Phytoplankton Population Dynamics Research Articles

西江下游浮游植物群落周年变化模式

西江肇庆段是珠江干流汇入珠三角河网水域的咽喉通道,对2009年该江段的浮游植物群落组成及变化进行系统阐析。调查期间共发现浮游植物7门,245种(包括变种、变型),其中硅藻和绿藻是浮游植物群落组成的最主要类群,分别占总种数的42.44%和34.69%,其次是裸藻和蓝藻。PCA分析结果显示,浮游植物各类群的种类丰富度和生物量的周年变化趋势主要受水温和径流量的影响。浮游植物种类丰富度的周年变化呈现明显的高温季节高,低温季节低的特征,除因大多数藻类物种直接喜好高温之外,径流量的增大有助于真浮游绿藻种类的外源注入及半浮游和偶然性浮游硅藻种类的增加。浮游植物生物量的周年变化呈现明显的双峰型,峰值分别出现在8月和11月。然而8月份第1个高峰出现之前,生物量波动不大,尽管水温的升高有助于生物量的增加,但是径流量增大所带来的稀释作用掩盖了水温上升对浮游植物生长的促进作用。真浮游植物生物量的变化趋势和数值与总浮游植物极其接近,主要得益于真浮游硅藻物种颗粒直链藻在总种群中的绝对优势地位。综上,水温升高对浮游植物种类丰富度和生物量的增长均有促进,径流量的增大虽然有助于种类丰富度的增加,但不利于生物量的增加。;The study on population dynamics of phytoplankton was still an important basic work for ecological investigations in large rivers. Through continuous sampling at the downstream of Xijiang River in 2009, the annual variation pattern of phytoplankton community structure and its correlation with environmental factors were demonstrated in this study. During the investigation, the 245 taxonomic species (including variant and derivative) in 7 groups were identified. The results showed that the diatom (Bacillariophyaceae) and chlorophytes were most abundant and they were 42.44% and 34.69% to total numbers respectively, and the Euglenophyta and Cyanobacteria were subsidiary to them. The above structure pattern was the similar to those of other large rivers in the world. 15 main species (dominant and frequent species) were listed in table 1, but only 3 species showed both high biomass contribution and high occurrence. For all the species, <em>Aulacoseira granulata</em> var. <em>granulata</em> was the predominant one because it showed continuous dominance except for its biggest occurrence. The annual variation pattern of total species abundance was high in warm seasons and low in cold seasons, which was also consistent with the diatom and green algae group. One reason is that many species favorite the high water temperature and the other is that the high discharge of warm seasons could also promote the inoculations from out-of-channel sources of true planktonic green algae and the complement of tychoplanktonic diatom species. This result has been confirmed by the annual pattern of true planktonic species richness, since the true planktonic diatom showed almost steady during the whole year, and the PCA analysis confirmed the two key factors. The annual phytoplankton biomass showed apparent bimodal pattern, and the two peaks appeared after the flood period. In addition, the biomass values showed almost no fluctuations besides the two peaks, which was because that the positive role of rising water temperature was covered by the negative role from the dilution impact of high discharge. According to the previous studies, self-sustaining populations of riverine algae were primarily based on meroplanktonic diatom species, whereas true planktonic populations, mostly chlorophytes depended on periodic inoculations from outer sources. Therefore, diatom would apparently precede chlorophytes when water discharge increased. In conclusion, the diatom and green algae were the most important groups of phytoplankton community in Xijiang River, and their annual variation pattern could strictly affect the total phytoplankton community. The phytoplankton species abundance was mainly determined by the true planktonic green algae and tychoplanktonic diatoms, and both water temperature and water discharge were the main reasons for their increments, and Si concentration was only beneficial for diatoms. The phytoplankton biomass was mainly determined by several dominant species (especially the true planktonic diatom species), and water temperature and discharge played important roles for the phytoplankton biomass during the seasons.

Variations of net primary productivity and phytoplankton community composition in the Indian sector of the Southern Ocean as estimated from ocean color remote sensing data

Abstract. Phytoplankton population dynamics play an important role in biogeochemical cycles in the Southern Ocean during austral summer. Recent environmental changes such as a rise in sea surface temperature (SST) are likely to impact on net primary productivity (NPP) and phytoplankton community composition. However, their spatiotemporal relationships are still unclear in the Southern Ocean. Here we assessed the relationships between NPP, dominant phytoplankton groups, and SST in the Indian sector of the Southern Ocean over the past decade (1997–2007) using satellite remote sensing data. As a result, we found a statistically significant reduction in NPP in the polar frontal zone over the past decade during austral summer. Moreover, the decrease in NPP positively correlated with the dominance of diatoms (Kendall's rank correlation τ = 0.60) estimated by a phytoplankton community composition model, but not correlated with SST. In the seasonal ice zone, NPP correlated with not only the dominance of diatoms positively (τ = 0.56), but also the dominance of haptophytes (τ = −0.54) and SST (τ = −0.54) negatively. Our results suggested that summer NPP values were strongly affected by the phytoplankton community composition in the Indian sector of the Southern Ocean.

Nitrate–nitrite dynamics and phytoplankton growth: Formulation and experimental evaluation of a dynamic model

A multi‐nutrient quota model was modified to describe the coupled dynamics of nitrate and nitrite utilization for four phytoplankton species, Picochlorum atomus (Butcher) (Chlorophyta), Nannochloropsis oculata (Droop) (Ochrophyta), Isochrysis sp. (Haptophyta), and Pyrocystis lunula (Schütt) (Dinophyta). Although rarely considered in nutrient‐limited phytoplankton models, nitrite can be an important nitrogen source, as it can be either released due to incomplete reduction of nitrate or taken up to supplement low nitrogen availability. The model accurately characterizes the dynamics of nitrite uptake and excretion, nitrate uptake and assimilation efficiency, and population growth for the study species in batch culture, despite the fact that the species display a range of qualitatively different nutrient utilization patterns. The good performance of the model suggests that per‐capita secretion and re‐assimilation of nitrite, together with changes to the per‐capita internal nitrogen supply, can be inferred from daily observations of medium nitrate and nitrite utilization and population growth. The model also reproduces qualitative characteristics of nitrite dynamics that have been observed in previous empirical studies, such as a rise in per‐capita nitrite secretion when culture medium nitrate concentrations and intracellular nitrogen levels are high. Our model therefore provides a new framework for evaluating the potential broader trophic consequences of the effects of nitrite uptake and release on the dynamics of phytoplankton populations.

ALGAE AS BIOINDICATORS FOR WATER POLLUTION IN THE AL-SORA - AL-SOFIA DRAINAGE CANAL AND ITS EFFECT ON EUPHRATES RIVER - AL-KALDIA

The present study aims to use algae ( Phytoplankton ) as bioindicators for the Evaluation of degree of pollution in the Al-sora Al-Sofia drainage canal and in Euphrates river from Al-Kaldia pre and post its confluence with drainage canal.Spatial variations of the major environmental factors effected phytoplankton Population dynamics were studied at 3 sites in drainage canal and 2 sites in Euphrates river in monthly basis from Nov. 2010 to Apr. 2011 . Result revealed that drainage canal is polluted according to high values of biological oxygen demand ( BOD ) with low level of dissolved oxygen , and high values of electrical conductivity , Total hardness , Total alkalinity , Sulphate and reactive phosphate values than Euphrates river . Four biological indices of pollution like Saprobic index( S.I ) , Pollution tolerance index ( P.T.I ) , Algal genus pollution index ( A.G.P.I ) and Shannon weaver - diversity index ( H ) , were adopted to classify the water quality of drainage canal and Euphrates river in comparison with the measured physical – chemical water quality . The result shows that the Shannon weaver – diversity index appear to be much more applicable for the classification of water quality of drainage canal and Euphrates river than Saprobic index , Pollution tolerance index and Algal genus pollution index . A total of ( 73 species ) of algae ( Phytoplankton ) were recorded . The diatoms were dominant ( 47 ) . The second dominating group was Cyanophyta ( 14 ) followed by Chlorophyta ( 4 ) Pyrrophyta ( 4 ) Euglenophyta ( 3 ) and then by Cryptophyta ( 1 ) . The result also indicated that following species were the dominant : Nitzschia dissipata , N. palea , Oscillatoria lacostris and O. tenuis .

Classification of marine diatoms using pigment ratio suites

Diatoms are widely distributed in many temperate areas and some species frequently form extensive blooms in spring. Hence, monitoring the variations of specific genera or species of diatoms is necessary for studying phytoplankton population dynamics in marine ecosystems. To test whether pigment ratios can be used to identify diatoms at a below-class taxonomic level, we analyzed 14 species/strains of diatoms isolated from Chinese seas using high performance liquid chromatography (HPLC). We normalized all pigment concentrations to total chlorophyll a to calculate the ratios of pigment to chlorophyll a, and calculated the ratios between accessory pigments (or pigment sums). Cluster analysis indicated that these diatoms could be classified into four clusters in terms of three accessory pigment ratios: chlorophyll c2: chlorophyll c1, fucoxanthin:total chlorophyll c and diadinoxanthin:diatoxanthin. The classification results matched well with those of biological taxonomy. To test the stability of the classification, pigment data from one species, cultured under different light intensities, and five new species/strains were calculated and used for discriminant analysis. The results show that the classification of diatom species using pigment ratio suites was stable for the variations of pigment ratios of species cultured in different light intensities. The introduction of new species, however, may confuse the classification within the current scheme. Classification of marine diatoms using pigment ratio suites is potentially valuable for the fine chemotaxonomy of phytoplankton at taxonomic levels below class and would advance studies on phytoplankton population dynamics and marine ecology.

Phytoplankton responses to changes in macrophyte density in a tropical artificial pond in Zaria, Nigeria

The response of phytoplankton population dynamics to changes in densities of Nymphaea lotus L. and Polygonum limbatum Meisn. was studied in an artificial pond in Zaria, Nigeria, from June to November 2007. Antagonistic effects of these macrophytes on Netrium sp., Staurastrum sp., Ulothrix sp., Marssionella sp. and Closterium sp. were collinear and clearly separated from other environmental effects. Dermatophyton sp., Cyanoderma sp. and Pernia sp. were sensitive to high densities of both macrophytes, and were closely positively associated with DO and pH. Qualitative analysis confirmed the presence of glycosides, anthraquinone, saponins, steroids, triterpenes, flavonoids and alkaloids in N. lotus and P. limbatum. Fourier transform infra-red analysis peaks were recorded, confirming the presence of these allelochemical groups in both species. The observed variations in phytoplankton community structure and dynamics were closely linked to the presence of these macrophytes as well as to environmental conditions in the pond.

Population dynamics of phytoplankton, heterotrophic bacteria, and viruses during the spring bloom in the western subarctic Pacific

We characterized the community composition of phytoplankton in the western subarctic Pacific from the pre-bloom to the decline phase of the spring bloom with special reference to decreases in the silicic acid concentration in surface waters as an index for diatom bloom development. Furthermore, responses of heterotrophic bacteria and viruses to the spring bloom were also concomitantly investigated. Under pre-bloom conditions when nutrients were abundant but the surface mixed layer depth was relatively deep, chlorophyll (Chl) a concentrations were consistently low and green algae (chlorophytes and prasinophytes), cryptophytes, and diatoms were predominant in the phytoplankton assemblages as estimated by algal pigment signatures. Together with the shallowing of the mixed layer depth and the decrease in silicic acid concentration, diatoms bloomed remarkably in the Oyashio region, though the magnitude of the bloom in the Kuroshio–Oyashio transition (hereafter Transition) region was relatively small. A total of 77 diatom species were identified, with the bloom-forming diatoms mainly consisting of Thalassiosira, Chaetoceros, and Fragilariopsis species. It has become evident that the carotenoid fucoxanthin can serve as a strong indicator of the diatom carbon biomass during the spring diatom bloom. Differences in the species richness of diatoms among stations generally enabled us to separate the Oyashio bloom stations from the Transition and the Oyashio pre-bloom stations. Relatively high values of the Shannon–Wiener index for the diatom species were also maintained during the Oyashio bloom, indicating that a wide variety of species then shared dominance. In the decline phase of the Oyashio bloom when surface nutrient concentrations decreased, senescent diatom cells increased, as inferred from the levels of chlorophyllide a. Although the cell density of heterotrophic bacteria changed little with the development of the diatom bloom, viral abundance increased toward the end of the bloom, suggesting an increased likelihood of mortality among organisms including diatoms resulting from viral infection. This is the first report on the microbial trophodynamics, including viruses, during the spring diatom bloom in the western subarctic Pacific.

Water Quality and Phytoplankton Population in Sewage Fed River of Mahanadi, Orissa, India

Seasonal dynamics of phytoplankton populations and nutrient status of water were studied in sewage fed river Mahanadi of Orissa for a period of one year covering three seasons. Phytoplankton population and water analysis was performed using standard procedure. Maximum population density was observed in the winter season followed by summer and monsoon. Higher phytoplankton populations were encountered in Sikharpur (site IV) which corresponded to the fluctuation of prevailing conductivity, turbidity, dissolved oxygen, better organic load and chemical oxygen demand content of the said habitat. A total of 25 species belonging to three different groups were recorded during the study period. Spirogyra ornata, Navicula cuspidate, Oscillatoria limnosa were the most abundant followed by Zygnema, Ulothrix, Nitchia and Phormidium. Higher concentration of diatom at Sikharpur site indicates polluted zone of the river. Oscillatoria and Nitchella species at sewage affected sites can be used as an indicator of organic pollution in the river. Our findings highlighted the deterioration of water quality in the river due to industrialization and human activities. Proper biological and chemical treatment of domestic sewage and industrial effluents before discharge to river system is suggested.

Temporal Patterns in Glycolate-Utilizing Bacterial Community Composition Correlate with Phytoplankton Population Dynamics in Humic Lakes

Previous observations of correlated community dynamics between phytoplankton and bacteria in lakes indicate that phytoplankton populations may influence bacterial community structure. To investigate the possibility that bacterial use of phytoplankton exudates contributes to observed patterns of community change, we characterized the diversity and dynamics of heterotrophic bacterioplankton with genetic potential to use glycolate, a photorespiration-specific exudate, in five lakes over a 15-week period. Culture-independent approaches were used to track different bacterial phylotypes represented by DNA sequence variation in the functional gene glycolate oxidase subunit D (glcD). glcD gene sequences from freshwater bacteria exhibited broad phylogenetic diversity, including sequences representing the Alpha-, Beta-, and Gammaproteobacteria, Actinobacteria, Bacteroidetes, Firmicutes, and Verrucomicrobia. The majority of glcD gene sequences were betaproteobacterial, with 48% of the sequences clustering with the glcD gene from the cosmopolitan freshwater species Polynucleobacter necessarius. Terminal restriction fragment length polymorphism fingerprinting of the glcD gene revealed changes in glycolate-utilizing assemblages over time. An average of 39% of within-lake temporal variation in glycolate-utilizing assemblages across five lakes was explained by phytoplankton community composition and dynamics. The interaction between phytoplankton populations and the environment explained an additional 17% of variation on average. These observations offer new insight into the diversity and temporal dynamics of freshwater bacteria with genetic potential to use glycolate and support the hypothesis that algal exudates influence the structure of bacterial communities.

Dynamics of marine bacterial and phytoplankton populations using multiplex liquid bead array technology

Heterotrophic bacteria and phytoplankton dominate the biomass and play major roles in the biogeochemical cycles of the surface ocean. Here, we designed and tested a fast, high-throughput and multiplexed hybridization-based assay to detect populations of marine heterotrophic bacteria and phytoplankton based on their small subunit ribosomal DNA sequences. The assay is based on established liquid bead array technology, an approach that is gaining acceptance in biomedical research but remains underutilized in ecology. End-labelled PCR products are hybridized to taxon-specific oligonucleotide probes attached to fluorescently coded beads followed by flow cytometric detection. We used ribosomal DNA environmental clone libraries (a total of 450 clones) and cultured isolates to design and test 26 bacterial and 10 eukaryotic probes specific to various ribotypes and genera of heterotrophic bacteria and eukaryotic phytoplankton. Pure environmental clones or cultures were used as controls and demonstrated specificity of the probes to their target taxa. The quantitative nature of the assay was demonstrated by a significant relationship between the number of target molecules and fluorescence signal. Clone library sequencing and bead array fluorescence from the same sample provided consistent results. We then applied the assay to a 37-day time series of coastal surface seawater samples from the Southern California Bight to examine the temporal dynamics of microbial communities on the scale of days to weeks. As expected, several bacterial phylotypes were positively correlated with total bacterial abundances and chlorophyll a concentrations, but others were negatively correlated. Bacterial taxa belonging to the same broad taxonomic groups did not necessarily correlate with one another, confirming recent results suggesting that inferring ecological role from broad taxonomic identity may not always be accurate.

Patterns of Diversity in Marine Phytoplankton

Spatial diversity gradients are a pervasive feature of life on Earth. We examined a global ocean circulation, biogeochemistry, and ecosystem model that indicated a decrease in phytoplankton diversity with increasing latitude, consistent with observations of many marine and terrestrial taxa. In the modeled subpolar oceans, seasonal variability of the environment led to competitive exclusion of phytoplankton with slower growth rates and lower diversity. The relatively weak seasonality of the stable subtropical and tropical oceans in the global model enabled long exclusion time scales and prolonged coexistence of multiple phytoplankton with comparable fitness. Superimposed on the decline in diversity seen from equator to pole were "hot spots" of enhanced diversity in some regions of energetic ocean circulation, which reflected lateral dispersal.

Seasonal dynamics of macrophytes and phytoplankton in shallow lakes: a eutrophication‐driven pathway from plants to plankton?

Summary1. Seasonal relationships between macrophyte and phytoplankton populations may alter considerably as lakes undergo eutrophication. Understanding of these changes may be key to the interpretation of ecological processes operating over longer (decadal‐centennial) timescales.2. We explore the seasonal dynamics of macrophytes (measured twice in June and August) and phytoplankton (measured monthly May–September) populations in 39 shallow lakes (29 in the U.K. and 10 in Denmark) covering broad gradients for nutrients and plant abundance.3. Three site groups were identified based on macrophyte seasonality; 16 lakes where macrophyte abundance was perennially low and the water generally turbid (‘turbid lakes’); 7 where macrophyte abundance was high in June but low in August (‘crashing’ lakes); and 12 where macrophyte abundance was high in both June and August (‘stable’ lakes). The seasonal behaviour of the crashing and turbid lakes was extremely similar with a consistent increase in nutrient concentrations and chlorophyll‐a over May–September. By contrast in the stable lakes, seasonal changes were dampened with chlorophyll‐a consistently low (&lt;10–15 μg L−1) over the entire summer. The crashing lakes were dominated by one or a combination of Potamogeton pusillus, Potamogeton pectinatus and Zannichellia palustris, whereas Ceratophyllum demersum and Chara spp. were more abundant in the stable lakes.4. A long‐term loss of macrophyte species diversity has occurred in many shallow lakes affected by eutrophication. One common pathway is from a species‐rich plant community with charophytes to a species‐poor community dominated by P. pusillus, P. pectinatus and Z. palustris. Such compositional changes may often be accompanied by a substantial reduction in the seasonal duration of plant dominance and a greater tendency for incursions by phytoplankton. We hypothesise a slow‐enacting (10–100 s years) feedback loop in nutrient‐enriched shallow lakes whereby increases in algal abundance are associated with losses of macrophyte species and hence different plant seasonal strategies. In turn such changes may favour increased phytoplankton production thus placing further pressure on remaining macrophytes. This study blurs the distinction between so‐called turbid phytoplankton‐dominated and clear plant‐dominated shallow lakes and suggests that plant loss from them may be a gradual process.

Benthic–pelagic coupling and the seasonal silica cycle in the Bay of Brest (France): new insights from a coupled physical–biological model

A fully transient, 2-dimensional physical and biological model has been developed to quantify the seasonal cycle of silica in the estuaries-coastal zone continuum of the Bay of Brest (France). The numerical model includes an explicit representation of the benthic-pelagic coupling, which is stimulated by the increasing density of an invasive megabenthic filter feeder, the slipper limpet Crepidula fornicata. The selected spatial resolution allows resolution of the heterogeneous density distribution of these organisms in the bay. Results show that the benthic nutrient dynamics are highly variable and strongly depend on the local conditions. This heterogeneity is not reflected in the pelagic phytoplankton Population dynamics because transport and mixing homogenize the distribution of nutrients and biomass. A seasonally resolved silica budget over the entire bay and estuaries emphasizes the important contribution of the benthic recycling fluxes to the supply of dissolved silica (dSi) during the productive period (similar to 50%, from 1 April to 1 September). In a prognostic scenario which forecasts the impact of removing the invasive benthic filter feeders, the dSi efflux is reduced by 63% and a pronounced harmful algal bloom of dinoflagellates develops in late summer.

Coupled Effects of Small-Scale Turbulence and Phytoplankton Biomass in a Small Stratified Lake

Recent laboratory studies demonstrated that small-scale fluid motion mediates phytoplankton physiological responses. We have investigated to what extent the laboratory studies are consistent with field measurements in a small stratified lake. We propose the rate of energy dissipation and corresponding Kolmogorov velocity are important scaling variables that describe the enhanced algal growth and the uptake of nutrients in a moving fluid under laboratory and field conditions. The ratio of nutrient flux to an alga in a moving fluid versus the nutrient flux in a stagnant fluid (Sherwood number) is quantified by the ratio of advective nutrient transport to molecular diffusion of a nutrient (Péclet number, PeK). The advective transport of nutrients is described by the layer-averaged Kolmogorov velocity (ũK). An enhanced algal growth due to fluid motion is proposed over the Péclet number range 6.7>PeK>1.3, with the maximal growth at PeK=2.9. Field measurements recorded by a microstructure profiler demonstrated encouraging agreement between laboratory and field findings. The current mechanistic models of phytoplankton population dynamics could consider the proposed Péclet number with redefined characteristic velocity scale (ũK) in the formulation of subgrid scale closure fluxes on nutrient uptake and growth rate. Furthermore, the laboratory and field results presented in this study are intended to motivate researchers to question the validity of standard laboratory biotoxicity protocols and to modify existing procedures in the examination of effluent toxicity in the environment by including the fluid motion.

A dynamic model of darkness tolerance for phytoplankton: model description

To analyze various effects of prolonged darkness on phytoplankton population dynamics, we developed a dynamic model of darkness tolerance for phytoplankton and investigated its characteristics. To construct the basic concepts of the model, we categorized various changes in abundance of phytoplankton both during prolonged darkness and after reillumination into several patterns, and then considered the physiological processes producing these patterns. The nature of darkness tolerance was considered to incorporate previously experienced light conditions, including darkness, as a physiological activity, and members of the same phytoplankton species exhibit different dynamics even in identical light conditions due to such career effects. Taking this into consideration, we developed a cell quota model in relation to darkness tolerance. State variables for abundance were indicated by cell numbers, and physiological condition by three intracellular carbon pools with different physiological functions. Using our model, we analyzed the various changes in abundance of phytoplankton in relation to exposure to prolonged darkness. Various responses in terms of phytoplankton abundance to prolonged darkness and after reillumination were successfully reproduced by the model that simply assumed that deterioration of physiological mechanics, such as photosynthetic functions, was due to a prolonged dark condition. On the basis of the results of calculation and assumptions for the model, we discuss the limitations, problems, and effectiveness of the model.

Light-limited population dynamics of phytoplankton: modeling light and depth effects

Light has received very less attention as a selective factor, probably because the changing vertical light gradient makes light a rather complex factor when compared with the nutrient competition. In our study we modified an analytically tractable model based upon the Beer–Lambert law. The study aimed to predict the outcome of phytoplankton competition for light, on the basis of field measurements. When we considered competition theory, Fragilaria was found to be more competitive than other genera. The overall result shows that the trends flow in the following manner; Fragilaria > Gomphonema > Diatoma > Amphora > Achnanthes.

INFLUENCE OF IRRADIANCE ON VIRUS-ALGAL HOST INTERACTIONS(1).

The effect of different irradiance levels on the interactions between the algal host and its virus was investigated for two marine phytoplankton, Phaeocystis globosa Scherff. and Micromonas pusilla (Butcher) Manton et Parke. The algal cultures were acclimated at 25, 100, and 250 μmol photons · m(-2) · s(-1) (LL, ML, and HL, respectively), after which they were infected with a lytic virus (PgV-07T and MpV-02T) and monitored under the appropriate irradiance and in darkness. The effect of irradiance levels on the host-virus interactions differed for the two algal host-virus systems examined. For P.globosa, the LL-acclimated cultures showed a 4 h prolonged latent period (11-16 h), which may be related to the subsaturated growth observed at this irradiance. The burst size was reduced by 50% at LL and HL compared to ML (525 PgV · cell(-1) ). The fraction of infectious viruses, however, remained unchanged. Viral replication was prevented when the LL P.globosa cultures were kept in darkness (up to 48 h) but recovered when placed back into the light. PgV-07T still replicated in the dark for the ML- and HL-acclimated cultures, but viral yield was reduced by 50%-85%. For M.pusilla, the burst size (285-360 MpV · cell(-1) ), the infectivity, and the latent period of MpV-02T (7-11 h) remained unaffected by the incident light. Conversely, darkness not only inhibited MpV replication but also resulted in substantial cell lysis of the noninfected cultures. Our study implies that irradiance level is an important factor controlling algal host-virus interactions and hence the dynamics of phytoplankton populations.

Laboratory study on the effects of nutrient enrichment on a phytoplankton population in Sawa Lake, Iraq

Nutrient enrichment of Sawa lake water was made using different nitrogen and phosphorus concentrations during autumn and spring at three stations. Different concentrations of nitrogen, phosphorus and N: P ratios were used to test variations in phytoplankton population dynamics. Nitrogen at a concentration of 25 µmole.l-1 and N: P ratio of 10:1 gave highest phytoplankton cell number at all stations and seasons. A total of 64 algal taxa dominated by Bacillariophyceae followed by Cyanophyceae and Chlorophyceae were identified. The values of Shannon index of diversity were more than one in the studied stations.

Laboratory study on the effects of nutrient enrichment on a phytoplankton population in Sawa Lake, Iraq

Nutrient enrichment of Sawa lake water was made using different nitrogen and phosphorus concentrations during autumn and spring at three stations. Different concentrations of nitrogen, phosphorus and N: P ratios were used to test variations in phytoplankton population dynamics. Nitrogen at a concentration of 25 µmole.l-1 and N: P ratio of 10:1 gave highest phytoplankton cell number at all stations and seasons. A total of 64 algal taxa dominated by Bacillariophyceae followed by Cyanophyceae and Chlorophyceae were identified. The values of Shannon index of diversity were more than one in the studied stations.

Furtive foes: algal viruses as potential invaders

AbstractLawrence, J. E. 2008. Furtive foes: algal viruses as potential invaders. – ICES Journal of Marine Science, 65: 716–722. Viruses are abundant in the world's oceans, existing through parasitic relationships with their various hosts. Algal viruses infect representatives of all major algal taxa, influencing phytoplankton population dynamics, marine foodweb interactions, and global biogeochemical cycling. Although the transportation, spread, and persistence of specific viruses remain to be explored fully, the potential for algal virus introductions and invasions is clearly evident. An estimated 3 × 1022 viruses are transported globally in ballast water alone, destined for ports where few physiological or physical barriers inhibit their invasive success. This fact, coupled with recent findings that viruses are not homogeneously distributed throughout the world's oceans, suggests that virus invasions pose a potential threat to marine ecosystems.