Spatial and temporal nutrient variations in the Yellow Sea and their effects on Ulva prolifera blooms

The world's largest trans-regional Ulva prolifera blooms (green tides) have been observed along the coast of the Yellow Sea in the seven years since 2007. In this study, the spatial and temporal distributions of dissolved inorganic nutrients (DIN, PO4–P and SiO3–Si) and dissolved organic nutrients (DON and DOP) were analyzed through field surveys in the southern Yellow Sea (SYS), particularly in the Subei coastal area, during green tide occurrences. The horizontal distributions of nutrient concentrations generally decreased from inshore to offshore areas. Nutrient concentrations were relatively high in coastal areas, especially in estuaries influenced by terrigenous input, such as the Sheyang River and the Guanhe River. The concentrations of all nutrients generally decreased over time in spring. Under optimal temperature and salinity conditions, U. prolifera preferentially assimilates inorganic nutrients, but when the concentrations of inorganic nutrients are relatively low, organic nutrients uptake occurs; this has been confirmed by in vitro studies.