Phototrophic Picoplankton Research Articles

Factors influencing the pigment composition and dynamics of photoautotrophic picoplankton in shallow eutrophic lakes.

Photoautotrophic picoplankton (0.2–2 μm) can be a major contributor to primary production and play a significant part in the ecosystem carbon flow. However, the understanding about the dynamics of both eukaryotic and prokaryotic components of picoplankton in shallow eutrophic freshwater environments is still poor. Very few studies in these ecosystems reveal the taxonomic composition of picoeukaryotes. The main objective of this study was to investigate the seasonal dynamics of phototrophic picoplankton with the emphasis on the eukaryote community composition in a large shallow, eutrophic lake of the northern temperate zone (Lake Võrtsjärv). Phytoplankton pigments were employed to determine the taxonomic composition of photoautotrophic picoplankton. We found out that photoautotrophic picoplankton constitutes an important part of the phytoplankton community in Lake Võrtsjärv and its contribution can be highly variable (from ~9.3% to ~39%) in different years. The eukaryotic photoautotrophic picoplankton was dominated by diatoms followed by chrysophytes and other minor groups. Picoeukaryotes were prevailing in low-light conditions and low temperatures as their predominance in the picoplankton community was tightly linked to the presence or absence of ice cover. Ice cover strongly suppressed the growth of picocyanobacteria. Total phosphorus, turbidity and metazooplankton abundance had a clear relationship with photoautotrophic picoplankton chlorophyll a.

Species Diversity of Phototrophic Picoplankton in the Kara and Laptev Seas

Species Diversity of Phototrophic Picoplankton in the Kara and Laptev Seas

The pico-sized Mamiellophyceae and a novel Bathycoccus clade from the summer plankton of Russian Arctic Seas and adjacent waters.

Global climate changes and anthropogenic activity greatly impact Arctic marine biodiversity including phytoplankton which contribute greatly to atmospheric oxygen production. Thus the study of microalgae has rising topicality. Class Mamiellophyceae is an important component of phototrophic picoplankton. To gain more knowledge about Mamiellophyceae distribution and diversity special studies were performed in such remote areas as the Russian Arctic seas. A metabarcoding of pico-sized Mamiellophyceae was undertaken by high-throughput sequencing of the 18S rRNA gene sequence V4 region from samples collected in July-September 2017 in the Barents, Kara and Laptev seas, and in the adjacent waters of the Norwegian Sea. Our study is the first to show that Mamiellophyceae among the summer picoplankton of Russian Arctic seas are diverse and represented by 16 algae species/phylotypes. We discovered a new candidate species of Bathycoccus assigned to a new Bathycoccus clade A-uncultured Bathycoccus Kara 2017. It was found that several Micromonas species can co-exist, with Micromonas polaris dominating north of 72°N. The presence of Ostreococcus tauri, Ostreococcus lucimarinus and Ostreococcus mediterraneus at high latitudes beyond 65°N was documented for the first time, similar to findings for some other taxa. Our results will be important for obtaining a global view of Mamiellophyceae community dynamics.

The Spatial Distribution of Plankton Picocyanobacteria on the Shelf of the Kara, Laptev, and East Siberian Seas

The spatial distribution of picocyanobacteria at the arctic longitude section passing through the shelf of the Kara, Laptev, and East Siberian seas from 58° to 168° E was studied. The average abundance of picocyanobacteria was 0.48 ± 1.2 × 109 cells/m3 in the Kara Sea, 0.16 ± 0.24 × 109 cells/m3 in the Laptev Sea, and 0.25 ± 0.43 × 109 cells/m3 in the East Siberian Sea. The fluctuations of picocyanobacterial abundance were determined by their presence in allochthonous sources: river flow and transformed North Atlantic waters. The highest abundance was observed in the areas of the runoff influence of the Ob, Khatanga, Indigirka, and Kolyma Siberian rivers: 0.5 × 109, 0.2 × 109, 0.4 × 109, and 1.6 × 109 cells/m3, respectively. The average contribution of picocyanobacteria to the total abundance and biomass of picophytoplankton in the western part of the Kara Sea was 37 and 36%, respectively. In other regions, the average contribution of picocyanobacteria to the total abundance and biomass of phototrophic picoplankton did not exceed 7 and 6%, respectively. A highly reliable (p$$ \ll $$ 0.01) positive correlation between the abundance and biomass of picocyanobacteria and the water temperature (p = 0.003) was revealed in the entire dataset obtained.

Pico- and Nanoplankton in Aquatic Ecosystems in the Valley of the Lakes and Great Lakes Depression (Mongolia)

The abundance and biomass of bacterioplankton, phototrophic picoplankton, and heterotrophic nanoflagellates has been determined in lakes, rivers, and reservoirs located in the Valley of the Lakes and Great Lakes Depression (Mongolia). The species richness of the heterotrophic flagellates and their consumption of bacteria are estimated. Pico- and nanoplankton are the most abundant in shallow mineral lakes Orog and Tatsyn and in the freshwater Durgun Reservoir. Heterotrophic nanoflagellates consume 26–92% (on average 66%) of the daily bacterioplankton production. Thus, flagellates are important in the transfer of bacterial carbon to the higher levels of planktonic trophic webs. A total of 30 species and their forms of heterotrophic flagellates from 14 large taxa are identified. The highest species diversity of these protists are found in the Durgun and Taishyr reservoirs.

Phototrophic plankton of siderotrophic meromictic Lake Kuznechikha (Republic Mari El, Russia)

During summer thermal stratification, a broad transition zone with hypoxic conditions is formed in meromictic ferruginous Lake Kuznechikha between the thermocline and the main gradient of water mineralization. In this zone, the chemical composition of water undergoes an ecologically significant transformation due to overlapping gradients of nutrient concentrations and redox conditions. We present an analysis of a strongly vertically structured community of prokaryotic and eukaryotic phototrophs developing in the lake as a whole and especially in the transition zone. In early summer 2009, a sequence of phototrophic organisms with depth in order Chlorophyceae → Chromatiales → Chloroflexales → Euglenales → Chlorobiales was observed in the transition zone, while cyanobacteria were almost completely absent. Biomass maximum of anoxygenic phototrophic bacteria was located between the peaks of phototrophic picoplankton and euglenoids. Such a coexistence of oxygenic and anoxygenic phototrophs in a wide range of depths is highly unusual and sharply distinguishes Lake Kuznechikha from waterbodies with sulphide-containing monimolimnion.

Unusual behaviour of phototrophic picoplankton in turbid waters.

Autotrophic picoplankton (APP) abundance and contribution to phytoplankton biomass was studied in Hungarian shallow lakes to test the effect of inorganic turbidity determining the size distribution of the phytoplankton. The studied lakes displayed wide turbidity (TSS: 4–2250 mg l-1) and phytoplankton biomass (chlorophyll a: 1–460 μg l-1) range, as well as APP abundance (0 and 100 million cells ml-1) and contribution (0–100%) to total phytoplankton biomass. Inorganic turbidity had a significant effect on the abundance and contribution of APP, resulting in higher values compared to other freshwater lakes with the same phytoplankton biomass. Our analysis has provided empirical evidence for a switching point (50 mg l-1 inorganic turbidity), above which turbidity is the key factor causing APP predominance regardless of phytoplankton biomass in shallow turbid lakes. Our results have shown that turbid shallow lakes are unique waters, where the formerly and widely accepted model (decreasing APP contribution with increasing phytoplankton biomass) is not applicable. We hypothesize that this unusual behaviour of APP in turbid waters is a result of either diminished underwater light intensity or a reduced grazing pressure due to high inorganic turbidity.

Structure and functioning of the microbial loop in a boreal reservoir

The abundance and biomass of the main components of the microbial plankton food web (“microbial loop”)—heterotrophic bacteria, phototrophic picoplankton and nanoplankton, heterotrophic nanoflagellates, ciliates and viruses, production of phytoplankton and bacterioplankton, bacterivory of nanoflagellates, bacterial lysis by viruses, and the species composition of protists—have been determined in summer time in the Sheksna Reservoir (the Upper Volga basin). A total of 34 species of heterotrophic nanoflagellates from 15 taxa and 15 species of ciliates from 4 classes are identified. In different parts of the reservoir, the biomass of the microbial community varies from 26.2 to 64.3% (on average 45.5%) of the total plankton biomass. Heterotrophic bacteria are the main component of the microbial community, averaging 63.9% of the total microbial biomass. They are the second (after the phytoplankton) component of the plankton and contribute on average 28.6% to the plankton biomass. The high ratio of the production of heterotrophic bacteria to the production of phytoplankton indicates the important role of bacteria, which transfer carbon of allochthonous dissolved organic substances to a food web of the reservoir.

Microbial Food-Web Drivers in Tropical Reservoirs.

Element cycling in aquatic systems is driven chiefly by planktonic processes, and the structure of the planktonic food web determines the efficiency of carbon transfer through trophic levels. However, few studies have comprehensively evaluated all planktonic food-web components in tropical regions. The aim of this study was to unravel the top-down controls (metazooplankton community structure), bottom-up controls (resource availability), and hydrologic (water residence time) and physical (temperature) variables that affect different components of the microbial food web (MFW) carbon stock in tropical reservoirs, through structural equation models (SEM). We conducted a field study in four deep Brazilian reservoirs (Balbina, Tucuruí, Três Marias, and Funil) with different trophic states (oligo-, meso-, and eutrophic). We found evidence of a high contribution of the MFW (up to 50% of total planktonic carbon), especially in the less-eutrophic reservoirs (Balbina and Tucuruí). Bottom-up and top-down effects assessed through SEM indicated negative interactions between soluble reactive phosphorus and phototrophic picoplankton (PPP), dissolved inorganic nitrogen, and heterotrophic nanoflagellates (HNF). Copepods positively affected ciliates, and cladocerans positively affected heterotrophic bacteria (HB) and PPP. Higher copepod/cladoceran ratios and an indirect positive effect of copepods on HB might strengthen HB-HNF coupling. We also found low values for the degree of uncoupling (D) and a low HNF/HB ratio compared with literature data (mostly from temperate regions). This study demonstrates the importance of evaluating the whole size spectrum (including microbial compartments) of the different planktonic compartments, in order to capture the complex carbon dynamics of tropical aquatic ecosystems.

Microbial food web components, bulk metabolism, and single-cell physiology of piconeuston in surface microlayers of high-altitude lakes

Sharp boundaries in the physical environment are usually associated with abrupt shifts in organism abundance, activity, and diversity. Aquatic surface microlayers (SML) form a steep gradient between two contrasted environments, the atmosphere and surface waters, where they regulate the gas exchange between both environments. They usually harbor an abundant and active microbial life: the neuston. Few ecosystems are subjected to such a high UVR regime as high altitude lakes during summer. Here, we measured bulk estimates of heterotrophic activity, community structure and single-cell physiological properties by flow cytometry in 19 high-altitude remote Pyrenean lakes and compared the biological processes in the SML with those in the underlying surface waters. Phototrophic picoplankton (PPP) populations, were generally present in high abundances and in those lakes containing PPP populations with phycoerythrin (PE), total PPP abundance was higher at the SML. Heterotrophic nanoflagellates (HNF) were also more abundant in the SML. Bacteria in the SML had lower leucine incorporation rates, lower percentages of “live” cells, and higher numbers of highly-respiring cells, likely resulting in a lower growth efficiency. No simple and direct linear relationships could be found between microbial abundances or activities and environmental variables, but factor analysis revealed that, despite their physical proximity, microbial life in SML and underlying waters was governed by different and independent processes. Overall, we demonstrate that piconeuston in high altitude lakes has specific features different from those of the picoplankton, and that they are highly affected by potential stressful environmental factors, such as high UVR radiation.

Photosynthetic Characteristics of Picoplankton Compared with Those of Larger Phytoplankton Populations, in Various Water Masses in the Gulf of Maine

AbstractCell numbers of eucaryotes and cyanobacteria in phototrophic picoplankton and ratios of in vivo fluorescence of phycoerythrin: chlorophyll a indicated that chroococcalean cyanobacteria played a more prominent role in phytoplankton communities, at the least productive stations. At stations displaying large vertical density gradients, subsurface maxima of phytoplankton pigments were observed. Ratios of in vivo fluorescence of phycoerythrin: chlorophyll a were always greater at the pigment maximum than at the surface. Cyanobacteria from pigment maxima demonstrated greater phycoerythrin fluorescence intensity and photosynthetic rates than cyanobacteria from the surface. Photosynthetic characteristics of picoplankton ( 3 μm populations. The picoplankton differed from larger phytoplankton, in that (1) their pattern of photosynthetic carbon fixation did not vary significantly with decreasing light intensity, and at optimal intensities ...

Investigating the spatial distribution of phototrophic picoplankton in a tropical estuary

We sampled extensively (29 stations) at the Klang estuarine system over a 3-day scientific expedition. We measured physical and chemical variables (temperature, salinity, dissolved oxygen, total suspended solids, dissolved inorganic nutrients) and related them to the spatial distribution of phototrophic picoplankton (Ppico). Multivariate analysis of variance of the physicochemical variables showed the heterogeneity of the Klang estuarine system where the stations at each transect were significantly different (Rao's F₁₈, ₃₆ = 8.401, p < 0.001). Correlation analyses also showed that variables related to Ppico abundance and growth were mutually exclusive. Distribution of Ppico was best explained by the physical mixing between freshwater and seawater whereas Ppico growth was correlated with temperature.

Stratified distribution of nutrients and extremophile biota within freshwater ice covering the surface of Lake Baikal

Biological entities and gradients of selected chemicals within the seemingly barren ice layers covering Lake Baikal were investigated. Ice cores 40-68 cm long were obtained from in shore and offshore sites of Southern Lake Baikal during the cold period of a year (March-April) in 2007 and 2008. In microscopic observations of the melted ice, both algae and bacteria were found in considerable numbers (>10(3) cells/L and >10(4) cells/ml, respectively). Among all organisms found, diatom was generally the most predominant taxon in the ice. Interestingly, both planktonic and benthic algae were present in considerable numbers (2-4×10(4) cells/L). Dominant phototrophic picoplankton were comprised of small green algae of various taxa and cyanobacteria of Synechococcus and Cyanobium. The bacterial community consisted mostly of short rod and cocci cells, either free-living or aggregated. Large numbers of yeast-like cells and actinomycete mycelium were also observed. Concentrations of silica, phosphorus, and nitrate were low by an order of magnitude where biota was abundant. The profile of the ice could be interpreted as vertical stratification of nutrients and biomass due to biological activities. Therefore, the organisms in the ice were regarded to maintain high activity while thriving under freezing conditions. Based on the results, it was concluded that the freshwater ice covering the surface of Lake Baikal is considerably populated by extremophilic microorganisms that actively metabolize and form a detritus food chain in the unique large freshwater ecosystem of Lake Baikal.

Bacterivory by phototrophic picoplankton and nanoplankton in Arctic waters

Mixotrophy, the combination of phototrophy and heterotrophy within the same individual, is widespread in oceanic systems. Yet, neither the presence nor ecological impact of mixotrophs has been identified in an Arctic marine environment. We quantified nano- and picoplankton during early autumn in the Beaufort Sea and Canada Basin and determined relative rates of bacterivory by heterotrophs and mixotrophs. Results confirmed previous reports of low microbial biomass for Arctic communities in autumn. The impact of bacterivory was relatively low, ranging from 0.6 × 10(3) to 42.8 × 10(3) bacteria mL(-1) day(-1) , but it was often dominated by pico- or nanomixotrophs. From 1% to 7% of the photosynthetic picoeukaryotes were bacterivorous, while mixotrophic nanoplankton abundance comprised 1-22% of the heterotrophic and 2-32% of the phototrophic nanoplankton abundance, respectively. The estimated daily grazing impact was usually < 5% of the bacterial standing stock, but impacts as high as 25% occurred. Analysis of denaturing gradient gel electrophoresis (DGGE) band patterns indicated that communities from different depths at the same site were appreciably different and that there was a shift in community diversity at the midpoint of the cruise. Sequence information from DGGE bands reflected microbes related to those from other Arctic studies, particularly from the Beaufort Sea.

Abundance and biomass of prokaryotic and eukaryotic microorganisms coupled with environmental factors in an arid multi-pond solar saltern (Sfax, Tunisia)

The distribution of abundance and biomass of prokaryotes, flagellates, ciliates and phytoplankton, were studied in five ponds of increasing salinity in the Sfax solar saltern (Tunisia) coupled with environmental factors. The results showed that abundance of eukaryotic microorganisms decreased with increasing salinity of the ponds whereas prokaryotes (heterotrophic bacteria and Archaea) were abundant in the hyper-saline ponds. Phototrophic picoplankton was found in a large range of salinity values (70 and 200‰). Phototrophic non-flagellated nanoplankton which dominated in the first sampled pond was substituted by phototrophic flagellated nanoplankton in the other ponds. Heterotrophic nanoplankton dominated in the crystallizer pond but its quantitative importance declined in the less saline ponds. Diatoms and dinoflagellates were the major contributors to phytoplankton abundance in the first ponds (&gt;90% of total abundance). Ciliated protozoa were found in all the ponds except in the crystallizer in which prokaryotes proliferated. Oligotrichida and Heterotrichida were the most abundant ciliate groups. Overall, species richness decreased with salinity gradient. We propose a simplified diagram of the Sfax saltern's food web showing the dominant role of the microbial loop along the salinity gradient.

Seasonal variation of phototrophic picoplankton in Lake Biwa (1994?1998)

Seasonal abundances of phototrophic picoplankton (PP) and heterotrophic nanoflagellates in Lake Biwa were studied from 1994 to 1998. Seasonal variation in cell volume and biomass of the phototrophic picoplankton were also studied. PP were counted using disposable glass microscopic plates, which gave superior accuracy to sample filtration onto membrane filters. Phycoerythrin-rich rod-shaped cyanobacteria (PEC), one of the major components of the picoplankton community, were sparse (about 104 cells ml −1) in winter and began to increase in April. Several PEC peaks were observed during the period of thermal stratification, and a rapid fall took place after October or November. In the northern basin, PEC peaked during late June and early July in 3 of the 5 years, and in late summer in the remaining years. Phycocyanin-rich rod-shaped cyanobacteria (PCC) were abundant in the southern basin and were present in smaller numbers in the eutrophic nearshore area of the northern basin; they peaked several times during the period from July to October. Seasonal variations of these two kinds of picoplankton were correlated with seasonal changes in water temperature. Phycoerythrin-rich cylinder-shaped cyanobacteria exhibited narrow peaks in July, their abundance declining as the year progressed. The density of heterotrophic nanoflagellates was greatest in early spring. Average cell volume of PEC was largest in winter, then decreased gradually to a minimum in late summer; after the fall, it recovered to the winter cell volume. This change can likely be attributed to the depletion of nitrogen in the warmer seasons.

Seasonal variability of picophytoplankton and bacteria in the western subarctic Pacific Ocean at station KNOT

Picoplankton community structure in the upper 200 m at Station KNOT in the western subarctic North Pacific was studied by flow cytometric analysis of the time-series samples collected from June 1998 through June 2000. Phototrophic picoplankton, Synechococcus and picoeukaryotes, displayed a clear seasonal cycle in population abundance during the 2-yr period, where chlorophyll a concentration remained relatively low and constant throughout the year, except in spring when the diatom bloom occurred. High picoplankton abundance occurred after the spring diatom bloom when the water column became more stratified. The maximum abundance of Synechococcus occurred in late June to early August, whereas the peak in picoeukaryotes abundance appeared to take place earlier in May and remained high through the summer. Heterotrophic bacteria abundance also displayed a seasonal variation pattern that was closely related to the picoplankton biomass, but not total chlorophyll biomass.

Underwater light conditions, phytoplankton photosynthesis and bacterioplankton production in the Hungarian section of the River Danube

Underwater light climate, phytoplankton composition and photosynthesis, bacterioplankton production and heterotrophic nanoflagellate abundance were studied in the River Danube near Budapest in 1991. During the winter months water transparency was high, the euphotic zone deep (3 m), but the phytoplankton biomass and the primary production were low as a consequence of low water temperature and reduced global radiation. An increase in phytoplankton abundance (chlorophyll-a concentration reaching 164 μg.l -1 ) during the spring low water period in April and May was observed. This large population was lost to the summer floods. The months of July and August experienced low chlorophyll-a concentrations even though water temperature increased to 20°C. This spring peak was superseded by a second peak in September. The abundance of phototrophic picoplankton in the river was low when compared to that of lakes (10 3 -10 5 cells.ml -1 ). These low concentrations suggest that their contribution towards primary production in the river is not important. The value of the vertical attenuation coefficient (Kd) was mainly influenced by the concentration of suspended solids. In winter the Z eu / Z avg ratio approached 1.0 suggesting that the algae were not light limited this period. The ratio ranged from 0.5-0.7 during the spring and autumn algal blooms and decreased to 0.2-0.3 during the summer floods. The P/R ratio of phytoplankton in the whole water column approached 1.0 in June and July and exceeded 2.0 during the rest of the period. This result supported the hypothesis that light limitation is solely sufficient to prevent algal growth during the summer floods. The mineral nutrients (N, P) do not limit algal growth in the River Danube. Bacterial production measured by 3 H-thymidine incorporation averaged 1.19 nmol.l -1 .d -1 in 1991. The annual average net bacterial production was found to be only 10% that of primary production. Bacterial production seasonal dynamics were found to be independent of phytoplankton production. Zooplankton grazing was considered unimportant in the River Danube. Heterotrophic nanoflagellates (HNF) attained high numbers and were considered to be the main consumer of bacterioplankton and so could play a determining role in the processes of the nutrient cycling in the River Danube.

Seasonal variation in the regulation of phytoplankton by nitrogen and grazing in a salt‐smarsh estuary

In North Inlet, a tidally dominated salt‐marsh estuary near Georgetown, South Carolina, the summer chlorophyll maximum correlates with an annual peak in ambient NH4+ concentration. This relationship suggests that phytoplankton population growth during the summer bloom is limited by factors other than nutrient supply, because NH4+ is the major inorganic nitrogen source available to phytoplankton in North Inlet, and phosphorus should not be limiting (N:P is generally ~7). We tested the hypothesis that phytoplankton population growth during the bloom was controlled by grazing. Natural samples were incubated in treatments designed to differentiate between nutrient and grazing effects, and time‐course changes in total phytoplankton biomass and phototrophic community composition were followed. Marked seasonal differences were observed in the relative contribution of pica‐, nano‐, or microplankton to phytoplankton community biomass, as well as the mechanisms controlling phytoplankton population growth. During the summer bloom, phototrophic picoplankton (mostly Synechococcus spp.) and nanoplankton (mostly flagellates) were relatively abundant, and phytoplankton population growth was unaffected by NH4+ addition, but was greatly stimulated by dilution that reduced microzooplankton grazing pressure. During the winter, when diatoms dominated the phytoplankton, the response to dilution was relatively minor, while NH4+ addition significantly stimulated the growth of various phytoplankton groups and total chlorophyll. The results indicate a seasonal transition in microbial food‐web trophic structure and regulation in North Inlet estuary. During the summer, microzooplankton grazing is an important factor regulating phytoplankton population growth during the nanoflagellate‐ prevalent bloom, whereas in the winter, a diatom‐dominated community is limited by nutrient supply.

Abundance of phototrophic and heterotrophic picoplankton in boreal lakes of varying trophic state and humic matter content

Abundance of phototrophic and heterotrophic picoplankton in boreal lakes of varying trophic state and humic matter content