Declining Phytoplankton Biomass in Chinese Coastal Oceans Linked to Climate Warming

Coastal ecosystems in China are increasingly threatened by climate change, affecting biodiversity and fisheries. Rising ocean temperatures and more frequent heatwaves have intensified phytoplankton blooms and hypoxic zones. To better understand these dynamics, we developed a 20-year data set of phytoplankton biomass (a_ph(443)) using MODIS satellite data. Our analysis shows a 23.8% decline in biomass over two decades, with the most significant reductions in spring, summer, and autumn. This decline is linked to warming sea surface temperatures (SST), which limit nutrient availability by enhancing ocean stratification. In contrast, winter warming was associated with a slight increase in biomass. Using machine learning, we identified SST as the dominant driver, explaining up to 65% of the seasonal trend. These findings offer valuable insights into the complex interactions between temperature, nutrients, and phytoplankton growth, informing coastal ecosystem management under climate change.