Consulta: creatorFacets:"Youenou, Agnes"
Registros recuperados: 19
Data/hora: 08/06/2024 17:56:53

Nutrient and phytoplankton distribution in the Loire River plume (Bay of Biscay, France) resolved by a new Fine Scale Sampler
Provedor de dados: Institutional Archive of Ifreme (ArchiMer)
Autores: Lunven, Michel; Guillaud, Jean-francois; Youenou, Agnes; Crassous, Marie-pierre; Berric, Roger; Le Gall, Erwan; Kerouel, Roger; Labry, Claire; Aminot, Alain.
A new Fine Scale Sampler (FSS) was designed and used in the Loire River plume (Bay of Biscay, France) in order to study phytoplankton distribution in highly stratified water columns. The FSS consists of a linear array of 15 sampling bottles, set horizontally at 20 cm intervals. Data acquired from the CTD and fluorescence probe of the FSS enable it to be precisely positioned at the depth of the highest density gradient or at the chlorophyll a maximum. The FSS made it possible to investigate fine scale vertical distribution of phytoplankton and relationships with water density, nutrient concentrations or light availability, for spring and summer conditions. Under spring conditions, the entire upper layer exhibited a dominant diatom population (Chaetoceros...
Tipo: Text
Palavras-chave: Plankton patchiness; Density discontinuity; Sampling; Thin layer; Nutrients; Phytoplankton.
Ano: 2005
URL: http://archimer.ifremer.fr/doc/2005/publication-533.pdf

Comparaison de l'hétérotrophie phytoplanctonique en laboratoire et in situ : efflorescence estivale en eau côtière et populations printanières en mer stratifiée
Provedor de dados: Institutional Archive of Ifreme (ArchiMer)
Autores: Arzul, Genevieve; Videau, Christiane; Bodennec, Guy; Crassous, Marie-pierre; Youenou, Agnes.
Pour mieux connaître les facteurs qui agissent sur les interactions trophiques entre le phytoplancton et le milieu nutritif, nous avons étudié la capacité hétérotrophe du phytoplancton en conditions contrôlées, non axéniques, au laboratoire. Les expériences réalisées avec la [U-14C] glutamine, étaient basées sur l'étude des vitesses d'assimilation. Les résultats obtenus avec deux espèces du genre Gymnodinium et une diatomée ont été vérifiés lors d'efflorescences en eau côtière et estuarienne, montrant l'adaptation des algues au milieu riche en substances organiques et leur capacité hétérotrophe en fonction de l'éclairement. L'effet de l'éclairement sur la capacité phagotrophe de Gymnodinium a été observé au laboratoire. L'étude réalisée sur les particules...
Tipo: Text
Ano: 2002
URL: http://archimer.ifremer.fr/doc/00105/21599/19179.pdf

Competition for phosphorus between two dinoflagellates: A toxic Alexandrium minutum and a non-toxic Heterocapsa triquetra
Provedor de dados: Institutional Archive of Ifreme (ArchiMer)
Autores: Labry, Claire; Erard-le Denn, Evelyne; Chapelle, Annie; Fauchot, Juliette; Youenou, Agnes; Crassous, Marie-pierre; Le Grand, Jacqueline; Lorgeoux, Benedicte.
The understanding of the dominance of one species with respect to others is a pertinent challenge in HAB growth dynamics studies and the nutrient supply mode is one of the factors potentially involved. The competition for phosphorus (P) between a toxic species, Alexandrium minutum, and a non-toxic species, Heterocapsa triquetra, was studied (1) along a gradient of P depletion, (2) testing different P depletion degrees before a single PO4 supply and (3) experimenting different PO4 supply frequencies. In conditions Of PO4 depletion, H. triquetra stopped growing after two days both in monospecific and mixed batch cultures whereas A. minutum grew progressively from day 2 until the end of the experiment. This time-lag growth of A. minutum is associated to its...
Tipo: Text
Palavras-chave: Semi continuous culture; Batch culture; Ecophysiology; Pulse; Phosphorus storage; Dinoflagellates; Heterocapsa triquetra; Alexandrium minutum.
Ano: 2008
URL: http://archimer.ifremer.fr/doc/2008/publication-4067.pdf

Etude écophysiologique et paramétrisation du rôle du phosphore sur la croissance d'Alexandrium minutum, espèce responsable d'eaux colorées toxiques en estuaire de Penzé, et de son principal compétiteur Heterocapsa triquetra - Rapport final PNEC-ART3
Provedor de dados: Institutional Archive of Ifreme (ArchiMer)
Autores: Labry, Claire; Erard-le Denn, Evelyne; Chapelle, Annie; Youenou, Agnes; Crassous, Marie Pierre; Martin-jezequel, Véronique; Le Grand, Jacqueline.
Suite à un premier criblage des facteurs environnementaux favorables à la croissance d'Alexandrium minutum comparativement à celle d'une espèce compétitrice en rivière de Penzé, Heterocapsa triquetra (rapport ART3 2002-2003) cette étude vise à préciser et quantifier les réponses physiologiques respectives des deux espèces à différentes conditions d'apports en phosphate (taux de croissance, vitesse d'assimilation des phosphates, capacité à stocker le phosphore intracellulaire). Elle montre qu'Alexandrium minutum a plutôt une stratégie de « stockage », capable d'assimiler rapidement le phosphate après un apport mais le stockant pour une meilleure croissance ultérieure quand la ressource sera à nouveau épuisée. Comparativement, Heterocapsa triquetra aurait,...
Tipo: Text
Ano: 2004
URL: http://archimer.ifremer.fr/doc/00105/21598/19178.pdf

Hydrologie et populations phytoplanctoniques dans le panache de la Loire et en Baie de Vilaine en période estivale : résultats de la campagne VILOIR.
Provedor de dados: Institutional Archive of Ifreme (ArchiMer)
Autores: Lunven, Michel; Guillaud, Jean-francois; Crassous, Marie Pierre; Youenou, Agnes; Gohin, Francis; Huret, Martin; Danielou, Marie-madeleine; Kerouel, Roger; Labry, Claire; Aminot, Alain.
Inscrite dans le cadre du Grand Défi Golfe de Gascogne, la campagne VILOIR a été réalisée du 19 au 26 Juin 2003 à bord du Côtes de la Manche avec pour objectif l’étude en période estivale des structures hydrologiques et phytoplanctoniques des panaches de la Loire et de la Vilaine. Elle fait suite, sur la même thématique, à la campagne hivernale NUTRIGAS (2001) et à la campagne printanière GASPROD (2002).
Tipo: Text
Palavras-chave: Surveillance; Littoral; Phytoplancton; Phycotoxines; Bretagne; Pays de Loire.
Ano: 2005
URL: http://archimer.ifremer.fr/doc/00144/25494/23648.pdf

Impact of Oyster Farming on Diagenetic Processes and the Phosphorus Cycle in Two Estuaries (Britanny, France)
Provedor de dados: Institutional Archive of Ifreme (ArchiMer)
Autores: Andrieux, Francoise; Azandegbe, Afi; Caradec, Florian; Philippon, Xavier; Kerouel, Roger; Youenou, Agnes; Nicolas, Jean-louis.
This study aims to compare the impact of oyster cultures on diagenetic processes and the phosphorus cycle in the sediments of the Aber Benoît and the Rivière d’Auray, estuary of Brittany, France. Our results showed clear evidence of the seasonal impact of oyster cultures on sediment characteristics (grain size, organic matter parameters), and the phosphorus cycle, especially in the Aber Benoît. At this site, seasonal variations of sulfide and Fe concentrations in pore waters, as well as Fe-P concentrations in the solid-phase highlighted a shift from a system governed by iron reduction (Reference) to a system governed by sulphate reduction (Beneath Oyster). This could be partly explained by the increase in labile organic matter (ie, biodeposits) beneath...
Tipo: Text
Palavras-chave: Sediment; Phosphorus; Sulfide; Dissolved Fe/P ratios; Labile organic matter; Oyster cultures.
Ano: 2014
URL: http://archimer.ifremer.fr/doc/00209/32003/30441.pdf

Rapport de synthèse de l'essai interlaboratoire pour la mesure des nutriments en milieu marin - Essai du 14/02/06
Provedor de dados: Institutional Archive of Ifreme (ArchiMer)
Autores: Daniel, Anne; Kerouel, Roger; Aminot, Alain; Youenou, Agnes.
Cet essai interlaboratoire (EIL) pour l’analyse des sels nutritifs en milieu marin a été organisé par le laboratoire DYNECO/PELAGOS de l’IFREMER le 14 février 2006. Il a été proposé en septembre 2005 aux Laboratoires Environnement Ressources (LER) de l’IFREMER, aux sous-traitants ou collaborateurs des LER, aux laboratoires effectuant des analyses dans le cadre du RNO-hydrologie, aux laboratoires du CNRS participant à SOMLIT (Service d’Observation du Milieu LITtoral) et aux laboratoires de l’IRD. Les 26 laboratoires qui ont participé à cet essai sont listés en Annexe 1. Aucune consigne n’a été donnée sur le choix de la technique analytique : chaque laboratoire a utilisé sa méthode de routine.
Tipo: Text
Ano: 2006
URL: http://archimer.ifremer.fr/doc/00020/13144/10186.pdf

Inter and intra-specific transcriptional and phenotypic responses of   Pseudo-nitzschia   under different nutrient conditions
Provedor de dados: Institutional Archive of Ifreme (ArchiMer)
Autores: Lema, Anais Kimberley; Metegnier, Gabriel; Quéré, Julien; Latimier, Marie; Youenou, Agnes; Lambert, Christophe; Fauchot, Juliette; Le Gac, Mickael.
Untangling the functional basis of divergence between closely related species is a step towards understanding species dynamics within communities at both the evolutionary and ecological scales. We investigated cellular (i.e: growth, domoic acid production, nutrient consumption) and molecular (transcriptomic analyses) responses to varying nutrient concentrations across several strains belonging to three species of the toxic diatom genus Pseudo-nitzschia. Three main results were obtained. First, strains from the same species displayed similar transcriptomic, but not necessarily cellular, responses to the experimental conditions. It showed the importance of considering intra-specific diversity to investigate functional divergence between species. Second, a...
Tipo: Text
Palavras-chave: Phenotype; Transcriptomics; Pseudo-nitzschia; Divergence; Nutrients.
Ano: 2019
URL: https://archimer.ifremer.fr/doc/00482/59392/62157.pdf

Recent comparability of oceanographic nutrients data: Results of a 2003 intercomparison exercise using reference materials
Provedor de dados: Institutional Archive of Ifreme (ArchiMer)
Autores: Aoyama, M; Becker, S; Dai, M; Daimon, H; Gordon, L; Kasai, H; Kerouel, Roger; Kress, N; Masten, D; Murata, A; Nagai, N; Ogawa, H; Ota, H; Saito, H; Saito, K; Shimizu, T; Takano, H; Tsuda, A; Yokouchi, K; Youenou, Agnes.
An intercomparison exercise was conducted using the recently developed Reference Material for Nutrients in Seawater (RMNS). Discrepancies of reported values among laboratories were greater than the homogeneity of RMNS samples and the reported analytical precision of nutrients. The variability of in-house standards of the participating laboratories might be the most likely source of interlaboratory discrepancies. Therefore, the use of common reference materials, i.e. certified RM, is essential to establish and improve the comparability of nutrient data of the world's oceans.
Tipo: Text
Ano: 2007
URL: http://archimer.ifremer.fr/doc/2007/publication-3010.pdf

Phosphorus dynamics and bioavailability in sediments of the Penze Estuary (NW France): in relation to annual P-fluxes and occurrences of Alexandrium Minutum
Provedor de dados: Institutional Archive of Ifreme (ArchiMer)
Autores: Andrieux-loyer, Francoise; Philippon, Xavier; Bally, Gabriel; Kerouel, Roger; Youenou, Agnes; Le Grand, Jacqueline.
The macrotidal estuary of Penze (Brittany, Western part of the Channel, France) has been subjected to recurrent annual toxic blooms of Alexandrium minutum since 1988. This study aims to specify the phosphorus dynamics and bioavailability in sediments in order to improve our understanding of Alexandrium occurrences. Sediment-P pools and diffusive phosphate fluxes were studied under similar hydrodynamic conditions, in the intermediate estuary in May, June and July 2003 and along the salinity gradient from August 2004 to June 2005. The results highlight a decrease in bioavailable phosphorus (iron and organic bound) from the inner part of the estuary seaward. The ratio of iron-bound phosphorus to iron-oxyhydroxides is lower in the inner and intermediate...
Tipo: Text
Palavras-chave: Sequential extraction; Sediment phosphorus; Pore water; Phosphate fluxes; Estuary; Alexandrium minutum.
Ano: 2008
URL: http://archimer.ifremer.fr/doc/2008/publication-4306.pdf

Addressing the measurement of particulate organic and inorganic phosphorus in estuarine and coastal waters
Provedor de dados: Institutional Archive of Ifreme (ArchiMer)
Autores: Labry, Claire; Youenou, Agnes; Delmas, Daniel; Michelon, Pascale.
The speciation of particulate phosphorus (TPP) into inorganic (PIP) and organic phosphorus (POP), has been scarcely investigated in suspended particulate matter (SPM), contrary to numerous sediment studies. This work evaluates the actual capacity of methods for TPP, POP and PIP determination in SPM to measure efficiently and specifically each pool. Methods were tested on a range of plankton-associated organic and inorganic P compounds, on microalgal cultures and estuarine samples. Then results are specifically discussed reviewing P speciation in phytoplankton. For TPP analysis, the method of Solorzano and Sharp (1980) is recommended compared with that of Aspila et al. (1976), originally dedicated to sediment, as there is one step less, the protocol is more...
Tipo: Text
Palavras-chave: Phosphorus; Speciation; Waters; Phytoplankton; HTC; CWO.
Ano: 2013
URL: http://archimer.ifremer.fr/doc/00149/26046/26385.pdf

Vertical and horizontal controls of a haptophyte thin layer in the Bay of Biscay, France
Provedor de dados: Institutional Archive of Ifreme (ArchiMer)
Autores: Farrell, Hazel; Gentien, Patrick; Fernand, Liam; Lazure, Pascal; Lunven, Michel; Youenou, Agnes; Reguera, Beatriz; Raine, Robin.
Investigations into the phytoplankton of the Bay of Biscay in July 2006 revealed an extensive bloom of an unidentified haptophyte species. High-resolution sampling techniques identified the region in the vicinity of the mouth of the Loire estuary as an area of high (106–107 cells l−1) cell densities of the haptophyte in a thin sub-surface layer. This organism dominated the phytoplankton population regionally. Measurements of the vertical distribution of horizontal shear showed that the population, located at ca. 20 m depth, was confined to a layer lying between two density discontinuities with high shear. Physical measurements indicated that the population was being advected southeastwards, along the coast. Seaward spreading of the population was also...
Tipo: Text
Palavras-chave: Haptophyte; Bay of Biscay; Horizontal dispersal; Thin layers.
Ano: 2014
URL: http://archimer.ifremer.fr/doc/00160/27129/25327.pdf

High alkaline phosphatase activity in phosphate replete waters: The case of two macrotidal estuaries
Provedor de dados: Institutional Archive of Ifreme (ArchiMer)
Autores: Labry, Claire; Delmas, Daniel; Youenou, Agnes; Quere, Julien; Leynaert, Aude; Fraisse, Stephane; Raimonet, Melanie; Ragueneau, Olivier.
The occurrence of alkaline phosphatase activity (APA) that hydrolyses organic phosphorus into phosphate (PO4) is commonly related to PO4 deficiency of oceanic, coastal and fresh waters. APA is almost never investigated in PO4-rich estuaries, since very low activities are expected to occur. As a consequence, microbial mineralization of organic phosphorus into PO4 has often been ignored in estuaries. In this study, we examined the importance of potential APA and the associated microbial dynamics in two estuaries, the Aulne and the Elorn (Northwestern France), presenting two different levels of PO4 concentrations. Unexpected high potential APA was observed in both estuaries. Values ranged from 50 to 506 nmol L−1 h−1, which range is usually found in very...
Tipo: Text
Ano: 2016
URL: https://archimer.ifremer.fr/doc/00337/44840/44428.pdf

Motility and autotoxicity in Karenia mikimotoi (Dinophyceae)
Provedor de dados: Institutional Archive of Ifreme (ArchiMer)
Autores: Gentien, Patrick; Lunven, Michel; Lazure, Pascal; Youenou, Agnes; Crassous, Marie-pierre.
Karenia mikimotoi is one of the most common red-tide dinoflagellates proliferating in the eastern North Atlantic and around Japan. Kills of marine fauna are associated with its blooms. In mixed water columns it migrates vertically, while in stratified water columns, the population remains confined within pycnocline layers. Wind events, increasing mixing and agitation initiate declines in its populations. This paper is focused on the formulation of mortality rate relative to shear rate. Autotoxicity is demonstrated by the use of a synthetic toxin. Bioconvection observed in cultures allows the establishment of a trade-off between phototropism, which leads to the local accumulation of cells, and their autotoxicity, which would prevent cell concentration. The...
Tipo: Text
Ano: 2007
URL: http://archimer.ifremer.fr/doc/2007/publication-2436.pdf

Effect of P depletion on the functional pools of diatom carbohydrates, and their utilization by bacterial communities
Provedor de dados: Institutional Archive of Ifreme (ArchiMer)
Autores: Labry, Claire; Delmas, Daniel; Moriceau, Brivaela; Gallinari, Morgane; Quere, Julien; Youenou, Agnes.
Phosphorus (P) limitation of phytoplankton growth is known to affect the accumulation and release of carbohydrates (CHO) by micro-algae. However, relatively little is known about the fate of algal exudates, notably their bacterial degradation. The CHO chemical characterization is also not exhaustive, especially in ‘functional’ pools relevant for phytoplankton physiology (particulate reserve [R] or structural [S] CHO) and for bacterial degradation (dissolved mono- [MDCHO] and polysaccharides [P-DCHO]). In this study, we investigated how P depletion and repletion affect the CHO composition in diatom Thalassiosira weissflogii cultures, and the shortterm response of free and diatom-attached bacteria in terms of abundance and potential βglucosidase activity...
Tipo: Text
Palavras-chave: P limitation; Phytoplankton; Diatom; Bacteria; Mineralization; Carbohydrate; Glucosidase.
Ano: 2020
URL: https://archimer.ifremer.fr/doc/00628/74045/73532.pdf

Vertical distribution of phytoplankton communities and relationships with physico-chemical parameters resolved by a fine scale sampler
Provedor de dados: Institutional Archive of Ifreme (ArchiMer)
Autores: Lunven, Michel; Guillaud, Jean-francois; Youenou, Agnes; Crassous, Marie-pierre; Berric, Roger; Le Gall, Erwan; Kerouel, Roger; Labry, Claire; Aminot, Alain.
Many studies in coastal areas have shown the existence of thin chemical and biological layers. Their thickness and vertical extension are mainly controlled by hydrological and physical forcing. An accurate description of the phytoplankton communities growing within these layers is difficult to obtain without a well-adapted sampling system. A new Fine Scale Sampler (FSS) has been designed in Ifremer in order to study phytoplankton distribution and associated dissolved properties in high stratified water column. This FSS consists in a vertical array of 15 sampling bottles, horizontally laid with 20 cm intervals. Data acquired from a CTD and Fluorescence probe provide a precise FSS positioning at the depth of highest density gradient or at chlorophyll a...
Tipo: Text
Palavras-chave: Surveillance; Littoral; Phytoplancton; Phycotoxine.
Ano: 2005
URL: http://archimer.ifremer.fr/doc/00144/25493/23647.pdf

Alexandrium minutum growth controlled by phosphorus An applied model
Provedor de dados: Institutional Archive of Ifreme (ArchiMer)
Autores: Chapelle, Annie; Labry, Claire; Sourisseau, Marc; Lebreton, Carole; Youenou, Agnes; Crassous, Marie-pierre.
Toxic algae are a worldwide problem threatening aquaculture public health and tourism Alexandrium a toxic dinoflagellate proliferates in Northwest France estuaries (i e the Penze estuary) causing Paralytic Shellfish Poisoning events Vegetative growth and in particular the role of nutrient uptake and growth rate are crucial parameters to understand toxic blooms With the goal of modelling in situ Alexandrium blooms related to environmental parameters we first try to calibrate a zero-dimensional box model of Alexandrium growth This work focuses on phosphorus nutrition Our objective is to calibrate Alexandrium minutum as well as Heterocapsa triquetra (a non-toxic dinoflagellate) growth under different rates of phosphorus supply other factors being optimal and...
Tipo: Text
Palavras-chave: Toxic algal blooms; Alexandrium; Phosphorus uptake; Models; Competition; Northwest France.
Ano: 2010
URL: http://archimer.ifremer.fr/doc/00018/12901/9905.pdf

Étude sur la prolifération de la micro algue Alexandrium minutum en rade de Brest
Provedor de dados: Institutional Archive of Ifreme (ArchiMer)
Autores: Chapelle, Annie; Le Bec, Claude; Amzil, Zouher; Dreanno, Catherine; Guillou, Laure; Klouch, Khadidja; Labry, Claire; Le Gac, Mickael; Pineau-guillou, Lucia; Siano, Raffaele; Abernot, Chantal; Andrieux, Francoise; Caradec, Florian; Destombe, Christophe; Dia, A.; Doner, Anne; Duval, Julia; Gouriou, Jeremie; Lazure, Pascal; Le Brun, Luc; Le Gal, Dominique; Malestroit, Pascale; Petton, Sebastien; Plus, Martin; Quere, Julien; Savar, Veronique; Schmitt, Sophie; Terre, A.; Youenou, Agnes.
Suite à l’événement de grande ampleur d’efflorescence d’Alexandrium minutum et des toxicités associées en Rade de Brest en 2012, un projet a été élaboré avec la Région Bretagne dans le cadre du développement du port de Brest. L’Ifremer a organisé un échantillonnage dans l’estuaire de la rivière de Daoulas, zone la plus touchée en 2012, au cours des printemps-été 2013 et 2014. Un suivi de la présence d’A. minutum dans les sédiments a également été réalisé en hiver 2014. De ces suivis, des mesures réalisées au laboratoire à ce jour, des simulations du modèle Prévimer ainsi que des résultats du réseau Rephy et Velyger, il ressort que: * La rade de Brest peut aujourd’hui être considérée comme une zone à risque pour Alexandrium minutum. En effet, depuis 2012...
Tipo: Text
Ano: 2014
URL: http://archimer.ifremer.fr/doc/00254/36487/35029.pdf

Growth and phosphorus uptake by the toxic dinoflagellate Alexandrium catenella (dinophyceae) in response to phosphate limitation
Provedor de dados: Institutional Archive of Ifreme (ArchiMer)
Autores: Jauzein, Cecile; Labry, Claire; Youenou, Agnes; Quere, Julien; Delmas, Daniel; Collos, Yves.
Alexandrium catenella (Whedon et Kof.) Balech has exhibited seasonal recurrent blooms in the Thau lagoon (South of France) since first reported in 1995. Its appearance followed a strong decrease (90%) in phosphate (PO(4)3-) concentrations in this environment over the 1970-1995 period. To determine if this dinoflagellate species has a competitive advantage in PO(4)3--limited conditions in terms of nutrient acquisition, semicontinuous cultures were carried out to characterize phosphorus (P) uptake by A. catenella cells along a P-limitation gradient using different dilution rates (DRs). Use of both inorganic and organic P was investigated from measurements of 33PO(4)3- uptake and alkaline phosphatase activity (APA), respectively. P status was estimated from...
Tipo: Text
Palavras-chave: Alexandrium catenella; Alkaline phosphatase; Limitation; Phosphorus; Semicontinuous cultures.
Ano: 2010
URL: http://archimer.ifremer.fr/doc/00015/12641/9570.pdf