1,721,021 research outputs found
Quantitative aspects of the ecology of marine planktonic ciliated protozoans, with special reference to Uronema marinum Dujardin
No full textThe seasonal abundance of ciliates and other microseston components a I t Calshot was investigated between January 1974 and March 1975. Samples were collected by pumping and were size fractionated. Ciliates were found to be present throughout the year. The standing crops of both tintinnids and naked ciliates were at a maximum in late spring; a second peak was found in the autumn for tintinnids. Thirteen species of tintinnid were found although two species, StenosWella ventricosa and Tintinnopsis beroidea, dominated the tintinnid,assemblage throughout the year. Some tintinnid species showed seasonal succession and could be divided into seasonal groups.Laboratory studies were carried out A The bacteriovorous ciliateUronema marinum. The effects of salinity, food type and temperature-on reproduction were investigated. Experiments were carried out to determine rates of consumption, growth and reproduction in relation to food concentration and temperature. I Mean cell volumes and gross growth efficiencies were also measured. Spectrophotometry, using calibration by bacterial organic carbon measurements,' was used to determine food concentration. A method was developed for separating ciliates from their food for biomass estimation using the ciliate's migratory behaviourv Models were derived for consumption, growth and reproduction based on the forcing functions of food concentration and temperature. Tentative estimates were made for the- production of naked ciliate; and 'their consumption of bacteria at Calshot by integrating the field work data with the models of consumption and growth. Estimates were also made for the production of tintinnids and their consumption of nanophytoplankton using field study data and-literature derived information on consumption and reproduction. The results obtained suggest that the grazing of bacteria by naked ciliates is negligible in proportion to bacterial standing crop and production but that tintinnids may be important' in controlling phytoplankton production.</p
The herbivorous impact of microzooplankton during two short-term Lagrangian experiments off the NW coast of Galicia in summer 1998
No full textMicrozooplankton (heterotrophic microplankton and heterotrophic nanoflagellates) and their herbivorous activity were estimated from dilution experiments in August 1998 during two Lagrangian drift experiments that sampled contrasting conditions—an upwelling/relaxation event along the shelf edge and an oligotrophic offshore filament. During upwelling/relaxation, heterotrophic microplankton were present at mean surface concentrations between 15,000 and 48,000 cells l?1. Heterotrophic nanoflagellate concentrations were between 200 and 700 cells ml?1 and the most abundant component of the heterotrophic microplankton was the aloricate choreotrich ciliates which increased dramatically in concentration from 6,000 to 24,000 cells l?1 during the first 4 days of the study. Total microzooplankton biomass reached a maximum of 39mgC.m?3. In the filament, which developed from the upwelling, cell concentrations were lower and averaged 4,500 cells l?1 for heterotrophic microplankton and 250 cells ml?1 for heterotrophic nanoflagellates. Total microzooplankton biomass was about 10–12mgC.m?3. Microzooplankton turned over between 40 and 85% of the phytoplankton standing stock, thereby consuming between 5 and 78mg phytoplankton carbon.m?3.d?1. The magnitude of this activity was highest during upwelling/relaxation and was positively correlated to heterotrophic nanoflagellate biomass and chlorophyll-a concentration but not heterotrophic microplankton biomass. The proportion of primary production grazed decreased from 160 to 59% d?1 during upwelling/relaxation and ranged between 60 and 90% d?1 in the filament. Microzooplankton herbivory within the euphotic zone increased from 684 to >2000mgC.m?2.d?1 during upwelling/relaxation and was between 327 and 802mgC.m?2.d?1 in the filament. Although microzooplankton herbivory was lower and less variable during the filament study, microzooplankton consumed on average 60% of the phytoplankton standing stocks which was higher than found during upwelling/relaxation. Microzooplankton assimilation efficiency ranged between 3 and 33% during upwelling/relaxation and between 0 and 13% in the filament. Our data demonstrate a close coupling between phytoplankton growth and microzooplankton herbivory in surface waters off the Galician Coast and suggest that microzooplankton may have been a significant sink for phytogenic carbon during August 1998
European Project on Ocean Acidification (EPOCA): Objectives, Products, and Scientific Highlights. Box 2. European time series of calcareous organisms and carbonate chemistry
No full textAssaying picoplankton distribution by flow cytometry of underway samples collected along a meridional transect across the Atlantic Ocean
Full text linkThe composition of picoplankton in near-surface samples collected underway at least every 6 h from a ship sailing from the Falkland Islands to the British Isles was determined by flow cytometry, using both autofluorescence markers and staining with the DNA dye SYBR Green I. Prochlorococcus (0.1 to 0.3 X 106 cells ml-l) dominated the phytoplankton in the oligotrophic northern (24" to 38" N) and southern (8" to 34" S) gyre regions. In the equatorial region (8" S to 24" N) the more productive waters supported 10 to 100 times more picoeukaryote algae and Synechococcus than in the gyres. The collection of samples underway proved to be a very economical method of obtaining a good indication of the concentration of heterotroph~c bactena and of these 3 classes of picophytoplankton in the surface mixed layer (coefficient of correlation, r2 = 0.88 to 0.98) throughout a very long transect, but correlated less well with picoplankton standing stocks in the top 200 m of the water column (r2 = 0.39 to 0.88). Daily variations in the flow cytometry profiles of stained Prochlorococcus observed over a distance of some 8000 km of the tropical and subtropical Atlantic were interpreted as an indication of their synchronised cell division in surface waters. Their estimated average minimum growth rate (0.15 d-l) was similar in both southern and northern oligotrophic gyres and in equatorial waters
Microzooplankton grazing activity in the temperate and sub-tropical NE Atlantic: summer 1996
No full textMarine bacterioplankton can increase evaporation and gas transfer by metabolizing insoluble surfactants from the air-seawater interface
No full textHydrophobic surfactants at the air–sea interface can retard evaporative and gaseous exchange between the atmosphere and the ocean. While numerous studies have examined the metabolic role of bacterioneuston at the air–sea interface, the interactions between hydrophobic surfactants and bacterioplankton are not well constrained. A novel experimental design was developed, using Vibrio natriegens and 3H-labelled hexadecanoic acid tracer, to determine how the bacterial metabolism of fatty acids affects evaporative fluxes. In abiotic systems, >92% of the added hexadecanoic acid remained at the air–water interface. In contrast, the presence of V. natriegens cells draws down insoluble hexadecanoic acid from the air–water interface as an exponential function of time. The exponents characterizing the removal of hexadecanoic acid from the interface co-vary with the concentration of V. natriegens cells in the underlying water, with the largest exponent corresponding to the highest cell abundance. Radiochemical budgets show that evaporative fluxes from the system are linearly proportional to the quantity of hexadecanoic acid at the interface. Thus, bacterioplankton could influence the rate of evaporation and gas transfer in the ocean through the metabolism of otherwise insoluble surfactants.<br/
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Bacterial growth and grazing loss in contrasting areas of North and South Atlantic
No full textSamples were collected from the top 200 m of the water column at 50 stations during two cruises in different, near equinoctial seasons on an Atlantic transect near the 20°W meridian between 50°N and 50°S. These samples were analysed to determine characteristics of the heterotrophic bacterial populations. Flow cytometry was used to enumerate these bacteria and determine their average size so as to calculate their biomass. Heterotrophic bacterial production, and the rate of grazing of these bacteria by heterotrophic nanoplankton in the main depth layers, were determined using 3H thymidine and 14C leucine techniques. The biomass of heterotrophic nanoplankton in these layers was determined using a glucosaminidase assay. Five provinces were distinguished along the transect and characterized by average values of all measured parameters. The relative composition and activity of the microbial community in the water columns within each province changed little between the two cruises. Lowest heterotrophic bacterial biomass of 1–2 mg C m–3 and production of 0.1–0.2 mg C m–3 day–1 were found in the northern and southern Atlantic gyres, and were relatively similar in both seasons. Biomass and production were 2–4 times higher in the northern and southern temperate waters, and in equatorial waters, than in the gyres and tended to show more seasonal variation. Production and biomass in the layer below the pycnocline were lower by 10–30% and about 50%, respectively, than values determined in the surface mixed layer, and varied less with latitude. Depth-integrated values of these two parameters were generally of similar size in the mixed water layer and the layer of the chlorophyll maximum and pycnocline, and tended to vary with season. The specific growth rate of heterotrophic bacteria was in the range 0.05 to 0.12 day–1 in the top mixed layer at all latitudes. In spite of the elevated temperatures, bacterial growth appears to be restricted by a shortage of nutrients so that the microbial community cycles very slowly, with a turnover time of the order of 1 week or more. The depth-integrated biomass of heterotrophic nanoplankton was generally about 100% of the heterotrophic bacterial biomass in the same water. Grazing by these nanoplankton at the rate measured could consume all of the new production of heterotrophic bacteria in all waters, and they probably control the populations of both heterotrophic and phototrophic bacteria
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
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