Analysis on the red tide of Prorocentrum dantatum in the north coastal water of Zhejiang

The red tide of Prorocentrum dantatum occurred in the north coastal water of Zhejiang in May,2003 was analyzed.The result showed that the abundance of 10~6/L of P.dantatum is critical value for red tide occurrence.The algae abundance showed the positive correlation with DO,COD,Chla,Tunicata and Coelanterate,and the opposite trend with Copepoda and Chaetognatha.The occurrence of red tide of P.datatum does not need the high level concentration of nutrient salt.The occurrence in series and large-scale may be relation with changes of marine fishery resource and marine ecosystem.