Spatial and temporal dynamics of phytoplankton communities along a regulated river system, the Nakdong River, Korea

The longitudinal distribution and seasonal fluctuation of phytoplankton communities was studied along the middle to lower part of a regulated river system (Nakdong River, Korea). Phytoplankton biomass decreased sharply in the middle part of the river (182 km upward the estuary dam), and then increased downstream reaching a maximum at the last sampling station (27 km upward the estuary dam). In contrast, there was little downstream fluctuation in species composition, irrespective of pronounced differences in nutrient concentrations (TN, TP, NO₃, NH₄, PO₄) as well as in algal biomass. In the main river channel, small centric diatoms (Stephanodiscus hantzschii, Cyclotella meneghiniana) and pennate diatoms (Synedra, Fragilaria, Nitzschia) were dominant from winter to early spring (November–April). A mixed community of cryptomonads, centric and pennate diatoms, and coenobial greens (Pediastrum, Scenedesmus) was dominant in late spring (May–June). Blue-green algae (Anabaena, Microcystis, Oscillatoria) were dominant in the summer (July–September). A mid-summer Microcystis bloom occurred at all study sites during the dry season, when discharge was low, though the nutrient concentration varied in each study site. Nutrients appeared everywhere to be in excess of algal requirement and apparently did not influence markedly the downstream and seasonal phytoplankton compositional differences in this river.     

水东湾海域浮游植物潮汐分布特征及其与环境因子的关系

2014年秋、冬两季,每个季节在大潮期和小潮期对水东湾海域浮游植物群落结构和环境因子进行了调查,共鉴定出4门57属134种。其中硅藻门42属106种,占浮游植物种类数的79.1%;甲藻门13属26种,占浮游植物种类数的19.4%;蓝藻门1属1种,占浮游植物种类数的0.8%;针胞藻纲1属1种,占浮游植物种类数的0.8%。优势种15种,主要为尖布纹藻Gyrosigma aluminatum、圆海链藻Thalassiosira rotula、中肋骨条藻Skeletonema costatum、丹麦细柱藻Leptocylindrus danicus和舟形鞍链藻Campylosira cymbelliformis等。4个航次共有种类数在18—40种,Jaccard种类相似性指数范围在0.200—0.404,多样性指数和均匀度平均值分别为2.60和0.60。秋季大、小潮期多样性指数差异较显著(P0.05),冬季细胞丰度、多样性指数和均匀度大、小潮期均无明显差异。浮游植物细胞丰度变化范围为0.95×10~4个/L—28.0×10~4个/L,平均为6.86×10~4个/L,平均丰度冬季小潮期(9.46×10~4个/L)秋季小潮期(7.56×10~4个/L)冬季大潮期(5.97×10~4个/L)秋季大潮期(4.44×10~4个/L)。主成分分析(PCA)表明:盐度和营养盐可能是影响水东湾海域生态环境的主导因子。对水东湾海域浮游植物群落结构与主要环境因子进行Spearman相关性分析,细胞丰度与盐度在秋季大、小潮期为负相关,在冬季大、小潮期呈显著正相关;与无机氮和磷酸盐在冬季大、小潮期呈极显著负相关,在秋季大、小潮期均无相关性。冬季小潮期水温与多样性指数、均匀度和细胞丰度均呈正相关;从测定结果来看浮游植物细胞丰度、多样性指数和均匀度与叶绿素a含量均无统计学意义上的相关性。     

流沙湾海草床海域浮游植物的时空分布及其影响因素

2008年2月至11月对广东省流沙湾海草床海域的浮游植物进行了周年的季节调查,结果共检出浮游植物151种:冬季57种、春季66种、夏季73种、秋季66种,其中硅藻门44属123种,占浮游植物种类数的81.4%;甲藻门11属26种,占浮游植物种类数的17.2%;绿藻门和蓝藻门各1属1种,各占浮游植物种类数的0.7%。优势种共有26种,主要为夜光藻Noctiluca scintillans、威氏角毛藻Chaetoceros weissflogii、圆海链藻Thalassiosira rotula、菱形海线藻Thalassionema nitzschioides等,都是链状群体或个体较细长或较大的种类,没有个体较短小的优势种群;各季节间共有种类数在22-43种,Jaccard种类相似性指数范围在0.211-0.448,多样性指数和均匀度平均值分别为2.12和0.35,群落结构较脆弱;细胞丰度在0.24×10⁴-5.72×10⁴ 个/L,秋季最高,夏季次之,冬季最低,属季节单峰型变化,与一般亚热带春、秋季出现丰度高峰不一致。相关性分析发现,浮游植物丰度与活性硅酸盐呈极显著的正相关,与盐度呈显著的负相关,与其他因子不存在明显的相关性;叶绿素a浓度与水温呈极显著的负相关,与浮游动物丰度呈显著的负相关。从浮游植物吸收N、P的配比分析,N为四季的营养限制因子,但从N、P的绝对值看,N和P都是全年的营养限制因子,因此其水质营养类型属于亚热带贫营养型。     

Winter phytoplankton community structure in three shallow temperate lakes during ice cover

The general model of seasonal phytoplankton succession in temperate lakes suggests that winter phytoplankton growth is minimal under ice-cover. However, some studies have found diverse phytoplankton communities during winter. The primary objectives of this study were to determine the species composition and the changes in the winter phytoplankton community structure under the ice. For 2 consecutive winters, phytoplankton samples were collected under ice-cover at 4 sites on 3 lakes in Arrowwood National Wildlife Refuge (ANWR), near Pingree, North Dakota. Ninety taxa were identified and enumerated. Densities of several of these taxa frequently exceeded 10⁶ cells l^–1. The winter phytoplankton communities in these lakes were dominated by flagellates, principally cryptomonads, a synurophyte (Synura uvella), small chrysophytes (Chrysococcus spp., Kephyrion spp.) and a dinoflagellate (Peridinium aciculiferum), as well as non-flagellate microchlorophytes (Monoraphidium spp., Ankistrodesmus spp., and Pseudodictyosphaerium sp.), a cyanobacterium (Gloeocapsa aeruginosa) and centric diatoms (Stephanodiscus minutulus, S. parvus and Cyclotella meneghiniana).     

Composition and variation of phytoplankton communities during Microcystis bloom in an artificial lagoon of Hangzhou Bay,China

The interaction of various environmental triggers on phytoplankton communities of an artificial lagoon of Hangzhou Bay China, was studied during a Microcystis bloom in summer 2016. Forty-two phytoplankton genera (six phyla) were defined, with Bacillariophyta accounting for half of all phytoplankton genera. It was determined that Melosira, Chlorella, Cyclotella, Microcystis, Merismopedia, Anabaena and Selenastrum, which were identified and counted by an inverted microscope, were the dominant genera. In addition, a series of environmental indicators were analyzed, including salinity, seawater temperature, dissolved inorganic nitrogen, soluble reactive phosphorus (PO₄-P), ammonium (NH₄-N), nitrate nitrogen (NO₃-N), nitrite (NO₂-N), silicate (SiO₄-Si), and chemical oxygen demand of the water samples, as well as zooplankton community. The results of variance partitioning by R language revealed that the most influential factor driving the change in the phytoplankton community was the environment (49.7%), and zooplankton grazing represented only 7.9%. The results of redundancy analysis indicated that the change and composition of the phytoplankton community correlated significantly with the interaction of salinity, PO₄-P, transparency, seawater temperature, and the dominant zooplankton species. Notably, salinity and temperature fluctuation were the key factors inducing the rapid succession of the plankton community in artificial lagoons such as within the Jinshan City Beach (Shanghai, China).

     

Seasonal variation of phytoplankton community in Thale Sap Songkhla, a lagoonal lake in southern Thailand

The phytoplankton in Thale Sap Songkhla was investigated at 2–3 month intervals from August 1991 to October 1993. The abundance of phytoplankton ranged from 1.4×10⁶ to 1.3×10⁹ cells m^–3. A total of 6 divisions with 103 genera were identified as Bacillariophyta: 49 genera, Chlorophyta: 21 genera, Pyrrhophyta: 15 genera, Cyanophyta: 12 genera, Chrysophyta: 3 genera and Euglenophyta: 3 genera. Although phytoplankton abundance was distinctly greater in the first year of study (August 1991–June 1992) than in the second year (August 1992–October 1993), their patterns are similar: 2 peaks yearly. The peaks of phytoplankton occurred in the heavy rainy season (northeast monsoon) and the light rainy season (southwest monsoon). The main bloom was found during December–January, with a predominance of blue-green algae (e.g. Aphanizomenon andPhormidium) and green algae (e.g. Eudorina). Their species composition also increased, an effect of the large amount of rainfall resulting in low salinity during the northeast monsoon. The minor bloom was produced by diatoms during June–July when water salinity was moderate to seawater. Both phytoplankton numbers and species composition were high. However, unpredictably heavy rainfall during the southwest monsoon period may reduce diatom production due to rapid immediate replacement by blue-green species. Besides salinity concentration, a low total nitrogen: total phosphorus (TN: TP) ratio tended to support the growth of blue-green algae. The diversity of phytoplankton was lowest in the heavy rainy period.     

Seasonal Dynamics of Phytoplankton and Planktonic Protozoan Communities in a Northern Temperate Humic Lake: Diversity in a Dinoflagellate Dominated System

Species diversity and richness, and seasonal population dynamics of phytoplankton, planktonic protozoa, and bacterioplankton sampled from the epilimnion of Crystal Bog in 2000, were examined in order to test the hypothesis that these groups diversity and abundance patterns might be linked. Crystal Bog, a humic lake in Vilas County, Wisconsin, is part of the North Temperate Lakes Long-Term Ecological Research Site. Phytoplankton and planktonic protozoa were identified and enumerated in a settling chamber with an inverted microscope. Bacterial cells were enumerated with the use of fluorescence 4, 6-diamidino-2-phenylindole (DAPI)-staining procedures, and automated ribosomal intergenic spacer analysis (ARISA) was used to assess bacterioplankton diversity. Bacterial cell counts showed little seasonal variation and averaged 2.6 × 10⁶ cells/mL over the ice-free season. Phytoplankton and planktonic protozoan numbers varied by up to two orders of magnitude and were most numerous in late spring and summer. Dinoflagellates largely dominated Crystal Bog throughout the ice-free period, specifically Peridiniopsis quadridens in the spring, Peridinium limbatum in summer, and Gymnodinium fuscum and P. quadridens in fall. Brief blooms of Cryptomonas, Dinobryon, and Synura occurred between periods of dinoflagellate domination. The dominant dinoflagellate, Peridinium limbatum, was calculated to have a growth rate of 0.065 day^–1 and a doubling time of 10.7 days. Heterotrophic nanoflagellates (HNFs) were a consistent component of the planktonic protozoa; seasonal patterns were determined for three genera of HNFs (Monosiga, Bicosoeca, and Desmarella moniliformis). Three genera of ciliates (Coleps, Strobilidium, and Strombidium) comprised the greater part of the planktonic protozoa in Crystal Bog. The number of species of planktonic protozoa was too low to calculate a diversity index. Shannon–Weaver diversity indices for phytoplankton and bacterioplankton in the epilimnion followed very similar seasonal patterns in this lake, supporting the hypothesis that in freshwaters, diversity patterns of these groups are linked.     

Phytoplankton sterol contents vary with temperature,phosphorus and silicate supply: a study on three freshwater species

The understanding of environmentally induced changes in the biochemical composition of phytoplankton species is of great importance in both physiological studies and ecological food web research. In extensive laboratory experiments we tested the influence of two different temperatures (10°C and 25°C) and a phosphorus supply gradient on the sterol concentrations of the three freshwater phytoplankton species Scenedesmus quadricauda, Cryptomonas ovata and Cyclotella meneghiniana. The diatom C. meneghiniana was additionally exposed to a silicate gradient. In two separate experiments we analysed (1) possible interactive effects of temperature and phosphorus supply and (2) the effect of four phosphorus levels and three silicate levels on algal sterol concentrations. We observed that sterol concentrations were higher at 25°C than at 10°C in S. quadricauda and C. meneghiniana, but were not affected by temperature in C. ovata. Interactive effects of temperature and phosphorus supply on sterol concentrations were found in C. meneghiniana. This presumably was due to the bioconversion of one sterol (24-methylenecholesterol) into another (22-dihydrobrassicasterol). Increasing phosphorus supply resulted in species-specific effects on sterol concentrations, viz. an optimum curve response in S. quadricauda, a saturation curve response in C. meneghiniana and no change in sterol concentration in C. ovata. Effects of silicate supply on the sterols of C. meneghiniana equalled the effects of phosphorus supply. Albeit we did not observe a general trend in the three phytoplankton species tested, we conclude that sterol concentrations of phytoplankton are strongly affected by temperature and nutrient supply. Interactive effects point out the importance of taking into account more than just one environmental factor when assessing the effects of environmentally induced changes on phytoplankton sterol concentrations.     

辽宁碱蓬根际土壤真菌多样性的季节变化及其耐盐性

采用稀释平板法和形态学鉴定法进行了辽宁碱蓬(Suaeda liaotungensis)根际土壤真菌的分离鉴定及季节、盐度对真菌多样性的影响分析。结果表明:春、夏、秋、冬四季辽宁碱蓬根际土壤中的真菌菌落数分别为6410、4180、5730和3340,种类分别为6属13种、9属16种、11属31种、6属12种,共分离鉴定出13属42种真菌;其根际土壤真菌的多样性指数、丰富度指数和均匀度指数,从大到小的次序均为秋夏春冬,3种指数均在秋季达到峰值;多样性指数和丰富度指数差异较大,均匀度指数波动较小,春季和冬季的均匀度指数相近。辽宁碱蓬根际土壤真菌种类明显多于无植被土壤,是无植被土壤的7倍,多样性指数和均匀度指数分别是无植被土壤的4—8倍和1—1.2倍;其根际土壤真菌优势种群包括青霉属(Penicillium)、葡萄穗霉属(Stachybotrys)、枝孢属(Cladosporium)、木霉属(Trichoderma)、曲霉属(Aspergillus)和镰孢属(Fusarium);4个季节的优势菌不尽相同,但均有一个共同的优势菌属青霉属。以Na Cl浓度梯度法制造盐胁迫生境,检测辽宁碱蓬根际土壤真菌对盐胁迫的响应,结果表明:60%左右的菌种能耐受5%以下盐度、15%左右的菌种能耐10%—20%盐度;筛选出了6株高度耐盐菌:细交链孢霉、草酸青霉、产黄青霉、烟曲霉、细极链格孢和赭曲霉,其中最高耐盐菌种赭曲霉可耐20%盐度。创新之处在于以盐度和季节为变量检测辽宁碱蓬根际土壤真菌的种群构成,为其深入研究奠定了理论基础。     

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.     

Seasonal and long term changes of the phytoplankton in the lake Tortum in relation to environmental factors, Erzurum, Turkey

Seasonal changes in phytoplankton community structure of the lake Tortum were studied over one year period, from March 2002 to February 2003. The collected data were compared with the data collected 21 years ago. Chlamydomonas microsphaerella, Cyclotella krammeri, C. glomerata, and Ceratium hirundinella were identified to be dominant several times during the study period. Species diversity and biomass of the phytoplankton were very low in spite of sufficient and high levels of nutrient concentrations. Maximum phytoplankton density levels were observed during summer and late autumn. Phytoplankton density was positively correlated with nutrients, temperature and pH, and it was negatively correlated with Secchi depth and dissolved oxygen. Phytoplankton growths were negatively affected from water transparency and high levels of water mass transport (circulation) and velocity in the lake.     

西沙宣德群岛海域浮游植物群落及其影响因子

为了解西沙宣德群岛海域浮游植物群落结构特征,于2019年2月和11月对该海域进行采样调查,分析浮游植物群落组成及环境影响因素。两个航次共发现109种浮游植物,其中硅藻门最多,有81种。冬秋季节优势种不尽相同,冬季优势种为铁氏束毛藻(Trichodesmium thiebautii)、红海束毛藻(T. erythraeum)和标志星杆藻(Asterionella notata)等,秋季优势种为菱形海线藻(Thalassionema nitzschioides)、丹麦细柱藻(Leptocylindrus danicus)和劳氏角毛藻(Chaetoceros lorenzianus)。冬季浮游植物平均丰度[(5.27±6.14)×10⁷ cells/L]显著高于秋季[(1.56±1.40)×10⁵ cells/L]。浮游植物群落分布主要受亚硝酸盐、盐度等环境因子影响。冬秋季各站位浮游植物群落的多样性指数、均匀度指数和丰富度指数平均值分别为3.15、0.71、1.36和3.28、0.75、1.77。因此,宣德群岛海域冬秋季节浮游植物群落多样性较高,物...     

Effects of increases in salinity on phytoplankton in the Broadwater of the Myall Lakes, NSW, Australia

The Broadwater of the Myall Lakes system is highly susceptible to cyanobacterial bloom formation after heavy rain events. During prolonged low flow periods, saline intrusion from the lower Myall River increases salinity levels and effectively controls some bloom forming algal taxa. To assess the effect of low-to-moderate increases in salinity (up to 4 ppt) on phytoplankton chlorophyll a, cell abundance, diversity and assemblage structure, salinity enhancement experiments were conducted on Broadwater samples collected in June 2005 (salinity 1.5 ppt), October 2005 (4 ppt) and January 2006 (12 ppt). Natural phytoplankton assemblages were incubated in the laboratory for 10 days, under different treatments of salinity (no addition, +2 ppt, + 4 ppt) and nutrient conditions (no addition, excess N+P). The greatest impact of salinity enhancement in N+P enriched samples was observed in June (1.5–5.5 ppt); chlorophyll a was significantly reduced in samples with the highest salinity treatment, and the taxon most negatively affected by an elevation in salinity to 5.5 ppt was Anabaena circinalis. Taxonomic richness and diversity (Shannon–Wiener index) were unexpectedly significantly higher at 5.5 ppt than at 1.5 ppt. This result, in part, explains the observed significant differences in phytoplankton assemblage structure over this salinity range. In October, the main effect of elevating salinity levels from 4 ppt to 8 ppt was a reduction in the abundance of chlorophytes, particularly Scenedesmus. Phytoplankton samples that were collected when the lake salinity level was 12 ppt were little affected by salinity increases of 2 ppt and 4 ppt, most likely because field samples were already relatively high in salt content. We suggest that further investigations focus on phytoplankton responses to salinity under a range of nutrient regimes that are common to coastal lakes.     

Effects of the severe winter 1995/96 on the biological oceanography of the Sylt-Rømø tidal basin

Water temperature, salinity and precipitation, micronutrients (N, P, Si) and chlorophyll a concentrations in the Sylt-R?m? tidal basin (German Bight) deviated between the early 1990s, with mild winters, and the years 1996–1997 with a severe winter and a moderate winter. As a consequence of low temperature, offshore winds and low precipitation in the severe winter 1995/96, salinity peaked in February 1996 and nitrate concentrations were low. The latter further decreased in March as chlorophyll a peaked with an exceptional bloom of the diatom Odontella aurita, probably triggered by low water temperature. Winter temperatures and spring chlorophyll a in the Sylt-R?m? tidal basin correlate well with the climatic North Atlantic Oscillation index. Received in revised form: 7 May 2001 Electronic Publication     

Materials on the flora of Bacillariophyta in aquatic ecosystems of the Yarayakha River basin (Yamal Peninsula)

The study of phytoplankton in lakes, sors, streams, and rivers of the Yarayakha River basin with the help of scanning electron microscopy has made it possible to broaden the taxonomic spectrum of Bacillariophyta; 236 specific and intraspecific taxa from 63 genera are detected. A total of 16 species and varieties that are new for the flora of Russia were documented; 30 forms from 18 genera are identified only to the species. The maximum species diversity is recorded in a stream in the Yarayakha River mouth (82 species) and in the channel of the Khureikhotarka River (105 species). Species such as Cyclotella meneghiniana, Fragilaria exiguiformis, Navicula hanseatica, Neidium bisulcatum, Stauroneis anceps, Thalassiosira inserta, and Tabellaria flocculosa are the most widespread in the waterbodies.     

Structural variations of phytoplankton in the coastal seas of Yucatan,Mexico

A study was done of the relationship between hydrographic variables and the composition, abundance, community structure and biomass spectrums of coastal phytoplankton at scales greater than 100 km on the Yucatan Peninsula (SE Gulf of Mexico). This was done during the season of greatest environmental instability in the region, the northwind season (late fall to winter). Samples were collected at stations in the west (Campeche), north (Yucatan), and east (Quintana Roo) zones of the Peninsula. Measurements were taken of temperature, salinity, dissolved oxygen, dissolved inorganic nutrients (ammonia, nitrite, nitrate and phosphate) and chlorophyll a, and samples were taken for phytoplankton analysis. The hydrographic results showed the Campeche zone as having the lowest salinity (<35 psu) values, as well as the highest inorganic nutrient and chlorophyll a values, all of which are related to continental water contributions. The Yucatan zone had the lowest temperatures and the lowest inorganic nutrient values, indicating influence from the Yucatan Current and the Gulf of Mexico. A total of 159 phytoplankton species were identified, dominated by diatoms (>80%) and dinoflagellates. Phytoplankton exhibited greater concentration, richness, equitability and diversity in Campeche, while the lowest community structure values were had in the Quintana Roo zone. The ordination analysis demonstrated that the dominant genera were the diatoms Chaetoceros, Pseudonitzschia and Thalassionema. The biomass spectrums exhibited the lowest slope in environments of higher heterogeneity, with Campeche being the most disturbed and heterogeneous zone and Quintana Roo that with the least heterogeneity.     

Comparative limnology of Sambhar and Didwana lakes (Rajasthan,NW India)

Two alkaline saline inland lakes of Indian arid region were studied during 1984 and 1985, to assess functioning and interaction of various environmental and biological factors. Changes in physical and chemical variables, planktonic composition, chlorophyll content and phytoplankton primary productivity were examined.Salinity in both lakes fluctuated from almost fresh water (1.80), to hypersaline (300) and acted as the main controlling factor for almost all the biotic parameters. Maximum total alkalinities were 2162 mg l^–1 and 2090 mg l^–1, respectively in Sambhar and Didwana lakes. Dissolved oxygen ranged from completely anoxic conditions to maxima of 11.68 and 7.29 mg 1^–1, respectively in Sambhar and Didwana lakes. Nutrient enrichment in the lakes was low.The phytoplankton species composition of Sambhar lake was reduced from an earlier reported 20 genera to only 11 (Nostoc, Microcystis, Spirulina, Aphanocapsa, Oscillatoria, Merismopedia, Nitzschia, Navicula, Synedra, Cosmarium and Closterium). Phytoplankton of Didwana was composed of only 9 genera including Anabaena and Nodularia. Sambhar lake, which once contained Artemia, is now totally devoid of them. On the other hand, Artemia was the most dominant zooplankter in Didwana lake at a salinity range of 15–288. Other zooplankters such as Moina, Cyclops and Brachionus flourished at lower salinity levels in Didwana lake. The seasonal quantitative and qualitative phyto- and zooplankton changes in relation to salinity are documented.     

Importance and abundance of the recently established speciesCoscinodiscus wailesii Gran & Angst in the German Bight

Grids of 17 to 50 stations in the German Bight were sampled 18 times within the framework of the multidisciplinary programmes ZISCH and PRISMA in winter and spring of 1988/89 and from April 1991–April 1992. The frequent abundance ofCoscinodiscus wailesii Gran & Angst, a recently established large diatom, was noteworthy, as it dominated the phytoplankton biomass over long periods (e.g. 12/88–3/89 and 8/91–11/91). The bulk of the phytoplankton carbon during these periods (up to 90%) could be attributed to this species. Blooms ofCoscinodiscus wailesii producing up to 1400 μg carbon 1⁻¹, were recorded in early spring of 1989 and autumn of 1991. The potential consequences for the whole ecosystem refer to the huge size of this organism, which may cause reduced exploitation of its primary production by native consumers. Furthermore, sedimentation and remineralisation processes may be affected. ForC. wailesii, a doubling of biomass in 70 h could be estimated on the basis of data from four successive surveys in 1991. Results from laboratory cultures under comparable conditions confirm this rate. In the survey area, no increase in biomass was recorded for the relatedCoscinodiscus granii Gough, although there was sufficient silicate supply for growth. Field data showed 8–10 times lower copper and 10–20 times lower cadmium and zinc accumulation inC. wailesii, compared to concentrations found in native phytoplankton species. Subsequent laboratory tests suggested that one reason for the remarkable success ofC. wailesii, mainly in inshore regions, may be derived from its tolerance of higher doses of heavy metals due to very low sorption.     

Seasonal correlations of elemental and ω3 PUFA composition of seston and dominant phytoplankton species in a eutrophic Siberian Reservoir

The elemental and fatty acid composition of seston was studied for 3 years, from May to October, in a small Reservoir. Under comparatively low C:P ratio, multivariate canonical analysis revealed no straightforward simple correlations between phosphorus and single ω3 PUFA species, but complex significant interaction between elemental composition (stoichiometry) of seston and total sestonic ω3 PUFA as a whole. Since sestonic C, P and N were found to originate mostly from phytoplankton, the contents of particulate elements and PUFA were attributed to single species in periods of their pronounced dominance. Phytoplankton species of genera of Stephanodiscus, Peridinium, Gomphosphaeria, Planktothrix and Anabaena in periods of their pronounced dominance had relatively constant species-specific elemental and PUFA composition. Phytoplankton species significantly differed in their elemental and PUFA composition, as well as in ratios of C:N, N:P, PUFA:P and partly C:P that indicate food quality for zooplankton. Hence, there were no phytoplankton species of clearly high or low nutritional value. All of phytoplankters, or at least detritus, that originated from them, may meet specific elemental and biochemical requirements of specific groups of zooplankton. Dividing phytoplankton on basis of their elemental and biochemical composition, i.e., nutrition quality, into large taxa (cyanobacteria, diatoms, etc.) appeared to be too coarse for assessing nutritional value for zooplankton.     

Responses of phytoplankton species to diel temperature fluctuation patterns

Diel temperature fluctuation might promote the dominance of cyanobacteria and result in the advance of bloom onset timing in spring. However, knowledge of how temperature fluctuations impact phytoplankton shift and then favor cyanobacterial growth in spring is limited. In this study, we analyzed photosynthesis and growth responses of phytoplankton species to different temperature fluctuation patterns in the laboratory. We also performed daily monitoring to detect the relationship between phytoplankton groups and diel temperature fluctuations. The results of the laboratory experiments suggested that the photosynthetic performance and growth rate of Microcystis aeruginosa were better adapted to temperature fluctuations than those of Chlorella pyrenoidosa and Cyclotella meneghiniana. Temperature fluctuations slowed the proliferation of Ch. pyrenoidosa and Cy. meneghiniana, while promoting M. aeruginosa. Moreover, the response dynamics of different phytoplankton species to diel temperature fluctuations depended on the mean temperature. The results from the field also indicated that there was a positive relationship between cyanobacterial biomass and diel temperature fluctuations. Our study offers further understanding of the effect of temperature fluctuation on phytoplankton composition shift and the formation of cyanobacterial dominance in spring.