Red Tide Characteristics And Disaster Risk Assessment In The Coastal Waters Of Beibu Gulf Of Guangxi

Red tide(HAB,Harmful Algal Bloom)is a common ecological anomaly in coastal waters.The occurrence of red tide disasters will cause the marine ecosystem to lose balance,affect the coastal environment,tourism and marine fisheries,could even cause the destruction of local marine living resources and harm human health.Under the background of global warming and the increasing influence of human activities,red tides have increased significantly in the spatial range and frequency of global coastal waters in recent decades,and the red tides in Chinese coastal waters are getting worse and worse,even the relatively"clean"Beibu Gulf is not spared.The outbreak of red tide has intensified its impact on public health,tourism,fishery and ecosystem in Beibu Gulf,and the potential threat of it is becoming more and more pronounced.Therefore,it is of great significance for the management of marine environment and the development of aquaculture industry to clarify the characteristics of red tide in coastal waters of Beibu Gulf and carry out disaster risk assessment of red tide.This paper collects the data of red tide occurrence in Beibu Gulf of Guangxi over the years,and clarifies the evolution characteristics of red tide outbreak in this sea area.Based on the theory and method of red tide disaster risk assessment,and combine with the characteristics of coastal waters of Guangxi Beibu Gulf,the red tide disaster assessment system of coastal waters of Guangxi Beibu Gulf is constructed.The entropy weight method is used to calculate the index weight,and the red tide disaster risk assessment model is constructed.According to the model calculation results,the Arc GIS geostatistical module is used to realize the visualization of the red tide disasters hazard degree,receptors’vulnerability and disaster risk results in the coastal waters of Guangxi Beibu Gulf.The main conclusions are as follows:(1)From 1985 to 2021,46 red tides occurred in Beibu Gulf of Guangxi,with cumulative duration of 151 days and cumulative occurrence area of 7516.874 km~2.Compared the pre-2000,2000～2010 and 2011～2021 periods,the cumulative occurrence frequency,duration and area of red tides increased significantly.In terms of time,1985 to 2010,red tide mainly occurred in spring and summer(63.2%from April to June);after 2010,red tide mainly occurred in winter(31.3%in February)and rarely occurred in summer.In space,the red tide mainly occurred in the sea area of Weizhou Island at 1985 to 2010,and the sea area involved after 2010 almost covers the whole Beibu Gulf of Guangxi(mainly sea areas of Qinzhou and Beihai).In terms of the cause species of red tide,cyanobacteria were the main species before 2000,which changed to the coexistence of ccyanobacteria,dinoflagellates and diatoms from 2001 to 2010,and then to Phaeocystis globosa and Noctiluca scintillans after 2010.(2)In spring,summer,autumn and winter,the hazard degree of red tide disaster causing factors,inducing environment factors and red tide disaster are mainly low and medium level,while very high and high risk areas account for a small proportion.Spatially,the very high and high hazard degree are mainly distributed in the interior of the bay,while the rest of the sea areas are in low and medium hazard degree.The overall hazard degree is higher in the interior of the bay than in the outer part of the bay,and higher in the near sea area than in the far sea area.(3)The degree of red tide disasters receptors’vulnerability:The Fangchenggang sea area is in a state of very high vulnerability,the Qinzhou sea area is in a state of high vulnerability,and the Beihai sea area is in a state of low vulnerability.(4)In spring,summer,autumn and winter,red tide disasters are dominated by low and medium risks,while very high and high risks only occur in spring and autumn,and the overall distribution area account for a small proportion.Spatially,very high risk and high risk are mainly distributed in the bay,but also in the sea area of Xieyang Island.The other sea areas are in low and medium risk,and the overall risk level is higher in the bay than outside the bay.Seasonally,there is no obvious trend in the distribution of risk levels in spring,but the risk levels in near coastal waters were higher than those in far coastal waters in summer,autumn and winter.(5)This study summarizes the occurrence of red tide in Guangxi Beibu Gulf over the past years,and systematically analyzed the red tide from 2010 to 2021.It is the first time to assess the risk of red tide disaster in the coastal waters of Guangxi Beibu Gulf,and put forward targeted countermeasures and suggestions for red tide disaster prevention based on the research results.The results can provide a basis for red tide monitoring and control,marine environmental safety,and marine utilization planning in Guangxi Beibu Gulf.