Increased diversity and environmental threat of harmful algal blooms in the Southern Yellow Sea, China

Harmful algal blooms (HABs) in the Southern Yellow Sea (SYS) have shown a trend of increasing diversity and detrimental effects. While the Bohai Sea, East China Sea, and South China Sea have experienced a high incidence of HABs since the 1980s, the Yellow Sea provides a relatively healthy ecological environment in which fewer HABs have been documented before the 21 st century. Yet large-scale blooms of the green macroalga Ulva prolifera (so-called “green tides”) have occurred annually since 2007 in the Yellow Sea. Six people were poisoned and one person died in Lianyungang in 2008 due to ingestion of algal toxins. Moreover, the Yellow Sea experienced co-occurrence of harmful red tides, green tides, and golden tides in 2017. This combination of events, rare worldwide, indicates the potential for further deterioration of the marine environment in the Yellow Sea, which may be related to climate change, aquaculture, and other human activities. Using the SYS as an example, we collected data of the frequency and scale of HABs over the years, as well as that of marine algal toxins, and analyzed the trend in the diversity of HABs in the SYS, to explore the causes and impacts of HABs, as well as the interrelationships among different types of HABs, including harmful red tides, green tides, and golden tides. We also attempted to improve our understanding of HAB evolution under the influence of global climate change and intensified human activities.