The spatial and temporal characteristics of harmful algal blooms in the southwest Bohai sea

• The application of Geo-statistics tools within GIS systems and SPSS (usually applied for terrestrial environment) for analyzing HABs data in the Southwest Bohai Sea.
• A comprehensive, full description and perspective foranalysis of the spatial and temporal characteristic of HAB events, including the causative species, seasonality, trend, spatial patterns, frequency and harm ofthreat from HABs events in the southwest Bohai Sea.
• This study identified some areas where management programs should be emphasizedconcentrated, some of which were not identified and/or not given enough attention in previous management actions, e.g. some offshore areas with low nutrient concentrations.

Harmful algal blooms (HABs) are harmful to coastal ecosystems, fisheries, the aquaculture industry, and even human health, thus they have received great attention worldwide. In this study, geostatistical tools in Geographic information system (GIS) were used to analyze HAB data collected over the last 11 years in the southwest Bohai Sea with the goal of detecting spatial and temporal characteristics of HAB events in this area. The seasonality, trend of HAB occurrences and the spatial pattern of HAB events were examined by time-series analysis and nearest neighbor analysis, respectively. The frequency of HAB occurrences was mapped using kernel density estimation, and the harm caused by HAB events was assessed and then categorized using a characteristic-based empirical model. The occurrences of HABs not only exhibited significant seasonality and a “single peak” trend in time but also were clustered in space. HABs had both a high frequency of occurrence and a high harm in the north Bohai Bay and the Yellow River estuary. In addition, HABs posed a high harm in the nearshore area near the city of Huanghua in Bohai Bay and the offshore area in the middle Bohai Bay; thus, HAB monitoring and/or management should be concentrated in these locales. Compared to previous descriptions, this research utilized a visualizable approach to more fully identify the scope, distribution, and characteristics of HAB occurrences in the southwest Bohai Sea, thus providing useful information to support the implementation of a monitoring and management program for HABs.