Spatio-Temporal Variations Of Red Tide Events And Their Environmental Drivers Along The Coast Of Ningde,Fujian

Red Tide is a frequent marine ecological disaster,especially the red tide caused by toxic algae would cause damage to marine ecology and aquaculture,and may even harm human health through the food chain.Ningde,Fujian Province is the area where red tides occur most frequently and is also an important aquaculture base.Therefore,it is necessary to analyze the characteristics of red tide evolution and its environmental driving factors in Ningde coastal area.The research results can provide reference for the monitoring and early warning of red tide disasters and the comprehensive prevention and control in this sea area.This paper based on the basic information of red tide,historical data of water quality observation,buoy temperature data and remote sensing temperature data in ningde coastal area,the spatial-temporal variation characteristics of red tide and the inter-annual variation characteristics of main environmental factors are analyzed,and the correlation between environmental factors.The results show that:(1)The red tide events recorded along the coast of ningde increased year by year from 2000 to 2003 and then decreased.The number of red tides,the cumulative duration of days,and the cumulative affected area from 2010 to 2020 were lower than those from 2000 to 2009.Red tides occur mainly from late April to early June in the coastal area of Ningde,with the peak occurring in May.The recorded red tides were mainly distributed in Lvxia sea area and the sea area from Yushan island to Sishuang Islands,while the occurrence of red tides was rarely recorded in Sansha Bay,and the red tides during the period from 2010 to 2020 were mainly concentrated in the relatively coastal waters.There were 12 dominant species of red tide in the coastal area of Ningde,among which the red tide caused by Prorocentrum donghaiense and Karenia mikimotoi was the most frequently recorded red tide and the one causing the most serious losses in the coastal area of Ningde,respectively..(2)From 2003 to 2015,inorganic nitrogen,active phosphate,COD and eutrophication index of Sansha Bay and Funing Bay showed an increasing trend,but the occurrence intensity of red tide showed a decreasing trend.Statistics showed that DIN,DIP and E had significant negative correlation with the number of red tide occurrence and duration days in the years off Ningde.If the red tide events in 2003 were not considered,the mean SST from April to June in 2000～2020 was significantly positively correlated with the number of red tide occurrences and the number of red tide occurrences.It can be seen that the interannual variation of red tide is not only related to the variation of nutrients,but also affected by the variation of SST.(3)The occurrence of Prorocentrum donghaiense red tide is usually accompanied by the sudden rise of water temperature.During the red tide,the water temperature ranged from 17.45 ℃ to 24.00 ℃,with an average of 20.75℃.The duration of Prorocentrum donghaiense red tide had a significant positive correlation with the increase of water temperature 3d before the occurrence,and a significant negative correlation with the average water temperature during the red tide;at the same time,the algae density and SST during the red tide had a significant negative correlation.Within a certain temperature range,lower temperature seems to be more conducive to the maintenance of higher density and longer duration of Prorocentrum donghaiense red tide..