Growth potential of Ulva prolifera in the South Yellow Sea and effectiveness of countermeasures

The effectiveness of green tide countermeasures was assessed using a model of Ulva prolifera growth factors and drift patterns in the South Yellow Sea. The reliability of the model was confirmed using satellite data showing the green tides in 2018, 2019, and 2021. The point of zero growth (biological zero) was determined to be 5.2 °C. The highest growth potential occurred successively in the sea area near 33.0°N and 123.5°E, Subei Shoal, and the north of Subei Shoal, from April to June, in the same chronological order with ascending order of surface sea temperature. Differences in growth potential were attributed to differences in dissolved inorganic nitrogen. Among the different countermeasures assessed, salvaging floating U. prolifera in open waters and early recycling of Neopyropia rafts were found to be the most effective in reducing the biomass of U. prolifera and the extent of green tides. In comparison, chemical treatment contributed only minimally to the reduction in U. prolifera biomass.