Cruise observation of Ulva prolifera bloom in the southern Yellow Sea, China

Four cruises were carried out in the southern Yellow Sea from May to June of 2012 with the aim of observing the development of green tides. Free-floating patches of green algae dominated by Ulva prolifera occurred in early May in coastal waters of the southern Yellow Sea with an average biomass of 0.05 g m−2. The average biomass of free-floating green algae developed rapidly and reached 3.20 gm−2 in mid-May, and the affected area reached 8.7 × 103 km2 with a total biomass of 1.37 × 105 tons. In late May, the average biomass reached 5.81 gm−2, and the affected area reached 3.2 × 104 km2 with a total biomass of 2.5 × 105 tons. In early June, the average biomass reached 8.47 gm−2, the affected area covered 3.6 × 104 km2, and the total biomass of floating green algae was 3.64 × 105 tons. The affected areas of green tide in our observed data were higher than those estimated from remote sensing images in the early two cruises, and basically matched the remote sensing data in the last two cruises. With the increased biomass and the expansion of the affected area, the free-floating algal patches moved progressively northward. They first appeared in coastal water of middle Jiangsu province, gradually reached 35°N in early May, and finally drifted to the southern coast of the Shandong Peninsula (36°N) after one month. This work can offer help for the early prediction and warning of a green algal bloom and provide decision-making bases for governmental departments.