Remote sensing of early-stage green tide in the Yellow Sea for floating-macroalgae collecting campaign

The world's largest green tide originated from the Jiangsu Shoal of the Yellow Sea was due to fast reproduction of floating green macroalgae (Ulva prolifera). It brought significant impacts on marine environment and ecosystem in the Yellow Sea. In this study, we examined the expansion of green tide from the Jiangsu Shoal during the period from 29 April to 25 June 2016. Using high-resolution satellite images, we revealed a declined growth rate during the northward drifting of early-stage green tide for the first time, i.e., the green tide had higher growth rate (up to 25% per day) in the turbid waters of the Jiangsu Shoal in May and a lower growth rate (low to 3% per day) in the relatively clear waters in the middle of the western Yellow Sea in June, which suggests that water clarity might not be the key factor controlling the growth rate of the floating macroalgae in the surface waters under natural conditions. The high growth rate led to shortened time windows for controlling the green tide by employing macroalgae collecting campaigns at the initial sites of the green tide, which was no more than 14 days in the 2016 case.