Phaeocystis globosa is an important member of the plankton community and was considered to be a typical bloom-forming algae. Its life cycle is variable, comprising both solitary and colony cells. The growth process of P. globosa is vulnerable to UV-B radiation. However, the influence of UV-B on photosynthetic activity and the resulting programmed cell death (PCD) process is not entirely understood. Our findings demonstrated that Fv/Fm, rETRmax, Y(II) and α of solitary and colony cells were significantly decreased after UV-B treatment (p < 0.05). The colony cells showed a lower damage rate and higher repair rate than solitary cells (p < 0.05), suggesting that colony cells have better UV-B radiation resistance. After UV-B radiation, we found the characteristic markers of PCD-phosphatidylserine (PS) externalization and DNA fragmentation were discovered in the two cell morphologies, with increased caspase-3-like activity, proving the onset of PCD. In addition, the reactive oxygen species (ROS) content and antioxidant enzyme activities were examined. The results showed that, the ROS content went up, the solitary cells were significantly greater than colony cells under UV-B radiation (p < 0.001). In addition, the superoxide dismutase (SOD) and catalase (CAT) activities increased, and solitary cells always had significantly higher activity than colony cells (p < 0.05), but the changing trend in ROS content did not match the changes in CAT and SOD activities. This may have been due to the necrosis of solitary cells. The findings show that, besides PCD, solitary cells also developed necrosis under UV-B radiation. This study provides evidence that different morphological cells of marine microalgae present different reactions to UV-B radiation. It helps to further improve the knowledge of the environmental adaptation mechanism of P. globosa.

The Qinzhou Bay, a typical semi-enclosed bay, is facing environmental pressure from local fast-growing industrial and aquacultural development. Dominant species of phytoplankton community (based on microscopic examination) show a trend of miniaturization, while pico-phytoplankton (based on CHEMTAX analysis) is widely distributed in Qinzhou Bay. However, most previous investigations of phytoplankton community based on microscopic method that undetected small-sized cell (< 3 μm), and limited by scarce studies on CHEMTAX analysis, the long-term dynamic data of small-size phytoplankton are lacking in Qinzhou Bay. It is recognized that combining microscopic examination with CHEMTAX analysis could provide a good taxonomic reliability for large cells and valuable information about small-size groups. In this study, microscopic examination and High Performance Liquid Chromatography (HPLC)-CHEMTAX analysis were employed to characterize the spatiotemporal variability of the phytoplankton community structure in Qinzhou Bay in winter and summer of 2021. The results of microscopic observations showed that the phytoplankton community was characterized by diatoms and dinoflagellates mainly. Diatoms dominated in both seasons, of which Skeletonema costatum bloom occurred in the summer. CHEMTAX analysis not only agreed well with microscopy data for diatoms and dinoflagellates, but also helped identification of other small-sized flagellates and cyanobacteria that hard to observe by microscope. The results of CHEMTAX analysis found that diatoms, prasinophytes and cryptophytes co-dominated the total chlorophyll a in winter while diatoms became the dominant group in summer. In addition, our results indicate that the proportion of small-sized flagellates has increased in the past decade in Qinzhou Bay, especially for cryptophytes. Temperature, nutrient availability, and selective grazing of oyster affected the succession of phytoplankton community from co-dominance of diatoms and flagellates in winter to absolute diatoms dominance in summer. The distribution of prasinophytes and cryptophytes on a spatial scale were related to the location of shellfish culture area and estuary, respectively, rather than by nutrients. Eutrophication, selective grazing of oyster and warming were the driving factors of long-term changes in phytoplankton composition in Qinzhou Bay. This study enhanced our understanding of entire phytoplankton community dynamics and its relationship with environmental factors in Qinzhou Bay.

广西北部湾近岸海域虽常年为磷限制状态,但球形棕囊藻(Phaeocystis Globosa)赤潮灾害频繁发生.球形棕囊藻暴发时主要以囊体形式存在,赤潮衰退后,囊体破裂产生大量的透明胞外聚合颗粒物(Transparent Exopolymer Particles,TEP),在海洋动力作用下形成高碳、高黏性泡沫,影响渔业和核电取水安全.本文通过设置氮磷比为32∶1和64∶1的半连续培养实验,探讨磷限制对球形棕囊藻的生长,以及透明胞外聚合颗粒物产量的影响.结果表明:在氮磷比为32∶1和64∶1的磷限制条件下,球形棕囊藻的细胞密度、叶绿素a浓度、囊体密度及囊体表面细胞数,在培养的后半期都受到了抑制.与控制组相比,两个磷限制的处理组在囊体直径上并没有表现出显著的差异(显著性水平p＞0.05).在氮磷比为32∶1的条件下,球形棕囊藻的TEP生产量与控制组相比没有显著差异(p＞0.05),在氮磷比为64∶1的条件下,TEP的生产量显著降低(p＜0.05),磷限制程度的加剧对球形棕囊藻细胞分泌TEP产生影响.研究结果为进一步研究环境胁迫下球形棕囊藻TEP形成机制提供了依据.

球形棕囊藻(Phaeocystis globosa)藻华频繁暴发,不仅会危害海洋生态系统和渔业生产安全,还会堵塞核电站冷源取水系统产生严重安全隐患.球形棕囊藻藻华的暴发有明显的季节性特征,本研究采用梯度升温降温实验,研究不同温度(高温、低温)条件下球形棕囊藻的生理生化响应及温度胁迫诱导的细胞程序性死亡(Programmed Cell Death,PCD)过程.结果显示:低温胁迫抑制球形棕囊藻细胞的正常生长繁殖,但不会激活其进入PCD响应;高温胁迫使球形棕囊藻出现氧化应激,从而导致其发生PCD响应,超氧化物歧化酶(SOD)、过氧化氢酶(CAT)活性显著提高,半胱氨酸天冬氨酸蛋白酶-3(Caspase-3)被激活后球形棕囊藻细胞出现An-nexin V-FITC阳性反应.环境胁迫使球形棕囊藻细胞产生氧化应激,抗氧化酶活性快速升高,并激活Caspase-3使藻细胞发生PCD响应,表现出细胞磷脂酰丝氨酸(PS)外翻、细胞收缩和质膜从细胞壁分离等特征.本研究可为深入探讨球形棕囊藻藻华的生消机制与防治赤潮灾害提供一定的理论基础.

为了研究钦州湾外湾海域浮游植物群落分布特征,于2021年1月(冬季)在该海域进行综合调查.研究应用高效液相色谱(HPLC)技术分析表层水的光合色素组成,进而使用CHEMTAX软件估算浮游植物的群落结构.调查结果表明,调查海域浮游植物的优势类群为硅藻,其后依次为隐藻和青绿藻,它们分别占据了浮游植物总生物量的62.29％、20.25％和9.77％.从粒级结构上看,小型浮游植物(主要为硅藻)的贡献率为39.25％,粒径小于20μm的浮游植物贡献率为60.75％;硅藻的细胞粒径范围较广,而隐藻、甲藻和蓝藻的细胞粒径多在20μm以下.在空间分布上,硅藻的生物量由近岸向远岸海域逐渐升高,隐藻和青绿藻的分布则相反;微型和微微型浮游植物在盐度低、营养盐含量较高的近岸区占优势,小型浮游植物的生物量则由近岸向高盐度、低营养盐的远岸海域逐渐增大.浮游植物类群的空间分布特征与核电站温排水、盐度、潮流、营养盐以及贝类养殖等环境因素关系密切.

Phaeocystis globosa (P. globosa) often colonizes and produces mucus, which may cause massive blooms in coastal areas. To understand mechanism of the growth and the impact factors for better control of the bloom, we conducted a laboratory experiment on the effect of nitrogen (N) or phosphorus (P) limitation on the cell growth, production of exopolysaccharide (EPS), and transparent exopolymeric particles (TEP) of P. globosa. Results show no obvious differences in the N-and/or P-limitation in TEP production, polysaccharide secretion, and colony growth of P. globosa. Particularly in the death phase of the algae growth, the TEP production level in the experiment differed significantly, and was higher in the P-limitation group than that in the N-limitation group; additionally, the P-limitation group produced a relatively higher amount of EPS than N-limitation group, with greater cellular chlorophyll -a content, and in greater photosynthetic reaction rate of P. globosa cells, than those of the N-limitation group. However, under N-limited conditions, the algae colony survived longer. Under P-limited condition, P. globosa cells spend the photosynthesis-produced substances and energy for the secretion of extra -cellular substances but for cell reproduction, which was indicated by P. globosa cell growth and carbon content ratio between TEP and biomass.

球形棕囊藻(Phaeocystis globosa)是我国北部湾海域主要的有害藻华原因种,囊体的生长是藻华发生和持续的关键.为了研究在富营养化日趋严重的钦州湾海域中营养盐输入对球形棕囊藻藻华形成的影响,采集钦州湾含球形棕囊藻的表层海水进行了添加不同营养盐的室内培养实验.根据钦州湾历史调查数据,进行了不同营养盐、不同氮磷比和不同添加方式的培养.结果表明,同时添加氮和磷显著促进浮游植物的生长,球形棕囊藻囊体继浮游植物细胞密度高峰期后大量形成.一次性添加磷对囊体生长的刺激作用较添加氮时强,丰度最高可达4.8×103 colonies·L–1,囊体平均直径为(115±84)μm,且具有较高囊体细胞密度,但囊体衰退较快.单独添加氮时,囊体细胞分布稀疏,囊体数量及直径皆较低.每天添加磷的方式相比一次性添加更有利于囊体丰度的维持.总体上,磷营养的添加能刺激囊体数量、囊体细胞数和囊体直径的生长.在具有较高N/P比值的钦州湾,应加强磷的排放管理,避免突发性磷污染对球形棕囊藻囊体生长的刺激作用.

球形棕囊藻(Phaeocystis globosa)在囊体结构形成的过程中可以产生大量的溶解有机物(Dissolved Organic Carbon,DOC),随之带来的水体黏度变化对桡足类摄食活动产生的影响仍然有争议.为揭示球形棕囊藻赤潮带来的海域水体黏度增加对柱形宽水蚤(Temora stylifera)摄食的影响,利用不同浓度的球形棕囊藻培养液和海藻酸钠溶液设置黏度摄食实验,测定柱形宽水蚤对牟氏角毛藻(Chaetoceros muelleri)的摄食率,并对球形棕囊藻的生长过程中胞外颗粒聚合物(Transparent Exopolymer Particles,TEP)含量和培养液的黏度进行分析.研究结果表明,在球形棕囊藻的生长过程中,TEP含量和水体黏度均表现出上升趋势,分别为(2.63±3.72)-(677.33±34.92)μg/liter xanthan equiv.和(2.96±0.58)-(4.92±0.19)Mpa·s,且球形棕囊藻的游离细胞丰度、囊体丰度和囊体直径与TEP含量、黏度均呈显著正相关关系.在球形棕囊藻培养液和海藻酸钠溶液摄食实验组中,黏度高、低规格组的摄食率和滤水率均呈显著差异,低黏度组的摄食率和滤水率高于高黏度组的(P<0.05).推测柱形宽水蚤的摄食率受到水体黏度的抑制.