Individual Phytoplankton Groups Research Articles

Eukaryotic algal community composition in tropical environments from solar salterns to the open sea

Tropical environments with unique abiotic and biotic factors—such as salt ponds, mangroves, and coral reefs—are often in close proximity. The heterogeneity of these environments is reflected in community shifts over short distances, resulting in high biodiversity. While phytoplankton assemblages physically associated with corals, particularly their symbionts, are well studied, less is known about phytoplankton diversity across tropical aquatic environments. We assess shifts in phytoplankton community composition along inshore to offshore gradients by sequencing and analyzing 16S rRNA gene amplicons using primers targeting the V1-V2 region that capture plastids from eukaryotic phytoplankton and cyanobacteria, as well as heterotrophic bacteria. Microbial alpha diversity computed from 16S V1-V2 amplicon sequence variant (ASV) data from 282 samples collected in and around Curaçao, in the Southern Caribbean Sea, varied more within the dynamic salt ponds, salterns, and mangroves, compared to the seemingly stable above-reef, off-reef, and open sea environments. Among eukaryotic phytoplankton, stramenopiles often exhibited the highest relative abundances in mangrove, above-reef, off-reef, and open sea environments, where cyanobacteria also showed high relative abundances. Within stramenopiles, diatom amplicons dominated in salt ponds and mangroves, while dictyochophytes and pelagophytes prevailed above reefs and offshore. Green algae and cryptophytes were also present, and the former exhibited transitions following the gradient from inland to offshore. Chlorophytes and prasinophyte Class IV dominated in salt ponds, while prasinophyte Class II, including Micromonas commoda and Ostreococcus Clade OII, had the highest relative abundances of green algae in mangroves, above-reef, off-reef, and the open sea. To improve Class II prasinophyte classification, we sequenced 18S rRNA gene amplicons from the V4 region in 41 samples which were used to interrelate plastid-based results with information on uncultured prasinophyte species from prior 18S rRNA gene-based studies. This highlighted the presence of newly described Ostreococcus bengalensis and two Micromonas candidate species. Network analyses identified co-occurrence patterns between individual phytoplankton groups, including cyanobacteria, and heterotrophic bacteria. Our study reveals multiple uncultured and novel lineages within green algae and dictyochophytes in tropical marine habitats. Collectively, the algal diversity patterns and potential co-occurrence relationships observed in connection to physicochemical and spatial influences help provide a baseline against which future change can be assessed.

Phytoplankton Sensitivity to Heavy Metals in Baltic Coastal Lakes.

This study aimed to compare concentrations of chlorophyll-a between individual phytoplankton groups for four shallow Baltic coastal lakes, varying in type of connection with the sea. For two years, the research focused on quantifying the effects of abiotic factors—concentrations of heavy metals (Ba, Bi, Cr, Cu, Mn, Fe, Ni, Pb, and Zn) and hydrological connectivity—on phytoplankton composition, biomass, and photosynthetic activity. Our results show that hydrological factors are the main predictors of phytoplankton structure. The lakes differed in salinity: freshwater vs. brackish vs. transitional lakes. Irrespective of lake type, the dominant group was that of Cyanobacteria (~80%), but their percentage contribution was lower in the brackish lake. Baltic seawater intrusion resulted in a decrease in heavy-metal concentrations in lake water for Fe, Zn, Pb, and Bi. Redundancy analysis (RDA) suggested positive effects of some heavy metals on the biomass of the Chlorophyta and Bacillariophyta. For the Cryptophyta only, a slight decrease in biomass was linked with increased metal concentrations in open water.

Biogeochemical Model Optimization by Using Satellite-Derived Phytoplankton Functional Type Data and BGC-Argo Observations in the Northern South China Sea

Marine biogeochemical models have been widely used to understand ecosystem dynamics and biogeochemical cycles. To resolve more processes, models typically increase in complexity, and require optimization of more parameters. Data assimilation is an essential tool for parameter optimization, which can reduce model uncertainty and improve model predictability. At present, model parameters are often adjusted using sporadic in-situ measurements or satellite-derived total chlorophyll-a concentration at sea surface. However, new ocean datasets and satellite products have become available, providing a unique opportunity to further constrain ecosystem models. Biogeochemical-Argo (BGC-Argo) floats are able to observe the ocean interior continuously and satellite phytoplankton functional type (PFT) data has the potential to optimize biogeochemical models with multiple phytoplankton species. In this study, we assess the value of assimilating BGC-Argo measurements and satellite-derived PFT data in a biogeochemical model in the northern South China Sea (SCS) by using a genetic algorithm. The assimilation of the satellite-derived PFT data was found to improve not only the modeled total chlorophyll-a concentration, but also the individual phytoplankton groups at surface. The improvement of simulated surface diatom provided a better representation of subsurface particulate organic carbon (POC). However, using satellite data alone did not improve vertical distributions of chlorophyll-a and POC. Instead, these distributions were improved by combining the satellite data with BGC-Argo data. As the dominant variability of phytoplankton in the northern SCS is at the seasonal timescale, we find that utilizing monthly-averaged BGC-Argo profiles provides an optimal fit between model outputs and measurements in the region, better than using high-frequency measurements.

Phytoplankton production in relation to simulated hydro- and thermodynamics during a hydrological wet year – Goczałkowice reservoir (Poland) case study

Phytoplankton is one of the crucial components of water body ecosystems. Its presence and development depend on biological, physical and chemical factors and in consequence it is an important indicator of ecosystem condition. Monitoring of phytoplankton production, measured as chlorophyll a concentration, is a useful tool for assessing the status of dam reservoirs. Modeled chlorophyll a concentrations are used as water quality indicators in locations not included in monitoring systems, in situations when the temporal resolution of the monitoring is not enough, and in assessments of the impacts of future activities. Therefore, the aim of this study was to find correlations between hydro- and thermodynamics and the chlorophyll a concentration for possible application in reservoir monitoring and management, using an ELCOM-CAEDYM model. The analysis included summer and fall which are most prone to algal blooms, and four phytoplankton groups identified as dominant in the reservoir based on periodic observations.Comparisons of simulated water temperature and both observed and simulated chlorophyll a concentrations confirmed that these variables are significantly correlated (correlation of hourly chlorophyll a and water temperature was 0.70, ranging from 0.55 to 0.81 in the bottom and surface water layers, respectively, while for daily outputs it was 0.74, ranging from 0.60 to 0.83). This relation was stronger than that of chlorophyll a to nutrient (N, P and Si) concentrations. What is more, the method used allowed the assessment of a much more detailed spatial and temporal distribution of phytoplankton groups compared with conventional monitoring techniques.The study indicated that the phytoplankton community was dominated by Chlorophytes and Diatoms with a larger share of Chlorophytes in shallow parts of the reservoir. This domination was weaker after short water mixing events in summer and especially after the fall turnover. The increase in phytoplankton diversity was estimated to occur mainly near the surface and in shallow parts of the reservoir. Most of the observed concentrations of individual phytoplankton groups differed from simulation results by less than 25% and the model reflected accurately 74% of observed trends in concentrations. Calculated chlorophyll a concentration was well matched to hourly monitoring data (mean squared error = 5.6, Nash–Sutcliffe model efficiency coefficient = 0.51, Pearson correlation coefficient = 0.72 and p-value = 0.0007).High compatibility of the model to the values measured in the reservoir make it a promising tool for the prediction and planning of actions aimed at maintaining good functioning of the reservoir.

Under-ice mesocosms reveal the primacy of light but the importance of zooplankton in winter phytoplankton dynamics.

Factors that regulate planktonic communities under lake ice may be vastly different from those during the open‐water season. Expected changes in light availability, ice cover, and snowfall associated with climate change have accelerated the need to understand food web processes under ice. We hypothesized that light limitation (bottom‐up control) outweighs zooplankton grazing (top‐down control) influence on phytoplankton biovolume and community structure under ice in a north temperate lake. Using in situ under‐ice mesocosm experiments, we found that light had stronger effects on phytoplankton abundance than zooplankton, as expected. Specifically, low light limited growth of diatoms, cryptophytes, and chrysophytes. Zooplankton, however, also significantly affected some individual phytoplankton groups by decreasing diatoms and cryptophytes, in contrast to the common assumption that zooplankton grazing has negligible effects under ice. Ammonium and soluble reactive phosphorus (SRP) were lowest in high light treatments presumably through uptake by phytoplankton, whereas ammonium and SRP were highest in high zooplankton treatments, likely a result of zooplankton excretion. In situ experimental studies are commonly applied to understand food web dynamics in open‐water conditions, but are extremely rare under ice. Our results suggest that changes in the light environment under ice have significant, rapid effects on phytoplankton growth and community structure and that zooplankton may play a more active role in winter food webs than previously thought. Changes in snow and ice dynamics associated with climate change may alter the light environment in ice‐covered systems and significantly influence community structure.

Phytoneuston and Chemical Composition of Surface Microlayer of Urban Water Bodies

The concentration of chemical and biological parameters in the ecotone of the surface microlayer (SML) occurring between the hydrosphere and the atmosphere of urban water bodies was investigated. Parallel, sub-surface water (SUB) analyses were carried out to compare the SML properties with the water column. The concentrations of trace metals, macronutrients, nutrients, chlorophyll a, pheophytin, abundance and biomass of phytoplankton and the number of heterotrophic bacteria in both studied layers were analyzed. Each of the studied groups of chemical parameters was characterized by specific properties of accumulation. Trace metals occurring in concentrations below 1 ppm, such as Al, Ba, Cd, Cr, Cu, Fe, Mn, Ni, Zn and metalloid As, were accumulated to a higher degree in SML than in SUB. Macroelement concentrations, with the exception of Mg, were lower in the SML compared to the SUB. Nutrients, autotrophic and heterotrophic microorganisms occurred in the SML to a higher degree than in the SUB. Bacillariophyceae dominated the analyzed water bodies, which are typical for the spring period, as well as Chrysophyceae, Chlorophyceae, Dinophyceae and Euglenophyceae. Cyanobacteria dominated in one of the ponds. The abundance of individual phytoplankton groups was significantly correlated with Ca, K, Na, P-org, SO42−, F−, Al and Sr.

Spatio-temporal dynamics of phytoplankton functional groups in the South China Sea and their relative contributions to marine primary production

The sea-surface distribution of four phytoplankton functional groups in the South China Sea (SCS) namely Coccolithophores (Coc), Diatoms (Dia), Cyanobacteria (Cya) and Chlorophytes (Chlo) was studied across spatial and temporal scales. The time-series datasets derived from the National Aeronautic and Space Administration (NASA) Ocean Biogeochemical Model and retrieved via the Giovanni Portal were analysed statistically with well-known methods including Pearson’s correlation coefficient, ordinary least square regression (OLR), Maximum Entropy Spectral Analysis (MESA) and Principal Components Analysis (PCA). The data were analysed for relative abundance, seasonality, cyclicity, long-term trends, spatial variability, inter-relationships, and relative contributions of individual phytoplankton groups to primary production (PP, using Chl-a as a proxy). The results reveal that the numerically dominant phytoplankton group in terms of relative abundance is Cya, comprising about 57% of the planktonic biomass, followed closely by Coc (about 40%), while Dia constitutes almost 3% of the total abundance. Dia was found to have the strongest annual cycle, and hence displayed the highest rate of seasonal variability. Clear spatial segregation patterns have also been uncovered; Coc and Dia are strongly correlated in the Northern SCS (NSCS) while Cya dominate in Southern SCS (SSCS). Coc and Dia display a strong positive correlation with PP, whereas the seasonal relationships between Cya and Chlo with PP are non-linear, and hence appear statistically non-significant. The rise in the trend of Cya and decrease in Coc, since 2004, may be indicative of changes in successional patterns of phytoplankton functional groups in the SCS. This study, therefore, sets the precedence for more robust research to uncover the immediate and remote causes of the observed spatiotemporal changes in marine phytoplankton dynamics and to develop predictive models of marine primary productivity (MPP) and ecological health.

Assimilation of Global Total Chlorophyll OC‐CCI Data and Its Impact on Individual Phytoplankton Fields

AbstractThe coupled ocean circulation‐ecosystem model MITgcm‐REcoM2 is used to simulate biogeochemical variables in a global configuration. The ecosystem model REcoM2 simulates two phytoplankton groups, diatoms and small phytoplankton, using a quota formulation with variable carbon, nitrogen, and chlorophyll contents of the cells. To improve the simulation of the phytoplankton variables, chlorophyll‐a data from the European Space Agency Ocean‐Color Climate Change Initiative (OC‐CCI) for 2008 and 2009 are assimilated with an ensemble Kalman filter. Utilizing the multivariate cross covariances estimated by the model ensemble, the assimilation constrains all model variables describing the two phytoplankton groups. Evaluating the assimilation results against the satellite data product SynSenPFT shows an improvement of total chlorophyll and more importantly of individual phytoplankton groups. The assimilation improves both phytoplankton groups in the tropical and midlatitude regions, whereas the assimilation has a mixed response in the high‐latitude regions. Diatoms are most improved in the major ocean basins, whereas small phytoplankton show small deteriorations in the Southern Ocean. The improvement of diatoms is larger when the multivariate assimilation is computed using the ensemble‐estimated cross covariances between total chlorophyll and the phytoplankton groups than when the groups are updated so that their ratio to total chlorophyll is preserved. The comparison with in situ observations shows that the correlation of the simulated chlorophyll of both phytoplankton groups with these data is increased whereas the bias and error are decreased. Overall, the multivariate assimilation of total chlorophyll modifies the two phytoplankton groups separately, even though the sum of their individual chlorophyll concentrations represents the total chlorophyll.

Spatial and temporal structure of phytoplankton in 2014-2016 in the Poddabie area on the southern Baltic Sea

In the Baltic Sea, there can be observed seasonal changes of the phytoplankton structure during which the species composition, abundance and phytoplankton biomass change. However, the spatial and temporal variability of individual phytoplankton groups is not the same in all the regions of the Baltic. The only research (and available studies) of phytoplankton in these shallow central sea basin zones is conducted by Institute of Meteorology and Water Management (IMWM) as part of the HELCOM Baltic Sea Monitoring at station P16, which is located closest to the studied area. Therefore, in the years 2014-2016 phytoplankton seasonality studies were carried out, which allowed to supplement data in the area of the central coast of the south Baltic [61]. Based on the above literature, the aim of this study was to determine the temporal and spatial structure and to examine the species composition of phytoplankton occurrence and biodiversity in the Poddabie region from November 2014 till September 2016. The following article presents the results obtained at 3 measuring stations (P1, P2 and P3) in the area of Poddabie. These results confirm typical changes of phytoplankton on 3 measurement stations depending on the season of the year. The collected data for this article is the second part of the three monographs on the area on the central coast of the southern Baltic. It show the exact results of the species composition and seasonal changes of phytoplankton in the Poddabie region. The average values of phytoplankton abundance and biomass were typical for this sort of coastal waters and there were no significant species differences between these stations. Comparing the results obtained in this study with the data from the IMWM annual reports for the last decade, it can be noticed that the volumes and fluctuations of total biomass and phytoplankton abundance in the three analysed areas are in line with trends typical for the South Baltic coastal area

Seasonal variability of phytoplankton in river Słupia of the southern Baltic Sea

In the Baltic Sea, there can be observed seasonal variations in the structure of phytoplankton. These organisms are particularly sensitive to changes in different environmental parameters. The consequence of these changes is cyclical repeated every year fluctuation of the species composition, their abundance and biomass of phytoplankton. The spatial and temporal variability of individual phytoplankton groups is not the same in different regions of the Baltic Sea, and this is why the study was conducted in the area of the central Baltic coast, since in that particular region data on phytoplankton is not available. One of the main goals was to determine the temporal and spatial structure of the occurrence of phytoplankton, as well as to study biodiversity in the area of the estuary of the Slupia river in southern Baltic for the period between November 2014 and September 2016. The results of the research confirm typical changes of phytoplankton in three studied areas depending on the given season. The average values of phytoplankton abundance and biomass were typical for this kind of coastal waters and there were no significant species differences between these stations. The only research (and available studies) on phytoplankton in central sea basin areas is being conducted by Institute of Meteorology and Water Management (IMWM) as part of the HELCOM Baltic Sea Monitoring at station P16, which is the closest location to the studied area. When comparing the results obtained in this study to the data from the IMWM annual reports for the last decade, it can be noticed that the size and fluctuations of total biomass and phytoplankton abundance in the three studied areas are typical for the coastal region of the South Baltic.

Impacts of Shifts in Phytoplankton Community on Clouds and Climate via the Sulfur Cycle

AbstractDimethyl sulfide (DMS), primarily produced by marine organisms, contributes significantly to sulfate aerosol loading over the ocean after being oxidized in the atmosphere. In addition to exerting a direct radiative effect, the resulting aerosol particles act as cloud condensation nuclei, modulating cloud properties and extent, with impacts on atmospheric radiative transfer and climate. Thus, changes in pelagic ecosystems, such as phytoplankton physiology and community structure, may influence organosulfur production, and subsequently affect climate via the sulfur cycle. A fully coupled Earth system model, including explicit marine ecosystems and the sulfur cycle, is used here to investigate the impacts of changes associated with individual phytoplankton groups on DMS emissions and climate. Simulations show that changes in phytoplankton community structure, DMS production efficiency, and interactions of multielement biogeochemical cycles can all lead to significant differences in DMS transfer to the atmosphere. Subsequent changes in sulfate aerosol burden, cloud condensation nuclei number, and radiative effect are examined. We find the global annual mean cloud radiative effect shifts up to 0.21 W/m2, and the mean surface temperature increases up to 0.1 °C due to DMS production changes associated with individual phytoplankton group in simulations with radiative effects at the 2,100 levels under an 8.5 scenario. However, changes in DMS emissions, radiative effect, and surface temperature are more intensive on regional scales. Hence, we speculate that major uncertainties associated with future marine sulfur cycling will involve strong region‐to‐region climate shifts. Further understanding of marine ecosystems and the relevant phytoplankton‐aerosol‐climate linkage are needed for improving climate projections.

Seasonal variability of phytoplankton in the shallow waters of the southern Baltic Sea

The Baltic Sea is characterized by seasonal variation of phytoplankton structure. These organisms are particularly sensitive to changes in various environmental factors. Because of annually repeated changes, turnover of species composition, abundance and biomass of phytoplankton is observed. Spatial and temporal variability of individual phytoplankton groups is diversified in a district parts of the Baltic Sea. Therefore, of three different coastal areas were chosen: Ustka – estuary habitat, Poddąbie – sandy habitat and Rowy – rocky bottom habitat. The aim of this paper is to determine temporal and spatial structure of phytoplankton occurrence chosen coastal areas between November 2014 and September 2016. All three studies regions the same dominants, abundance and biomass were observed. Only in Ustka region increase of the diatoms was observed. Which could see the cause of river waters wave. Seasonal phytoplankton studies in three selected habitats revealed, that in those areas that abundance and biomass is similar (75%-80%). Based on this evaluation it is can be stated that conducting phytoplankton more frequently is more important than number of research stations.

A consistent structure of phytoplankton communities across the warm–cold regions of the water mass on a meridional transect in the East/Japan Sea

Three cruises were undertaken along a meridional transect in the East/Japan Sea (EJS) in spring (May 2007), summer (July 2009), and fall (October 2012) to determine the geographic variations in phytoplankton biomass and community composition. This study revealed a gradient of surface temperature and a fluctuation of hydrographic conditions along the transect. Although a subpolar front (SPF) formed between the warm- and cold-water masses (37–40°N), no significant differences in phytoplankton biomass and community composition were detected between the southern and northern parts of the EJS. These results disprove our initial hypothesis that different water masses may contain differently structured phytoplankton communities. In the present study, isothermal layers (≤ 12°C) fluctuated over a depth of 50m in both warm- and cold-water masses, depending on the SPF. In contrast, the nitracline (i.e. 2.5μM nitrate isopleth) depth was recorded within a limited range of 20–40m in spring, 30–50m in summer, and 40–60m in fall. The chlorophyll a concentrations at the subsurface chlorophyll maxima (SCM) were significantly higher in spring and summer (356 ± 233 and 270 ± 182ngL–1, respectively) than in fall (117 ± 89ngL–1). The relative contributions of individual phytoplankton groups to the depth-integrated chlorophyll a concentration conformed to the composition of the phytoplankton community in the SCM layer, showing a dominance of diatoms (58 ± 19% in spring, 48 ± 11% in summer, and 30 ± 20% in fall). Canonical correspondence analysis revealed that the geographic structures of phytoplankton communities were strongly associated with the vertical structures of water temperature and nutrient concentration in the water column rather than with horizontal gradients of hydrographic conditions. Finally, our findings suggest that water column stability and light–nutrient availability in the euphotic zone play a key role in determining geographical consistency of the biomass and the community structure of phytoplankton in the EJS.

Spatial distributions of external and internal phosphorus loads in Lake Erie and their impacts on phytoplankton and water quality

Re-eutrophication in Lake Erie has led to new programs to reduce external phosphorus loads, and it is important to understand the interrelated dynamics of external and internal phosphorus loads. In addition to developing phosphorus load response curves for algal biomass in the western basin and hypoxia in the central basin, we used a two-dimensional (vertical-longitudinal) hydrodynamic and ecological model to show that both external and internal phosphorus loads were distributed homogeneously in the water column in Lake Erie's western basin. In the stratified central and eastern basins phosphorus released by organic matter decay and crustacean zooplankton excretion was concentrated in the upper water column, contributing 100–119% of the phytoplankton phosphorus demand, while phosphorus released by dreissenids and from anoxic sediments was distributed primarily in the hypolimnion during the growing season. Simulated reductions in external phosphorus loads decreased individual phytoplankton groups most at times when they were normally most abundant, e.g., Microcystis decreased the most during September. Phosphorus was limiting over the simulation periods, but water temperature and light conditions also played critical roles in phytoplankton succession. While water column phosphorus responded quickly to external phosphorus reduction, pulses of phosphorus (riverine input or sediment resuspension) occurring immediately before the Microcystis bloom period could allow it to bloom despite long-term external phosphorus load reduction. Studies are warranted to assess the contribution of seasonal dynamics in phosphorus loading (including sediment resuspension) to Microcystis bloom development.

Seasonal dynamics of the phytoplankton community in Sendai Bay, northern Japan

Sendai Bay is located on the Pacific coast of northern Japan and suffered serious damage following the 2011 off the Pacific coast of Tohoku earthquake and tsunami in March 2011. To assess the impact on the marine ecosystem, information was needed on the phytoplankton communities and their seasonal variation. However, such information was limited. Therefore, an intensive monitoring of the phytoplankton was carried out from March 2012 to April 2014. Seasonal variation of the phytoplankton community was similar at coastal and offshore stations. Total phytoplankton biomass, based on Chl a concentration, peaked in spring and then decreased to a minimum in summer, before gradually increasing during early winter and peaking again in the following spring. This seasonal pattern was consistent with previous studies conducted before the earthquake and tsunami. Also, size structure of the phytoplankton community and its four main groups was estimated from the size-fractioned samples of Chl a. Our results also showed that the spring bloom consisted of large diatoms, with their growth ceasing due to nitrogen depletion. The bloom was followed by a summer period where cyanobacteria and picoeukaryote became dominant, with high cell densities in spite of low nutrient concentrations. In addition, sporadic environmental changes, such as those following typhoons, were observed. These resulted in large increases/decreases in individual phytoplankton groups.

Phytoplankton community response to changing physico-chemical environment of subtropical Lake Mansar (INDIA)

This paper describes the diversity and community dynamics of phytoplankton group in lake Mansar. A total of 33 phytoplankton taxa were recorded during a period of one year (March-2009 to February-2010) which belonged to three groups i.e. chlorophyceae, bacillariophyceae and cyanophyceae. Members of cyanophyceae dominated phytoplankton population throughout the study with predominance of 3 species of Microcystis i.e. M. elabens, M. pulvera and M. aeruginosa. Bacillariophyceae was dominated by genus Navicula. Overall phytoplankton population peaked in summer while decline was recorded during monsoon season. However, individual phytoplankton groups except cyanophyceae were observed to show maxima in spring season. Maximum value for Shannon diversity (H`=2.9) was observed in spring season with high values of evenness. Shannon’s diversity and Pielou’s evenness values were observed to be negatively related to both total nitrogen and total phosphorus levels. Thus, with increasing nutrient enrichment due to anthropogenic activities around lake Mansar, not only its water quality is deteriorating but negative impacts may also be inflicted on phytoplankton population and its diversity.

Temporal and spatial variability of phytoplankton monitored by a combination of monitoring buoys, pigment analysis and fast screening microscopy in the Fehmarn Belt Estuary.

For 2years, a baseline investigation was carried out to collect reference information of the present environmental status in the Fehmarn Belt and adjacent area. The temporal and spatial variability of phytoplankton was monitored by a combination of monitoring buoys, pigment analysis and fast screening microscopy. The overall phytoplankton succession in the Fehmarn Belt area was found to be influenced primarily by the seasonal changes, where various diatoms dominated the spring and autumn blooms and flagellates like Chrysochromulina sp., Dictyocha speculum and various dinoflagellates were occasionally abundant in late spring and summer. The phytoplankton groups were remarkably uniform horizontally in the investigation area while large differences in both biomasses and composition of individual phytoplankton groups were seen vertically in the water column, especially in the summer periods, in which the two-layer exchange flow between the North Sea and the Baltic Sea is showing a particularly strong stratification in the Fehmarn Belt. The chlorophyll a concentrations ranged continuously from 1 to 3μg/L at the three permanent buoy stations during the 2years of monitoring, except for the spring and autumn blooms where chlorophyll a increased up to 18μg/L in the spring of 2010 and up to 8μg/L in the autumn of 2009. Recurrent blooms of filamentous cyanobacteria are common during the summer period in the Baltic Sea and adjacent areas, but excessive blooms of cyanobacteria did not occur in 2009 and 2010 in the Fehmarn Belt area. The combination of the HPLC pigment analysis method and monitoring buoys continuously measuring fluorescence at selected stations with fast screening of samples in the microscope proved advantageous for obtaining information on both the phytoplankton succession and dynamic and, at the same time, getting information on duration and intensity of the blooms as well as specific information on the dominant species present both temporally and spatially in the large Fehmarn Belt area.

An analysis of the relationship between phytoplankton internal stoichiometry and water column N:P ratios in a dynamic lake environment

The N:P stoichiometry of a water body is one of the most commonly used indicators of its nutrient status and algal growth. However, in a dynamic aquatic ecosystem the N:P stoichiometry of phytoplankton is highly variable and depends on environmental conditions and key microbial interactions that influence their growth, such as grazing pressures and the microbial loop. Here we determine the influence of the nutrient-dependent microbial interactions between zooplankton, phytoplankton and bacteria on the ecological stoichiometry at different trophic levels and how they relate to water column properties. A 1D hydrodynamic–ecological model (DYRESM–CAEDYM) was applied to Lake Kinneret (Israel) for examining how the internal nutrient ratios of several phytoplankton functional groups correlate with nutrient ratios within the water column, and further explore how the microbial loop shapes the patterns of stoichiometry within the food web by testing two microbial loop configurations. The results showed that the average internal N:P ratios of the phytoplankton community followed their total carbon biomass patterns, and that seasonal patterns of simulated dissolved inorganic N to total P (DIN:TP) ratios in the water column were a useful indicator for reflecting the bulk phytoplankton N:P stoichiometry as compared with total N to total P (TN:TP) ratios and dissolved inorganic N to dissolved inorganic P (DIN:DIP) ratios. However, the internal N:P ratio patterns of individual phytoplankton groups did not necessarily correlate with DIN:TP ratio patterns in the water column. This was because different microbial processes regulate nutrient flows to individual phytoplankton groups. Our simulations with the microbial loop highlight the ability of bacteria to regulate phytoplankton stoichiometry. These results provide an improved mechanistic understanding of the food web in aquatic ecosystems.

Do phytoplankton nutrient ratios reflect patterns of water column nutrient ratios? A numerical stoichiometric analysis of Lake Kinneret

Abstract The N:P stoichiometry of a water body is one of the most commonly used indicators of its nutrient status. However, in a dynamic aquatic ecosystem the N:P stoichiometry of phytoplankton is highly variable depending on a range of factors that influence their growth. In this study, a 1D hydrodynamic-ecological model was used to examine how the internal nutrient ratios of phytoplankton relate to nutrient ratios within the water column in Lake Kinneret, Israel. We identified that seasonal patterns of the simulated dissolved inorganic N to total P (DIN:TP) ratios in the water column were a useful indicator of the N:P stoichiometry of the combined phytoplankton community. However, the internal N:P patterns of individual phytoplankton groups did not necessarily relate to DIN:TP patterns.

Identification and quantification of phytoplankton groups in lakes using new pigment ratios – a comparison between pigment analysis by HPLC and microscopy

Summary1. Pigment analysis by high‐performance liquid chromatography (HPLC) combined with data analysis using the CHEMTAX program has proven to be a fast and precise method for determining the abundance of phytoplankton groups in marine environments. To determine whether CHEMTAX is applicable also to freshwater phytoplankton, 20 different species of freshwater algae were cultured and their pigment/chlorophyll a (Chl a) ratios determined for exponential growth at three different light intensities and for stationary growth at one light intensity.2. The different treatments had a relatively insignificant impact on the absolute values of the diagnostic pigment/Chl a ratios, with the exception of cyanobacteria and cryptophytes for which the zeaxanthin/Chl a and alloxanthin/Chl a ratios varied considerably.3. The pigment ratios were tested on samples collected in six different eutrophic Danish lakes during two summer periods using the CHEMTAX program to calculate the biomass of the phytoplankton groups as Chl a. The CHEMTAX‐derived seasonal changes in Chl a biomass corresponded well with the volume of the microscopically determined phytoplankton groups. More phytoplankton groups were detected by the pigment method than by the microscopic method.4. Applying the pigment ratios developed in this study, the pigment method can be used to determine the abundance of the individual phytoplankton groups, which are useful as biological water quality indicators when determining the ecological status of freshwater lakes.