Spatial and temporal variation in community composition and photosynthetic characteristics of phytoplankton in the upper Westerschelde estuary (Belgium,SW Netherlands)

Community composition, biomass and primary production of phytoplankton were studied in the east- ernmost section of the Westerschelde estuary in 1984. Photosynthetic characteristics were compared with distribution of some dominant phytoplankton species along a salinity gradient from 5 to 22 Spring phytoplankton, with Cyclotella meneghiniana (freshwater) and Skeletonema costatum (marine) as the dominant species grew faster than summer phytoplankton. In summer, biomass achieved its maximum, due to the riverine Scenedesmus species and the marine diatoms Thalassiosira levanderi and Ditylum brightwellii, as dominants. Growth conditions were more favourable to phytoplankton communities above 15%, than below this salinity. The data were compared with previous studies (1972) of species composition in the area.     

石油烃污染对海洋浮游植物群落的短期毒性效应

海上溢油和船舶含油废水排放等石油污染给海洋生态环境带来严峻考验。为了解石油污染对海洋浮游植物的短期群落效应, 于实验室对采自浙江省乐清湾海域的四季浮游植物进行了14天的微宇宙实验研究。通过测定不同浓度原油水溶性成分(water accommodated fraction, WAF)胁迫下浮游植物群落各种类的细胞密度, 发现原油WAF对浮游植物群落的种类数、多样性、均匀度和优势种组成及优势度均有极显著影响。原油污染组的种类数均低于对照组, 多样性指数也总体上低于对照组, 但均匀度指数无明显规律。WAF对各季节浮游植物群落优势种的影响存在季节、浓度梯度和种类差异: 1)在高浓度WAF (≥2.28 mg·L^-1)胁迫下, 各季节浮游植物群落中中肋骨条藻(Skeletonema costatum)的优势度均呈升高趋势, 除秋季外, 长菱形藻(Nitzschia longissima)在其余季节的优势度均显著下降, 另外秋季实验中微小原甲藻(Prorocentrum minimum)的优势度呈先升高后下降的趋势, 秋冬季斜纹藻(Pleurosigma sp.)和念珠直链藻(Melosira moniliformis)的优势度呈下降趋势; 2)在低浓度WAF (≤1.16 mg·L^-1)胁迫下, 除秋季中肋骨条藻仍为绝对优势种外, 其余季节该种微藻的优势度均呈下降趋势, 春、夏季长菱形藻的优势度逐渐升高, 而冬季则是念珠直链藻的优势度不断增加。原油WAF影响下, 可能r策略种将逐渐取代k策略种, 导致浮游植物群落趋于小型化。     

Do phytoplankton communities evolve through a self-regulatory abundance–diversity relationship?

A small group of phytoplankton species that produce toxic or allelopathic chemicals has a significant effect on plankton dynamics in marine ecosystems. The species of non-toxic phytoplankton, which are large in number, are affected by the toxin-allelopathy of those species. By analysis of the abundance data of marine phytoplankton collected from the North-West coast of the Bay of Bengal, an empirical relationship between the abundance of the potential toxin-producing species and the species diversity of the non-toxic phytoplankton is formulated. A change-point analysis demonstrates that the diversity of non-toxic phytoplankton increases with the increase of toxic species up to a certain level. However, for a massive increase of the toxin-producing species the diversity of phytoplankton at species level reduces gradually. Following the results, a deterministic relationship between the abundance of toxic phytoplankton and the diversity of non-toxic phytoplankton is developed. The abundance-diversity relationship develops a unimodal pathway through which the abundance of toxic species regulates the diversity of phytoplankton. These results contribute to the current understanding of the coexistence and biodiversity of phytoplankton, the top-down vs. bottom-up debate, and to that of abundance-diversity relationship in marine ecosystems.     

广西溢油海域的浮游植物跟踪监测与比对分析

针对广西涠洲岛海域的突发溢油事件,于2008年9月下旬进行了溢油海域浮游植物跟踪监测,并与历史资料比对,探讨溢油对浮游植物群落的影响。调查中,共记录4门106种,硅藻92种,甲藻12种,蓝藻1种,着色鞭毛藻1种,主要优势种为旋链角毛藻(Chaetoceros curvisetus)、菱形海线藻(Thalassionema nitzschioides)和洛氏角毛藻(Chaetoceros lorenzianus)。浮游植物种类多,站间差异小,分布均匀。浮游植物细胞密度高,平均2 645.32×10⁴cells·m^-3,密集中心位于涠洲岛西北部海域。优势种密度分布与浮游植物细胞密度分布态势基本一致。多样性指数(H')和均匀度(J')均较高,群落结构稳定。与国家海洋局同期调查资料及相关文献报道比对,表明溢油海域浮游植物种类组成无较大变化,细胞密度有较小降幅,密集中心不同,优势种变更明显,群落结构稳定,应重视溢油应急反应的迫切性。     

Identification of phytoplankton from flow cytometry data by using radial basis function neural networks.

We describe here the application of a type of artificial neural network, the Gaussian radial basis function (RBF) network, in the identification of a large number of phytoplankton strains from their 11-dimensional flow cytometric characteristics measured by the European Optical Plankton Analyser instrument. The effect of network parameters on optimization is examined. Optimized RBF networks recognized 34 species of marine and freshwater phytoplankton with 91. 5% success overall. The relative importance of each measured parameter in discriminating these data and the behavior of RBF networks in response to data from "novel" species (species not present in the training data) were analyzed.     

Consensus methods based on machine learning techniques for marine phytoplankton presence–absence prediction

We performed different consensus methods by combining binary classifiers, mostly machine learning classifiers, with the aim to test their capability as predictive tools for the presence–absence of marine phytoplankton species. The consensus methods were constructed by considering a combination of four methods (i.e., generalized linear models, random forests, boosting and support vector machines). Six different consensus methods were analyzed by taking into account six different ways of combining single-model predictions. Some of these methods are presented here for the first time. To evaluate the performance of the models, we considered eight phytoplankton species presence–absence data sets and data related to environmental variables. Some of the analyzed species are toxic, whereas others provoke water discoloration, which can cause alarm in the population. Besides the phytoplankton data sets, we tested the models on 10 well-known open access data sets. We evaluated the models' performances over a test sample. For most (72%) of the data sets, a consensus method was the method with the lowest classification error. In particular, a consensus method that weighted single-model predictions in accordance with single-model performances (weighted average prediction error — WA-PE model) was the one that presented the lowest classification error most of the time. For the phytoplankton species, the errors of the WA-PE model were between 10% for the species Akashiwo sanguinea and 38% for Dinophysis acuminata. This study provides novel approaches to improve the prediction accuracy in species distribution studies and, in particular, in those concerning marine phytoplankton species.     

Presence of free D-amino acids in microalgae

Several species of microalgae (phytoplankton), 4 species of freshwater algae and 4 species of marine diatoms, were cultured germ-free in the laboratory. The presence of free D-amino acids was verified in these species by a reversed-phase HPLC analysis. D-Aspartate was detected in all the microalgae examined, but D-alanine was only present in the marine diatoms. The D-amino acid content in Asterionella sp. of the marine diatoms increased from the exponential phase to the stationary phase and then decreased to the phase of decline.     

钦州湾春、夏季浮游植物群落特征及其与环境因子的关系

为了探究人类活动对钦州湾浮游植物群落的影响,分别于2013年3月和7月进行了两航次综合调查。采用聚类和典型对应分析法,分别对浮游植物群落及其与环境因子的关系进行了研究。结果表明春夏两季浮游植物共有3门45属115种,其中硅藻100种、甲藻14种、蓝藻1种。两季浮游植物生态类群分别以暖温带广布种和暖温带近岸种为主,季节性差异明显。典型对应分析表明,影响浮游植物分布的主要环境因子是悬浮物、pH、盐度和营养盐。受入海径流和外来水团等因子影响,钦州湾浮游植物群落在夏季更易聚为相似性群落,春季则呈斑块化分布。     

Phosphorus physiological ecology and molecular mechanisms in marine phytoplankton

Phosphorus (P) is an essential nutrient for marine phytoplankton and indeed all life forms. Current data show that P availability is growth‐limiting in certain marine systems and can impact algal species composition. Available P occurs in marine waters as dissolved inorganic phosphate (primarily orthophosphate [Pi]) or as a myriad of dissolved organic phosphorus (DOP) compounds. Despite numerous studies on P physiology and ecology and increasing research on genomics in marine phytoplankton, there have been few attempts to synthesize information from these different disciplines. This paper is aimed to integrate the physiological and molecular information on the acquisition, utilization, and storage of P in marine phytoplankton and the strategies used by these organisms to acclimate and adapt to variations in P availability. Where applicable, we attempt to identify gaps in our current knowledge that warrant further research and examine possible metabolic pathways that might occur in phytoplankton from well‐studied bacterial models. Physical and chemical limitations governing cellular P uptake are explored along with physiological and molecular mechanisms to adapt and acclimate to temporally and spatially varying P nutrient regimes. Topics covered include cellular Pi uptake and feedback regulation of uptake systems, enzymatic utilization of DOP, P acquisition by phagotrophy, P‐limitation of phytoplankton growth in oceanic and coastal waters, and the role of P‐limitation in regulating cell size and toxin levels in phytoplankton. Finally, we examine the role of P and other nutrients in the transition of phytoplankton communities from early succession species (diatoms) to late succession ones (e.g., dinoflagellates and haptophytes).     

全球气候变化下的海洋浮游植物多样性

理解全球气候变化对地球生态系统的影响是全世界广泛关注的问题, 而相比于陆地生态系统, 海洋生态系统对全球气候变化更为敏感。全球气候变化对海洋的影响主要表现在海洋暖化、海洋酸化、大洋环流系统的改变、海平面上升、紫外线辐射增强等方面。浮游植物是海洋生态系统最重要的初级生产者, 同时对海洋碳循环起到举足轻重的作用, 其对全球气候变化的响应主要体现在物种分布、初级生产力、群落演替、生物气候学等方面。具体表现在以下方面: 暖水种的分布范围在扩大, 冷水种分布范围在缩小; 浮游植物全球初级生产力降低; 浮游植物群落会向细胞体积更小的物种占优势的方向转变; 浮游植物水华发生的时间提前、强度增强; 一些有害物种水华的发生频率也会增加; 海洋表层海水的酸化会影响浮游植物特别是钙化类群的生长和群落多样性; 紫外辐射增强对浮游植物的生长起到抑制作用; 厄尔尼诺、拉尼娜、降水量的增加通常抑制浮游植物生长。浮游植物生长和分布的变化会体现在多样性的各个层面上。对于浮游植物在全球变化各种驱动因子下的生理生态学和长周期变动观测等是今后研究的重要方向, 也将为理解全球变化下的浮游植物-多样性-生态系统响应与反馈机制提供基本信息。     

长江口夏季浮游植物群落与环境因子的典范对应分析

于2004年8月28日至9月6日在长江口水域进行了水文、化学和生物的综合嵌套式外业调查,应用CANOCO4.0软件对获得的浮游植物物种数据和环境因子数据进行了典范对应分析(CCA),并作出了物种、样点分布与环境因子关系的二维排序图。结果表明,长江水入海所带来的泥沙及其形成的营养盐梯度差异是影响这一区域物种分布格局最重要的因素。根据环境因子与排序轴的相关系数,影响这一海区浮游植物分布的主要环境因子依次为透明度、硝酸盐和硅酸盐。主要浮游植物优势种中肋骨条藻(Skeletonema costatum)和细长翼鼻状藻(Proboscia alata f. gracillima)的分布和硝酸盐以及盐度、浊度密切相关,中肋骨条藻适合在低盐度高浊度高硝酸盐浓度的河口水域生存,而细长翼鼻状藻则分布于高盐度高透明度低硝酸盐浓度的开阔海。排序揭示了浮游植物物种对于生态环境的需求以及它们在不同资源维上的生态分化现象。     

Phytoplankton flora in the Warri/Forcados Estuary of southern Nigeria

The phytoplankton flora of the Warri/Forcados estuary varied from typical fresh and brackish water forms to purely distinct marine species. These were made up of members of the Bacillariophyta (about 80 species), Chlorophyta (over 90 species), Cyanophyta (16 species), Dinophyceae (10 species) and the Euglenophyta (8 species). The bulk of the species belonging to the Chlorophyta, Cyanophyta and the Euglenophyta were almost exclusively fresh-water in distribution, being limited to habitats of less than 0.5 salinity. Members of the Bacillariophyta were found in all habitats, occurring freely in freshwater, estuarine, and marine ecosystems. In all cases, no true examples of euryhalinity were recorded. The majority of dinoflagellates encountered, as well as a number of marine diatoms, manifested stenohaline peculiarities as they could not tolerate a wide salinity range.The overall influence of the periodic shift in salinity and some physico-chemical parameters along the stretch of the estuary brought about by strong tidal effects and the variable seasonal volume of water discharge or runoff on the pattern and limit of distribution of phytoplankton species is highlighted.     

Extending the phytoplankton tool kit for the UK Water Framework Directive: indicators of phytoplankton community structure

The Water Framework Directive (WFD) demands consideration of normative definitions for assessing ecological state of marine waters. For phytoplankton, ‘deviations from the ideal’ need to be considered for species composition and abundance, average biomass and the occurrence of blooms. A combination of phytoplankton metrics has been developed which, when considered in combination, should provide a confident assessment of the ecological state of each water body under assessment. The aim of this study was to evaluate phytoplankton community structure in different coastal and estuarine water bodies within England and Wales, and to contribute evidence towards the development of a community-based phytoplankton indicator. Influences of seasonality on the species assemblage were tested using a long-term data set available from a long-term monitoring site just offshore of Plymouth, UK. There is a substantive seasonal influence to the data, with a maximum of 10–14 common species (out of a potential 20) reoccurring within the same calendar month over a 10-year time span. Comparisons between reference and test water bodies give a range of common species of between 3 and 11 species within water type and season. A statistical and qualitative approach for comparing the most common species occurring between a reference and test site were tested for development of a WFD phytoplankton assessment tool. Overall, the results indicate that there are distinct phytoplankton assemblages over seasons which could form the basis of a community assessment metric. However, differences in boundary conditions are negligible between the different areas. There is evidence that community populations may be ubiquitous across marine water types in England and Wales, and development of generic seasonal lists across typologies could be appropriate in the further development of this tool.     

From mice to elephants: overturning the ‘one size fits all’ paradigm in marine plankton food chains

It is widely believed that consumer control is a weak regulator of marine phytoplankton communities. It remains unclear, however, why this should be the case when marine consumers routinely regulate their prey at higher trophic levels. One possibility is that the weak consumer control of phytoplankton communities results from the inability of field researchers to effectively account for consumer–prey trophic relationships operating at the scale of the plankton. We explored this issue by reviewing studies of trophic control in marine plankton. Experimental studies indicate that size is a critical determinant of feeding relationships among plankton. In sharp contrast, of the 51 field studies reviewed, 78% did not distinguish among the sizes or species of phytoplankton and their consumers, but instead assumed a general bulk phytoplankton–zooplankton trophic connection. Such an approach neglects the possibility that several trophic connections may separate the smallest phytoplankton (0.2 μm) from the larger zooplankton (~ 1000 μm), a remarkable size differential exceeding that between a mouse (~10 cm) and an elephant (~2500 cm). The size‐based approach we propose integrates theory, experiments and field observations and has the potential to greatly enhance our understanding of the causes and consequences of recently documented restructuring of plankton communities.     

安徽沱湖夏季浮游植物群落结构特征与环境因子关系

为了揭示沱湖浮游植物群落结构特征及其与水环境因子的关系,于2016年7月(夏季),对沱湖流域上游至下游11个采样点浮游植物种类组成、细胞丰度、生物量等进行调查研究。结果显示,沱湖共有浮游植物96种(含变种),隶属8门48属,其中绿藻门(Chlorophyta)和硅藻门(Bacillariophyta)种类最多,绿藻门有23属39种,占总种数的40.63%,硅藻门有7属20种,占总种数的20.83%;其次为裸藻门(Euglenophyta),有5属17种,占总种数的17.71%,蓝藻门(Cyanophyta) 8属14种,占14.58%;甲藻门(Pyrrophyta) 2属2种,隐藻门(Cryptophyta) 1属2种,各占总种数的2.08%,黄藻门(Xanthophyta)与金藻门(Chrysophyta)均有1属1种,均占总种数的1.04%。绿藻和硅藻类物种在沱湖浮游植物群落结构中处于优势地位,沱湖夏季浮游植物种类组成表现为绿藻-硅藻型。沱湖夏季浮游植物细胞丰度与生物量从上游到下游呈逐渐增加趋势,细胞丰度与生物量平均值分别为4.022×106cells/L与3.046 mg/L,蓝藻门和绿藻门类群为沱湖浮游植物细胞丰度主体,硅藻门和裸藻门类群为沱湖浮游植物生物量的主体;上游浮游植物多样性指数与均匀度指数均略高于下游采样点,沱湖水质呈β中污型-无污染型,上游水质优于下游水质。浮游植物群落结构与水环境因子的典型对应分析(CCA)结果表明,电导率、透明度、水深及pH值等环境因子与沱湖夏季浮游植物群落结构有较强的相关性。     

Cell-specific beta-N-acetylglucosaminidase activity in cultures and field populations of eukaryotic marine phytoplankton.

It is widely appreciated that eukaryotic marine phytoplankton can hydrolyze a variety of compounds within the dissolved organic matter (DOM) pool in marine environments. Herein, cultures and field populations of marine phytoplankton were assayed for beta-N-acetylglucosaminidase activity, a terminal enzyme of chitin degradation. A traditional bulk assay, which can assess hydrolytic rate, but is not cell-specific, was complemented with a cell-specific assay that images the activity associated with single cells using an enzyme labeled fluorescence (ELF) substrate. beta-N-acetylglucosaminidase activity was widespread across various taxa of marine phytoplankton, and activity was observed both under controlled culture conditions and in field populations. The number of cells with enzyme activity varied with the nutritional physiology of the test species in three of the 17 cultures tested. In these three cases the number of cells with activity in the low nutrient medium was higher than in nutrient replete medium. Taken together, these data suggest that a broad group of marine phytoplankton may be a relevant part of chitin-like DOM degradation and should be incorporated into conceptual models of chitin cycling in marine systems.     

Predictable ecological response to rising CO2 of a community of marine phytoplankton

Rising atmospheric CO₂ and ocean acidification are fundamentally altering conditions for life of all marine organisms, including phytoplankton. Differences in CO₂ related physiology between major phytoplankton taxa lead to differences in their ability to take up and utilize CO₂. These differences may cause predictable shifts in the composition of marine phytoplankton communities in response to rising atmospheric CO₂. We report an experiment in which seven species of marine phytoplankton, belonging to four major taxonomic groups (cyanobacteria, chlorophytes, diatoms, and coccolithophores), were grown at both ambient (500 μatm) and future (1,000 μatm) CO₂ levels. These phytoplankton were grown as individual species, as cultures of pairs of species and as a community assemblage of all seven species in two culture regimes (high‐nitrogen batch cultures and lower‐nitrogen semicontinuous cultures, although not under nitrogen limitation). All phytoplankton species tested in this study increased their growth rates under elevated CO₂ independent of the culture regime. We also find that, despite species‐specific variation in growth response to high CO₂, the identity of major taxonomic groups provides a good prediction of changes in population growth and competitive ability under high CO₂. The CO₂‐induced growth response is a good predictor of CO₂‐induced changes in competition (R² > .93) and community composition (R² > .73). This study suggests that it may be possible to infer how marine phytoplankton communities respond to rising CO₂ levels from the knowledge of the physiology of major taxonomic groups, but that these predictions may require further characterization of these traits across a diversity of growth conditions. These findings must be validated in the context of limitation by other nutrients. Also, in natural communities of phytoplankton, numerous other factors that may all respond to changes in CO2, including nitrogen fixation, grazing, and variation in the limiting resource will likely complicate this prediction.     

Cytotoxicity in the marine dinoflagellate Prorocentrum mexicanum from Brazil

The microscopic algae in the oceans are crucial food for filter feeding bivalve shellfish (oysters, mussels, scallops, clams, etc.) as well as for the larvae of commercially important crustaceans. Some species of microalgae have the capacity to produce potent toxins, such as saxitoxins and ciguatoxins, which may intoxicate humans. Among the marine phytoplankton, the dinoflagellates are the main toxin producers. Studies on the marine phytoplankton from the S?o Sebasti?o Channel, southeastern coast of Brazil, showed a great diversity of dinoflagellates. Some species were collected and cultured at the Marine Biology Center of the S?o Paulo University (USP). The polar (PEs) (aqueous) and apolar (AEs) (methylene chloride) extracts of the cultivated dinoflagellate species were tested on different stages of the sea urchin development, on mouse erythrocytes and on microfilaments organization in a neuroblastoma cell line. Prorocentrum mexicanum PE and AE induced cells anomalies and cell division inhibition of sea urchin eggs at EC50 of 78.75 microg/mL (95% CI from 32.56 to 190.50) and 22.50 microg/mL (95% CI from 2.96 to 170.80) respectively (n=3). Both AE and PE of P. mexicanum induced hemolysis with EC50 of 65.07 microg/mL (95% CI from 27.40 to 154.60) and 84.29 microg/mL (95% CI from 53.26 to 133.40 microg/mL), respectively. P. mexicanum PE was tested in immunofluorescence for actin filaments organization in neuroblastoma cultured cell.     

Temperature-influenced species competition in mass cultures of marine phytoplankton

Five marine phytoplankton species (Phaeodactylum tricornutum, Thalassiosira pseudonana, Skeletonema costatum, Monochrysis lutheri, and Dunaliella tertiolecta) were grown in enriched laboratory continuous cultures and natural populations were mass cultured outdoors for 16 months. Competition among the species was shown to be highly dependent on temperature, although the actual production of plant organic matter at the low growth rates used was relatively independent of this variable. Control of marine species in mass cultures does not appear economically feasible, but this drawback may be overcome by selecting herbivorous shellfish that are capable of assimilating those temperature-dependent phytoplankton species dominating in a particular locale.     

Downstream changes in phytoplankton composition and biomass in a lowland river–lake system (Warnow River, Germany)

To determine longitudinal changes in phytoplankton composition and biomass in the Warnow River (Germany), single water parcels were followed during their downstream transport in August and October 1996 and April 1997. In summer, the phytoplankton assemblage was dominated by centric diatom and cyanobacteria species. Stephanodiscus hantzschii, Pseudanabaena limnetica, Planktothrix agardhii and Aulacoseira granulata var. angustissima were the most frequent species. In autumn, small centric diatoms dominated the whole river course. Irrespective of the season, in the fluvial lakes of the upper river, a substantial increase of phytoplankton biomass was observed. Shallow upstream river stretches were associated with large biomass losses. In the deep, slow flowing lower regions, total biomass remained constant. Longitudinal changes in biomass reflected downstream variations in flow velocity and river morphology. Cyanobacteria, cryptophytes and diatom species were subjected to large biomass losses along fast flowing, shallow river sections, whereas chlorophytes were favoured. Diatoms and cryptophytes benefited from low flow velocity and increased water depth in the downstream river. Changes in water depth and flow velocity have been found as key factors that cause the longitudinal differences in phytoplankton composition and biomass in small rivers.