Temporal And Spatial Distribution Of Phytoplankton In The East China Sea Based On Remote Sensing Data And Its Relationship With Environmental Factors

The East China Sea(ESC)is China's largest shelf edge of the sea,it has a lot of water along the coast.The intertidal sea water system and the intermittent water convergence form a unique marine physical environment,which is beneficial to the growth of phytoplankton.Phytoplankton is commonly found in various water bodies and is an indicator of water quality.Scholars use chlorophyll a concentration to characterize phytoplankton biomass.In the two methods of using chlorophyll a concentration to monitor the biomass of phytoplankton,the remote sensing method has the advantages of strong timeliness,large amount of data and less input.Many researchers have been concerned about the characteristics of phytoplankton blooms in the North Atlantic Ocean;however,there are few relevant studies in this region.As biological indicators of water quality,information regarding temporal and spatial distributions of phytoplankton biomass and growth cycles,as well as modifications caused by climate change is important for understanding the ecology of the ECS.It is important to give a clear description of the long-term ecological changes in the East China Sea in the representative ecological regions such as the Yangtze River Estuary and the Nanji Islands.The present study selected nine regions with the same area at different geographical locations,latitudes,and ecological characteristics,and applied chlorophyll a(Chl-a)data and environmental data(sea surface temperature(SST),wind speed(WS),photosynthetically active radiation(PAR))from remote sensing satellite to analyze the spatial-temporal variation of phytoplankton biomass and phytoplankton bloom phenomenon in the ECS.In this paper,the temporal and spatial distribution of phytoplankton biomass in the ECS was studied using the chlorophyll a data from SeaViewing Wide Field-of-View Sensor and Moderate-Resolution Imaging Spectroradiometer during 1997–2015.We have demonstrated the consistency of the two different sensor data,and analyzed the temporal and spatial changes of phytoplankton in normal years according to the change of chlorophyll biomass in 19 years,in order to eliminate the effect of abnormal environmental factors on algal blooms.Then we obtained the Chl-a concentration data from the time of bloom initiation,bloom peak,bloom completion,and bloom duration in the ECS according to the Gaussian curve model.Finally,we performed partial correlation analysis by selecting monthly data for 2003-2015,and combined the results of partial correlation analysis to obtain the effect of environmental factors on phytoplankton growth.The results of this study are summarized as follows :1)The research demonstrated the distribution pattern at the spatial scale,with phytoplankton biomass in the open sea being lower than that in the offshore area.The areas with maximum biomass were the seas of the Yangtze River estuary,the Taizhou region,and the two areas closest to the Yellow Sea.The areas with minimum biomass were the seas of the Nanji Islands and Taiwan Strait.Therefore,the closer the phytoplankton was to the South China Sea,the lower was the biomass.Algal blooms occurred in the Yangtze River estuary from June to September and in the Yangtze River estuary in May and from July to August.Phytoplankton blooms at Taizhou Island occurred during May and July.The algae in the eastern part of the ECS occurred from November and December to January and February in the following year.Phytoplankton blooms at Nanji Islands concentrated during February and March,and the ECS algae in the northern areas between May and June.The biomass of phytoplankton in the northern outer seas was low and algae were mostly present in March and April.2)Temporal and spatial patterns of phytoplankton algae in the East China Sea: the time of bloom peak of phytoplankton algae in Taizhou Islands waters is the earliest.The algae in the eastern part of the ECS to reach the peak of the time is the latest.The time of bloom duration in these two regions lasted longer.The duration of phytoplankton algae in the northern PARt of the ECS and the Taiwan Strait is shorter.The number of days to reach the peak and the duration of algal blooms in coastal and remote areas of the Yangtze River estuary and the northern part of ESC,are basically the same.In general,the two sections of the research region,which were divided by the Nanji Islands,demonstrated the same regularity,the time taken for phytoplankton to reach peak biomass was prolonged,and the duration of the phytoplankton blooms increased from high latitudes to low latitudes.3)The SST of the ECS from north to south China increased in turn;WS in the Yangtze River estuary and Taizhou Islands is the weakest sea,in the northern part of the ECS is the middle,in the south is the strongest;PAR is basically the same in the central and northern parts of the ECS and is the largest in the south.The research showed that biomass distribution of phytoplankton in the ECS were as following: The areas with maximum are the Yangtze River estuary and the sea of Taizhou region,next are two areas close to northern.The areas with minimum are close to southern.The biomass of the phytoplankton coastal areas was higher than that in the open seas.There was a highly significant negative correlation between phytoplankton biomass and sea surface temperature in the northern part of the ECS,and there was a significant positive correlation between phytoplankton biomass and photosynthetic active radiation in the Yangtze River estuary.There was a highly significant negative correlation between phytoplankton biomass and wind speed in the out of the Yangtze River estuary,and negatively correlated with wind speed in Taizhou Islands.There was a significant negative correlation between phytoplankton biomass and sea surface temperature in the Nanji Islands,and a highly significant negative correlation with sea surface temperature in the coastal waters of Fujian,and there was a highly significant positive correlation with the sea surface temperature in the south of the ECS.The most relevant factors in the northern part of the ECS need to be analyzed by other environmental factors.