Annual patterns of green tides blooms in the coastal waters of Qinhunagdao from 2018 to 2020

Green tide disasters have been occurring along the Qinhuangdao coastal area for several years since 2015. This study investigated the interannual changes of green tides in Qinhuangdao from 2018 to 2020 and found that the green algae biomass was significantly reduced in 2020. The peak biomass of the green tide in July was only 151.5 g m⁻³, which is significantly lower than 7789.4 g m⁻³ in July 2018 and 5873.9 g m⁻³ in July 2019. Further comparative analysis showed that the decrease in nutrients, reduction in the density of Ulva microscopic propagules, and low biomass of attached macroalgae on the seaweed beds along the Jinmenghaiwan bath coastal area were the main causes for the decrease in the scale of green tides in Qinhuangdao in 2020. This paper also summarizes the factors of green tide formation in Qinhuangdao and proposes relevant prevention and control suggestions for the local governments based on the previous research.