The low temperature characteristics in Zhejiang coastal region in the early spring of 2005 and its influence on harmful algae bloom occurrence of Prorocentrum donghaiense

In spring of recent years, a large scale harmful algae bloom (HAB) of Prorocentrum donghaiense nearly occurs annually in the end of April or beginning of May in the Zhejiang coastal and off Changjiang estuary region, however, it didn't occur until the end of May of 2005.Temperature characteristic in the study area in early spring of 2005 and its influence on a large scale HAB of Prorocentrum donghaiense are analyzed on the basis of survey data carried out in spring of 2002-2005 and some related historical meteorologic data. The results show that water temperature in March 2005 is obviously lower than that of 15-year-averaged(1985-2001) in Zhejiang coastal sea, especially in nearshore region of Zhejiang coastal sea,compared to the same period of 2004, water temperature in early spring(early April) 2005 is about 2.6℃ lower. Special meteorologic conditions (the lowest air temperature in the past ten years and strong northern monsoon)and feeblish Taiwan Warm Current in winter of 2004/2005 are the main causes of low water temperature in investigated area. Low temperature characteristic may be main causative factor that a HAB of Prorocentrum donghaiense in spring 2005 occurred late which differ from that of Spring 2002-2004 in Zhejiang coastal sea.