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Artificial neural network analysis (ANN) is used to study the seasonal distribution of viruses and microbial food web (MFW) components in the open Adriatic Sea. The effect of viruses within the MFW is often overlooked, although viruses play an important role in microbial community dynamics. The results showed that the strongest influence is found in the nonlinear relationship between viruses and temperature. In addition, the algorithm showed that the number of viral populations in the P-limited open sea varies by season and according to the abundance of their main hosts, HB. A strong positive relationship between viruses and HB was found in more than 50% of the observed data. Moreover, this algorithm confirmed the association of the virus with the autotrophic part of the picoplankton and with heterotrophic nanoflagellates. The dynamics of the four resulting clusters, characterized by biological and environmental parameters, is described as a cyclic pattern in the water layer above the thermocline. Neural gas network analysis has been shown to be an excellent tool for describing changes in MFW components in the open Adriatic. [ABSTRACT FROM AUTHOR]

Abstract—The structure and spatial distribution of picoseston in the Saratov Reservoir in July 2011 and August 2014 are described. On average, the total abundance of cells and particles forming picoseston was 1.87 ± 0.73 × 106 cells (part.)/mL; and the total biomass of picoseston was 43.8 ± 19.4 μg C/L. During the study period, single heterotrophic bacteria and phototrophic picocyanobacteria prevailed in the picoseston of the Saratov Reservoir, amounting to 77–100% of its total abundance and biomass. The proportion of picodetrital particles was extremely small (on average, 4.1% of the total biomass of picoseston). The high heterogeneity of picoceston distribution (Cv was 130 and 110% for abundance and biomass, respectively) was found in the Saratov Reservoir during the study period. On average, the abundance and biomass of heterotrophic bacterioplaknton and picodetritus at stations of the tributary estuaries were slightly higher than in the riverbed. At the same time, the abundance of picocyanobacteria was higher and the biomass was lower at the estuarine stations compared to the riverbed ones. The total number of bacterioplankton and autotrophic picoplankton in the Saratov Reservoir in 2011 and 2014 corresponded to the mesotrophic level of productivity. Picodetrital particles, in contrast to the Upper Volga and Kama reservoirs, make no significant contribution to the planktonic food webs of the Saratov Reservoir, at least during the study period. [ABSTRACT FROM AUTHOR]

Abstract—The structure and spatial distribution of picoseston in the Saratov Reservoir in July 2011 and August 2014 are described. On average, the total abundance of cells and particles forming picoseston was 1.87 ± 0.73 × 106 cells (part.)/mL; and the total biomass of picoseston was 43.8 ± 19.4 μg C/L. During the study period, single heterotrophic bacteria and phototrophic picocyanobacteria prevailed in the picoseston of the Saratov Reservoir, amounting to 77–100% of its total abundance and biomass. The proportion of picodetrital particles was extremely small (on average, 4.1% of the total biomass of picoseston). The high heterogeneity of picoceston distribution (Cv was 130 and 110% for abundance and biomass, respectively) was found in the Saratov Reservoir during the study period. On average, the abundance and biomass of heterotrophic bacterioplaknton and picodetritus at stations of the tributary estuaries were slightly higher than in the riverbed. At the same time, the abundance of picocyanobacteria was higher and the biomass was lower at the estuarine stations compared to the riverbed ones. The total number of bacterioplankton and autotrophic picoplankton in the Saratov Reservoir in 2011 and 2014 corresponded to the mesotrophic level of productivity. Picodetrital particles, in contrast to the Upper Volga and Kama reservoirs, make no significant contribution to the planktonic food webs of the Saratov Reservoir, at least during the study period. [ABSTRACT FROM AUTHOR]

Autotrophic picoplankton (APP) is responsible for the vast majority of primary production in oligotrophic marine areas, such as the Alboran Sea. The increase in atmospheric dust deposition (e.g., from Sahara Desert) associated with global warming, together with the high UV radiation (UVR) on these ecosystems, may generate effects on APP hitherto unknown. We performed an observational study across the Alboran Sea to establish which factors control the abundance and distribution of APP, and we made a microcosm experiment in two distinct areas, nearshore and offshore, to predict the joint UVR × dust impact on APP at midterm scales. Our observational study showed that temperature ( T) was the main factor explaining the APP distribution whereas total dissolved nitrogen positively correlated with APP abundance. Our experimental study revealed that Saharan dust inputs reduced or inverted the UVR damage on the photosynthetic quantum yield (ΦPSII) and picoplanktonic primary production (PPP) in the nearshore area but accentuated it in the offshore. This contrasting effect is partially explained by the nonphotochemical quenching, acting as a photorepair mechanism. Picoeukaryotes reflected the observed effects on the physiological and metabolic variables, and Synechococcus was the only picoprokaryotic group that showed a positive response under UVR × dust conditions. Our study highlights a dual sensitivity of nearshore versus offshore picoplankton to dust inputs and UVR fluxes, just at the time in which these two global-change factors show their highest intensities and may recreate a potential future response of the microbial food web under global-change conditions. [ABSTRACT FROM AUTHOR]

Introduction: The lagoon is a component of coastal zones, whose populations of autotrophic picoplankton (APP) remain largely unstudied. These lagoons display high-nutrient productivity and additionally may also be subjected to anthropogenic activities. This study selected Laguna Macapule, located on the eastern shore in the mid-region of the Gulf of California, due to the fact that a drainage network servicing the surrounding agricultural region (>230,000 hectares under cultivation) directs irrigation runoff, shrimp farm effluents, and urban wastewater containing large quantities of nutrients to be discharged into this lagoon. We propose to identify the APP's response to various types of environmental and anthropogenic influence in this highly impacted coastal lagoon. Methods: Two sites (separated by 2.7 km) were monitored from December 2007 to December 2008. One, located at the entrance to Laguna Macapule (oceanic influence) and the other a discharge canal (eutrophic conditions) inside the lagoon at El Tortugón. Results: APP was the numerically dominant phytoplankton fraction (15 × 10 to 620 × 10 cells L) with coccoidal cyanobacteria as the dominant fraction throughout the year. Peak levels were reached in spring-early autumn and they were the second largest contributor to biomass. Abundance of APP cells corresponds to the lagoon's eutrophic status. Maximum numbers and a higher average of APP were recorded at the El Tortugón channel during the warm season (months with SST higher than 24 °C). The general positive relationship of the APP's annual cycle at both sites as well as a negative relationship with heterotrophic nanoflagellates (HNF) abundance, supports the idea that natural forcing, in particular sea surface temperature (SST) is the predominant influences on APP's seasonal variability. Conclusions: Distinguishable significant differences in APP abundances and nutrients were recognizable between the two sites. The interplay of these variables contributed to lower densities of APP in winter and high densities in spring-early autumn. N:P = ~4 suggests that spring-early autumn abundance of the APP autotrophic component was sustained by urea from shrimp farm discharge water. Thus, a total nutrient-based approach is likely the most suitable tool for establishing nitrogen limitation of biological production in Laguna Macapule and similarly impacted ecosystems around the world. [ABSTRACT FROM AUTHOR]

Introduction: The lagoon is a component of coastal zones, whose populations of autotrophic picoplankton (APP) remain largely unstudied. These lagoons display high-nutrient productivity and additionally may also be subjected to anthropogenic activities. This study selected Laguna Macapule, located on the eastern shore in the mid-region of the Gulf of California, due to the fact that a drainage network servicing the surrounding agricultural region (>230,000 hectares under cultivation) directs irrigation runoff, shrimp farm effluents, and urban wastewater containing large quantities of nutrients to be discharged into this lagoon. We propose to identify the APP's response to various types of environmental and anthropogenic influence in this highly impacted coastal lagoon. Methods: Two sites (separated by 2.7 km) were monitored from December 2007 to December 2008. One, located at the entrance to Laguna Macapule (oceanic influence) and the other a discharge canal (eutrophic conditions) inside the lagoon at El Tortugón. Results: APP was the numerically dominant phytoplankton fraction (15 × 10 to 620 × 10 cells L) with coccoidal cyanobacteria as the dominant fraction throughout the year. Peak levels were reached in spring-early autumn and they were the second largest contributor to biomass. Abundance of APP cells corresponds to the lagoon's eutrophic status. Maximum numbers and a higher average of APP were recorded at the El Tortugón channel during the warm season (months with SST higher than 24 °C). The general positive relationship of the APP's annual cycle at both sites as well as a negative relationship with heterotrophic nanoflagellates (HNF) abundance, supports the idea that natural forcing, in particular sea surface temperature (SST) is the predominant influences on APP's seasonal variability. Conclusions: Distinguishable significant differences in APP abundances and nutrients were recognizable between the two sites. The interplay of these variables contributed to lower densities of APP in winter and high densities in spring-early autumn. N:P = ~4 suggests that spring-early autumn abundance of the APP autotrophic component was sustained by urea from shrimp farm discharge water. Thus, a total nutrient-based approach is likely the most suitable tool for establishing nitrogen limitation of biological production in Laguna Macapule and similarly impacted ecosystems around the world. [ABSTRACT FROM AUTHOR]

A systematic limnological survey of water bodies of Byers Peninsula (Livingston Island, South Shetland Islands) was carried out during the summer of 2001/02. Abundances of microbial plankton were determined which allowed a delineation of the pelagic food web structure. We also report the nutrient status of these lakes. We demonstrate the occurrence of a trophic gradient that extended from upland lakes (oligotrophic) to the coastal ones (eutrophic). The study shows that a lake's morphology regulates the relative importance of the pelagic and benthic habitats, whereas nutrient loads mainly determine its trophic status. Yet, some of the variability observed could be also a legacy of the landscape. Photosynthetic pigments analyses by high-performance liquid chromatography of the lake waters revealed a major occurrence of chlorophytes, chrysophytes and diatoms. The chlorophyll a concentrations in lakes in the central plateau were consistently lower (< 2.5 μg l-1) than coastal sites, which were one order of magnitude higher. Numbers of both bacterioplankton and autotrophic picoplankton also increased from inland to coastal sites. However, the relative role of autotrophic picoplankton in the total phytoplankton assemblage decreased with the increase in nutrients loads. Our results show that the trophic status clearly plays a significant role in structuring the pelagic communities of these lakes despite climatic constraints. [ABSTRACT FROM PUBLISHER]

Two coastal zones (influenced by the Coatzacoalcos and Grijalva-Usumacinta rivers) and an oceanic one (Campeche Canyon), from the southern Gulf of Mexico, were sampled during the ‘nortes’ or windy (February, 2004) season, to study the concentration and distribution of the phytoplanktonic pigments and the picoeukaryote fraction. Vertical profiles of accessory pigments indicated the presence and potential importance of autotrophic picoplankton in the waters of the Southern Gulf of Mexico. These pigments showed different distributions, associated with different hydrographic conditions between the oceanic zone and the coastal regions (e.g. presence and depth of a thermocline), indicating contrasting phytoplankton communities. The highest concentrations of accessory pigments (fucoxanthin, zeaxanthin, divinyl-chlorophyll a) were associated with shallow coastal zones (above 1% PARI), except for prasinoxanthin that also showed high concentrations in the Campeche Canyon. Pigments associated with prokaryotic picoplankton (zeaxanthin, divinyl-chlorophyll a) were more distinguishable in the Campeche Canyon than in the coastal zones. Chlorophyll a was not directly related to accessory pigments in most of the stations studied. Relatively high cell abundances of Prasinophyte Micromonas pusilla occurred at one coastal zone station, using molecular probes (FISH-TSA), and revealed the potential importance of this Prasinophyte in the picoeukaryote fraction from the study area, providing a new insight into their ecological role, relative to diatoms and coccolithophorids. [ABSTRACT FROM AUTHOR]

The first data on the content of pico-sized detrital particles (0.2-2.0 μm) are obtained by epifluorescence microscopy in the upper Volga reservoirs. The spatial and temporal distributions of density and mass of picodetritus are described. The quantitative proportions between heterotrophic bacteria, picophytoplankton, and pico-sized detritus were revealed. [ABSTRACT FROM AUTHOR]

The species composition, abundance and biomass of autotrophic picoplankton and larger phytoplanktonic organisms were analysed in 17 non-stratified lakes of Pomerania. Water samples were collected in August in 1995–1999. The composition and structure of phytoplankton varied among the lakes. Two groups of lakes could be distinguished: with a low and with a high species richness. Phytoplankton abundance ranged from about 1 × 102 to 1.5 × 106 cells ml-1 and was usually dominated by green algae, cyanobacteria, chrysophytes and dinoflagellates. Phytoplankton biomass ranged from 0.04 to 16.9 mg l-1 and in half of the lakes was dominated by cyanobacteria or dinoflagellates. Biomass of the smallest size fraction i.e. autotrophic picoplankton (APP) was always small in comparison with that of larger phytoplanktonic organisms. Cyanobacterial cells were usually the main components of APP, while eukaryotic APP were rare. Colonial forms accounted for 6–93% of the total APP abundance. In terms of total phytoplankton biomass, organisms from one of the other fractions, i.e. nanoplankton or microplankton, were usually more important. As the community structure of phytoplankton showed clear differences among lakes, special attention was paid to the variation in the relative abundance and biomass of some species or groups of species. [ABSTRACT FROM AUTHOR]

1. Lago Maggiore is a deep subalpine lake that has regained its previous oligotrophic state during the last decade after going through a process of cultural eutrophication and subsequent restoration. Autotrophic picoplankton (APP) have been studied in Lago Maggiore since 1992, with the primary production of the fraction being measured in 1994 and 1995. In 1998, we began to study the population structure and photosynthetic characteristics of APP after the restoration of the lake. We also compared the seasonal dynamics of APP and nanoplankton biomass and production. In this paper, we show the trend of annual and interannual dynamics of APP from 1993 to 1998. 2. Since 1993 and 1994, APP have almost tripled in numbers (mean values: 1993=44 × 103 cell mL–1 1998=123 × 103 cell mL–1 ) and in production. On average, APP produced 16 gC m–2 year–1 in 1994 and 41.2 gC m–2 year–1 in 1998, accounting for 10 and 20%, respectively, of total phototrophic production. 3. Although nanoplankton dominated in terms of biomass and production in the first 6 months of the year, APP were able to compete successfully with them in periods of P limitation. In September 1998, APP carbon fixation actually surpassed that of nanoplankton, reaching 13 mgC m–3 h–1 at 3 m. In a comparison of the daily chlorophyll-specific photosynthesis rates of nanoplankton and APP, the latter proved to be more efficient in fixing carbon, particularly in summer and autumn. 4. While the spatial distribution of APP abundance and production followed the isotherms of 18 and 20 °C, and was strictly related to water stratification and thermocline appearance, the APP efficiency [mgC (mg chl)–1 Em–2 ] had its maximum at the bottom of the euphotic zone, with irradiance in the range 0.5–18 μE... [ABSTRACT FROM AUTHOR]

The distribution of primary components of the microbial community (autotrophic pico- and nanoplankton, phototrophic bacteria, heterotrophic bacteria, microscopic fungi, heterotrophic flagellates, ciliates and heliozoa) in the water column of Lake Shira, a steppe brackish-water, stratified lake in Khakasia, Siberia (Russia), were assessed in midsummer. Bacterioplankton was the main component of the planktonic microbial community, accounting for 65.3 to 75.7% of the total microbial biomass. The maximum concentration of heterotrophic bacteria were recorded in the monimolimnion of the lake. Autotrophic microorganisms contributed more significantly to the total microbial biomass in the pelagic zone (20.2–26.5%) than in the littoral zone of the lake (8.7–14.9%). First of all, it is caused by development of phototrophic sulphur bacteria at the oxic-anoxic boundary. The concentrations of most aerobic phototrophic and heterotrophic microorganisms were maximal in the upper mixolimnion. Heterotrophic flagellates dominated the protozoan populations. Ciliates were minor component of the planktonic microbial community of the lake. Heterotrophic flagellates were the most diverse group of planktonic eucaryotes in the lake, which represented by 36 species. Facultative and obligate anaerobic flagellates were revealed in the monimolimnion. There were four species of Heliozoa and only three of ciliates in the lake. [ABSTRACT FROM AUTHOR]

The objective of the present study was to evaluate the influence of UV radiation on photosynthesis rate, in situ and in laboratory incubations, on size fractionated natural algal assemblages (picoplankton: 0.2-2 μm, nanoplankton: >2 μm) and whole water (total organic carbon TOC). Near surface samples from a mesotrophic high mountain lake (LCD: L. Cadagno, Swiss Alps, Switzerland, 1923 m a.s.l.) and from the oligotrophic pre-alpine L. Lucerne (LLU: Swiss Alps, Switzerland, 434 m a.s.l.) were both incubated at a depth of 30 cm (50 % of surface UV at 323 nm ) in L. Cadagno. At the same time, biological weighting functions for UV inhibition of photosynthesis (BWFs) were determined for the autotrophic picoplankton and whole fraction in a spectral incubator. Photosynthetic assimilation of the pico- and nanoplanktonic algal communities as well as the assimilated total organic carbon (TOC) was estimated separately by 14C uptake under three irradiance conditions: PAR (photosynthetically active radiation), PAR + UVA and PAR + UVA + UVB. UV radiation reduced significantly photosynthesis rate in samples from both lakes (LLU: P = 0.0012; LCD: P = 0.0001). It appears that UVA plus UVB significantly affect the algal assemblage in both lakes; however most of the effect is due to UVA (Mann Whitney U test, two tailed: P = 0.0022). The natural assemblages from LLU transplanted to LCD were more inhibited by UV than the autochthonous assemblages of LCD. Photosynthetic rates of picoplankton from LLU and LCD under full UV exposure was reduced by 73 % and 55 % respectively relative to PAR only. A higher sensitivity of autotrophic picoplankton to the UV radiation, with respect to the nanoplankton, was observed in the biological weighting functions. However this difference was not statistically significant for the in situ incubations. [ABSTRACT FROM AUTHOR]

The autotrophic picoplankton of the pelagic zone of the mesotrophic Lake Constance is dominated by phycoerythrin-rich unicellular cyanobacteria phylogenetically related to the marine Synechococcus and Prochlorococcus cluster. In Lake Constance, the abundance of picocyanobacteria shows a recurrent pattern of seasonal variations. Evidence of diverse subpopulations was obtained by electron-microscopic examination of natural water samples and isolated strains that unveiled different surface structures of picocyanobacteria. Further evidence was obtained by DNA analysis of 26 clonal isolates representing 12 different genotypes. Variations in light and nutrient supply revealed distinct abilities of the genetically different strains to cope with these stress situations. Furthermore, cultured heterotrophic nanoflagellates exhibited differential feeding preferences for certain Synechococcus strains. The findings imply that growth and loss rates of the natural cyanobacterial community may be influenced by its genetic composition. Phylogenetic analyses of isolated strains indicated that the physiological diversification of pelagic Synechococcus spp. has occurred during a recent adaptive radiation. An example for genetic mechanisms underlying physiological diversification is indicated by mobile DNA elements found in a Synechocystis strain also isolated from the pelagic zone of Lake Constance. The observations suggest that dominance of Synechococcus spp. was achieved by evolutionary adaptation and coexistence of numerous genotypes generating a physiologically highly diversified population. [ABSTRACT FROM AUTHOR]

Spatial and seasonal fluctuations in autotrophic picoplankton (APP) abundance in a eutrophic, dimictic lake (Lake Aydat, France) were measured concurrently with a variety of environmental variables. Cell number ranged from 0.03 to 2.36×10 cells·ml (highest concentrations were >5-fold higher than in oligotrophic lakes) and averaged 24 ± 7% of total picoplankton abundance (APP + heterotrophic bacteria). APP abundance (1) peaked in spring simultaneously with heterotrophic flagellate and ciliate densities, (2) decreased during the nitrogen-limited and summer stratification period, and (3) increased with fall turnover. In summer-autumn, the contribution of single-cell eukaryotic (up to 66%) and colonial prokaryotic (18%) forms to total abundance peaked in the bottom waters. Multivariate regression analyses suggest that >40% variance in APP number changes may be explained by ciliate abundance (at 0-4 m depth-range), heterotrophic flagellate number and oxygen concentration (5-9 m), and ciliate carbon biomass (10-14 m). The model accounting for changes in heterotrophic bacterial abundance (5-9 m) indicates chlorophyll a concentration ( r=58%) and ciliate abundance ( r=34%) as dominant covariates. The data presented here suggest that micrograzers control APP abundance in Lake Aydat. [ABSTRACT FROM AUTHOR]

An assessment of the temperature increase effect on processes within the microbial food web provides a better insight into the carbon transfer and energy flow processes in marine environments in the global warming perspective. Modified laboratory dilution experiments that allow simultaneous estimates of protozoan grazing and viral lysis on picoplankton groups (bacteria, Prochlorococcus, Synechococcus and pico-eukaryotic algae) under in situ and 3°C above in situ temperatures were performed at seasonal scale. Picoplankton mortality due to grazing was generally higher than that caused by viral lysis, especially in the cold months. The largest part of HNF carbon demand was satisfied by grazing on bacteria throughout the year. Although ciliates satisfied their carbon demand predominantly through grazing on HNF and bacteria, the role of autotrophic picoplankton (APP) as their prey increased significantly in the cold months. Bacteria constituted the most important host for viruses throughout the year. However, during the warm months, APP groups were also significant hosts for viral infection. Under the warming condition the amount of picoplankton biomass transferred to protozoan grazers exceeded the lysed biomass, suggesting that global warming could further increase picoplankton carbon flow toward higher trophic levels in the Adriatic Sea. [ABSTRACT FROM AUTHOR]

1. We examined the effects of nutrients, turbulent mixing, mosquitofish, Gambusia affinis Baird and Girard and sediments on algal composition, algal biomass and autotrophic picoplankton (APP) abundance in a 6-week experiment of factorial design in twenty-four 5-m3 outdoor mesocosms during late autumn 1995. 2. Turbulent mixing decreased surface temperature and increased turbidity, which also was increased by the addition of sediments. Total algal biomass was significantly enhanced by nutrients and mixing, and decreased by the sediment treatment. In the mixing × nutrient treatment, algal biomass increased more than expected from the individual effects, while the fish × mixing and mixing × sediment treatments increased algal biomass less than expected. 3. Cryptomonas (cryptomonad) blooms were observed in the unmixed, high nutrient treatment; Synedra (diatom) blooms were observed in the high nutrient, high sediment treatment; Ulothrix (green algae) blooms were observed in the mixed, high nutrient, low sediment treatment. 4. Eukaryotic APP abundances were increased by sediment addition and by turbulent mixing, and increased synergistically by mixing × sediment and mixing × nutrient interactions. Prokaryotic APP abundances were decreased by nutrient enhancement and by a mixing × nutrient interaction. There were no main effects of fish on APP abundance, but fish were involved in some of the two–way interactions. 5. The large number of significant interaction effects indicates that APP and other phytoplankton are regulated by a complex set of interdependent factors which should be considered simultaneously in studies of phytoplankton population dynamics and community composition. [ABSTRACT FROM AUTHOR]