Occurrence and potential risks of harmful algal blooms in the East China Sea.

Harmful algal blooms (HABs) have drawn great attention in coastal areas worldwide in the past decades because of their multiple effects on marine ecosystems as well as public health. This study utilized geographic information system (GIS) techniques to analyze the primary data on HABs, as well as shellfish toxins data, in the East China Sea from 2000 to 2006. The frequency of HABs was mapped by kernel density estimation, and the relative risk posed by HABs was assessed based on their physical-chemical characteristics. In addition, the spatial patterns and the trend of HAB events were examined by nearest neighbor analysis and time series analysis, respectively. The results revealed that HAB events not only had an increasing trend and significant seasonality, but also were clustered in space and time. HAB events displayed a higher frequency and a higher risk in Zhejiang coastal waters, particularly in the Zhoushan Archipelago, the largest marine fishery in China. Shellfish toxins were detected in areas with high HAB risk, but were not correlated with the risk. This paper provides a novel method to assess the relative risk caused by HABs and some useful information for HAB monitoring and management and aquaculture development.