Study Of Temporal-spatial Variations Of Offshore Phytoplankton And Their Environmental Response In The North Of Yancheng

In order to make up for the lack of previous understanding of phytoplankton in the northern offshore area of yancheng and identify the key factors influencing the change of phytoplankton community structure in this area,seasonal investigations on phytoplankton community structure and 14 water quality indicators of the offshore area were investigated and analyzed in July,November,2018 and January,April,2019.An analysis of Shannon Winner index,species richness index?Margalef index?and evenness index?Pielou index?show that the phytoplankton diversity is lower in summer and spring,and higher in autumn and winter,among them there were low values in the middle part of the survey area in summer and spring.A total of 135species belonging to 6 phyla were detected,and the abundance of phytoplankton is summer>autumn>spring>winter.In summer,the abundance of phytoplankton in the far shore was higher than the abundance of phytoplankton in the near shore,and the abundance of phytoplankton in the outer part of the estuary was higher than the the abundance of phytoplankton in the rest part.There was no obvious spatial distribution pattern in the remaining three seasons.Using the methods of multidimensional scaling analysis?MDS?,analysis of similarities?ANOSIM?analysis and the percentage similarity analysis?SIMPER?to analyze the differences in phytoplankton community structure,the greatest differences in community structure were found between summer and autumn,winter and spring;autumn and spring come next,the community structure difference between autumn and winter&winter and spring is smaller.The main species that cause seasonal differences are Skeletonema costatum,Melosira sulcate and Coscinodiscus jonesianus.Finally,the relationships between phytoplankton community and environmental factors were analyzed by Person correlation and redundancy analysis?RDA?.The results show that the total biomass of phytoplankton had a strong response to environmental factors such as water temperature,pH,salinity,suspended matter,BOD₅,COD,nitrate and phosphate.Redundancy analysis?RDA?show that the response relationship of environmental factors to each dominant specie was different,which might be due to the differences in energy utilization and nutrient uptake of algae with different physiological characteristics.