Significantly decreasing harmful algal blooms in China seas in the early 21st century.

Harmful algal blooms (HABs) are one of primary worldwide environmental problems with severe consequences for aquatic ecosystems, human health, marine fisheries and local economy. During the past few decades, coastal waters of China Seas have experienced a significant increase in the occurrence of the HAB events, which is common across the vast majority of coastal waters of the world. Here we report the absence of the widespread increase over the early 21st century in China Seas. Both frequency and coverage area of annual HAB events have decreased at statistically significant rates for the 2000-2017 period. Despite the multiple factors determining the outbreak of HABs, the improvement of water quality in the marginal sea off China and changes in the sea surface temperature in the early 21st century may play an important role in the decrease in the HABs.