The Dissipation of Ulva Prolifera and its Effects on Environmental Factors: Based on Different Spatial and Temporal Scales

Abstract

Since 2007, green tides caused by Ulva prolifera have been observed annually in the South Yellow Sea (SYS). Research indicates that Ulva prolifera typically emerges near the Jiangsu shoal in May and subsequently spreads northward, accumulating offshore of the Shandong Peninsula. As it decays in this region, it releases substantial nutrients and organic matter, significantly affecting the coastal ecosystem. This study examines the relationship between environmental parameters and the extinction of green tides across three characteristic areas: the SYS study area in 2019, the Qingdao coastal area from 2017 to 2022, and the Ulva prolifera accumulation area in 2023. The findings reveal that while green tide outbreaks do not significantly impact the annual nitrogen and phosphorus budgets of the entire SYS, they have notable effects in regions where Ulva prolifera decays. Specifically, its disappearance has resulted in decreased dissolved oxygen (DO) levels in the Qingdao coastal area, thereby increasing the risk of hypoxia. The nutrients released during this decay promote phytoplankton growth, leading to an elevated N/P ratio. After the complete decay of Ulva prolifera and the associated phytoplankton, nutrient concentrations in Qingdao's coastal waters increased, suggesting that Ulva prolifera may have long-lasting environmental effects. Although this study focuses on the short-term impacts of Ulva prolifera, further investigation into its long-term effects is essential.

Keywords: Green tides, Nutrients structure, Qingdao's coastal waters, short-term impacts