A Revisit of Landsat-Observed Macroalgal Blooms in the Yellow Sea and East China Sea Before 2008

Harmful macroalgal blooms caused by Ulva prolifera and Sargassum horneri are increasing in the Yellow Sea and East China Sea. However, our understanding of macroalgal blooms before 2008 is fragmented and unclear. Using time-series Landsat imagery from 1984 to 2008, we examined macroalgal bloom events and their evolutionary patterns. The results suggest that no macroalgal blooms were observed before 1999. Ulva blooms could be traced back to 1999 and occurred on a small scale in 2000, 2004 and 2005, before escalating into large green tides in 2007 and 2008. Notably, these Ulva blooms were confined to the southern Yellow Sea from May to August. In comparison, Sargassum blooms were first detected in the East China Sea in March 2000 and occurred almost every year thereafter, although the size of the blooms showed significant interannual variation. The distribution areas generally moved northwards from March until the bloom dissipated in May or June, suggesting the influence of the monsoon and currents. Our investigation provided some insight into the bloom history of these two harmful macroalgal blooms in the Yellow Sea and East China Sea.