part than on the southern part, and the influence of the TWC is stronger on the southern part than on the northern part. The quantities of SiO3-Si and DIN supply were higher than PO4P in CDW，while TWC supplied more PO4P then the other nutrients. Moreover, the release of sediment is one of the important source of supply for SiO3-Si.
