Comparative Study Of Spatiotemporal Difference Of Floating Macroalgae In The Eastern China Seas And Their Influence Factors

Due to human activities and environmental changes,frequent marine ecological disasters caused by large-scale floating macroalgae outbreaks have occurred in the Eastern China seas in recent years.The main ones are the green tide disaster caused by the outbreak of Ulva prolifera and the golden tide disaster caused by the outbreak of Sargassum.These events not only affect the economic activities and marine ecological environment of coastal cities,but also pose a threat to human health.Conducting spatial and temporal analysis of large-scale floating algae in the Eastern China seas and analyzing their causes using remote sensing is not only beneficial for reducing the economic losses caused by such outbreaks,but also for improving China’s ability to prevent and control marine ecological disasters.In this study,high-resolution multi-source remote sensing data,including Sentinel-2,Gaofen-1,and Landsat-8 with a resolution better than 30 meters,were used to extract the floating macroalgae in the Eastern China seas from 2016 to 2021.The spatiotemporal differences between Ulva prolifera and Sargassum were analyzed,and the possible influencing factors of their outbreaks from the perspectives of environmental changes and human activities were explored.This study aims to provide theoretical and data support for the management of large-scale floating algae disasters in the Eastern China seas.The main conclusions are as follows:(1)Large-scale floating macroalgae mainly occur in the Yellow Sea and East China Sea,and no large-scale outbreaks of large floating macroalgae have been detected in the Bohai Sea.The green tide formed by the outbreak of Ulva prolifera mainly occurs in the Yellow Sea,while the golden tide formed by the outbreak of Sargassum mainly occurs in the East China Sea and the Yellow Sea.(2)The outbreaks of Ulva prolifera and Sargassum have significant differences in time and space.Ulva prolifera appears in the waters of Jiangsu Province from late May to early June each year,drifts to the waters south of the Shandong Peninsula in late June,and reaches its maximum coverage area.In July,the coverage area of Ulva prolifera begins to decrease,and it disappears by August.Sargassum,on the other hand,appears in the East China Sea in March each year,appears in the waters where the Yellow Sea and the East China Sea meet in April,drifts to the east of Jiangsu Province in May,and reaches its annual peak.It disappears in the waters where the Jiangsu and Shandong Provinces meet and the waters south of the Shandong Peninsula in June.(3)In terms of human activities,the cultivation of Pyropia yezoensis in the Northern Jiangsu shoal of Jiangsu Province can affect the outbreak of Ulva prolifera,but has no significant impact on Sargassum.The recovery process of Pyropia yezoensis cultivation rafts can affect the scale of Ulva prolifera,and completing the recovery process too early may exacerbate the scale of Ulva prolifera,which may be an important reason for the great Ulva prolifera disaster in 2021.(4)In terms of environmental changes,sea surface temperature,water transparency,and sea surface wind have significant effects on the outbreaks of Ulva prolifera and Sargassum.During the growth period of Ulva prolifera in May and June,suitable sea surface temperatures are conducive to its rapid proliferation,while high sea temperatures in July and August can limit its growth.However,changes in sea surface temperature do not significantly affect the growth of Sargassum.Compared with Ulva prolifera,changes in water transparency have a more significant impact on Sargassum.Ulva prolifera is not sensitive to changes in water transparency,while Sargassum grows better in waters with higher transparency and grows slower or even dies in waters with lower transparency.In May and June,the water transparency of the water body significantly decreases,which is not conducive to the growth of Sargassum and constrains its growth status.In addition,the drift of Ulva prolifera and Sargassum is mainly affected by southeast winds,drifting from south to north.The overall sea water salinity is within the range suitable for the growth of Ulva prolifera and Sargassum,and has no significant effect on their growth status.