Consulta: creatorFacets:"Christaki, Urania"
Registros recuperados: 12
Data/hora: 09/06/2024 11:36:08

Shifts in bacterial community composition associated with increased carbon cycling in a mosaic of phytoplankton blooms
Provedor de dados: Institutional Archive of Ifreme (ArchiMer)
Autores: Landa, Marine; Blain, Stephane; Christaki, Urania; Monchy, Sebastien; Obernosterer, Ingrid.
Marine microbes have a pivotal role in the marine biogeochemical cycle of carbon, because they regulate the turnover of dissolved organic matter (DOM), one of the largest carbon reservoirs on Earth. Microbial communities and DOM are both highly diverse components of the ocean system, yet the role of microbial diversity for carbon processing remains thus far poorly understood. We report here results from an exploration of a mosaic of phytoplankton blooms induced by large-scale natural iron fertilization in the Southern Ocean. We show that in this unique ecosystem where concentrations of DOM are lowest in the global ocean, a patchwork of blooms is associated with diverse and distinct bacterial communities. By using on-board continuous cultures, we identify...
Tipo: Text
Ano: 2016
URL: https://archimer.ifremer.fr/doc/00421/53293/54115.pdf

Succession of primary producers and micrograzers in a coastal ecosystem dominated by Phaeocystis globosa blooms
Provedor de dados: Institutional Archive of Ifreme (ArchiMer)
Autores: Grattepanche, Jean-david; Breton, Elsa; Brylinski, Jean-michel; Lecuyer, Eric; Christaki, Urania.
The community structures and succession of phytoplankton, protozooplankton and copepods were studied from February 2007 to July 2009 in a coastal area of the eastern English Channel subject to Phaeocystis globosa blooms. While diatom blooms preceded P. globosa blooms each year, the community structure and stock of heterotrophic protists appeared to be related to the dominant P. globosa life cycle stages. In 2007, the dominance of large colonies (&gt; 100 mu m, up to 316 mu g C L(-1)), which resulted in a high biomass of healthy free cells (up to 132 mu g C L(-1)), accompanied high spirotrich ciliate stocks (up to 58 mu g C L(-1)) and high abundances of the copepods Acartia clausi and Temora longicornis (up to 11 ind. L(-1)). In 2008, the bloom which lasted...
Tipo: Text
Palavras-chave: Phaeocystis globosa; Diatoms; Micrograzer community; Eastern English Channel.
Ano: 2011
URL: https://archimer.ifremer.fr/doc/00373/48468/48714.pdf

Seasonal microbial food web dynamics in contrasting Southern Ocean productivity regimes
Provedor de dados: Institutional Archive of Ifreme (ArchiMer)
Autores: Christaki, Urania; Gueneugues, Audrey; Liu, Yan; Blain, Stéphane; Catala, Philippe; Colombet, Jonathan; Debeljak, Pavla; Jardillier, Ludwig; Irion, Solène; Planchon, Frederic; Sassenhagen, Ingrid; Sime Ngando, Telesphore; Obernosterer, Ingrid.
Spatial and seasonal dynamics of microbial loop fluxes were investigated in contrasting productivity regimes in the Indian sector of the Southern Ocean. Observations carried out in late summer (February–March 2018; project MOBYDICK) revealed higher microbial biomasses and fluxes in the naturally iron‐fertilized surface waters of Kerguelen island in comparison to surrounding off‐plateau waters. Differences were most pronounced for bacterial heterotrophic production (2.3‐fold), the abundance of heterotrophic nanoflagellates (HNF; 2.7‐fold). Independent of site, grazing by HNF was the main loss process of bacterial production (80–100%), while virus‐induced mortality was low (&lt; 9%). Combining these results with observations from previous investigations...
Tipo: Text
Ano: 2021
URL: https://archimer.ifremer.fr/doc/00649/76109/77064.pdf

Small-scale variability of protistan planktonic communities relative to environmental pressures and biotic interactions at two adjacent coastal stations
Provedor de dados: Institutional Archive of Ifreme (ArchiMer)
Autores: Genitsaris, Savvas; Monchy, Sebastien; Breton, Elsa; Lecuyer, Eric; Christaki, Urania.
The aim of this study was to analyze planktonic protistan assemblages under different environmental pressures at 2 adjacent coastal stations (inshore and offshore; similar to 6.4 km apart) in the eastern English Channel (EEC). Samples were collected between March 2012 and June 2013, and analyzed using bioinformatic analysis and tag pyrosequencing of the V2-V3 hypervariable region of the 18S rRNA gene. In addition to the taxonomic composition of the protistan communities, the detected operational taxonomic units (OTUs) were sorted into 6 major functional groups based on their trophic roles in marine systems. Comparisons of 13 environmental factors, including physical and chemical variables, indicated significant differences between the 2 stations. However,...
Tipo: Text
Palavras-chave: Unicellular eukaryotes; Community organization; Environmental parameters; Biotic interactions; 18S rRNA; Pyrosequencing; Bioinformatics; Ecological tools.
Ano: 2016
URL: https://archimer.ifremer.fr/doc/00373/48450/48765.pdf

Microzooplankton community associated with phytoplankton blooms in the naturally iron-fertilized Kerguelen area (Southern Ocean)
Provedor de dados: Institutional Archive of Ifreme (ArchiMer)
Autores: Christaki, Urania; Georges, Clement; Genitsaris, Savvas; Monchy, Sebastien.
The spatial and temporal community composition of microzooplankton (dinoflagellates and ciliates) was assessed in the Kerguelen area (Southern Ocean) during the KEOPS2 cruise in early spring (October-November) 2011. This naturally iron-fertilized region was characterized by a complex mesoscale circulation resulting in a patchy distribution of phytoplankton blooms. Collectively, 97 morphospecies of dinoflagellates and ciliates belonging to 41 genera were identified by microscopy, and 202 Alveolata-related OTUs (operational taxonomical units) were retrieved with tag-pyrosequencing. Microscopy and pyrosequencing data were in accordance, in that diatom-consuming dinoflagellates were the most enhanced taxa in the blooms. Dinoflagellates also showed significant...
Tipo: Text
Palavras-chave: Dinoflagellates; Ciliates; Natural iron fertilization; Southern Ocean.
Ano: 2015
URL: https://archimer.ifremer.fr/doc/00351/46255/46080.pdf

Marked spatiotemporal variations in small phytoplankton structure in contrasted waters of the Southern Ocean (Kerguelen area)
Provedor de dados: Institutional Archive of Ifreme (ArchiMer)
Autores: Irion, Solène; Jardillier, Ludwig; Sassenhagen, Ingrid; Christaki, Urania.
In the Southern Ocean, diatom blooms have attracted a lot of attention, while other small nonsilicified phytoplankton groups have been less studied. Here, small phytoplankton (&lt; 20 μ m, including small diatoms and nonsilicified small phytoplankton) are focused on in two contrasting areas: the productive Kerguelen plateau and its surrounding low productivity waters. To assess the diversity and spatial structuration of phytoplankton, discrete plankton samples (0–300 m layer) of two size fractions (&lt; 20 and 20–100 μ m) were analyzed with 18S rDNA amplicon sequencing in late summer. Phytoplankton seasonal succession was described using flow cytometry, pigments, and environmental data, from two previous cruises (during the onset and decline of the diatom...
Tipo: Text
Ano: 2020
URL: https://archimer.ifremer.fr/doc/00635/74746/74854.pdf

Development of a qPCR Method for the Identification and Quantification of Two Closely Related Tuna Species, Bigeye Tuna (     Thunnus obesus     ) and Yellowfin Tuna (     Thunnus albacares     ), in Canned Tuna
Provedor de dados: Institutional Archive of Ifreme (ArchiMer)
Autores: Bojolly, Daline; Doyen, Perine; Le Fur, Bruno; Christaki, Urania; Verrez-bagnis, Veronique; Grard, Thierry.
Bigeye tuna (Thunnus obesus) and yellowfin tuna (Thunnus albacares) are among the most widely used tuna species for canning purposes. Not only substitution but also mixing of tuna species is prohibited by the European regulation for canned tuna products. However, as juveniles of bigeye and yellowfin tunas are very difficult to distinguish, unintentional substitutions may occur during the canning process. In this study, two mitochondrial markers from NADH dehydrogenase subunit 2 and cytochrome c oxidase subunit II genes were used to identify bigeye tuna and yellowfin tuna, respectively, utilizing TaqMan qPCR methodology. Two different qPCR-based methods were developed to quantify the percentage of flesh of each species used for can processing. The first one...
Tipo: Text
Palavras-chave: Tuna; Authentication; Quantification; Canned products; TaqMan; QPCR; Species identification; Bigeye tuna (Thunnus obesus); Yellowfin tuna (Thunnus albacares).
Ano: 2017
URL: https://archimer.ifremer.fr/doc/00371/48217/48403.pdf

Small phytoplankton contribute greatly to CO2-fixation after the diatom bloom in the Southern Ocean
Provedor de dados: Institutional Archive of Ifreme (ArchiMer)
Autores: Irion, Solène; Christaki, Urania; Berthelot, Hugo; L’helguen, Stéphane; Jardillier, Ludwig.
Phytoplankton is composed of a broad-sized spectrum of phylogenetically diverse microorganisms. Assessing CO2-fixation intra- and inter-group variability is crucial in understanding how the carbon pump functions, as each group of phytoplankton may be characterized by diverse efficiencies in carbon fixation and export to the deep ocean. We measured the CO2-fixation of different groups of phytoplankton at the single-cell level around the naturally iron-fertilized Kerguelen plateau (Southern Ocean), known for intense diatoms blooms suspected to enhance CO2 sequestration. After the bloom, small cells (&lt;20 µm) composed of phylogenetically distant taxa (prymnesiophytes, prasinophytes, and small diatoms) were growing faster (0.37 ± 0.13 and 0.22 ± 0.09...
Tipo: Text
Palavras-chave: Biogeochemistry; Microbial ecology; Stable isotope analysis.
Ano: 2021
URL: https://archimer.ifremer.fr/doc/00684/79595/82286.pdf

Microplanktonic Community Structure in a Coastal System Relative to a Phaeocystis Bloom Inferred from Morphological and Tag Pyrosequencing Methods
Provedor de dados: Institutional Archive of Ifreme (ArchiMer)
Autores: Monchy, Sebastien; Grattepanche, Jean-david; Breton, Elsa; Meloni, Dionigia; Sanciu, Giovanna; Chabe, Magali; Delhaes, Laurence; Viscogliosi, Eric; Sime-ngando, Telesphore; Christaki, Urania.
Background: Massive phytoplankton blooms, like the recurrent Phaeocystis proliferation observed every year in the Eastern English Channel (EEC), have a significant influence on the overall planktonic community structure and their food web dynamics. As well as being an important area for local fisheries, the EEC is an ideal ecosystem for work on microbial diversity. This is because, although its environmental context is relatively complex, it is reasonably well understood due to several years of monitoring and morphological observations of its planktonic organisms. The objective of our study was to better understand the under-explored microbial eukaryotic diversity relative to the Phaeocystis bloom. Methodology and Principal Findings: The community...
Tipo: Text
Ano: 2012
URL: https://archimer.ifremer.fr/doc/00373/48460/48724.pdf

Composition of diatom communities and their contribution to plankton biomass in the naturally iron fertilized region of Kerguelen in the Southern Ocean
Provedor de dados: Institutional Archive of Ifreme (ArchiMer)
Autores: Lasbleiz, Marine; Leblanc, Karine; Armand, Leanne K.; Christaki, Urania; Georges, Clement; Obernosterer, Ingrid; Queguiner, Bernard.
In the naturally iron-fertilized surface waters of the northern Kerguelen Plateau region, the early spring diatom community composition and contribution to plankton carbon biomass were investigated and compared with the High Nutrient Low Chlorophyll (HNLC) surrounding waters. The large iron-induced blooms were dominated by small diatom species belonging to the genera Chaetoceros (Hyalochaete) and Thalassiosira, which rapidly responded to the onset of favorable light-conditions in the meander of the Polar Front. In comparison, the iron-limited HNLC area was typically characterized by autotrophic nanoeukaryote-dominated communities and by larger and more heavily silicified diatom species (e.g. Fragilariopsis spp.). Our results support the hypothesis that...
Tipo: Text
Palavras-chave: Diatoms; Carbon biomass; Plankton community structure; Natural iron fertilization; Southern Ocean.
Ano: 2016
URL: https://archimer.ifremer.fr/doc/00347/45850/45512.pdf

Seasonal variations of marine protist community structure based on taxon-specific traits using the eastern English Channel as a model coastal system
Provedor de dados: Institutional Archive of Ifreme (ArchiMer)
Autores: Genitsaris, Savvas; Monchy, Sebastien; Viscogliosi, Eric; Sime-ngando, Telesphore; Ferreira, Stephanie; Christaki, Urania.
Previous microscopy-based studies in the eastern English Channel have revealed it to be a productive meso-eutrophic coastal ecosystem, characterized by strong repeating patterns in microplankton succession. The present study examines the seasonal structure of the entire protistan community from March 2011 to July 2013, using tag pyrosequencing of the V2-V3 hypervariable region of the 18S rRNA gene. A total of 1242 OTUs and 28 high-level taxonomic groups, which included previously undetected taxa in the area, were identified. The detected OTUs were considered according to taxon-specific traits, which included their trophic role, abundance and specialization level. Taxa differentiation based on specialization level rather than abundance was more informative...
Tipo: Text
Palavras-chave: Unicellular eukaryotes; Tag pyrosequencing; 18S rRNA gene; Succession; Generalists; Specialists.
Ano: 2015
URL: https://archimer.ifremer.fr/doc/00373/48454/48738.pdf

High spatial variability of phytoplankton assessed by flow cytometry, in a dynamic productive coastal area, in spring:the eastern English Channel
Provedor de dados: Institutional Archive of Ifreme (ArchiMer)
Autores: Bonato, Simon; Christaki, Urania; Lefebvre, Alain; Lizon, Fabrice; Thyssen, Melilotus; Artigas, Luis Felipe.
The distribution of phytoplankton (from pico-to microphytoplankton) was investigated, at single-cell level and at high spatial resolution, during an oceanographic cruise across the eastern English Channel (EEC) between April 27 and 29, 2012. Seawater was continuously collected from surface waters and analysed on board at high frequency (one sample every 10 min), by using a new generation of pulse-shape recording scanning flow cytometer (CytoSense, Cytobuoy©). A Bray-Curtis matrix analysis based on phytoplankton composition allowed the discrimination of 4 communities. Within these communities, abundance, cell size as well as single cell and total red fluorescence of 8 phytoplankton groups were measured. Picoeukaryotes and Synechococcus spp. cells dominated...
Tipo: Text
Palavras-chave: Phytoplankton dynamics; High spatial resolution; Flow cytometer; Red fluorescence.
Ano: 2015
URL: https://archimer.ifremer.fr/doc/00248/35885/34406.pdf