北部湾首次记录到的大规模夜光藻赤潮期间浮游植物与细菌群落分析

Analysis of phytoplankton and bacterial community during the first recorded massive Noctiluca scintillans bloom in the Beibu Gulf,China

北部湾位于南海西北部,最近30年赤潮暴发频率、持续时间和范围正经历显著增长。为了了解北部湾大规模夜光藻赤潮期间的浮游植物和细菌群落特征,于2021年2月21日在涠洲岛西部首次大规模夜光藻暴发海域采集海水样品,对环境因子、浮游植物和细菌群落进行了研究。结果表明:该海域水质符合一类海水水质标准,主要为绝对P限制状态,结合近年来其他研究指出的非赤潮期间,涠洲岛邻近及北部湾中部海域为贫营养及主要为P限制,可推断本次夜光藻赤潮属于一次非富营养化下发生的赤潮。海水中共鉴定出浮游植物2门5属5种,其中夜光藻(Noctiluca scintillans)为绝对优势种,其细胞密度为2.00×10^(3)~3.75×10^(3)cells/L。结合现场水色,可确定本次赤潮生物为红色异养型夜光藻。系统发育和遗传距离分析则表明本次赤潮原因种属于我国沿海常见的夜光藻株系。对海水样品细菌16S rRNA基因V3-V4区高通量测序发现海水细菌群落操作分类单元(OTU)数量为294~414,以α-变形菌纲(Alphaproteobacteria)和γ-变形菌纲(Gammaproteobacteria)为优势菌群;细菌群落结构受COD、DO、DIN、PO_(4)^(3-)-P、N/P多种环境因子的影响,其中COD为主要影响因子。研究结果可为明确北部湾大规模夜光藻赤潮期间的环境特征、微生物组成及海洋生态保护提供科学依据。

Beibu Gulf is located in the northwestern part of the South China Sea and is experiencing a significant in-crease in the frequency,duration and extent of harmful algal blooms(HABs)outbreaks in the last 30 years.To char-acterize phytoplankton and bacterial communities during the massive Noctiluca scintillans bloom in the Beibu Gulf,seawater samples were collected from the area of a massive N.scintillans outbreak west from Weizhou Island on February 21,2021,and environmental factors,along with phytoplankton and bacterial communities were analyzed.The results showed that the sea water quality of this area met the standards of Chinese Class I seawater quality,mainly in the absolute phosphate limit state.In recent years,other studies reported low nutrient content and limited phosphorus in waters adjacent to Weizhou Island and in the central part of Beibu Gulf during the non-harmful algal bloom(HAB)period.Therefore,N.scintillans bloom investigated in this study belonged to a non-eutrophication HAB event.Two phyla,five genera,and five species of phytoplankton were identified in seawater,among which N.scintillans was the absolute dominant species,with a cell density of 2.00×10^(3)–3.75×10^(3)cells/L.The red discolora-tion of the sea water was caused by the red heterotrophic N.scintillans.Both phylogenetic and genetic distance ana-lyses demonstrated that the causative N.scintillans in the Beibu Gulf was similar to N.scintillans along the coast of China.High-throughput sequencing of the V3–V4 region of the 16S rRNA gene in seawater samples revealed that the number of OTUs(operational taxonomic units)in bacterial community ranged from 294 to 414,with Alphapro-teobacteria and Gammaproteobacteria as the dominant groups.The bacterial community structure was affected by PO3-4various environmental factors,including COD,DO,DIN,PO_(4)^(3-)-P,and N/P,among which COD was predominant.This research provides new insights into the environmental characteristics and microbial composition of sea water during a massive N.scintillans bloom and will aid bloom management in the Beibu Gulf.