Influence of Sea Surface Temperature on Outbreak of Ulva prolifera in the Southern Yellow Sea, China

In this study, using Moderate Resolution Imaging Spectroradiometer (MODIS) satellite images and environmental satellite CCD images, the spatio-temporal distribution of Ulva prolifera in the southern Yellow Sea during the period of 2011–2018 was extracted and combined with MODIS Level3 Photosynthetically Active Radiation (PAR) product data and Earth System Research Laboratory (ESRL) Sea Surface Temperature (SST) data to analyze their influences on the growth and outbreak of Ulva prolifera. The following conclusions were drawn: 1) comprehensive analysis of Ulva prolifera distribution during the eight-year period revealed that the coverage area of Ulva prolifera typically exhibited a gradually increasing trend. The coverage area of Ulva prolifera reached a maximum of approximately 1714.21 km2 during the eight-year period in late June 2015. The area affected by Ulva prolifera fluctuated. In mid-July 2014, the area affected by Ulva prolifera reached a maximum of approximately 39 020.63 km2. 2) The average growth rate of Ulva prolifera was positive in May and June but negative in July. During the outbreak of Ulva prolifera, the SST in the southern Yellow Sea tended to increase each month. The SST anomaly and average growth rate of Ulva prolifera were positively correlated in May (R2 = 0.62), but not significantly correlated in June or July. 3) The variation trends of PAR and SST were approximately the same, and the PAR during this time period maintained a range of 40–50 mol/(m2·d), providing sufficient illumination for the growth and outbreak of Ulva prolifera. In addition, the abundant nutrients and suitable temperature in the sea area near northern Jiangsu shoal resulted in a high growth rate of Ulva prolifera in May. In summary, the outbreak of Ulva prolifera was closely related to the environmental factors including SST, nutrients, and PAR. Sufficient nutrients and suitable temperatures resulted in a fast growth rate of Ulva prolifera. However, under poor nutrient conditions, even more suitable temperatures were not sufficient to trigger an outbreak of Ulva prolifera.