Temporal And Spatial Distribution Of Phytoplankton Community Structure In Day A Bay And Its Adjacent Waters From November 2017 To July 2018

Phytoplankton are important primary producers in the food web,and changes in the phytoplankton community structure affect marine ecosystem.Therefore,the study of phytoplankton community structure is fundamental for studying marine ecosystems.Daya Bay had been characterized by excellent seawater quality,abundant biological resources and diversified ecological environment.It is an important bay in the northeast of the South China Sea.However,since the 1980s,with the expansion of industry,tourism,and marine aquaculture along the Daya Bay,the quality of the seawater has deteriorated due to pollution,eutrophication and temperature rise due to global warming and nuclear power plant's cooling water discharge.In the 1990s,the number of phytoplankton species in Daya Bay declined significantly,indicating that human activities have caused negative impacts on the marine ecosystem of Daya Bay.In recent years,the Daya Bay Area authority has established a marine ecological red line area,formulated an environmental governance mechanism,and strengthened the protection of the marine ecosystem.However,the management of resource exploitation and environmental protection in this bay suffers from the lack of systematic information of ecological parameters such as spatial and temporal distribution of phytoplankton species and abundance.In this study,we investigated the distribution and seasonal variation characteristics of phytoplankton community structure in Daya Bay and its adjacent waters from November 2017 to July 2018.The main goal was to provide more comprehensive ecological background information for the planning and development of Daya Bay.The main research methods and results of this study are as follows:1?Using traditional morphological analysis methods,I identified and enumerated phytoplankton from samples fixed by Lugol's solution,and analyzed the spatial and seasonal distribution characteristics of phytoplankton richness,abundance,dominant species and diversity indices in each of the four seasons.I also analyzed the correlation between dominant species and environmental factors.The results showed that the dominant groups of phytoplankton in Daya Bay and its adjacent waters were diatoms(Bacillariophyceae),followed by dinoflagellates(Dinophyceae).The number of phytoplankton species measured from November 2017 to July 2018 increased significantly compared to recent historical data,and was close to that in 1987.Diatoms were most abundant throughout the four seasons,and the highest abundance occurred in summer,reaching 1.25 × 109 cells/m3.The highest number of dominant species occurred in autumn,dominated by diatoms,and the lowest was observed in spring,also dominated by diatoms.The highest biodiversity occurred in autumn,and the lowest was observed in summer.Dinoflagellates contributed the greatest number of dominant species in the spring community.2.I analyzed environmental DNA samples through high-throughput sequencing.To explore whether high-throughput sequencing can replace traditional morphological identification,we compared high-throughput sequencing results with traditional morphological results.In this study,high-throughput sequencing led to detection of small-sized phytoplankton,such as cryptophyceae,that were missed by traditional microscopic observation.When analyzing the composition of phytoplankton community structure,high-throughput sequencing and traditional morphology both detected the major phytoplankton groups.However,due to the inadequacy of speciesannotated DNA sequence database,it is difficult to accurately classify the dominant species to the species level by high-throughput sequencing.Therefore,when studying the structural characteristics of phytoplankton communities in seawater,a combination of high-throughput sequencing and traditional morphological identification may be the best choice of methodology.