Do phytoplankton communities correctly track trophic changes? An assessment using directly measured and palaeolimnological data

1. Measurements of total phosphorus (TP) concentrations since 1975 and a 50‐year time series of phytoplankton biovolume and species composition from Lake Mondsee (Austria) were combined with palaeolimnological information on diatom composition and reconstructed TP‐levels to describe the response of phytoplankton communities to changing nutrient conditions. 2. Four phases were identified in the long‐term record. Phase I was the pre‐eutrophication period characterised by TP‐levels of about 6 μg L^?1 and diatom dominance. Phase II began in 1966 with an increase in TP concentration followed by the invasion of Planktothrix rubescens in 1968, characterising mesotrophic conditions. Phase III, from 1976 to 1979, had the highest annual mean TP concentrations (up to 36 μg L^?1) and phytoplankton biovolumes (3.57 mm³ L^?1), although reductions in external nutrient loading started in 1974. Phases II and III saw an expansion of species characteristic of higher nutrient levels as reflected in the diatom stratigraphy. Oligotrophication (phase IV) began in 1980 when annual average TP concentration, Secchi depth and algal biovolume began to decline, accompanied by increasing concentrations of soluble reactive silica. 3. The period from 1981 to 1986 was characterised by asynchronous trends. Annual mean and maximum total phytoplankton biovolume initially continued to increase after TP concentration began to decline. Reductions in phytoplankton biovolume were delayed by about 5 years. Several phytoplankton species differed in the timing of their responses to changing nutrient conditions. For example, while P. rubescens declined concomitantly with the decline in TP concentration, other species indicative of higher phosphorus concentrations, such as Tabellaria flocculosa var. asterionelloides, tended to increase further. 4. These data therefore do not support the hypotheses that a reduction in TP concentration is accompanied by (i) an immediate decline in total phytoplankton biovolume and (ii) persistence of the species composition characterising the phytoplankton community before nutrient reduction.     

Effects of phytoplankton species composition on absorption spectra and modeled hyperspectral reflectance

Understanding the spectral characteristics of remotely-sensed reflectance by different phytoplankton species can assist in the development of algorithms to identify various algal groups using satellite ocean color remote sensing. One of the main challenges is to separate the effect of species composition on the reflectance spectrum from other factors such as pigment concentration and particle size structure. Measuring the absorption spectra of nine different cultured algae, and estimating the reflectance of the different species, provides a useful approach to study the effects of species composition on the bio-optical properties. The results show that the absorption spectra of different species exhibit different spectral characteristics and that species composition can significantly change the absorption characteristics at four main peaks (438, 536, 600 and 650 nm). A ‘distance angle index’ was used to compare different phytoplankton species. Results indicate that this index can be used to identify species from the absorption spectra, using a database of standard absorption spectra of known species as reference. By taking into account the role of species composition in the phytoplankton absorption model, the performance of the model can be improved by up to 5%. A reflectance-species model is developed to estimate the remotely-sensed reflectance from the absorption spectra, and the reflectance of different phytoplankton species at the same chlorophyll-a concentration is compared, to understand effects of species composition on the reflectance spectra. Different phytoplankton species can cause up to 33% difference in the modeled reflectance at short wavelengths under the condition of the same chlorophyll-a concentration, and variations in the reflectance spectrum correspond to the colors of the algae. The standard deviation of the reflectance among different species shows that the variations from 400 to 450 nm are sensitive to species composition at low chlorophyll-a concentrations, whereas variations in the 510 to 550 nm range are more sensitive under high chlorophyll-a concentrations. For this reason, the green bands may be more suitable for estimating species composition from hyperspectral satellite data during bloom conditions, whereas the blue bands may be more helpful in detection of species under low chlorophyll-a concentrations. In this theoretical approach, variations in reflectance at the same chlorophyll-a concentration can be used to identify phytoplankton species. Another approach to identify phytoplankton species from remotely-sensed hyperspectral reflectance measurements would be to derive the absorption spectra of phytoplankton from the reflectance measurements, and compare these with a standard database of absorption spectra.     

Late fall phytoplankton dynamics in three lakes, Rocky Mountain National Park

We studied phytoplankton population dynamics during the month preceding formation of ice cover in three small subalpine lakes in Rocky Mountain National Park, Colorado, U.S.A. The outflow from Emerald Lake, which is surrounded by talus, flows into Dream Lake, which is surrounded by sub-alpine forest. Nymph Lake is a lower seepage lake with abundant macrophytes in summer. The major ion concentrations in the three lakes were similar during the study, although Emerald and Dream Lakes had higher concentrations of nitrate and silica than Nymph Lake. A principal component analysis (PCA) showed that the phytoplankton in Emerald and Dream Lakes were distinct from the phytoplankton in Nymph Lake. The species composition changed in each lake during the late fall. The patterns of change in Emerald and Dream Lakes were similar on the PCA diagram despite the greater abundance of diatoms in Dream Lake and the decreasing flow from Emerald Lake into Dream Lake during the fall. In Nymph Lake, a progressive shift in species distribution occurred with a decrease in the most abundant chlorophyte, Chlamydomonas sp., and increases in several species, including two chrysophytes and the diatom Eunotia sp. The marked change in species composition in all three lakes suggests that phytoplankton populations are influenced by changes in water temperatures and incident solar radiation that occur during the late fall. We also compared these data with phytoplankton data for two fall periods from two other hydrologically connected Rocky Mountain lakes. PCA analysis showed that the difference between years was greater than the change during the fall and that the fall species composition in these two lakes was distinct from that in Emerald and Dream Lakes or in Nymph Lake. Studying phytoplankton dynamics in alpine and sub-alpine lakes may offer clues as to how these ecosystems may respond to projected climate changes in the Rocky Mountain region, such as warmer temperatures and later formation of ice-cover.     

Phytoplankton in the Marginal Ice Zone of the Greenland Sea during summer, 1984

Summary Phytoplankton biomass and species composition were studied in transects through the ice edge region of the Greeland Sea from 19 July to 8 August 1984. Biomass was estimated by vertical in situ chlorophyll fluorescence and pigment extraction of discrete samples. Preserved material was used for identification of phytoplankton species and calculation of their relative abundances. The results suggest that the various geographical regions of the Greenland Sea differ considerably in their phytoplankton development. Autotrophic biomass and species composition were closely associated with the extent of the annual and seasonal ice cover, hydrographic conditions, nutrient availability and the water masses typical of the different domains. In the NE Greenland polynya a deep mixed layer inhibited the development of a phytoplankton bloom, whereas greatest biomass concentrations were associated with a receding ice edge on the E Greenland Shelf. In the Fram Strait, the position of the relatively stationary ice edge is controlled by frontal dynamics, currents and wind. Due to rapidly changing physical and chemical conditions, phytoplankton biomass showed great variability between stations. High chlorophyll a concentrations may develop locally where melting ice causes stratification or can result from passive accumulation in eddies. In July/August 84 the Fram Strait area was dominated by a typical summer population of flagellates and large diatom species.Contribution 6 of the Alfred-Wegener-Institute for Polar and Marine Research     

Phosphorus decrease and climate variability: mediators of synchrony in phytoplankton changes among European peri-alpine lakes

1. In an attempt to discern long‐term regional patterns in phytoplankton community composition we analysed data from five deep peri‐alpine lake basins that have been included in long‐term monitoring programmes since the beginning of the 1970s. Local management measures have led to synchronous declines in phosphorus concentrations by more than 50% in all four lakes. Their trophic state now ranges from mesotrophic to oligotrophic. 2. No coherence in phytoplankton biomass was observed among lakes, or any significant decrease in response to phosphorus (P)‐reduction (oligotrophication), except in Lakes Constance and Walen. 3. Multivariate analyses identified long‐term changes in phytoplankton composition, which occurred coherently in all lakes despite the differing absolute phosphorus concentrations. 4. In all lakes, the phytoplankton species benefiting from oligotrophication included mixotrophic species and/or species indicative of oligo‐mesotrophic conditions. 5. A major change in community composition occurred in all lakes at the end of the 1980s. During this period there was also a major shift in climatic conditions during winter and early spring, suggesting an impact of climatic factors. 6. Our results provide evidence that synchronous long‐term changes in geographically separated phytoplankton communities may occur even when overall biomass changes are not synchronous.     

The relationship between phytoplankton species dominance and environmental variables in a shallow lake (Lake Vrana,Croatia)

The shallow Lake Vrana was studied over a 1-year period, special attention being paid to the phytoplankton. Phytoplankton was investigated monthly with respect to temporal variability of selected environmental factors. The regular annual development observed was in species contribution to total biomass rather than in seasonal changes in species composition. The assemblage was dominated by Cosmarium tenue Arch. and Synedra sp. In winter and in spring the phytoplankton assemblage was dominated by Cosmarium tenue and high contribution of Synedra sp. was observed during the summer and autumn. Results suggest that concentrations of inorganic nitrogen and phosphorus were critical in regulating phytoplankton biomass and species dominance.     

Structural characteristics of phytoplankton assemblages in tidal and non-tidal freshwater systems: a case study from the Schelde basin, Belgium

1. The Schelde estuary, its side basins and their tributaries were sampled in August 1995 and April 1996 for phytoplankton abundance, biomass, diversity and species composition. In order to clarify the underlying causes of differences in phytoplankton communities, the results were related to some important abiotic variables.
2. Although species richness and diversity did not differ significantly between the riverine and the freshwater tidal stations, multivariate ordination techniques based on species abundances differentiate between these two ecosystems. While in the rivers phytoplankton standing stocks were as high in summer as in spring, standing stocks in the freshwater tidal estuary were significantly higher in the August samples.
3. It is postulated that due to the resuspension of suspended solids by estuarine currents, light is limiting phytoplankton development in the freshwater tidal reaches in spring. At that stage, phytoplankton populations have already developed in the rivers. In summer, zooplankton prevent any further increase of riverine phytoplankton populations. In the freshwater tidal estuary, however, increased light levels, a higher residence time compared to rivers and the absence of zooplankton due to low oxygen concentrations permit phytoplankton populations to bloom.     

博斯腾湖浮游植物群落结构特征及其影响因子分析

2011年对博斯腾湖大湖区17个采样站位的浮游植物及水体主要理化因子进行了4次系统调查。结果表明, 在17个站位共鉴定出浮游植物127种（属）, 其中优势种（属）9种。浮游植物群落全年均以硅藻为主导, 冬、春季节, 浮游植物组成呈硅藻-甲藻型, 优势类群主要为贫-中营养型浮游藻类, 到夏、秋季节逐渐形成硅藻-绿藻型, 以富营养型的浮游藻类为优势类群。浮游植物总平均生物量为（2.512.95） mg/L, 生物量季节变动显著, 峰值出现在夏季, 冬季最低。基于Canoco的多变量分析表明: 环境变量共解释了浮游植物群落总变异的54.5%, 水温是影响浮游植物分布最重要的环境因子, 其次为枝角类丰度。水中氮含量是影响浮游植物丰度的主要因子, 同时浮游植物对水体有机物含量也有较大的影响。       

Seasonal and interannual variability in the taxonomic composition and production dynamics of phytoplankton assemblages in Crater Lake,Oregon

Taxonomic composition and production dynamics of phytoplankton assemblages in Crater Lake, Oregon, were examined during time periods between 1984 and 2000. The objectives of the study were (1) to investigate spatial and temporal patterns in species composition, chlorophyll concentration, and primary productivity relative to seasonal patterns of water circulation; (2) to explore relationships between water column chemistry and the taxonomic composition of the phytoplankton; and (3) to determine effects of primary and secondary consumers on the phytoplankton assemblage. An analysis of 690 samples obtained on 50 sampling dates from 14 depths in the water column found a total of 163 phytoplankton taxa, 134 of which were identified to genus and 101 were identified to the species or variety level of classification. Dominant species by density or biovolume included Nitzschia gracilis, Stephanodiscus hantzschii, Ankistrodesmus spiralis, Mougeotia parvula, Dinobryon sertularia, Tribonema affine, Aphanocapsa delicatissima, Synechocystis sp., Gymnodinium inversum, and Peridinium inconspicuum. When the lake was thermally stratified in late summer, some of these species exhibited a stratified vertical distribution in the water column. A cluster analysis of these data also revealed a vertical stratification of the flora from the middle of the summer through the early fall. Multivariate test statistics indicated that there was a significant relationship between the species composition of the phytoplankton and a corresponding set of chemical variables measured for samples from the water column. In this case, concentrations of total phosphorus, ammonia, total Kjeldahl nitrogen, and alkalinity were associated with interannual changes in the flora; whereas pH and concentrations of dissolved oxygen, orthophosphate, nitrate, and silicon were more closely related to spatial variation and thermal stratification. The maximum chlorophyll concentration when the lake was thermally stratified in August and September was usually between depths of 100 m and 120 m. In comparison, the depth of maximum primary production ranged from 60 m to 80 m at this time of year. Regression analysis detected a weak negative relationship between chlorophyll concentration and Secchi disk depth, a measure of lake transparency. However, interannual changes in chlorophyll concentration and the species composition of the phytoplankton could not be explained by the removal of the septic field near Rim Village or by patterns of upwelling from the deep lake. An alternative trophic hypothesis proposes that the productivity of Crater Lake is controlled primarily by long-term patterns of climatic change that regulate the supply of allochthonous nutrients.     

巨桉凋落叶分解对菊苣生长及光合特性的影响

采用盆栽试验,研究了巨桉凋落叶分解初期对菊苣幼苗生长和光合生理特性的影响.试验设置A₁(30 g·pot^-1)、A₂(60 g·pot^-1)、A₃(90 g·pot^-1)和对照（CK）4个凋落叶水平,将各处理的凋落叶分别与12 kg土壤混合后装盆,播种菊苣.待A₃处理植株的第3片真叶完全展开后测定菊苣光合生理指标及相关生长指标.结果表明：巨桉凋落叶分解初期明显抑制了菊苣生物量积累、叶面积的增加及光合色素的合成,且随着凋落叶施入量的增加抑制作用加大;菊苣叶片胞间CO₂浓度增加,而净光合速率、气孔导度和蒸腾速率均显著低于对照;随土壤中凋落叶含量的增加,除CO₂补偿点呈增加趋势外,其他光响应和CO₂响应的特征参数都呈明显下降趋势,并与对照差异显著.巨桉凋落叶分解过程中,其化感物质逐步释放并作用于受体植物,抑制其光合色素合成和光合作用,降低其环境适应能力,从而抑制菊苣的生长.     

The hydro-morphological index of diversity: a tool for describing habitat heterogeneity in river engineering projects

Species composition and seasonal succession of phytoplankton were analyzed in a lowland river located in South Banat (Ponjavica, Serbia). As a result of human activity, a network of irrigation channels was built on the Ponjavica River’s upper and lower courses. These channels reduce the water level in the river and help to create favorable conditions for accelerated eutrophication processes. Eight phytoplankton divisions with 444 taxa were present. Physical and chemical testing of water, phytoplankton abundance and biomass, as well as chlorophyll a concentration showed a high level of eutrophication. Cyanobacterial biomass developed in 2002 with dominance of Microcystis aeruginosa and Aphanizomenon flos-aquae. Changes in phytoplankton composition were observed during 2008, characterized by the appearance and dominance of Cylindrospermopsis raciborskii when this species accounted for more than 85% of the total phytoplankton biovolume. The change in dominant phytoplankton functional groups was observed: codons H₁ and M characterizing summer in 2002 were replaced by codons S_N and S₁ in 2008. This study compares the presence of C. raciborskii with other phytoplankton species in relation to water quality parameters. High abundance of this species correlated positively with biochemical oxygen demand and turbidity, and negatively with NO₃-N concentrations during the study period.     

Abiotic drivers of interannual phytoplankton variability and a 1999–2000 regime shift in the North Sea examined by multivariate statistics

The Dutch coastal zone is a region of the North Sea with a marked interannual and long‐term abiotic and phytoplankton variability. To investigate the relationship between abiotic variability and phytoplankton composition, two routine water monitoring data sets (1991–2005) were examined. Multivariate statistics revealed two significant partitions in the data. The first consisted of interannual abiotic fluctuations that were correlated to Rhine discharge that affected the abundance of summer and autumn diatom species. The second partition was caused by a shift in the abiotic data from 1998 to 1999 that was followed by a shift in phytoplankton composition from 1999 to 2000. Important factors in the abiotic shift were decreases in suspended matter (SPM) and phosphate (DIP) concentrations, as well as in pH. The decrease in SPM was caused by a reduction in wind speed. The increase in water column daily irradiance from the decrease in SPM led to increases in the abundance of winter–spring species, notably the prymnesiophyte Phaeocystis globosa. Because wind speed is related to the North Atlantic Oscillation (NAO) index it was possible to correlate NAO index and P. globosa abundance. Only five abiotic variables representing interannual and long‐term variability, including Rhine discharge and NAO index, were needed to model the observed partitions in phytoplankton composition. It was concluded that interannual variability in the coastal phytoplankton composition was related to year‐to‐year changes in river discharge while the long‐term shift was caused by an alternating large‐scale meteorological phenomenon.     

Temperature modulated effects of nutrients on phytoplankton changes in a mountain lake

Piburger See, a dimictic mountain lake in Austria, experienced moderate cultural eutrophication in the 1950s. Lake restoration led to a re-oligotrophication in the 1990s with a decrease in seasonal phytoplankton biovolume until the late 1990s, but a reversed trend from the early 2000s onwards. We hypothesize that recent changes in phytoplankton biomass and functional structure are triggered by changes in lake nitrogen and silica concentrations, and we expect climate-related factors to modulate the trophic status of Piburger See. Phytoplankton data were analyzed by non-metric multidimensional scaling (NMDS) applied on biovolume of morpho-functional groups, combined with correlation analyses of environmental variables. Since the 2000s, short-term changes in phytoplankton of Piburger See were explained by varying concentrations and ratios of nitrogen and silica, while the inter-annual variability in phytoplankton species composition was rather attributed to superimposed rising water temperature and lake thermal stability. Our results underline the co-dominant role of phosphorus and nitrogen as phytoplankton drivers in lakes that experience periods of nitrogen limitation. The combined impact of nutrients and climate on phytoplankton development can thus mimic short-term increases in the trophic level of less productive lakes.     

Distribution of the phytoplankton from the Guri Reservoir (Venezuela)

The distribution of phytoplankton species of a tropical blackwater reservoir is discussed on the basis of spatial differences in water composition and of species abundance and diversity. Spatial heterogeneity in water composition identified three different environments within the reservoir itself: (1) strongly colored waters, high turbidity and iron concentrations at the inflow; (2) calcium enriched, nearly uncolored waters at El Pao Bay; (3) lightly colored water, higher transparency and a higher ratio monovalent to divalent cations in the main body of the reservoir. Three corresponding phytoplankton associations were found. Principal Component Analysis helped to explore the relationship of particular species with the abiotic factors. Among them, water color, turbidity, and mineralization proved to be determinant in habitat diversification.     

A comparison of natural and human determinants of phytoplankton communities in the Kentucky River basin,USA

Physical, chemical, and biological characteristics of the Kentucky River and its tributaries were assessed for one year to compare effects of seasonal, spatial, and human environmental factors on phytoplankton. Phytoplankton cell densities were highest in the fall and summer and lowest in the winter. Cell densities averaged 1162 (± 289 SE) cells m1^–1. Cell densities were positively correlated to water temperature and negatively correlated to dissolved oxygen concentration and to factors associated with high-flow conditions (such as, suspended sediment concentrations). Chrysophytes, diatoms, and blue-green algae dominated winter, spring, and summer assemblages, respectively. Ordination analyses (DCCA) indicated that variation in taxonomic composition of assemblages was associated with stream size as well as season.Spatial variation in phytoplankton assemblages and effects of humans was investigated by sampling 55 sites in low flow conditions during August. Phytoplankton density increased with stream size. Assemblages shifted in composition from those dominated by benthic diatoms upstream to downstream communities dominated by blue-green algae and small flagellates. Human impacts were assumed to cause higher algal densities in stream basins with high proportions of agricultural or urban land use than in basins with forested/mined land use. While density and composition of phytoplankton were positively correlated to agricultural land use, they were poorly correlated to nutrient concentrations. Phytoplankton diversity changed with water quality: decreasing with nutrient enrichment and increasing with conditions that probably changed species composition or inhibited algal growth. Human impacts on phytoplankton in running water ecosystems were as great or greater than effects by natural seasonal and spatial factors. Our results indicated that phytoplankton could be useful indicators of water quality and ecosystem integrity in large river systems.     

Phytoplankton monitoring by high performance flow cytometry: a successful approach?

BACKGROUND: Regular phytoplankton monitoring in Dutch coastal waters is performed as an indicator of the ecological state of these waters. The monitoring program is focused on temporal and spatial changes of species composition and abundance. Flow cytometry has been introduced to provide additional information, to improve ecosystem understanding, and to increase the efficiency of analysis and reportage. METHODS: Phytoplankton community abundance and composition were routinely determined by flow cytometry and microscopy at six locations in the North Sea over three annual cycles between 2000 and 2003. Supplementary measurements were also made for fluorescence (chlorophyll-a and other pigments) and, in combination with flow cytometric and microscopic data, were used to determine phytoplankton abundance and composition as a function of their size distribution. Real-time imaging of species was also used to identify species on the basis of their flow cytometric optical characteristics. RESULTS: Flow cytometric analysis took 15 min on average. Analysis including data processing, and Web site reportage took less than 1 h. Phytoplankton concentrations (cells/ml), biomass (fluorescence/ml), and concentration of phycoerythrin- or phycocyanin-containing cells (cells/ml) as a function of their algal size were produced every 2 weeks on average. The phytoplankton integrated annual concentration and biomass were used as ecological indicators for overall phytoplankton status. Real-time imaging of cells in flow enabled the identification of dominant species and was applied as an early warning system for Phaeocystis spp. CONCLUSIONS: The reproducibility and count precision due to the large number of observations of the flow cytometric technique provided reliable data for monitoring long-term trends. Flow cytometrically based analyses extended the lower detection limit (<0.5 microm) of analysis beyond the capabilities of other techniques such as the relation between small and larger phytoplankton, the relation between cell counts and biomass as a function of cell size, but also the ability to monitor and report on blooms of harmful algae. A good correlation was found between concentrations (cells/ml) measured by flow cytometry and microscopy. In practice, flow cytometric analysis of a single marine sample took 15 min on average.     

长江口及其邻近水域冬季浮游植物群集

应用Uterm hl方法分析了2005年2月28日至3月10日在长江口及其邻近水域进行的大面调查所获浮游植物采水样品,报道了该水域浮游植物的群落特征.初步鉴定浮游植物5门67属130种(含未定名25种).调查水域浮游植物群落主要由硅藻组成,其次为甲藻,此外还有少量的金藻、蓝藻和绿藻.主要优势种为具槽帕拉藻(Paralia sulcata)、中肋骨条藻(Skeletonema costatum)、圆海链藻(Thalassiosira rotula)、标志布莱克里亚藻(Bleakeleya nota-ta)、辐射圆筛藻(Coscinodiscus radiatus)和离心列海链藻(Thalassiosira excentrica).调查区浮游植物的细胞丰度介于0.1~90.0cells.ml-1,平均值为10.1cells.ml-1.浮游植物的水平分布特征是近岸处浮游植物丰度高,远岸处丰度低.水体表层的浮游植物细胞丰度最高,表层之下细胞丰度略有降低,但变化不大.浮游植物的细胞丰度和叶绿素a与硝酸盐、亚硝酸盐、铵盐、磷酸盐和硅酸盐浓度呈显著正相关,而与盐度呈负相关.调查区中部香农-威纳多样性指数和Pielou均匀度指数较高,而东北部和近岸水域较低.     

金门岛北部海域浮游植物的季节变动及与环境的关联

采用2013—2014年四季度月在金门岛北部海域获取的浮游植物及环境因子监测数据, 分析该区浮游植物的群落结构和季节变化及其与温度、盐度、悬浮物、营养盐、叶绿素等的关系, 初步探讨涉海工程建设对浮游植物群落的潜在影响。结果显示, 鉴定出的浮游植物隶属3门43属82种(不含未定种), 群落构成以硅藻为主, 其次是甲藻, 蓝藻仅1种。物种组成的季节差异较大, 3月物种贫乏, 1月次之, 7月和11月最丰富。四季丰度平均为47.09×103 cells/L, 1月丰度最高, 7月次之, 11月最低, 3月高于11月少许。四季优势种均为硅藻, 13个优势种分别为柔弱几内亚藻(Guinardia delicatula)、短角弯角藻(Ecampia zoodicaus)、骨条藻(Skeletonema spp.)、具槽帕拉藻(Paralia sulcata)、微小海链藻(Thalassiosira exigua)、标志星杆藻(Asterionella notula)、旋链角毛藻(Chaetoceros curvisetus)、新月菱形藻(Nitzchia closterium)、派格棍形藻(Bacillaria paxillifera)、异常角毛藻(Chaetoceros abmormis)、小细柱藻(Leptocylindrus minutum)、宽角曲舟藻(Pleurosigma angulatum)和美丽曲舟藻(Pleurosigma formosum)。不同季节优势种有一定程度交错, 仅在单季占优的有6种, 有2/3在3个以上季节出现, 具槽帕拉藻、骨条藻为四季优势种。浮游植物物种多样性和均匀度总体较好, 群落结构稳定。与毗邻海区相比, 本区物种丰富度偏低, 丰度高于毗邻海区, 种类组成相似, 优势种却有较大差别。Pearson相关分析表明, 溶解无机氮及活性磷酸盐仅在1月与丰度存在极显著的正相关, 是促使丰度为四季最高的原因。涉海工程施工产生的悬浮物和冲击波是影响浮游植物群落的主要因素, 大量海洋工程建设案例表明, 施工期造成的浮游植物丰度下降趋势和优势种更替混乱在工程结束后能得以恢复。     

Impact of increased river discharge on the phytoplankton community in the outer Oslofjord,Norway

An extraordinary flood event occurred in SouthernNorway in May–June 1995. The impact of fresh waterdischarge from the river Glomma on phytoplanktonspecies composition and on primary production duringthe flood was studied. The phytoplankton community wasdominated by species usually found in the fjord, thediatom Skeletonema costatum dominated thecommunity together with cyanobacteria. Potentiallyharmful species (e.g. Chrysochromulinapolylepis) were found in low cell densities. No largeincrease in nutrient concentrations were found.Primary production and uptake rates of nitrate andammonium were very low in low-salinity water near theriver outlet. Nutrients from the river water wereefficiently utilized in the open part of the fjord.The flood trigged a phytoplankton bloom dominated byharmless species commonly observed in the fjordplankton. This revised version was published online in July 2006 with corrections to the Cover Date.     

Seasonal variation in marine phytoplankton and ice algae at a shallow antarctic coastal site

The phytoplankton population near Davis, Vestfold Hills, Antarctica was monitored throughout 1982. Chlorophyll-a determinations and counts of living cells in both the water column and sea ice demonstrated a marked seasonality in phytoplankton abundane and species composition. From April to October nanoplanktonic organisms contributed most of the chlorophyll-a in both the sea ice and water column. Blooms of diatoms occurred in May, November and December in the bottom of the sea-ice and in January and February in the water column. Phaeocystis pouchetii was dominant during December in the water column. Large numbers of dead diatoms were found in winter. The concentrations of nitrate, dissolved inorganic phosphate and dissolved silicate increased throughout the year until December, when the concentrations of nitrate and silicate fell sharply, followed a month later by a reduction in phosphate concentration. The diversity of phytoplankton was greatest during the summer months.