Spatiotemporal dynamics of early floating green algae in the Subei Shoal and their response to green tide development in the Yellow Sea based on remote sensing

Since 2007, large-scale green tide events have frequently occurred in the Yellow Sea, causing severe impacts on coastal ecosystems and fisheries. The Subei Shoal, as a primary aggregation zone for early-stage floating green algae, plays a crucial role in the evolution of green tides. In this study, multi-source remote sensing imagery was employed to extract early-stage floating algal information in the Subei Shoal from 2016 to 2023, and to analyze its spatiotemporal distribution patterns as well as its relationship with the maximum extent of Yellow Sea green tides. The results show that: (1) The earliest remote sensing detection of floating algae varied among years, with the earliest occurrence traced back to late April, predominantly along tidal channels near Jiangjiasha and Waimaozhusha on the eastern shoal. (2)The northeastern part of the Subei Shoal consistently exhibited high algal accumulation in multiple years, whereas the western part showed a pronounced response to the later development stages of Yellow Sea green tides in certain years. (3) The coverage area of early-stage floating algae in the Subei Shoal was significantly correlated with the annual maximum green tide extent (r = 0.77, p < 0.05).