The gas hydrate deposit in Shenhu, Northern South China Sea (NSCS) was one of the main sources for deep-water hydrocarbon and hydrate. Based on field observations on a gas hydrate deposit among 20 × 20 km² at Shenhu of the northern continental slope of SCS in May (before drilling) and September (after drilling) in 2015, environmental baseline, comparisons of phytoplankton community, biomass and potential environmental drivers were studied. Results indicated the deposit area was a typical low-nutrients low-chlorophyll a (LNLC) environment, characterized by low phytoplankton abundance and diversity. The maximum of abundance and Chl a were fixed at 75 m before and after drilling, but their decrease was larger from 0.53 mg/m³ to 0.40 mg/m³ and 1218 cells/L to 843 cells/L with non-significance found, respectively. After drilling, ammonium decreased significantly (2.13 μmol/L to 0.20 μmol/L), along with nitrite, salinity and dissolved methane, while pH increased significantly (8.10–8.19). Phytoplankton community was composed of 97 taxa of 47 genera in 4 classes, including diatoms, dinoflagellates, cyanobacteria and chrysophyte. The dominant diatom species before and after drilling remained the same, which included Navicula parva, Pseudonitzchia circumpora and Fragilariopsis doliolus. Dominant dinoflagellates shifted from the cosmopolitan Scrippsiella trochoidea to the warm-water adapted Gyrodinium flavum. The diazotrophic cyanobacterium Trichodesmium thiebaultii become more apparent in higher occurrence and abundance due to alleviation from lower-pH inhibition on nitrogen fixation. Redundancy analysis and Spearman correlation analysis revealed that the dominant species and Chl a were mainly associated to pH, DO and nitrite. The X-bar control chart indicated that a constrained maximum problem of phytoplankton abundance in particular layers (50 m, 75 m and 100 m). We clearly documented in the revisited stations (SH3–W2 and SH3–W14), the decrease of abundance and Chl a and the increase of pH and DO were evident in each sampling layer accompanied with lower dissolved methane associated to in situ anoxic or aerobic microniches activities, but the correlations with dissolved methane were not strong.

南海北部神湖（NSCS）的天然气水合物矿床是深水碳氢化合物和水合物的主要来源之一。基于 2015年5月（钻探前）和9月（钻探后）南海北部陆坡神户20×20 km ²之间天然气水合物沉积，环境基线，浮游植物群落，生物量和潜力的比较研究了环境驱动因素。结果表明，该沉积物区域是典型的低营养低叶绿素a（LNLC）环境，其特征是浮游植物的丰度和多样性低。丰度和叶绿素的最大一个被固定在75米之前和钻孔后，但其减少是从0.53毫克/米更大³分别为0.40 mg / m ³和1218细胞/ L至843细胞/ L，无显着性。钻井后，铵盐，亚硝酸盐，盐度和溶解的甲烷显着下降（2.13μmol/ L至0.20μmol/ L），而pH显着上升（8.10–8.19）。浮游植物群落由47个属的97个分类单元组成，分为4类，包括硅藻，鞭毛藻，蓝藻和金藻。之前和钻孔后的优势硅藻种基本保持一致，其中包括舟形麦穗鱼，Pseudonitzchia circumpora和Fragilariopsis doliolus。优势鞭毛虫从国际化的Stropsiella trochoidea转移到适应温水的Gyrodinium flavum。重氮营养性蓝藻Trichodesmium thiebaultii在较高的发生率和丰度下变得更加明显，这是由于较低的pH值对固氮的抑制作用减轻了。冗余分析和Spearman相关分析表明，优势种和叶绿素一个主要关联到pH，DO和亚硝酸盐。X线控制图表明，在特定层（50 m，75 m和100 m）中，浮游植物丰度受到限制的最大问题。我们明确记载在重新站（SH3-W2和SH3-W14），丰度的减少和叶绿素一个和pH和DO的增加而明显，在伴随有相关联的较低的溶解的甲烷每个采样层原位 缺氧或有氧微生态系统活动，但与溶解甲烷的相关性不强。