春、夏季秦皇岛海域超微型浮游植物

2017年6月和8月，通过对秦皇岛海域的超微型浮游植物进行现场调查和流式细胞仪分析，发现了聚球藻(Synechococcus)和超微型真核藻类(picoeukaryotes)两大类群，其中聚球藻又分为聚球藻Ⅰ和聚球藻Ⅱ两个亚群。调研期间，正处于秦皇岛海域褐潮高发期。通过分析超微型浮游植物细胞丰度、碳生物量及分布特点，研究了秦皇岛海域在褐潮高发期超微型浮游植物分布及相关环境因子影响。结果表明，6月份超微型真核藻、聚球藻Ⅰ和聚球藻Ⅱ平均丰度分别为1.14×104 个/mL、4.02×104 个/mL和1.04×104 个/mL，碳生物量均值分别为27.22 μg/L、8.49 μg/L和2.27 μg/L；在8月份超微型真核藻、聚球藻Ⅰ和聚球藻Ⅱ平均丰度分别为3.27×103 个/mL、5.79×104 个/mL 和2.58×104个/mL，碳生物量均值分别为6.35 μg/L、13.41 μg/L和5.83 μg/L。超微型真核藻、聚球藻Ⅰ和聚球藻Ⅱ在6月份和8月份表现出不同的分布特征。超微型真核藻的细胞丰度从6月到8月明显降低一个数量级，说明8月份过高的水体温度与低浓度的营养物质等因素限制了超微型真核藻中褐潮种的生长。聚球藻Ⅰ和聚球藻Ⅱ细胞丰度在6月份呈现从河口到近岸逐渐升高的分布趋势，而超微型真核藻呈现下降的分布趋势。与6月份聚球藻Ⅰ和聚球藻Ⅱ细胞丰度分布相反，超微型真核藻和聚球藻Ⅰ细胞丰度则在8月份呈现从河口到近岸逐渐降低的分布趋势，而聚球藻Ⅱ细胞丰度的区域分布趋势不明显，主要分布在水体表层。通过对超微型真核藻、聚球藻Ⅰ和聚球藻Ⅱ与环境因子相关性分析表明，6月份硝酸盐与铵盐是聚球藻Ⅰ细胞生长的主要控制因子，而聚球藻Ⅱ与环境因子没有明显的相关性，超微型真核藻的细胞丰度与硅酸盐浓度呈正相关。在8月份，超微型真核藻细胞的生长受到多种环境因子(硝酸盐、亚硝酸盐、硅酸盐、磷酸盐、温度以及光照)的共同作用的影响，聚球藻Ⅰ细胞丰度与硝酸盐呈正相关，温度与光照则是影响聚球藻Ⅱ细胞分布的关键因素。

Picophytoplankton from Qinhuangdao coastal waters in spring and summer

During June and August 2017, two picophytoplankton groups including Synechococcus and picoeukaryotes were found in Qinhuangdao coastal waters, and Synechococcus could be divided into two sub-groups of Synechococcus Ⅰ and Synechococcus Ⅱ. During the sampling period, it was during high-incidence period of brown tide. To investigate the effects of the related environmental factors on the spatical distributions of picophytoplankton in Qinhuangdao coastal waters, we compared their cell abundances, carbon biomass and distributional characteristics during the brown tide. The results showed that the average abundances of picoeukaryotes, Synechococcus Ⅰ and Synechococcus Ⅱ in June were 1.14×104 cell/mL, 4.02×104 cell/mL and 1.04×104 cell/mL, respectively, and the average carbon biomass were 27.22 μg/L, 8.49 μg/L and 2.27 μg/L respectively. While in August, the average abundances of picoeukaryotes, Synechococcus Ⅰ and Synechococcus Ⅱ were 3.27×103 cell/mL, 5.79×104 cell/mL and 2.58×104 cell/mL, and the average carbon biomass were 6.35 μg/L, 13.41 μg/L and 5.83 μg/L respectively. The abundance of picoeukaryotes decreased by an order of magnitude from June to August, indicating that the growth of dominant species of brown tide was limited by high temperature and low nutrients in August. Picoeukaryotes, Synechococcus Ⅰ and Synechococcus Ⅱ showed different distributions in June and August. Synechococcus Ⅰ and Synechococcus Ⅱ increased gradually from estuary to nearshore in June, while picoeukaryotes showed a downward trend. Inversely, picoeukaryotes and Synechococcus Ⅰ showed a decreasing trend from estuary to nearshore in August, and the distribution character of Synechococcus Ⅱ abundance was not obvious in Qinhuangdao coastal waters, mainly existing in surface layer. The results of correlation analysis with related environmental factors indicated that nitrate and ammonium salt were the key factor in controlling the growth of Synechococcus Ⅰ in June while picoeukaryotes was limited by the silicate concentration. There was no significant correlation between Synechococcus Ⅱ and environment factors in June. In August, the growth of picoeukaryotes was affected by a variety of environmental factors, such as nitrate, nitrite, silicate, phosphate, temperature and light while Synechococcus Ⅰ was positively correlated with nitrate. The temperature and light were the key factors affecting the Synechococcus Ⅱ distribution in August.