How does the resuspension of the biofilm alter the functioning of the benthos–pelagos coupled food web of a bare mudflat in Marennes-Oléron Bay (NE Atlantic)?
Intertidal mudflats are ecosystems submitted to natural hydrodynamical forcings during each tide. When the off-shore water flows at high tide, a proportion of the biofilm produced at low tide can be resuspended in the water column and interact with the pelagic food web. As a consequence, the resuspension creates a link between the benthos and the pelagos, modifying their properties and the stability of the meta-ecosystem they form together. The aim of this study is to describe the consequences of the microbial biofilm resuspension on the pelagic food web, and to investigate the question of the stability of the benthos–pelagos coupling resulting from the biofilm resuspension. Two food webs were considered, corresponding to different hydrodynamical conditions in sum-mer condition: one allowing the biofilm massive resuspension, and one without resuspension, but with particle sedimentation. The Monte-Carlo Markov Chain Linear Modelling was used to estimate the unknown flows of the food web. The comparison of the Ecological Network Analysis indices for the two food webs allowed defining their respective differences of structure and functioning. The results showed that the massive resuspension of the microbial biofilm stimulates pelagic primary production and microbial food web via a higher bacterivory. The higher activity of the whole system coupled with both a drop in the specialisation of the trophic pathways and a low cycling activity demonstrated that when massive resuspension occurs, the system is disturbed. In con-trast, when sedimentation occurs, the food webs show functioning features pointing out to a higher stability of the whole system.
(Journal of Sea Research (JSR). vol. 92, n° 1385-1101, pp. 144-157, 01/09/2014)
LIENSs, INSU - CNRS, ULR, CNRS, CRESCO, MNHN, IFREMER, BOREA, UNICAEN, NU, MNHN, IRD, SU, CNRS, UA, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, CRESCO, MNHN, IFREMER, LECOB, OOB, UPMC, CNRS, UPMC, CNRS, CNRS, LOG, INSU - CNRS, ULCO, CNRS, IRD [Ile-de-France], LMGE, UCA [2017-2020], CNRS, MMS, UM, UN UFR ST, UN, UFR SPB, UN, BioMEA, UNICAEN, NU, CNRS
A new sliced inverse regression method for multivariate response
A semiparametric regression model of a q-dimensional multivariate response y on a p-dimensional covariate x is considered. A new approach is proposed based on sliced inverse regression (SIR) for estimating the effective dimension reduction (EDR) space without requiring a prespecified parametric model. The convergence at rate square root of n of the estimated EDR space is shown. The choice of the dimension of the EDR space is discussed. Moreover, a way to cluster components of y related to the same EDR space is provided. Thus, the proposed multivariate SIR method can be used properly on each cluster instead of blindly applying it on all components of y. The numerical performances of multivariate SIR are illustrated on a simulation study. Applications to a remote sensing dataset and to the Minneapolis elementary schools data are also provided. Although the proposed methodology relies on SIR, it opens the door for new regression approaches with a multivariate response.
(Computational Statistics and Data Analysis. vol. 77, n° 0167-9473, pp. 285-299, 01/09/2014)
IMB, UB, Bordeaux INP, CNRS, CQFD, IMB, UB, Bordeaux INP, CNRS, Inria, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, MISTIS, Inria, LJK, UPMF, UJF, Grenoble INP, CNRS, Grenoble INP, ENSC
Physiological responses of Manila clams Venerupis (=Ruditapes) philippinarum with varying parasite Perkinsus olseni burden to toxic algal Alexandrium ostenfeldii exposure.
Manila clam stock from Arcachon Bay, France, is declining, as is commercial harvest. To understand the role of environmental biotic interactions in this decrease, effects of a toxic dinoflagellate, Alexandrium ostenfeldii, which blooms regularly in Arcachon bay, and the interaction with perkinsosis on clam physiology were investigated. Manila clams from Arcachon Bay, with variable natural levels of perkinsosis, were exposed for seven days to a mix of the nutritious microalga T-Iso and the toxic dinoflagellate A. ostenfeldii, a producer of spirolides, followed by seven days of depuration fed only T-Iso. Following sacrifice and quantification of protozoan parasite Perkinsus olseni burden, clams were divided into two groups according to intensity of the infection ("Light-Moderate" and "Moderate-Heavy"). Hemocyte and plasma responses, digestive enzyme activities, antioxidant enzyme activities in gills, and histopathological responses were analyzed. Reactive oxygen species (ROS) production in hemocytes and catalase (CAT) activity in gills increased with P. olseni intensity of infection in control clams fed T-Iso, but did not vary among A. ostenfeldii-exposed clams. Exposure to A. ostenfeldii caused tissue alterations associated with an inflammatory response and modifications in hemocyte morphology. In the gills, superoxide dismutase (SOD) activity decreased, and an increase in brown cell occurrence was seen, suggesting oxidative stress. Observations of hemocytes and brown cells in tissues during exposure and depuration suggest involvement of both cell types in detoxication processes. Results suggest that exposure to A. ostenfeldii disrupted the pro-/anti-oxidant response of clams to heavy P. olseni intensity. In addition, depressed mitochondrial membrane potential (MMP) in hemocytes of clams exposed to A. ostenfeldii suggests that mitochondrial functions are regulated to maintain homeostasis of digestive enzyme activity and condition index.
(Aquatic Toxicology. vol. 154, n° 0166-445X, pp. 27-38, 01/09/2014)
LEMAR, IRD, IFREMER, UBO EPE, CNRS, IFREMER, INSTM, UFPB, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
A framework for investigating general patterns of benthic β-diversity along estuaries
The description of major patterns in beta (β) diversity is important in order to understand changes in community composition and/or richness at different spatial and temporal scales, and can interrogate processes driving species distribution and community dynamics. Human impacts have pushed many estuarine systems far from their historical baseline of rich, diverse, and productive ecosystems. Despite the ecological and social importance of estuaries, there has not yet been an attempt to investigate patterns of β-diversity and its partitioning along estuarine systems of different continents. We aimed to evaluate if benthic assemblages would show higher turnover than nestedness in tropical than in temperate systems, if well-known impacted estuaries would show greater nestedness than less polluted systems, and to propose a conceptual framework for studying benthic macrofauna beta diversity along estuaries. We analyzed subtidal benthic macrofaunal data from estuaries in Brazil, USA and France. We estimated alpha (α), beta (β) and gamma (γ) diversity for each sampling time in each system, investigated patterns of β -diversity as multivariate dispersion and the partitioning (nestedness and replacement) of β-diversity along each estuary. There was a decrease in the α-diversity along marine to freshwater conditions at most of the estuaries and sampling dates. Beta diversity as multivariate dispersion showed high variability. Most of the estuaries showed a greater proportion of the β-diversity driven by replacement than nestedness. We suggest a conceptual framework for estuaries where relatively pristine estuaries would have their β-diversity mostly driven by replacement while impacted estuaries subjected to several anthropogenic stressors would show total nestedness or total replacement, depending on the stress.
(Estuarine, Coastal and Shelf Science. vol. 149, n° 0272-7714, pp. 223-231, 05/08/2014)
SJSU, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, LIENSs, INSU - CNRS, ULR, CNRS
Labrador current variability over the last 2000 years
The ice-loaded Labrador Current (LC) is an important component of the western North Atlantic circulation that influences the position and strength of the northern limb of the North Atlantic Current (NAC). This flow of cold and fresh Polar Waters originating from the Arctic has a marked impact on the North Atlantic climate, yet little is known about its variability beyond the instrumental period. In this study, we present the first sub-decadal alkenone-based 2000-year long sea-surface temperature (SST) records from the western Labrador Sea, a climatically crucial region at the boundary between the LC and the NAC. Our results show a clear link between the LC strength and the Northern Annular Mode (NAM), with a stronger NAM and a more vigorous LC during the Medieval Climate Anomaly (MCA). This suggests enhanced LC activity upon future global warming with implications for the Atlantic meridional overturning circulation (AMOC).
(Earth and Planetary Science Letters. vol. 400, n° 0012-821X, pp. 26-32, 01/08/2014)
BTP, LOCEAN, IPSL, ENS-PSL, UVSQ, UPMC, CEA, INSU - CNRS, X, CNES, CNRS, MNHN, IRD, UPMC, INSU - CNRS, CNRS, PALEOCEAN, LSCE, UVSQ, INSU - CNRS, CNRS, DRF (CEA), CEA, GEUS, LOCEAN, IPSL, ENS-PSL, PSL, UVSQ, UPMC, CEA, INSU - CNRS, X, IP Paris, CNES, CNRS, MNHN, IRD, UPMC, INSU - CNRS, CNRS, ULaval, INSU - CNRS, CNRS, LSCE, UVSQ, INSU - CNRS, CNRS, DRF (CEA), CEA, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, PARVATI, LOCEAN, IPSL, ENS-PSL, UVSQ, UPMC, CEA, INSU - CNRS, X, CNES, CNRS, MNHN, IRD, UPMC, INSU - CNRS, CNRS
Regional distributon of mercury in sediments of the main rivers of French Guiana
Use of mercury (Hg) for gold-mining in French Guiana (up until 2006) as well as the presence of naturally high background levels in soils, has led to locally high concentrations in soils and sediments. The present study maps the levels of Hg concentrations in river sediments from five main rivers of French Guiana (Approuague River, Comté River, Mana River, Maroni River and Oyapock River) and their tributaries, covering more than 5 450 km of river with 1 211 sampling points. The maximum geological background Hg concentration, estimated from 241 non-gold-mined streams across French Guiana was 150 ng g-1. Significant differences were measured between the five main rivers as well as between all gold-mining and pristine areas, giving representative data of the Hg increase due to past gold-mining activities. These results give a unique large scale vision of Hg contamination in river sediments of French Guiana and provide fundamental data on Hg distribution in pristine and gold-mined areas.
(SpringerPlus. vol. 3, n° 2193-1801, pp. 11 p., 15/07/2014)
BRGM, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
Detoxification and recovery capacities of Corbicula fluminea after an industrial metal contamination (Cd and Zn): A one-year depuration experiment
This study aimed to assess the recovery capacity of the freshwater bivalve Corbicula fluminea subjected to industrial metal discharges (Cd, Zn). After a 24-day exposure in a metal-contaminated river, bivalves were transferred and maintained in the laboratory for one year under metal-free conditions. Metal accumulation, metallothionein production and genetic expressions of genes involved in metal stress were studied. Results demonstrated the high persistence of Cd in tissues (only 73% eliminated after 365 days) whereas Zn was rapidly depurated. The Cd half-life was estimated around 240 days. Metallothioneins were strongly induced within the 28 first days of decontamination, then decreased by 45% after 365 days. The metal exposure of bivalves led to a significant gene induction. After 28 days, most of the genes were no longer overexpressed, suggesting that the bivalves may withstand small amounts of non-essential metals in their tissues without showing signs of detrimental effects on the tested genes.
(Environmental Pollution. vol. 192, n° 0269-7491, pp. 74-82, 09/07/2014)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
L'aléa submersion marine sur la rive interne du Bassin d'Arcachon : exposition actuelle, cartographie prévisionnelle et capacité d'atténuation par la restauration des marais salés
Le programme BARCASUB a porté sur le risque de submersion marine à l'intérieur du bassin d'Arcachon (France) et sur la gestion potentielle de ce risque par une mesure souple de défense : la "dépoldérisation". La communication détaille les méthodes suivies et les résultats obtenus aux différentes étapes de la méthode d'évaluation de la submersibilité: (1) détermination de la hauteur du plan d'eau lors des épisodes tempétueux Klaus et Xynthia, (2) évaluation des niveaux d'eau extrêmes au front des digues de mer en fonction de plusieurs scénarios de tempête et d'élévation du niveau marin, (3) modélisation des niveaux extrêmes « à terre », (4) suivi de l'accrétion sédimentaire et de la dynamique végétale dans les zones dépoldérisées.
(pp. p. 124-134, 03/07/2014)
PRODIG, UP1, IRD, EPHE, PSL, UP4, UPD7, CNRS, LGP, UP1, UPEC UP12, CNRS, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
Impact d'un sédiment dopé aux nanoparticules d'or ou de sulfure de cadmium sur un invertébré et un poisson d'eau douce
Le but de cette thèse était de déterminer l’impact de deux types de nanoparticules métalliques (sulfure de cadmium – CdS - et or - Au) sur deux organismes aquatiques modèles (vers tubifex et poisson zèbre Danio rerio). L’approche a consisté à doper le sédiment de la Garonne avec les deux types de nanoparticules et caractériser l’effet de cette contamination sur les deux organismes en utilisant plusieurs marqueurs à différents niveaux d'organisation biologique (réponses biochimiques, activité de neurotransmission, génotoxicité, expression génétique et activité de bioturbation). Les effets ont été évalués après exposition aux sédiments contaminés dans des systèmes expérimentaux de types microcosmes durant une vingtaine de jours. Dans un certain nombre de cas, ce travail a révélé un effet des nanoparticules qui n’était pas dû au métal mais aux propriétés nanoparticulaires. En effet, dans le cas des nanoparticules de CdS, nous avons observé des altérations du génome ainsi que la modification de l’activité de bioturbation des vers tubifex en réponse à la contamination aux nanoparticules mais pas à celle de la forme ionique. Dans ce travail nous avons pu observer le relargage des nanoparticules d’or depuis le sédiment vers la colonne d’eau, et sa biodisponibilité potentielle pour les poissons. Ces nanoparticules provoquaient des altérations de l’ADN chez les deux organismes, la modification de l’expression de certains gènes et l’augmentation de l’activité de l’acétylcholinestérase chez le poisson zèbre. Les résultats de bioturbation n’ont pas montré d’effets des nanoparticules d’or sur le mouvement des vers.
(01/07/2014)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
GLOBEX: Wave dynamics on a shallow sloping beach
As waves approach the shore, their non-linear dynamics becomes increasingly important. Most of our understanding of wave non-linearity has resulted from theoretical work, laboratory experiments and field studies on beaches slopes steeper than about 1:40. There, very strong non-linear processes happen locally and on a short time scale, as demonstrated by narrow surf zones with plunging or collapsing breakers. The non-linearity on gently-sloping beaches, typical of high-energy dissipative environments, has a different character, as it can build up over a long period of time and along an extensive cross-shore area. This contribution serves to introduce the GLOBEX project, during which a high-resolution (in space and time) data set of the cross-shore evolution of short and infragravity waves was collected on a low-sloping (1:80) non-mobile laboratory beach. As non-linear transfers also occur in the vertical from the free-stream flow downwards into the bottom boundary layer, additional flow measurements performed with Laser Doppler Anemometry are also briefly presented.
(01/07/2014)
LEGI, UJF, Grenoble INP, CNRS, IMAU, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, LEGOS, IRD, UT3, Comue de Toulouse, INSU - CNRS, CNES, CNRS, M2C, UNICAEN, NU, INSU - CNRS, UNIROUEN, NU, CNRS, PUC