Interannual variability of Ulva prolifera blooms in the Yellow Sea

A massive Ulva prolifera bloom occurred in the Yellow Sea in 2008. Since then, green tide events have occurred every year and two other massive bloom events occurred in 2009 and 2013. In this article, we investigate the spatial and temporal patterns of U. prolifera green tides in the Yellow Sea during 2007–2013 using satellite images from operational MODIS instruments on board the Terra and Aqua satellites. Satellite sea surface temperature (SST) data and sea surface wind products were analysed to study their impacts on the occurrence and evolution of the floating macroalgae. Results show that the U. prolifera blooms were most likely caused by the rapid expansion of coastal Porphyra aquaculture in Jiangsu province, China. The SST was not a controlling factor influencing the size of the algal bloom or determining the blooming time. Surface wind played a significant role on the movement and distribution of the floating macroalgae, which causes an interannual variability in the spatial and temporal patterns of the U. prolifera blooms. The weak connection between the increase in Porphyra aquaculture and the size of the bloom implies that there must have been a nutrient supplier (or suppliers) for the extensive growth of the macroalgae in 2008, 2009, and 2013. The tide-induced upwelling between the Subei Bank and the western-central Yellow Sea seems to be a nutrient source.