Spatio-temporal distribution of harmful algal blooms and their correlations with marine hydrological elements in offshore areas, China

Abstract

Harmful algal blooms (HABs) occur frequently in Chinese coastal areas, causing major economic losses and seriously threatening coastal marine environments. HAB research using remote sensing technology focuses on detecting and monitoring HABs. However, no study has explored the occurrence of HABs in response to hydrological factors based on remote sensing. This study used 30 years (1990–2019) of data to analyze the spatial and temporal characteristics of Chinese coastal HABs. The development and change trends of marine hydrological factors (sea surface salinity (SSS), sea surface temperature (SST), and chlorophyll (Chl) concentration) during the occurrence and disappearance of HABs were clarified, and correlations between marine hydrological parameters and HABs were described (Ahn and Shanmugam, 2006). From 1990 to 2019, 1,557 HABs occurred in coastal areas of China, and 961 HABs occurred from 2001 to 2012, accounting for 62.00% of the total. From 1998 to 2019, the total of 1393 HABs occurred, and 813, 249, 198 and 133 HABs occurred in the East China Sea, South China Sea, Bohai Sea, and Yellow Sea, respectively. From 2009 to 2019, the total of 612 HABs occurred, and 536 HABs occurred from April to September, accounting for 87.58% (Anderson et al., 2021). Spatially, kernel density estimation showed that most HABs were concentrated in the Bohai Bay and Yangtze and Pearl River deltas (Bao and Ren, 2014). During HABs, SST increased by 0.72–6.41 °C, Chl increased by 11.00–95.36 mg × m−3, and SSS decreased by 0.10–4.34 PSU. When HABs disappeared, SST decreased by 1.14–6.01 °C, Chl decreased by 4.50–96.46 mg × m−3, and SSS increased by 0.08–3.431 PSU. The SSS of a HAB year was relatively low, while the Chl was relatively high. SST between 8.00 °C and 28.00 °C induced HABs. The research illustrates the spatiotemporal characteristics of HABs in coastal areas of China and their sensitivity to marine hydrological factors. These findings are of great importance in regard to the impacts on human health and ecological damage caused by HABs.