Alexandrium blooms in the northwest area of the Bohai Sea(Qinhuangdao coastal area),China,produce large amounts of toxins that could be enriched in shellfish and consequently harm human bodies.To understand the succession of the phytoplankton community structure during Alexandrium bloom events in the northwest area of the Bohai Sea off Qinhuangdao from April 2 to May 7,2019,microscopy observations and high-performance chromatography(HPLC)-pigment analysis were performed.Sixty species of phytoplankton were identified,mainly diatoms and dinoflagellates.The abundance of Alexandrium reached the maximum on April 16(3.3×103 cells/L).HPLC-pigment CHEMTAX analysis showed that the phytoplankton community was composed mainly of diatoms,dinoflagellates,prasinophytes,and cryptophytes.Diatoms were the main contributor to the total Chl-a pool.There was a downward trend for the proportion of diatom biomass to the total Chl-a pool,followed by an upward trend.The proportion of dinoflagellate biomass showed the opposite trend,whereas that of the prasinophyte biomass presented an obvious increasing trend.Temperature,nutrients,and nutrient structures were the main factors on the distribution of different phytoplankton groups in the study area as shown in the redundancy analysis.This work illustrates the succession of phytoplankton community structures during Alexandrium blooms and provided a theoretical basis for studies on the mechanism underlying the outbreak of harmful algal blooms in sea areas.

School of Marine Technology and Geomaties,Jiangsu Ocean University,Lianyungang 222005,China;School of Ocean,Yantai University,Yantai 264005,China;Key Laboratory of Testing and Evaluation for Aquatic Product Safety and Quality,Ministry of Agriculture and Rural Affairs,Yellow Sea Fisheries Research Institute,Chinese Academy of Fishery Sciences,Qingdao 266071,China

[1]Yixuan XIE;Renye DING;Daojun ZHA;Yu LI;Guowang YAN;Yaya ZHANG;Haiyan WU;Guanchao ZHENG;Zhijun TAN;Tao JIANG-.Phytoplankton community dynamics during Alexandrium blooms in 2019 off the Qinhuangdao coast,Bohai Sea,China)[J].海洋湖沼学报（英文版）,2022(06):2416-2429

Qinhuangdao,prasinophytes,cryptophytes,prasinophyte

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