Rôle de l'espèce ingénieure Upogebia pusilla dans le fonctionnement biogéochimique des écosystèmes intertidaux à herbier (Zostera noltei) du bassin d'Arcachon
Dans le bassin d’Arcachon, le crustacé thalassinidé Upogebia pusilla habite préférentiellement les vasières intertidales colonisées par les zostères naines (Zostera noltei) où il trouve la stabilité sédimentaire indispensable à l’établissement durable de son terrier. Du fait de la profondeur de ce dernier (> 30 cm) et de sa grande mobilité, cette espèce ingénieure a souvent été négligée dans les études antérieures ayant pour objectif de mieux comprendre le rôle des communautés macro-benthiques dans le fonctionnement des herbiers de phanérogames et les conséquences de leur régression rapide. Ce manuscrit présente une étude intégrée du rôle d’U. pusilla dans le fonctionnement de son écosystème en s’attachant particulièrement à caractériser et quantifier les relations entre (1) ses différentes activités (fouissage, ventilation, locomotion, …), (2) les modes de bioturbation qui en résultent et (3)leurs impacts respectifs sur la dynamique biogéochimique sédimentaire. Ce travail montre qu’U. pusilla engendre un remaniement et une bioirrigation intenses de la matrice sédimentaire qui l’entoure. Sa présence stimule ainsi fortement la reminéralisation de la matière organique sédimentée et les échanges de solutés à travers l’interface eau-sédiment.Bien que l’influence d’U. pusilla sur ces processus écologiques et biogéochimiques soit très dépendante des conditions environnementales (e.g., saisonnalité, prévalence parasitaire),l’ensemble de mes résultats suggère que le déclin progressif de ses populations, conséquence directe de la dégradation de son habitat, est susceptible de fortement altérer le fonctionnement global des écosystèmes du bassin d’Arcachon.
(19/04/2017)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
Etude des réponses de la moule Mytilus spp exposée à des stress métallique et thermique durant les stades embryo-larvaires
Les écosystèmes marins côtiers sont soumis à des pressions anthropiques et naturelles qui placent les organismes aquatiques dans des situations de multi-stress.Ce travail doctoral avait pour objectif d’évaluer l’impact et de mieux comprendre les mécanismes d’adaptation des premiers stades de vie de moule exposés à deux facteurs environnementaux majeurs : la pollution métallique et l’accroissement des températures des eaux marines côtières. Les effets induits par l’exposition à deux polluants métalliques modèles (Cu et Ag) et à un stress thermique modéré seuls ou en combinaison ont été évalués sur les stades précoces de développement de deux espèces de moule : Mytilus galloprovincialis et Mytilus edulis ainsi que leurs hybrides. Nos résultats montrent une augmentation significative du pourcentage de larves D ma lformées avec l’augmentation de la température. Par ailleurs, l’Ag apparaît significativement plus toxique que le Cu pour les larves. De plus,la toxicité des métaux s’accroit avec l’augmentation de la température. La coexposition aux métaux et à une température modérée augmente les activités enzymatiques antioxydantes de la catalase (CAT), de la superoxyde dismutase (SOD)et de la glutathion-S-transférase (GST) et accroît le contenu cellulaire en métallothionéines et la peroxydation lipidique. A une température plus élevée de 22 °C,une diminution significative des activités des enzymes antioxydantes est observée.Les dommages à l’ADN chez les larves-D de moule M. gallo provincialis ont été évalués à l’aide du test des comètes avec et sans traitement par la Formamidopyrimidine ADN glycosylase. L’exposition aux métaux et/ou à la température aaugmenté de manière significative les lésions de l’ADN sur les larves de moule,avec un effet plus accentué sur les dommages oxydatifs. Il a été montré également que le Cu et l’Ag sont accumulés différentiellement dans les larves en fonction de la température d’exposition. L’étude de l’expression par RT-qPCR de 18 gènes impliqués dans les défenses antioxydantes, la réparation de l’ADN, l’apoptose,la protéolyse, la transcription, les réponses au stress thermique et la détoxification métallique a été conduite chez les larves-D de moule M. galloprovincialis.En cas d’un stress thermique modéré, une tendance à la surexpression des gènes impliqués dans les défenses cellulaires est observée. Toutefois, en cas d’une coexposition métallique et thermique, les voies d’apoptose et d’altération cellulaires sont activées.Un plugin et une macro ont été développés pour le logiciel ImageJ afin d’évaluer et de caractériser le comportement de nage des larves D de M. galloprovincialis.Une augmentation significative de la vitesse maximale des larves-Davec l’augmentation de la température est observée sans que la vitesse moyenne soit affectée. En revanche, l’exposition au Cu et à l’Ag à 22 °C augmente significativement les vitesses moyenne et maximale des larves. En condition contrôle à18 °C, les larves suivent principalement des trajectoires rectilignes (88 %). Avec l’augmentation de la température et/ou l’exposition aux métaux, les trajectoires circulaires augmentent considérablement au détriment des trajectoires rectilignes.Ces modifications de comportement pourraient être liées d’une part à l’induction de malformations mais aussi à la modulation de l’activité neuronale. Ainsi, une augmentation significative de l’activité acétylcholine estérase (AChE) des larves a été observée suite à l’exposition à un gradient de températures et/ou aux métaux.Des larves D viables et normalement développées ont été obtenues par hybridation de M. galloprovincialis et M. edulis. Les larves de M. edulis apparaissent plus sensibles à la température que les larves de M. galloprovincialis. Aucune différence significative de sensibilité n’a été observée entre les moules hybrides et pures quelque soit le métal testé. (...)
(10/04/2017)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
Sulfur diagenesis under rapid accumulation of organic-rich sediments in a marine mangrove from Guadeloupe (French West Indies)
The biogeochemistry of sulfur and carbon during early-diagenetic processes within organic-rich marine mangrove sediments was studied in the “Manche à Eau” lagoon, Guadeloupe, West Indies. These sediments are characterized by a total organic carbon content (TOC) mostly above 11 wt%, δ13CTOC below − 25‰ VPDB and C/Nmolar ratios exceeding 15. Rates of mangrove-derived organic carbon accumulation vary between ~ 200 and 400 gOC·m− 2·yr− 1, with highest rates at the shore of the lagoon. On the lagoon border, where colorless filamentous sulfur-oxidizing bacteria colonize the sediments, active sulfate reduction within the upper 20 cm, with a net removal rate of ~ 0.5 μmol·cm− 3·d− 1, is assumed to be essentially driven by organic carbon oxidation. This is expressed by relatively low apparent sulfur isotope fractionation (34εnet = − 33‰) and a gentle δ18O/δ34Ssulfate apparent slope of 0.36 ± 0.03 (2s). Further inside the lagoon, in the absence of sulfur-oxidizing bacteria, higher apparent sulfur isotope fractionation and a steeper δ18O/δ34Ssulfate slope (0.67 ± 0.20) suggest an overall lower sulfate removal rate that may be coupled to minor sulfur disproportionation. Spatial and vertical variation in sulfur cycling, reflected by oxygen and sulfur isotopic characteristics, seem to be mainly controlled by unsteady to relatively steady organic matter deposition and its reactivity. In all sediments, δ34S values of pyrite are positively correlated with the TOC/TS ratio and negatively correlated with δ13CTOC; suggesting a primary control of the quantity and quality of organic matter on the pyrite isotope records, despite potential iron-limiting conditions for the most active sites. Our results provide insights into the role of organic carbon input on sulfur cycling; stimulating sulfate reduction and in turn the presence of sulfur-oxidizing microbial mats, resulting in an intense cycling of both carbon and sulfur in these marine mangrove sediments.
(Chemical Geology. vol. 454, n° 0009-2541, pp. 67-79, 05/04/2017)
UiT, iEES, INRA, UPMC, UPEC UP12, CNRS, NGU, WWU, BM, UAG, UPMC, UNS, CNRS, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, LOG, INSU - CNRS, ULCO, CNRS, IRD [Ile-de-France], ULCO, ECOBIO, UR, INEE-CNRS, CNRS, CNRS
Updating modern pollen rain from southern Africa as a tool for the reconstruction of past vegetation and climate change
(03/04/2017)
WITS, EPHE, PSL, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
Early and efficient induction of antioxidant defense system in Mytilus galloprovincialis embryos exposed to metals and heat stress
(Ecotoxicology and Environmental Safety. vol. 138, n° 0147-6513, pp. 105-112, 01/04/2017)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
The climatic dependencies of urban ecosystem services from green roofs: Threshold effects and non-linearity
(Ecosystem Services. vol. 24, n° 2212-0416, pp. 223-233, 01/04/2017)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
Abrupt cooling over the North Atlantic in modern climate models
Observations over the 20th century evidence no long-term warming in the subpolar North Atlantic (SPG). This region even experienced a rapid cooling around 1970, raising a debate over its potential reoccurrence. Here we assess the risk of future abrupt SPG cooling in 40 climate models from the fifth Coupled Model Intercomparison Project (CMIP5). Contrary to the long-term SPG warming trend evidenced by most of the models, 17.5% of the models (7/40) project a rapid SPG cooling, consistent with a collapse of the local deep-ocean convection. Uncertainty in projections is associated with the models' varying capability in simulating the present-day SPG stratification, whose realistic reproduction appears a necessary condition for the onset of a convection collapse. This event occurs in 45.5% of the 11 models best able to simulate the observed SPG stratification. Thus, due to systematic model biases, the CMIP5 ensemble as a whole underestimates the chance of future abrupt SPG cooling, entailing crucial implications for observation and adaptation policy.
(Nature Communications. vol. 8, n° 2041-1723, pp. 14375, 01/04/2017)
LSCE, UVSQ, INSU - CNRS, CNRS, DRF (CEA), CEA, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, KNMI, I2M-BX, UB, CNRS, INRAE
Contamination of ivory gulls (Pagophila eburnea) at four colonies in Svalbard in relation to their trophic behaviour
The ivory gull (Pagophila eburnea) is a high-Arctic species considered endangered in most parts of its breeding range. Ivory gulls must cope with not only the reduction in sea ice cover triggered by climate change but also increasing contaminant loads due to changes in global contaminant pathways and the release of previously stored pollutants from melting snow and ice. This top predator may be affected by biomagnification processes of a variety of compounds with concentrations dramatically increasing from water to higher trophic levels. The objective of this study was therefore to assess the contaminant bioaccumulation of this species in four colonies located on Barentsøya, Svalbard, in link with its trophic behaviour. To that end, contaminants, including organochlorines (OCs), brominated flame retardants (BFRs), and perfluorinated alkyl substances (PFASs), were determined in the blood (plasma and whole blood) of ivory gulls sampled over several years. Carbon- and nitrogen-stable isotopes were also determined in different tissues (feathers, plasma and red blood cells, or whole blood) to infer the trophic level (δ15N) and feeding habitat (δ13C) during both the breeding and moulting periods. The most quantitatively abundant contaminants found in the ivory gull were p,p’-DDE (dichlorodiphenyldichloroethylene), RPCB (polychlorobiphenyl), and PFOS (perfluorooctane sulphonate). Several compounds including most of the PFASs, trans-nonachlor, cis-nonachlor, and BDE-28 were correlated with nitrogen values. This study highlighted variability in trophic behaviour among individuals during the breeding and the moulting periods. Overall, similar feeding habitats and strategies were used between breeding sites which was echoed by similar contaminant levels.
(Polar Biology. vol. 40, n° 0722-4060, pp. 917 - 929, 01/04/2017)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, LIENSs, INSU - CNRS, ULR, CNRS, NILU
Simulating wave setup and runup during storm conditions on a complex barred beach
The purpose of this study is to assess the ability of the SWASH model to reproduce wave setup and runup in highly dissipative stormy conditions. To proceed we use data collected during the ECORS Truc Vert’08 Experiment, especially during the Johanna storm in the winter of 2007-008 (wave setup under Hs= 8.2 m and Tp= 18.3 s and runup under 6.4 m and peak period up to 16.4 s). We test different model settings (1D and 2D mode) and model forcing (spectral and parametric) to reproduce sensor measured wave setup at several locations in the nearshore area and video measured runup on two beach profiles. For the whole tested configurations, the wave setup is reproduced accurately. Results considering all the sensor locations in the near shore area in 1D and 2D are significantly correlated to the observations with respectively ρ²=0.66 and 0.81; RMSE=0.13 m and 0.08 m without any significant bias. Observations and simulations of runup are investigated in terms of spectra and statistic component. 1D simulations produces an overall overestimation and no significant improvement is obtained by modifying the breaking parameters. The results for 2D simulations are fairly satisfactory reproducing significant swash height (S ), but are significantly improved with spectral forcing than parametric with respectively ρ²=0.73 and 0.71, RMSE=0.19 m and 0.43 m. Generally, the model reproduces accurately the infragravity component but tends to overestimate the incident component, leading to an overestimation of the energy density for moderate wave conditions and more accurate results for higher-energy wave conditions. Results in 2D with spectral forcing show a saturation of the infragravity component with a threshold around Hs=4 to 5 m, which is comparable to the observations collected at Truc Vert Beach. As regards the conventional statistical parameter for runup estimation (R2%) three methods are applied to derive the 2% exceedence value for runup from observed and simulated shoreline vertical elevation time series. When R2% is based on the sum of wave setup and half of the significant swash height, results provided by the model are close or even better than estimations provided by empirical formulas from the bibliography. Defining R2% as the exceeded 2% values of the time, derived considering the cumulative distribution function of the entire water-level time series also provide fairly good results. Results using only runup maxima time series are less satisfactory. In the two last cases, R2% is slightly underestimated for moderate wave conditions (Hs<4 m; Tp ≈ 14 s) and overestimated for higher-energy wave conditions. Generally results shows that where extreme wave conditions are concerned, the model setting must be considered carefully because the simplification of 1D (rather than 2D), or the use of parametric wave description (rather than spectral), can be a source of significant inaccuracy or overestimation in simulated run-up values.
(Coastal Engineering. vol. 123, n° 0378-3839, pp. 29-41, 31/03/2017)
BRGM, UB, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
Do Temporal and Spatial Parameters or Lifestyle of the Pacific Oyster Crasssostrea gigas Affect Pollutant Bioaccumulation, Offspring Development, and Tolerance to Pollutants?
This study evaluated the vulnerability of early life stages of native oysters (Crassostrea gigas) from the Arcachon Bay (SW, France) to pollutants at risk in the lagoon in particular copper and S-metolachlor. Developmental abnormalities in wild and cultivated oyster D-larvae were investigated during 2 breeding-seasons (2013 and 2014) at different sampling sites and dates. In addition, copper, and metolachlor concentrations were determined both in seawater and in mature oysters. Bioaccumulation of Cu was observed at higher levels in wild than in farmed specimens. Metolachlor was accumulated at much lower levels. After 24 h exposure, significant increases of the percentage of abnormal D-larvae were observed when exposed at 1 μg L−1 of copper or 10 ng L−1 of metolachlor in comparison with the controls whatever the date, the site, and rearing conditions of the genitors. The current study demonstrates that environmental concentrations of copper and metolachlor can induce a significant increase of developmental abnormalities in farmed and wild populations of oysters. However, no significant differences of sensitivity were observed according to temporal, spatial parameters, and lifestyle of genitors. In addition, oyster larvae obtained from the hatchery displayed the same sensitivity to pollutants as larvae from the field, demonstrating their suitability for toxicity assays and water quality monitoring.
(Frontiers in Marine Science. vol. 4, n° 2296-7745, 16/03/2017)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS