Strong interannual variation of green tides in the southern Yellow Sea: Crucial factors and implications on management strategies

In the Southern Yellow Sea (SYS), recurrent large-scale green tides of Ulva prolifera have been recorded since 2007, and nori cultivation rafts in Subei Shoal are generally considered as the major source of floating green algae. The control measures in Subei Shoal, however, didn't solve the problem, and the magnitude of green tides (as indicated by the coverage area of floating green algae) exhibited strong interannual variation. In this study, the dynamics of green tides in the SYS were analyzed using the data of remote sensing from 2017 to 2023, and the factors closely related to the magnitude of green tides were analyzed. The green tides were basically divided into initiation phase, development phase, and dissipation phase. The increased coverage of floating green algae at the early-development stage had strong positive correlation with magnitudes of green tides, and the precipitation in April, west wind in May, and nori cultivation area were crucial factors affecting the magnitudes of green tides. The study highlights strong impacts of weather conditions on the early development of green tides, and addresses the importance of integrated monitoring and early-warning besides source control measures in Subei Shoal.