Characteristics and influence of green tide drift and dissipation in Shandong Rongcheng coastal water based on remote sensing

Green tides in the Yellow Sea have occurred in large-scale blooms since 2007. Originating in the southern Yellow Sea and drifting northward continuously, these green tides have severely affected the coastal ecological environment. To analyze the influence of green tides on marine aquaculture in the Rongcheng coastal water (the northernmost sea area influenced by green tide), we used the Moderate Resolution Imaging Spectrometer (MODIS), GaoFen-1 (GF-1) satellite imagery and the sea surface wind (SSW) data. We also used field investigation to analyze the drift trajectory, drift speed, dissipation speed and distribution density of green tides. The results show that the main body of a green tide will drift northeast and continue in this direction after crossing the Rongcheng Chengshanjiao coastal water. Between 2013 and 2018, the drift speeds of green tides to the north of this area were within 1-5 km/d, the drift speed in the east-west direction was 0.3-4 km/d, and the interannual difference was not significant. The dissipation speed of the green tide in the Rongcheng Sea is generally within the range of 1-5 km(2)/d and shows little interannual difference. The distribution density in the southern area of Rongcheng is the highest, ranging from 3% to 7%. The area with the highest frequency of influence is also the area with the greatest distribution density of green tides, and disasters are most severe here. A reasonable collection area is proposed, based on the above analysis. This research provides the basis for understanding the characteristics of green tides in the dissipation phase, and the prevention and control methods of green tide disasters in the Rongcheng coastal water.