2007 - Identification of past and novel brominated flame retardants in common sole (Solea solea L.) from coastal areas in France
Auteurs : Munschy C., Héas-Moisan K., Loizeau V., Tixier C., Tronczynski J., Alaee M., Pacepavicius G.
Organohalogen Compounds, 69 : 2681-2685
2007 - Competition between shellfish farming, invasive species and natural trophic chain: study with a mass balance ECOPATH approach in the Mont Saint Michel Bay (France)
Auteurs : Arbach Leloup F., Desroy N., Le Mao P., Pauly D., Le Pape O.
Estuarine and Coastal Shelf Science (accepté)
2007 - Assessment of PCDD/F and nonylphenol contamination in a semi-enclosed bay (Masan bay) and a Mediterranean lagoon (Thau, France)
Auteurs : Hong S.H., Munschy C., Kannan N., Héas-Moisan K., Tixier C., Shim W.J., Tronczynski J.
Organohalogen Compounds, 69, 1606-1609
2007 - Microbial contamination and management scenarios in a Mediterranean coastal lagoon (Etang de Thau, France): application of a Decision Support System within the Integrated Coastal Zone Management context
Auteurs : Loubersac L., Do Chi T., Fiandrino A., Jouan M., Derolez V., Lemsanni A., Rey-Valette H., Mathe S., Pagès S., Mocenni C., Casini M., Paoletti S., Pranzo M., Valette F., Serais O., Laugier T., Mazouni N., Vincent C., Got P., Troussellier M., Aliaume C.
In the Thau lagoon (Southern Mediterranean Coast) the main anthropogenic pressure is represented by the urban development in the watershed, whilst oyster and mussel farming represents one of the main economical activities in the region. During the last decade, the increasing organic loads from watershed and urban settlements in the lagoon surroundings have caused a diffuse contamination by faecal bacteria. Also toxic algal blooms have been occurring, impairing water quality with major impacts on shellfish farming, fishery and bathing. In this study, indicators and scenarios identified for the lagoon have been integrated in a Decision Support System (DSS) to evaluate the best solutions for reducing pressures and improving both water quality and ecosystem status.The watershed has been analysed with reference to indicators of pollution sources and transfer rates to the lagoon. In parallel, socio-economic indicators and descriptors of urban growth and development have been assessed. Numerical models have been run in order to simulate the lagoon hydrodynamics in relation to both meteorological factors and watershed runoff. The impact of faecal bacteria contamination has been evaluated in terms of economical losses and social conflicts, arising from the restriction of shellfish farming and marketing during contamination events. Finally, the DSS prototype has been applied to the lagoon in support to management and future planning.
Contact : Annie.Fiandrino@ifremer.fr
Novembre 2007 - Typology of environmental conditions at the onset of winter phytoplankton blooms in a shallow macrotidal coastal ecosystem, Arcachon Bay (France)
Auteurs : Glé C., Del Amo Y., Sautour B., Froidefond J.-M., Gohin F., Maurer D., Plus M., Laborde P., Chardy P.
Phytoplankton dynamics were assessed in the macrotidal ecosystem of Arcachon Bay through high-frequency surveys over a 5-year period in order to characterize typology of environmental conditions at the onset of the productive period. Temporal variations of hydrological and biological parameters were examined in external and internal waters of the lagoon, during the winter-spring periods from 1999 to 2003. An additional survey was performed during winter-spring 2005 in order to study the vertical structure of the water column. The occurrence of winter phytoplankton blooms between January and March emerged as a recurrent event. The early onset of the productive period is influenced by the biological functioning of adjacent Bay of Biscay oceanic waters. It is hypothesized that under a propitious hydrodynamic regime, phytoplankton inocula from the Bay of Biscay enter in the Arcachon Bay where cells presumably find favourable conditions for their fast development. The timing of the onset of those winter blooms in Arcachon Bay seems to be mainly influenced by the presence of anticyclonic weather conditions (associated with an increase in incident irradiance) during late winter (i.e. by February), while the water column does not show any particular stabilization nor stratification liable to facilitate the onset of these blooms. Moreover, these winter blooms dominated by diatoms led to an early nutrient depletion which could have inevitable consequences on the structuration of the food web during spring and summer.
Keywords : winter blooms, onset, phytoplankton inoculum, macrotidal ecosystem
Novembre 2007 - Contribution of several nitrogen sources to growth of Alexandrium catenella during blooms in Thau lagoon, southern France
Auteurs : Collos Y., Vaquer A., Laabir M., Abadie E., Laugier T., Pastoureaud A., Souchu P.
Harmful Algae 6 (2007) 781–789
A monitoring program with a weekly sampling frequency over a 15-month period indicates that urea concentrations above a certain threshold level may trigger the blooms of Alexandrium catenella in Thau lagoon. However, urea concentrations were also sometimes related to ammonium and dissolved organic nitrogen concentrations, indicating that the role of urea may not be a direct one. An original approach is used to assess the relative contribution of several nitrogen sources (nitrate, nitrite, ammonium, urea) to growth of A. catenella by comparing nitrogen uptake rates to nitrogen-based growth rates estimated from dilution experiments during four blooms over a 4-year period (2001–2004) in Thau lagoon. Nitrate and nitrite contributed 0.1–14% and 0.1–5% respectively of growth requirements. Ammonium and urea were the main N sources fueling growth of A. catenella (30–100% and 2–59%, respectively). Indirect estimates indicated that an unidentified N source could also contribute significantly to growth at specific times. Concerning ammonium and urea uptake kinetics, half-saturation constants varied between 0.2 and 20 mgat N L_1 for ammonium and between 0.1 and 44 mgat N L_1 over the 4-year period, indicating that A. catenella can have a competitive advantage over other members of the phytoplankton even under low concentrations of ammonium and urea. However, the observed large changes in ammonium and urea uptake kinetics on a short time scale (days) during blooms preclude more precise estimates of those contributions to growth and require further investigation.
Novembre 2007 - Towards an optimal sampling strategy for Alexandrium catenella (Dinophyceae) benthic resting cysts
Auteurs : B. Genovesi (Université Montpellier) , D. Mouillot (Université Montpellier) , A. Vaquer (Université Montpellier) , M. Laabir (Université Montpellier) , Annie Pastoureaud (Ifremer)
The study proposes methodological developments to optimize sampling strategy of resting cysts of Alexandrium catenella to estimate their abundance with a predefined error. This work also aims to provide information on spatial distribution of resting cysts in sediments. The distribution mode of A. catenella resting cysts related to the abundance variability was studied through sediment cores sampling on four different spatial scales and using Ludox CLX gradient density method. The quantification method underestimates by a factor of 2 the resting cysts abundance in one gram of sediment. Application of Taylor's power law allowed us to define a compromise between sampling effort and abundance estimation error. In the case of A. catenella resting cysts from Thau lagoon, the optimal sampling strategy consists of sampling 10 stations on a surface of 2 km(2) for a given coefficient of variability (C) of 15%, sampling 3 sediment cores at each station (C = 30%) and counting only one replicate by core (C = 18%). Results related to the application of Taylor's power law are closely dependent on resting cyst density and aggregation in a given sediment. In our area, A. catenella resting cysts are mainly observed in the upper 3 cm of sediment. Horizontally, their heterogeneity is lower on 10 cm(2) surface and tends to stabilize itself beyond a surface of 10 m(2). Each author has to carry out this pre-sampling effort for his own resting cysts-fonning species, in his own area, in order to increase accuracy of resting cyst mapping. (C) 2007 Elsevier B.V. All rights reserved.
Keywords : Spatial-distribution, Vertical-profiles, Alexandrium-catenella, Toxic-dinoflagellate, Resting-cyst, Optimum-sample-size
Contact : Annie.Pastoureaud@ifremer.fr
Novembre 2007 - Spatial variations in biomarkers of Mytilus edulis mussels at four polluted regions spanning the Northern Hemisphere
Auteurs : F. Gagné, T. Burgeot, J. Hellou, S. St-Jean, E. Farcy, C. Blaise
Environmental Research, sous presse
Economic and social developments have taken place at the expense of the health of the environment, both locally and on a global scale. In an attempt to better understand the large-scale effects of pollution and other stressors like climate change on the health status of Mytilus edulis, mussels were collected during the first two weeks of June 2005 at three sites (one pristine and two affected by pollution) located in each of the regions of the Canadian West Coast, the St. Lawrence estuary, the Atlantic East Coast and the northwestern coast of France, covering a total distance of some 11 000 km. The mussels were analyzed for morphologic integrity (condition factor), gametogenic activity (gonado-somatic and gonad maturation index, vitellogenin(Vtg)-like proteins), energy status (temperaturedependent mitochondrial electron transport activity and gonad lipid stores), defense mechanisms (glutathione S-transferase, metallothioneins, cytochrome P4503A activity and xanthine oxidoreductase-XOR), and tissue damage (lipid peroxidation-LPO and DNA strand breaks). The results showed that data from the reference sites in each region were usually not normally distributed, with discriminant factors reaching the number of regions (i.e. four), except for the biomarkers gonadal lipids, XOR and LPO in digestive gland. The integrated responses of the biomarkers revealed that biomarkers of stress were significantly more pronounced in mussels from the Seine estuary, suggesting that the impacts of pollution are more generalized in this area. Mussels from the Seine estuary and the Atlantic East Coast (Halifax Harbor) responded more strongly for Vtg-like proteins, but was not related to gonad maturation and gonado-somatic indexes, suggesting the presence of environmental estrogens. Moreover, these mussels displayed reduced DNA repair activity and increased LPO. Factorial analyses revealed that energy status, cytochrome P4503A activity and Vtg-like proteins were the most important biomarkers. Adaptation to warmer temperatures was reflected at the energy status levels, mussels from both the polluted and warmer sites displaying increased ratios of mitochondrial activity to lipid stores. Regional observations of biomarkers of energy status, gametogenesis and pollutant-related effects were influenced by nutrition, oxygen availability (eutrophication), and thermal history.
Novembre 2007 - Investigating the relationship between embryotoxic and genotoxic effects of benzo[a]pyrene, 17a-ethinylestradiol and endosulfan on Crassostrea gigas embryos
Auteurs : N. Wessel, S. Rousseau, X. Caisey, F. Quiniou and F. Akcha
Aquatic Toxicology 85 (2007) 133–142
Genotoxicity biomarkers are widely measured in ecotoxicology as molecular toxic endpoints of major environmental pollutants. However, the long-term consequences of such damage still have to be elucidated. Some authors have suggested that the accumulation of unrepaired DNA lesions could explain the embryotoxicity of certain chemical pollutants. As embryotoxicity exerts a direct impact on the recruitment rate, genotoxicity could be closely related to disturbances of ecological concern and produce a possible impact upon population dynamics.
The aim of the present work was to study the genotoxicity and the embryotoxicity of three relevant pollutants for oyster embryos: the polycyclic aromatic hydrocarbon, benzo[a]pyrene (BaP), the synthetic estrogenic hormone, 17?-ethinylestradiol (EE2), and the organochlorine pesticide, endosulfan (ES). For each substance, gamete fertilization was performed and embryo development followed in contaminated reference seawater.
Following exposure, embryotoxicity was evaluated by calculating the percentage of abnormal D-larvae obtained at 20 h development. Genotoxicity was measured in parallel by conducting a comet assay on enzymatically dissociated cells of pre-shelled larvae (16 h development). The oxidized DNAbase,8-oxodGuo, was also measured by HPLC coupled to electrochemical detection. For each contaminant, there is a relationship between genotoxicity and embryotoxicity was then studied to check for the possible significance of genotoxicity in the population dynamics of marine bivalves from polluted areas.
For BaP, embryotoxicity and DNA strand breakage were both observed from the lowest tested concentration of 0.2 nM. Induction of 8-oxodGuo was significant from 20 nM. Endosulfan exposure resulted in similar effects for oyster embryos but from higher concentrations and followed a concentration-dependent manner. Embryotoxicity and genotoxicity in terms of DNA strand breaks were observed for endosulfan from 300 and 150nM,respectively. No change in 8-oxodGuo level was observed following endosulfan exposure.EE2 displayed no toxic effect for oyster embryos within the range of tested concentrations (from 0.02 to 1.7 nM). Taking into account all the data collected during this study, a positive and significant correlation was demonstrated in oyster embryos between genotoxicity as measured by the comet assay and embryotoxicity.
Novembre 2007 - Sustainability of exploited marine ecosystems through protected areas: A viability model and a coral reef case study
Auteurs : L. Doyen (CNRS) , M. De Lara (ENPC) , Jocelyne Ferraris (ORSTOM) , Dominique Pelletier (Ifremer)
Overexploitation of marine resources remains a problem worldwide. Many works advocate for the use of marine reserves as a central element of future stock management in a sustainable perspective. In the present paper, we address the influence of protected areas upon fisheries sustainability within an eco-systemic framework through a dynamic bio-economic model integrating a trophic web, catches and environmental uncertainties. The model is spatially implicit. The evaluation of the ecosystem is designed through the respect along time of constraints of both conservation and guaranteed captures. Using the mathematical concept of invariance kernel in a stochastic context, we define different MPA effects according to biodiversity catches or mixed points of view. Numerical simulations inspired from data of Abore coral reef reserve in New Caledonia illustrate the main concepts. In this case, it is pointed out how MPA conservation effect is not necessarily conflicting with MPA catches effect. it is shown that such a co-viability requires medium exploitation rate. Moreover, the climatic changes represented by rise in cyclonic events seem to reinforce these assertions. (C) 2007 Elsevier B.V. All rights reserved.
Keywords : Marine-ecosystems, Renewable-resource, Fisheries-management, Marine-protected-area, Co-viability, Invariance-analysis
Contact : Dominique.Pelletier@ifremer.fr
Novembre 2007 - Contribution of several nitrogen sources to growth of Alexandrium catenella during blooms in Thau lagoon, Southern France
Auteurs : Collos, Y., Vaquer, A., Laabir, M., Abadie, E., Laugier, T., Pastoureaud, A.
Harmful Algae, 6, 781-789
A monitoring program with a weekly sampling frequency over a 15-month period indicates that urea concentrations above a certain threshold level may trigger the blooms of Alexandrium catenella in Thau lagoon. However, urea concentrations were also sometimes related to ammonium and dissolved organic nitrogen concentrations, indicating that the role of urea may not be a direct one. An original approach is used to assess the relative contribution of several nitrogen sources (nitrate, nitrite, ammonium, urea) to growth of A. catenella by comparing nitrogen uptake rates to nitrogen-based growth rates estimated from dilution experiments during four blooms over a 4-year period (2001–2004) in Thau lagoon. Nitrate and nitrite contributed 0.1–14% and 0.1–5% respectively of growth requirements. Ammonium and urea were the main N sources fueling growth of A. catenella (30–100% and 2–59%, respectively). Indirect estimates indicated that an unidentified N source could also contribute significantly to growth at specific times. Concerning ammonium and urea uptake kinetics, half-saturation constants varied between 0.2 and 20 µgat N L-1 for ammonium and between 0.1 and 44 µgat N L-1 over the 4-year period, indicating that A. catenella can have a competitive advantage over other members of the phytoplankton even under low concentrations of ammonium and urea. However, the observed large changes in ammonium and urea uptake kinetics on a short time scale (days) during blooms preclude more precise estimates of those contributions to growth and require further investigation.
Keywords : Alexandrium catenella; HAB; Nitrogen; Growth; Urea; Ammonium; Uptake kinetics
Novembre 2007 - Motility and autotoxicity in Karenia mikimotoi ( Dinophyceae)
Auteurs : Patrick Gentien (Ifremer), Michel Lunven (Ifremer), Pascal Lazure (Ifremer), Agnès Youenou (Ifremer), Marie-Pierre Crassous (Ifremer)
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 combination of these processes allows diffusion of the toxin into the underlying water, where it subsequently degrades. Confinement of the population in the pycnocline layer results also from another trade-off between growth conditions and shear-rate-modulated mortality. A simplified encounter kernel was introduced into the population dynamics equation to account for a mortality factor. Under realistic forcing conditions with a small number of parameters, this model reproduced the confinement of the population in the pycnocline layer, the proper timing and the duration of the recurrent K. mikimotoi bloom on the Ushant front (France).
Contact : Patrick.Gentien@ifremer.fr
Auteurs : Perrot T., Ménesguen A, Dumas F.
La Houille Blanche, N°5 (Octobre 2007), pp. 49-55
Every spring and summer, and for two decades, mass-blooms produced by a green alga of the genus Ulva, have been polluting some localities along the Brittany coasts. The main aspect of the nuisance lies in the stranding and further decomposition of large amounts of algae along recreational zones inducing visual and odoriferous pollution. Sites which are favourable to Ulva mass-blooms are shallow areas where water exchange with the open sea is slow (weak residual drift of water masses and long residence time). Drifting algae and nutrients are both trapped in these zones thus allowing Ulva thalli to be kept in good cultivation conditions. In collaboration with Ifremer, the so-called "MARS-ulve" ecological model (coupling the biochemical model ELISE with the hydrodynamical model MARS 2D) has been developed. The main goal of the ecological model is to establish quantitative quality objectives relative to nitrate and ammonia in the tributaries of the main bays of Brittany severely polluted by Ulva « green tide ». A specific capability of this model is to allow quantifying the relative contribution of each source of inorganic supply in the feeding of the green tide. A new numerical technique which allows assessing the proportion of nitrogen in the nitrogen pool of the ulvae has been coupled with the ecological model and applied in the St Brieuc bay.
Octobre 2007 - Vers une modélisation opérationnelle du devenir des nutriments dans la bande côtière bretonne
Auteurs : Pénard C., Ménesguen A, Dumas F., Guillaud J.-F.
La Houille Blanche, N°5 (Octobre 2007), pp. 62-67
Eutrophication of French Brittany coastal shelf is a recurrent problem, more and more worrying. This eutrophication exhibits two main forms :- "green tides", which are constituted by local proliferations and strandings of green macro-algae (particularly the Ulva species) in nitrogen-enriched areas.- phytoplanktonic blooms, which are responsible of coloured water events. Toxic species can be present (Pseudonitzschia, Alexandrium, Dinophysis), and induce banning of shellfish consumption.Several programs and directives compel authorities to initiate actions in order to diminish these problems. (WFD, OSPAR). This implies a better understanding of these phenomena.This work deals with the influences of the plumes of Loire, Vilaine and bay of Brest rivers (Elorn and Aulne) on the nitrate enrichment of the French Brittany coastal shelf. A 3D hydrodynamic model, MARS 3D, is used. The nitrate is considered as a conservative tracer, which is advected and dispersed by the model. Thanks to the introduction of 4 different tracers, we can distinctively follow the nitrate from Loire, Vilaine, Bay of Brest rivers and other rivers.The study shows that the Loire river influences the southern and western parts of coastal shelf of Brittany. The plume propagates up to the north of Iroise sea, and contributes for a large part to its enrichment. On the other hand, the high enrichment of the bay of Brest remains confined and is smoothly dispersed in Iroise sea, except during flood events : in this case, nitrate jets are pulsed into the Iroise sea.
Septembre 2007 - Effects of short-term environmental disturbances on living benthic foraminifera during the Pacific oyster summer mortality in the Marennes-Oléron Bay (France)
Auteurs : Vincent Bouchet, Jean-Pierre Debenay, Pierre-Guy Sauriau, Joel Knoery, Patrick Soletchnik
Sediment cores were collected from April to August 2004 on tidal mudflats of the macrotidal Marennes-Oléron Bay (SW France), famous for the cultivation of Pacific oysters (Crassostrea gigas). The response of living (stained) benthic foraminifera to short-term biogeochemical disturbances in the sediment and overlying water, which may be involved in oyster summer mortality, was monitored. Short-term hypoxia occurred in early June, in conjunction with a sudden rise in temperature. In mid-June, the ammonia content of sediment porewater increased, leading to potentially maximal flux towards overlying waters. Foraminiferal assemblages, particularly in the topmost layer, were altered. Ammonia tepida was the most tolerant to temperature increase and hypoxic conditions whereas Brizalina variabilis and Haynesina germanica were sensitive to organic degradation and hypoxia. Cribroelphidium gunteri was the most opportunistic during recolonisation. Benthic foraminifera showed that short-term biochemical changes in the sediment are toxic and may be involved in the summer mortality of Pacific oysters.
Keywords : Intertidal, Crassostrea gigas, Aquaculture, Marennes-Oléron bay, Living benthic foraminifera, Organic matter, Hypoxia, Ammonium
Septembre 2007 - An integrated modelling approach to forecast the impact of human pressure in the Seine estuary
Auteurs : S. Even, B. Thouvenin, N. Bacq, G. Billen ,J. Garnier, L. Guezennec, S. Blanc, A. Ficht, P. Le Hir
Hydrobiologia (2007) 588:13–29
Within the framework of the European Water Framework Directive, the Seine-Normandie Water Agency has defined prospective scenarios describing possible trends of evolution of the pressures on water resources. In order to evaluate the resulting water quality improvement or degradation of water bodies in the Seine river basin, an integrated modelling was proposed. The approach consisted in coupling three models, the SENEQUE model for upstream sub-basins, the PROSE model for the Seine river and main tributaries and finally the SiAM1D model for the downstream estuary. After consistency verification, the integrated model was applied to scenarios proposed by the Seine-Normandie Water Agency. As a result of improvement in the nitrogen treatment by waste water treatment plants, the annual load of ammonia at the basin scale will be reduced by 65%. The oxygen and ammonia criteria in the estuary will improve from ‘‘bad’’ to ‘‘good’’. However the nitrate criteria will remain ‘‘poor’’, given the strong influence of non-point sources. Despite a 70–75% drop of the point orthophosphate loads, the criteria for this variable will also remain ‘‘poor’’. The nutrient levels will be high enough to maintain eutrophication in the system; a general trend to a shift from N-limitation to P-limitation will be accentuated.
Keywords : Integrated modelling - Aquatic ecosystems - European Water Framework Directive - Seine catchment - Seine estuary - Non-point and point sources - Oxygenation - Eutrophication
Septembre 2007 - Modelling Pb and Cd dynamics in the Seine estuary
Auteurs : Bénédicte Thouvenin (Ifremer) , Jean-Louis Gonzalez (Ifremer) , Jean-François Chiffoleau (Ifremer) , Bernard Boutier (Ifremer) , Pierre Le Hir (Ifremer)
The Seine estuary (France) is currently one of the world's most contaminated estuaries, due in particular to its high cadmium and lead content. Proper understanding of contaminant transfer, transformation and retention mechanisms throughout the estuary and up to the adjacent marine zone require a range of studies involving data collections, experiments, and modeling tool. A multivariable transport model (SiAM-3D) was used to simulate dissolved and particulate transport and it is applied to several calculation grids; a speciation model (MOCO) was used to select key species and obtain a schematic system representation. The coupled model for Cd and Pb was compared with field measurements. The complementary character of various tools (model applied to annual time scale, in situ measurements and experiments) allowed to explore and quantify various hypotheses on the high dissolved cadmium concentrations observed during low river flow. The target is to achieve a compromise between acceptable computing times and adequate result accuracy. Although particle and contaminant behaviour is globally well-reproduced by the coarse grid, calculation errors relating to bayward fluxes and stocks deposited inside the estuary were highlighted after comparison with the fine grid.
Keywords : Seine-estuary, Cd-and-Pb-trace-metals, 3D-modeling
Août 2007 - Investigating the relationship between embryotoxic and genotoxic effects of benzo[a]pyrene, 17-ethinylestradiol and endosulfan on Crassostrea gigas embryos
Auteurs : N. Wessel, S. Rousseau, X. Caisey, F. Quiniou and F. Akcha
Genotoxicity biomarkers are widely measured in ecotoxicology as molecular toxic endpoints of major environmental pollutants. However, the long-term consequences of such damage still have to be elucidated. Some authors have suggested that the accumulation of unrepaired DNA lesions could explain the embryotoxicity of certain chemical pollutants. As embryotoxicity exerts a direct impact on the recruitment rate, genotoxicity could be closely related to disturbances of ecological concern and produce a possible impact upon population dynamics.
The aim of the present work was to study the genotoxicity and the embryotoxicity of three relevant pollutants for oyster embryos: the polycyclic aromatic hydrocarbon, benzo[ a]pyrene (BaP), the synthetic estrogenic hormone, 17-ethinylestradiol (EE2), and the organochlorine pesticide, endosulfan (ES). For each substance, gamete fertilization was performed and embryo development followed in contaminated reference seawater.
Following exposure, embryotoxicity was evaluated by calculating the percentage of abnormal D-larvae obtained at 20 h development. Genotoxicity was measured in parallel by conducting a comet assay on enzymatically dissociated cells of pre-shelled larvae (16 h development). The oxidized DNA base, 8-oxodGuo, was also measured by HPLC coupled to electrochemical detection. For each contaminant, the relationship between genotoxicity and embryotoxicity was then studied to check for the possible significance of genotoxicity in the population dynamics of marine bivalves from polluted areas.
For BaP, embryotoxicity and DNA strand breakage were both observed from the lowest tested concentration of 0.2 nM. Induction of 8-oxodGuo was significant from 20 nM. Endosulfan exposure resulted in similar effects for oyster embryos but from higher concentrations and followed a concentration-dependent manner. Embryotoxicity and genotoxicity in terms of DNA strand breaks were observed for endosulfan from 300 and 150 nM, respectively. No change in 8-oxodGuo level was observed following endosulfan exposure. EE2 displayed no toxic effect for oyster embryos within the range of tested concentrations (from 0.02 to 1.7 nM).
Taking into account all the data collected during this study, a positive and significant correlation was demonstrated in oyster embryos between genotoxicity as measured by the comet assay and embryotoxicity.
Keywords : Pacific oyster; Embryotoxicity; DNA damage; Endosulfan; BaP; 17-Ethinylestradiol
Août 2007 - Genetically based resistance to summer mortality in the Pacific oyster ( Crassostrea gigas) and its relationship with physiological, immunological characteristics and infection process
Auteurs : Samain J.F., Degrémont P.L., Boudry P., Soletchnik P., Haure J., Bédier E., Ropert M., Moal J., Huvet A., Bacca H., Van Wormhoudt A., Delaporte M., Costil K., Pouvreau S., Lambert C., Boulo V., Soudant P., Nicolas J.L., Le Roux F., Renault T., Gagnaire B., Géret F., Burgeot T.
Summer mortality of Pacific oysters is known in several countries. However no specific pathogen has been systematically associated with this phenomenon. A complex combination of environmental and biological parameters has been suggested as the cause and is now starting to be identified. A high genetic basis was found for survival in oysters when a first generation (G1) was tested in three sites during summer. This paper presents a synthesis on physiological characteristics of two selected groups ('R' and 'S', from families selected for resistance and susceptibility to summer mortality respectively), of the second and third generations. R and S showed improvement or reduction of survival compared with the control in both field and laboratory trials confirming the high heritability of survival of juveniles < 1 year old. Interestingly, no correlation was observed between growth and survival.
Comparison between the two selected groups showed that S oysters invested more energy in reproduction and stayed a longer time without spawning than R oysters which had high synchronous spawning. This was mainly shown with high rather than low dietary rations (respectively 12% and 4% DW algae/DW oyster) in a controlled experiment. Moreover, early partial spawning was detected in S oysters and not R ones in the high dietary ration. S showed a higher respiration rate and an earlier decrease in absorption efficiency than R during gametogenesis, but they were not significantly different in glycogen or ATP utilisation. Two months before a mortality episode, hemocytes from S oysters had a higher adhesive capacity than R hemocytes and significantly higher reactive oxygen species production capacity. One month before mortality, S oysters had the highest hyalinocyte concentration and their expression of genes coding for glucose metabolism enzymes (Hexokinase, GS, PGM, PEPCK) was significantly lower in the labial palps. After a thermal increase from 13 °C to 19 °C, during 8 days in normoxia, S oysters showed a large HSP70 increase under hypoxia contrary to R oysters, suggesting their high susceptibility to stress. Their catalase activity was lower than in R oysters and showed no further change to subsequent hypoxia and pesticide stresses, in contrast to R oysters.
These observations suggest possible links between higher reproductive effort in S oysters, their specific stress response to temperature and hypoxia, ROS production, partial spawning, hyalinocyte increase and the infection process. To compare R and S oysters in a more integrated way, a suppression subtractive hybridisation (SSH) library and a micro-array strategy are being undertaken.
Keywords : Summer mortality, Pacific Oyster, Crassostrea gigas, Resistant oyster, Genetic selection, Reproduction, Hemocytes, Stress, Temperature, ROS
Août 2007 - Toxic ity assessment of peptaibols and contaminated sediments on Crassostrea gigas embryos
Auteurs : Poirier L., Quiniou F., Ruiz N., Montagu M., Amiard JC., Pouchus YF.
Peptaibols are known membrane-modifying peptides that were recently detected in marine sediments and mussels collected from a shellfish farming area (Fier d'Ars, Atlantic coast, France). In this investigation, embryotoxicity bioassays with oysters (Crassostrea gigas) were performed to assess acute toxicity of alamethicin and different groups of peptaibols produced by a Trichoderma longibrachiatum strain isolated from marine environment. C gigas embryos appeared very sensitive to all the metabolites examined with higher toxic effects for long-sequence peptides (EC50 ranging from 10 to 64nM). D-shaped larvae with mantle abnormality were particularly noticed when peptaibol concentrations increased. Disturbances of embryogenesis were also observed following exposure to organic and aqueous extract of sediments from Fier d'Ars (EC50 = 42.4 and 6.6 g L-1 dry weight, respectively). Although peptaibol concentrations measured in these sediments could explain only a part of the toxic effects observed, this study suggests that these mycotoxins can induce larval abnormalities in a population of exposed animals at environmentally realistic concentrations. Their detection in coastal areas devoted to bivalve culture should be taken into account. (c) 2007 Elsevier B.V. All rights reserved.
Keywords : Risk-assessment, Marine-fungi, Mycotoxins, Bivalve-bioassay, Embryotoxicity
Août 2007 - Use of biotic indices in semi-enclosed coastal ecosystems and transitional waters habitats - Implications for the implementation of the European Water Framework Directive
Auteurs : H. Blanchet, N. Lavesque, T. Ruellet, J.C. Dauvin, P.G. Sauriau ,N. Desroy, C. Desclaux, M. Leconte, G. Bachelet, A.-L. Janson, C. Bessineton, S. Duhamel, J. Jourde, S. Mayot, S. Simon, X. de Montaudouin
Ecological Indicators, Volume 8, Issue 4, July 2008, Pages 360-372
This study deals with the application of macrozoobenthos-based biotic indices (BI) within the frame of the implementation of the EuropeanWater FrameworkDirective.More precisely, this study aimed at assessing the performance of five recently developed methodologies (BI) for the assessment of ecological quality status (EcoQ) in two semi-enclosed, sheltered coastal ecosystems and in one transitional water body situated along theWestern French coast, namelyMarennes-Ole´ron Bay, ArcachonBay, and the Seine Estuary. This study showed that these five indices rarely agreed with each other, describing very different pictures of the overall EcoQ of the three study sites. This work also clearly underlined the limitations of these approaches, notably the dependency of most of these BI and the resulting EcoQclassifications on habitat characteristics, more particularly to natural levels of sediment silt–clay content and the location of stations in the subtidal or the intertidal. The implication of our observations concerning the use of these BI for implementation of theWFDis discussed in terms of definition of habitat-specific reference conditions and necessity to adjust thresholds to the particular habitat occurring in semi-enclosed ecosystems. Meanwhile, the unmodified use of these BI severely impaired accurate assessment of EcoQ and decision-making on the managers’ point of view.
Contact : Nicolas.Desroy@ifremer.fr
Juillet 2007 - The growth of the banded carpet shell ( Paphia rhomboides) in a contrasted region, the English Channel (Western Europe): A modelling study
Auteurs : Marie Savina (doctorante Ifremer) , Alain Ménesguen (Ifremer)
Paphia rhomboides is an infaunal filter-feeding bivalve, particularly widespread and abundant in the English Channel. In order to investigate the influence of the growth-related post-settlement processes on its distribution, a spatial growth model was developed and linked to an existing ecological model of the English Channel. This model was partially parameterized on the basis of a specific ecophysiological experimental study, and calibrated with growth data collected in the "Golfe Normand-Breton" (GNB), a region of the English Channel. Compared to the actual distribution of P. rhomboides, the results suggest a strong influence of the growth-related processes on the distribution of the species: particularly, the extremely low growth obtained with the model in the Western Channel can explain the almost complete absence of the species in this area. (c) 2007 Elsevier B.V. All rights reserved.
Keywords : Meroplanktonic-invertebrates, Distribution, Paphia rhomboides, English-channel, Growth-model, Ecophysiology
Contact : Alain.Menesguen@ifremer.fr
Juillet 2007 - Relationships between benthic macrofauna and habitat suitability for juvenile common sole ( Solea solea, L.) in the Vilaine estuary (Bay of Biscay, France) nursery ground
Auteurs : Delphine Nicolas (a), François. Le Loc’h (b), Yves Desaunay (c), Dominique Hamon (d), Aline Blanchet (d), Olivier Le Pape (a)
a Pôle halieutique, Agrocampus Rennes, 65, rue de Saint-Brieuc, CS 84215, 35042 Rennes Cedex, France
b IRD, UR RAP, Centre de Recherche Halieutique, Avenue Jean Monnet, B.P. 171, 34203 Sète Cedex, France
c IFREMER, EMH, rue d'Ile d'Yeu, B.P. 21105, 44311 Nantes Cedex, France
d IFREMER, DYNECO/Ecologie benthique,
Coastal and Shelf Science 73 (2007) 639- 650
Coastal and estuarine systems are among the most threatened by human activities which damage their ecological function and, in particular, their nursery role for many marine species. In this context, the protection of these vital ecosystems is a critical issue for the management of fisheries resources. To that aim, functional approaches have to be developed that make it possible to assess habitat suitability and quality. The common sole, Solea solea (L.) was selected as an indicator species to identify the features of coastal and estuarine nursery habitats in the Bay of Biscay (France).
Previous studies have shown that young-of-the-year (YOY) sole are strongly dependent upon various abiotic factors, and especially bathymetry, sediment cover and the extent of river plumes. We investigated whether taking into account biological variables, based on benthic macrofauna biomasses aggregated into trophic group, may improve the description of the juvenile sole distribution in the Vilaine estuary nursery. Results from Generalised Linear Models demonstrated the importance of integrating these biological variables in the determination of juvenile habitats at a local scale. The abundance of YOY sole was correlated with an index of the benthic invertebrates biomass and, more specifically, with the biomass of suspension feeders. This result was reinforced by a one-dimensional spatial statistical analysis, which pointed out the similar distribution of invertebrate macrobenthos and juvenile sole along the upstream/downstream gradient of the estuary. Moreover, the inter-annual variations of abundance and distribution of juveniles were synchronous with those of the macrobenthos.
Keywords : Solea solea, nursery ground, essential fish habitat, benthic macrofauna, functional indicators, Vilaine estuary
Densities of trawled YOY sole during the surveys in July 2004 and 2005
Contact : email@example.com
Juin 2007 - Bioturbation at the water-sediment interface of the Thau Lagoon: impact of shellfish farming
Auteurs : Schmidt S., Gonzalez J.-L., Lecroart P., Tronczynski J., Billy I., Jouanneau J.-M.
Quantifying of sediment reworking processes provides new insights into benthic ecosystem functioning of the Thau lagoon, an important European shellfish farming area. In order to evaluate bioturbation rates of surface sediments, profiles of 7Be (half-life: 53 days) and 234Th (half-life: 24.1 days) were measured in cores collected since December 2001 to December 2006. Several sites were selected to sample the diversity of the Thau lagoon: C4, T10, and T11 in the middle of the lagoon, C5, T7 and T8 nearby oyster farming, T2 and T4 in the western edge, T12 in the eastern part closed to industry. 234Th in excess (234Thxs; i.e. supplied to sediment by settling particles) and 7Be both show seasonal variations in activities and in penetration within sediment. Taking into account the moderate sedimentation rates of the Thau lagoon, sites (0.1-0.4 cm per year), the penetration of both short-lived radionuclides to variable depths, from 1 up to 8 cm, indicates efficient biological mixing of upper sediments. Bioturbation rates (Db) to the distribution of excess 234Th (234Pb-Db) and of 7Be (7Be-Db) range between 1 and 35 cm2 y-1, depending on site and season. Surface sediment mixing of the Thau lagoon is primarily controlled by the quality of particle input, i.e. the food supply to the benthic fauna, mainly governed by the hydrological and seasonal conditions. But locally shellfish production is a key parameter that influences bioturbation through biodeposition.
Quantifier les processus de remaniement sédimentaire procure une vision nouvelle du fonctionnement des écosystèmes benthiques de l'étang de Thau, lieu d'une importante production ostréicole. Afin d'évaluer les taux de bioturbation des sédiments de surface, des profils de deux traceurs radioactifs, le béryllium 7Be (T1/2 = 53 jours) et le thorium 234Th (T1/2 = 24.1 jours) ont été mesurés à partir de carottes sédimentaires prélevées entre décembre 2001 et décembre 2006. La sélection de plusieurs sites a permis de couvrir la diversité de l'étang de Thau : C4, T10, et T11 dans le bassin central, C5, T7 et T8 au niveau des secteurs ostréicoles, T2 et T4 à l'ouest du bassin, et T12 à l'est près de la zone industrielle. Le 234Th en excès (234Thxs ; i.e. apporté au sédiment par la sédimentation des particules) et le 7Be présentent des variations saisonnières de leurs activités et de leurs pénétrations dans le sédiment. Compte tenu des faibles taux de sédimentation reportés pour l'étang de Thau (0.1-0.4 cm par an), la pénétration à des profondeurs variables (de 1 à 8 cm) des deux radioéléments à courte durée de vie révèle un mélange efficace des sédiments superficiels en lien avec l'activité biologique. Les taux de bioturbation (Db) calculés au moyen des profils de 234Th en excès (234Th-Db) et de 7Be (7Be-Db) sont compris entre <1 et 35 cm2 an-1, selon les sites et la saison considérés. Le mélange des sédiments d'interface de l'étang de Thau apparaît principalement contrôlé par la qualité du flux de particules, apport de nourriture pour la faune benthique, en lien avec l'hydrologie et les saisons. Localement, l'activité ostréicole est le facteur prépondérant qui influence la bioturbation via les biodépôts.
Keywords : Sedimentation, Biodeposition, Radionuclides, Mediterranean Lagoon
Juin 2007- Sustainability of exploited marine ecosystems through protected areas: A viability model and a coral reef case study
Auteurs : Dominique Y., Maury-brachet R., Muresan B., Vigouroux R., Richard S., Cossa D., Mariotti A., Boudou A
Ecological Modelling 208, 353-366
Overexploitation of marine resources remains a problem worldwide. Many works advocate for the use of marine reserves as a central element of future stock management in a sustainable perspective. In the present paper, we address the influence of protected areas upon fisheries sustainability within an eco-systemic framework through a dynamic bio-economic model integrating a trophic web, catches and environmental uncertainties. The model is spatially implicit. The evaluation of the ecosystem is designed through the respect along time of constraints of both conservation and guaranteed captures. Using the mathematical concept of invariance kernel in a stochastic context, we define different MPA effects according to biodiversity, catches or mixed points of view. Numerical simulations inspired from data of Aboré coral reef reserve in New Caledonia illustrate the main concepts. In this case, it is pointed out how MPA conservation effect is not necessarily conflicting with MPA catches effect. It is shown that such a co-viability requires medium exploitation rate. Moreover, the climatic changes represented by rise in cyclonic events seem to reinforce these assertions.
Keywords : Marine ecosystems; Renewable resource; Fisheries management; Marine protected area; Co-viability; Invariance analysis
Juin 2007 - Experimental assessment of oyster transfers as a vector for macroalgal introductions
Auteurs : F. Mineur (Queen's University of Belfast) , T. Belsher (Ifremer) , M. P. Johnson (Queen's University of Belfast) , C. A. Maggs (Queen's University of Belfast) , M. Verlaque (UMR 6540 DIMAR, COM, Université de la Méditerranée)
Introduction of non-indigenous species can alter marine communities and ecosystems. In shellfish farming, transfer of livestock, especially oysters, is a common practice and potentially constitutes a pathway for non-indigenous introductions. Many species of seaweeds are believed to have been accidentally introduced in association with these transfers, but there is little direct evidence.
We experimentally simulated the transfer of oysters from the Thau Lagoon (France). These transfers involved increasing periods of aerial emersion and additional brine and hot water treatments. The brine and hot water treatments were evaluated as a means of reducing the probability of algal introductions with oyster transfers. Shells were cultured for 40 days in experimental tanks to identify the macroalgae likely to be introduced with any oyster transfer.
A total of 57 macroalgal taxa, including 16 taxa not indigenous to the Thau Lagoon, were recorded across all treatments and experiments. The abundance of some species increased in several cases following aerial emersion. Elimination treatments (immersion in brine or hot water) significantly reduced algal diversity, with hot water treatments resulting in no species or only tubular Ulva spp. present.
The results support the hypothesis that oyster transfers are effective as primary and secondary vectors of macroalgal introductions. Relatively simple changes to the transfer practice (particularly hot water treatments) are suggested as a means of reducing the risk of non-indigenous algal introductions.
Flow chart indicating examples of transfers of Crassostrea gigas involved in French and European mariculture production. All arrows indicate potential transfers of livestock. List of sites is based on personal informations in the text and on personal observations. Due to market sensitivities about the source of oysters it is difficult to obtain exact figures for the scale of these transfers
Contact : Thierry.Laugier@ifremer.fr
Juin 2007 - Sedimentation on intertidal mudflats in the lower part of macrotidal estuaries: Sedimentation rhythms and their preservation
Auteurs : J. Deloffre (CNRS) , Romaric Verney (Ifremer) , R. Lafite (CNRS) , P. Lesueur (CNRS) , S. Lesourd (CNRS) , A. Cundy (University of Sussex)
The objective of this study is to propose an original approach to the analysis of the formation of intertidal rhythmites, their preservation, and the evaluation of sedimentation rates on estuarine mudflats. Three mudflats, one from each of three estuaries, were analysed using a combination of long-term (>a year), high-frequency (1 burst/10 or 20 min), and high-resolution (0.2 cm) altimeter datasets and X-ray images of sediment cores collected during topographic surveys. The results highlight the roles played by sediment supply, hydrodynamics, and morphology of the lower estuaries on the sedimentation rhythms. While the sediment-starved Medway estuary (Kent, UK) remains stable at different time-scales, the annual sedimentation rates on the sheltered Authie mudflat (Pas-de-Calais, France) and the open Seine mudflat (Normandy, France) are relatively high at 18 and 15 cm y(-1), rrespectively. On the Authie mudflat, sedimentation rhythms correspond to the semi-lunar cycle, with a good correlation between tidal range and deposit thickness. Sedimentation occurs at the beginning of the recovery (mean value of 0.25 cm per semi-diurnal cycle), and is not disturbed by wind-induced waves. In the lower Seine estuary, semi-diurnal mechanisms of deposition occur mainly when the mudflat is covered by a minimal water height (tidal range threshold value=7.1 m). Sedimentation rhythms are discontinuous and deposition occurs only during the highest spring tides. Mean deposit thickness is 0.6 cm per semi-diurnal cycle, controlled by the turbidity maximum and the long high tide slack (2-3 h). The fluid mud is sensitive to wind-waves in this open funnel-sbaped estuary, which undergoes wind-induced erosion (0.2 to 2 cm) about 10 times per year.
Comparison of altimeter datasets and lithology of the sediments cored at the same points provided improved understanding of the sediment record rhythms and the sedimentation events. On the sediment-starved Medway mudflat, the result of sediment processes is a single superficial lamina. The elementary deposit in the Authie bay corresponds to a semi-lunar-linked layer, typical of sheltered environments. On the lower Seine mudflat, sedimentation rhythms are linked to the highest spring tides (i.e., the lunar cycle), resulting from increased sediment availability related to the high suspended matter concentration in the turbidity maximum. These results underline the complex response of intertidal mudflats to hydrodynamics and sediment supply conditions, from the semi-diurnal to the annual scales. (C) 2007 Elsevier B.V. All rights reserved.
Keywords : X-ray-imagery, Macrotidal-estuary, Morphology, Mud, Rhythmites, Altimeter
Contact : Romaric.Verney@ifremer.fr
Juin 2007 - PCB, PCDD/F and PBDE levels and profiles in crustaceans from the coastal waters of Brittany and Normandy (France)
Auteurs : Bodin N. Abarnou A., Fraisse D., Defour S., Loizeau V., Le Guellec A.M., Philippon X.
Polychlorinated biphenyls (PCBs), polybrominated diphenyl ethers (PBDEs) and polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs) were analysed in the muscle of various edible marine crustaceans (spider crab, edible crab, velvet swimming crab and Norway lobster) from the Brittany and Normandy coasts (France). The highest concentrations were measured in species collected from Antifer (Seine Bay). PCB and PBDE patterns in crustacean muscles were similar and independent of the geographical area with the predominance of the high chlorinated PCBs (CB 15 3, 138, 118 and 180), and of a few PBDE congeners (BDE47, BDE99, WE 100 and BDE28). Oppositely, dioxin contamination differed with site. The major component in crustaceans from the Seine Bay was 2378-TCDF, whereas specimens from cleaner areas had higher relative concentrations of OCDD. Finally, the comparison of the spider crab contaminant profiles to those measured in mussel and sea bass highlighted two different trends: decapod crustaceans possess relatively strong capacity to metabolise PCBs and PBDEs; however these species might be used as bioindicators for dioxin pollution monitoring in the marine coastal environment. (C) 2007 Elsevier Ltd. All rights reserved.
Keywords : Metabolisation, Food-safety, France, PCBs, PCDD/Fs, PBDEs, Decapod-crustaceans
Juin 2007 - Anti-rabbit immunoglobulin G detection in complex medium by PM-RAIRS and QCM. Influence of the antibody immobilization method
Auteurs : Briand E., Salmain M., Compère C., Pradier C.M.
Two antibody immobilisation procedures were compared to set up an immunosensor for goat anti-rabbit immunoglobulin (anti-rIgG), i.e. rIgG covalently bound or immobilised via affinity to protein A (PrA). In both cases, the first layer of protein was covalently bound to a mixed self-assembled monolayer (SAM) of mercaptoundecanoic acid (MUA) and mercaptohexanol (C6OH) on a gold surface. The elaboration of the sensitive surfaces, as well as their selectivity and sensitivity were studied step by step by polarization modulation-reflection absorption infra-red spectroscopy (PM-RAIRS) and quartz crystal trticrobalance (QCM) with impedance measurement. QCM measurements showed that the viscoelastic properties of the antibody layer were markedly modified during the antigen recognition when the antibody was bound by affinity to PrA. The specific detection of antigen within a complex medium was assessed by PM-RAIRS thanks to the grafting of cobalt-carbonyl probes. Affinity constants between the immobilised rIgG and the anti-rIgG were determined from PM-RAIRS analysis. (c) 2006 Elsevier B.V. All rights reserved.
Keywords : Immunosensors, QCM, PM-RAIRS, RIgG-immobilisation
Juin 2007 - Relation concentration-débit et évolution temporelle du nitrate dans 25 rivières de la région Bretagne (France)
Auteurs : Jean-Francois Guillaud (Ifremer) , Luc Bouriel (UFR Sciences et Techniques)
La concentration de nitrate dans les 25 principales rivières bretonnes est, dans 90 % des cas, corrélée positivement au débit. Les caractéristiques hydrogéologiques des bassins versants jouent sur les termes de cette corrélation ; ainsi un taux d'écoulement superficiel important (caractéristique des bassins versants peu perméables) renforce cette corrélation et diminue le décalage temporel entre les pointes de crue et de concentration de nitrate.
L'évolution pluriannuelle des concentrations de nitrate dans les rivières bretonnes est caractérisée par un quadruplement durant les trente dernières années. Par contre depuis le milieu des années 90, on observe sur 80 % des rivières une tendance à la décroissance, indépendamment des évolutions pluriannuelles des débits. Le taux annuel de décroissance est d'autant plus fort que le bassin versant présente une part importante d'écoulements superficiels, et a donc une moins grande inertie hydrogéologique.
Etant donné que les temps de réaction des bassins versants sont relativement courts (2-10 ans), il se peut que l'on commence à constater l'effet sur les eaux superficielles d'une inversion de tendance concernant la pression agricole (baisse des fumures organiques et minérales azotées depuis le début des années 90). Ces tendances restent à confirmer et ne permettent pas encore d'atteindre, dans de nombreuses rivières, des concentrations d'azote inférieures au seuil à partir duquel se produisent des proliférations macroalgales en zone côtière, ou de permettre sans problème la production d'eaux destinées à la consommation humaine.
The study of nitrate concentrations in the main twenty-five rivers of Brittany shows that these concentrations are positively correlated with the river flow, in 90 % of cases. The hydrogeological characteristics of the watersheds have an influence on these relationships; in this way, river basins characterized by prevalent surficial water runoff exhibit higher correlation coefficient and lower time lag between river flow sequences and nitrate concentration series.
The pluriannual trend of riverine nitrate concentrations has shown a fourfold increase for thirty years; nevertheless eighty percent of rivers exhibit a recent decrease in nitrate concentrations, independently of river flow fluctuations. The highest annual rates of nitrate decrease correspond to river basins where the fast surficial runoff is prevalent, that is a sign of lower hydrogeological "inertia".
It is probably the visible consequence of a decreasing agricultural pressure (i.e. decrease of organic manure and mineral fertilizer uses since the nineties) in waterwheds that have fairly short reaction time (between 2 and 10 years). Nevertheless this nascent decreasing tendency will must be strengthened in order to reach weak enough nitrate concentrations to limit macroalgal eutrophication in the coastal zone and to allow everywhere the production of drinking water.
Keywords : Bretagne, nitrate, évolution pluriannuelle, régression multiple, débit fluvial, eutrophisation
Contact : Jean.François.Guillaud@ifremer.fr
Mai 2007 - In situ measurements of surficial mud strength: A new vane tester suitable for soft intertidal muds
Auteurs : P. Bassoullet and P. Le Hir
Continental Shelf Research, Volume 27, Issue 8, 1 May 2007, Pages 1200-1205
A vane fitted to a standard shear vane tester is described, the purpose of which is to obtain better measurements of the rheological properties of soft, surficial, intertidal muds (and consequently, variations in their erodability). Specifications and geometry of this vane are presented. The computation procedure is detailed, so that the methodology can be applied to any vane tester. The main improvement is a greater vertical resolution, typically less than 1 cm. Sets of direct measurements with this equipment and correlation with dry densities for three intertidal mudflats (estuaries and bay) are presented. Direct easy and quick shear strength measurements with such a vane can constitute basic data to characterise the erodability of a mudflat.
Mai 2007 - Spatio-temporal variations in intertidal mudflat erodability: Marennes-Oléron Bay, western France
Auteurs : F. Orvain, P.-G. Sauriau, P. Le Hir, G. Guillou, P. Cann and M. Paillard
Continental Shelf Research, Volume 27, Issue 8, 1 May 2007, Pages 1153-1173
A portable erosion device (ERIS) was deployed in November 2000 and May 2001 to investigate the spatio-temporal variation of fine-grained sediment erosion over a transect on the intertidal mudflats of Marennes-Oléron Bay, western France. The objective was to relate changes in bed erodability over diurnal emersion periods to bioturbation, rapid changes in sediment characteristics, and microphytobenthos biomass. Macrofaunal assemblages were dominated by the bivalve, Scrobicularia plana, on the upper mudflat, and by the gastropod, Hydrobia ulvae, on the middle mudflat. A power relationship was obtained where tcr was plotted as a function of sediment density. Results from the upper part of the mudflat deviated from this relationship due to bioturbation by S. plana. No influence of microphytobenthos (either chlorophyll a or extracellular polymeric substances (EPS) content) was found on tcr. The bivalve feeding activities altered consolidated sediments (sediment dry mass concentration of not, vert, similar700 g l-1) so that they became resuspended easily (tcr<1 Pa). Fluff layer erosion was observed, with an erosion rate dependent upon the biomass of H. ulvae. It was also found that bioturbation by H. ulvae was implicated (combined with grazing activities) in chl a resuspension during the erosion of the fluff layer. Snail bioturbation stimulated the chl a enrichment of eroded material, whilst the high snail biomass produced a decrease in suspended chl a due to higher grazing rates.
Mai 2007 - Sediment erodability in sediment transport modelling: Can we account for biota effects ?
Auteurs : P. Le Hir, Y. Monbet (Ifremer) and F. Orvain
Continental Shelf Research, Volume 27, Issue 8, 1 May 2007, Pages 1116-1142
Sediment erosion results from hydrodynamic forcing, represented by the bottom shear stress (BSS), and from the erodability of the sediment, defined by the critical erosion shear stress and the erosion rate. Abundant literature has dealt with the effects of biological components on sediment erodability and concluded that sediment processes are highly sensitive to the biota. However, very few sediment transport models account for these effects. We provide some background on the computation of BSS, and on the classical erosion laws for fine sand and mud, followed by a brief review of biota effects with the aim of quantifying the latter into generic formulations, where applicable.
The effects of macrophytes, microphytobenthos, and macrofauna are considered in succession. Marine vegetation enhances the bottom dissipation of current energy, but also reduces shear stress at the sediment–water interface, which can be significant when the shoot density is high. The microphytobenthos and secreted extracellular polymeric substances (EPS) stabilise the sediment, and an increase of up to a factor of 5 can be assigned to the erosion threshold on muddy beds. However, the consequences with respect to the erosion rate are debatable since, once the protective biofilm is eroded, the underlying sediment probably has the same erosion behaviour as bare sediment. In addition, the development of benthic diatoms tends to be seasonal, so that stabilising effects are likely to be minimal in winter. Macrofaunal effects are characterised by extreme variability. For muddy sediments, destabilisation seems to be the general trend; this can become critical when benthic communities settle on consolidated sediments that would not be eroded if they remained bare. Biodeposition and bioresuspension fluxes are mentioned, for comparison with hydrodynamically induced erosion rates. Unlike the microphytobenthos, epifaunal benthic organisms create local roughness and are likely to change the BSS generated by the flow.
In this paper, we attempt to describe state-of-the-art sediment transport models accounting for biological processes. Such applications generally demonstrate a clear effect of the biota on erosion/deposition, but morphodynamic coupling is rarely achieved. In the present study, a modelling exercise of this type was run, based on a cross-shore morphodynamic model of an intertidal mudflat [Waeles, B., Le Hir, P., Silva Jacinto, R., 2004. Modélisation morphodynamique cross-shore d’un estran vaseux. Comptes Rendus Geoscience 336, 1025–1033] in which the equilibrium profile of the intertidal flat under tide and wave forcing is simulated. A seasonal presence of the microphytobenthos in late spring and summer, represented by a fourfold increase in the erosion threshold, generates sediment level changes of about 5 cm. However, these effects disappear in autumn and winter when the erosion threshold returns to its abiotic value, even when wave erosion is ignored. In contrast, the reduction of BSS in the upper flat to simulate the effect of a saltmarsh induces a spectacular seaward shift of the upper flat. The simulations show the strong, potential, long-term effect of vegetated beds, i.e. the protection of sediment from wave erosion. In contrast, local stabilisation by the microphytobenthos does not have a significant long-term effect.
Some recommendations are given on the need to define experimental protocols for erosion tests and studies on biota effects. A stochastic approach is suggested to cope with the problem of patchiness and extreme variability of erodability patterns, combined with histograms of BSS.
Mai 2007 - Motility and autotoxicity in Karenia Mikimotoi ( Dynecopheae)
Auteurs : P. Gentien, M. Lunven, P. Lazure, M.P. Crassous, A. Youenou (Ifremer)
Philosophical transactions of the Royal Society B, sous presse
Karenia mikimotoi is one of the most common red tide dinotlagellates proliferating in the eastern North Atlantic and around Japan. Kill of marine fauna is associated with its blooms. ln 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 the synthetic toxin. Bioconvection observed in cultures allow the establishment of a trade-off between phototropism that leads to the local accumulation of cells and their autotoxicity which would prevent cell concentration. The combination of these processes allows diffusion of the toxin into the underlying water, where it subsequently degrades. Confinement of the population in the pycnocline layer results also from another trade-off between growth conditions and shear-rate-modulated mortality. A simplified encounter kernel was introduced into the population dynamics equation to account for a mortality factor. Under realistic forcing conditions with a small number of parameters, this model reproduced the confinement of the population in the pycnocline layer, the proper timing and the duration of the recurrent K. mikimotoi bloom on the Ushant front (France).
Avril 2007 - New tools for modelling water quality of hydrosystems: An application in the Seine River basin in the frame of the Water Framework Directive
Auteurs : Stéphanie Even, Gilles Billen, Nicolas Bacq, Sylvain Théry, Denis Ruelland, Josette Garnier, Philippe Cugier, Michel Poulin, Stéphanie Blanc, François Lamy and Catherine Paffoni
Science of the Total Environment 375 (2007) 274–291
The implementation of the European Water Framework Directive requires new tools for predicting the effect of expected measures taken in the watershed on water quality at the scale of large regional river systems. In the Seine basin, four models, developed in a research context, have been chained to each other to simulate water quality and biogeochemical functioning of the hydrosystem from headwater streams to the coastal marine area. All four models are based on a similar deterministic approach and share a common description of the biogeochemical processes, allowing them to exchange information. Each model differently represents the hydro-sedimentological processes, and uses different time and space resolution, in order to tackle with the specific problematic of each sub-system. This cascade of models has been used for testing a prospective scenario of water resources management at the horizon of 2015, established by Water Authorities of the Seine–Normandy district. The simulation predicts a general improvement of water quality concerning those variables linked to point sources of pollution (ammonium, oxygen, phosphate), even if, locally, this improvement can be insufficient for meeting the expected quality standards. The predicted improvement of the quality of the Seine River downstream from Paris and its estuary is large. However, the predicted very significant drop of phosphate contamination, although beneficial for limiting the problems of coastal marine eutrophication, does not lead to a significant control of phytoplankton development in the rivers upstream from Paris. The simulation also predicts a general increase in nitrate contamination mainly linked to diffuse sources from agricultural areas.
Keywords : Ecological modelling, European Water Framework Directive, Integrated water management, Seine River basin, Eutrophication, Storm water discharge
Avril 2007 - Organochlorinated contaminants in decapod crustaceans from the coasts of Brittany and Normandy (France)
Auteurs : Bodin N., Abarnou A., Le Guellec A.M., Loizeau V., Philippon X.
The contamination and distribution of organ ochlorinated compounds were considered in three crustacean species (edible crab, Cancer pagurus; spider crab, Maja brachydactyla; velvet swimming crab, Necora puber) from five sites along the coasts of Brittany and Normandy (Western and North-Western France). PCBs (16 single congeners), pp'-DDE and HCB were measured in hepatopancreas, gonads and muscle: in all, 175 samples were analysed. The spider crab was the only species found in the five sampling sites, thus enabling comparison between areas. Specimens from Antifer were much more contaminated (Sigma(16)PCBs in hepatopancreas = 2000-4000 ng g(-1) dry weight) than those from other sites (50-1000 ng g(-1) d.w.). Among all the three species, the spider crab appeared more contaminated by PCBs than the edible crab, by a factor 2-3, probably in relation with specific differences in their life cycle. There was no difference due to the gender of the species. Within the different analysed tissues, contamination levels increased from muscle to gonads and hepatopancreas in relation with the fat content. A very similar PCB composition was observed in all samples, PCB fingerprints being characterised by the relative importance of the more persistent PCB congeners: CB153, 138, 180, 187, and 118. Finally, these results were compared to recent food regulations first of maximum marker PCB intake and secondly of maximum dioxin-like PCB intake. By considering the muscle, all samples were far below the regulatory limits; for hepatopancreas and gonads, however, some samples were unfit for human consumption. (c) 2006 Elsevier Ltd. All rights reserved.
Keywords : France, Human-diet, Polychlorobiphenyls, Crustaceans, Normandy, Brittany
Mars 2007 - The effect of wave-induced turbulence on intertidal mudflats: Impact of boat traffic and wind
Auteurs : Romaric Verney (Ifremer) , J. Deloffre (UMR CNRS 6143 M2C, University of Rouen) , J.-C. Brun Cottan (UMR CNRS 6143 M2C, University of Caen) , R. Lafite (UMR CNRS 6143 M2C, University of Rouen)
Semi-diurnal and fortnightly surveys were carried out to quantify the effects of wind- and navigation-induced high-energy events on bed sediments above intertidal mudflats. The mudflats are located in the upper fluvial part (Oissel mudflat) and at the mouth (Vasiere Nord mudflat) of the macrotidal Seine estuary. Instantaneous flow velocities and mudflat bed elevation were measured at a high frequency and high resolution with an acoustic doppler velocimeter (ADV) and an ALTUS altimeter, respectively. Suspended particulate matter concentrations were estimated by calibrating the ADV acoustic backscattered intensity with bed sediments collected at the study sites. Turbulent bed shear stress values were estimated by the turbulent kinetic energy method, using velocity variances filtered from the wave contribution. Wave shear stress and maximum wave-current shear stress values were calculated with the wave-current interaction (WCI) model, which is based on the bed roughness length, wave orbital velocities and the wave period (T-S). In the fluvial part of the estuary, boat passages occurred unevenly during the surveys and were characterized by long waves (T-S > 50 s) induced by the drawdown effect and by short boat-waves (T-S < 10 s). Boat waves generated large bottom shear stress values of 0.5 Nm(-2) for 2-5 min periods and, in burst of several seconds, larger bottom shear stress values up to 1 N m(-2). At the mouth of the estuary, west south-west wind events generated short waves (T-S < 10s) of H-S values ranging from 0.1 to 0.3 m. In shallow-water environment (water depth < 1.5 m), these waves produced bottom shear stress values between 1 and 2 N m(-2). Wave-current shear stress values are one order of magnitude larger than the current-induced shear stress and indicate that navigation and wind are the dominant hydrodynamic forcing parameters above the two mudflats. Bed elevation and SPM concentration time series showed that these high energy events induced erosion processes of up to several centimetres. Critical erosion shear stress (tau(ce)) values were determined from the SPM concentration and bed elevation measurements. Rough tau(ce) values were found above 0.2 N m(-2) for the Oissel mudflat and about 1 N m(-2) for the Vasiere Nord mudflat. These results demonstrate the advantages of combining the measurement of instantaneous velocity and bed elevation to determine in situ the erosion and deposition processes as a function of bottom shear stress variations. (c) 2006 Elsevier Ltd. All rights reserved.
Keywords : Bed erosion, Intertidal mudflat, Seine Estuary, Wind waves, Boat waves, Bottom shear stress, Bed roughness length
Contact : Romaric.Verney@ifremer.fr
Mars 2007 - Polychlorinated biphenyl contamination of the spider crab ( Maja brachydactyla): Influence of physiological and ecological processes
Auteurs : Bodin N., Caisey X., Abarnou A., Loizeau V., Latrouite D., Le Guellec A.M., Guillou M.
Environmental Toxicology and Chemistry 26, issue, 454-461
Maja brachydactyla is a decapod crustacean widely distributed along the Northeast Atlantic coasts. The main objective of this work was to establish the influence of ontogenic factors, such as growth, aging, seasonal migrations, and reproduction, on the contamination of this species by polychlorinated biphenyls (PCBs). Two populations were studied: One in the Seine Bay (Eastern English Channel), which is exposed to greatly contaminated discharges from the Seine River, and one in the Iroise Sea (Western Brittany), which is little contaminated by such man-made compounds. At both sampling areas, PCB analysis revealed concentrations in hepatopancreas that were 10- and 50-fold higher than concentrations in gonads and muscle, respectively. Levels of 2,2',4,4',5,5'-hexachlorobiphenyl (CB153) increased with the age of the spider crabs, whereas their seasonal migrations had no direct effect. No significant sex effect was observed with regards to CB153 levels, but adult females exhibited PCB fingerprints different from those of males, probably because of the influence of the reproductive cycle on enzymatic system activity. Finally, spawning gave rise to a higher CB153 decontamination of female body burdens for specimens from the Iroise Sea than for those from the Seine Bay.
Février 2007 - Habitat suitability for juvenile common sole (Solea solea, L.) in the Bay of Biscay (France): A quantitative description using indicators based on epibenthic fauna
Auteurs : Le Pape O., Baulier L., Cloarec A., Martin J., Le Loc’h F., Desaunay Y.
This study describes the spatial distribution of young-of-the-year common sole based on beam trawl surveys conducted in late summer in the coastal and estuarine parts of the Bay of Biscay (France). Previous studies showed that habitat suitability for juvenile common sole varies according to physical factors and notably bathymetry and sediment structure. Nevertheless, the use of these descriptors alone to model habitat suitability led to considerable unexplained variability in juvenile common sole distribution. Hence, the epibenthic macro- and megafauna collected during beam trawl surveys was taken into account to improve models of habitat suitability for these juvenile flatfish. Ecotrophic guilds based on life traits (behaviour, mobility and feeding) were used to develop generic indicators of trawled benthic fauna. These synthetic descriptors were used in generalized linear models of habitat suitability in order to characterize the distribution of juvenile common sole. This approach significantly improved the description based on physical descriptors and allowed demonstrating that young common sole distribution is related to the density of trawled deposit and suspension feeders and also of carnivorous organisms. These models provide a reliable method to develop indicators of nursery habitat suitability from trawl survey data with the aim of assessing and surveying their quality. (c) 2006 Elsevier B.V. All rights reserved.
Keywords : Habitat-suitability-models, Epibenthic-fauna, Solea-solea, Nursery-ground, Ecotrophic-guilds, Bay-of-Biscay
Janvier 2007 - Nitrogen uptake and assimilation kinetics in Alexandrium minutum (Dinophyceae): effect of N-limited growth rate on nitrate and ammonium interactions
Auteurs : Maguer J.F., L’Helguen S., Madec C., Labry C, Le Corre P.
Uptake and assimilation kinetics of nitrate and ammonium were investigated along with inhibition of nitrate uptake by ammonium in the harmful dinoflagellate Alexandrium minutum Halim at different nitrogen (N)–limited growth rates. Alexandrium minutum had a strong affinity for nitrate and ammonium ( K s=0.26±0.03 and 0.31±0.04 µmol·L-1, respectively) whatever the degree of N deficiency of the cells. Ammonium was always the preferred form of nitrogen taken up rho (NO3)/rho(NH4) =0.42–0.50). In the presence of both forms, nitrate uptake was inhibited by ammonium, and inhibition was particularly marked in N-sufficient cells (l-max similar to 0.9 and K i=0.31–0.56 µmol·L-1). In the case of N assimilation, ammonium was also the preferred form in N-deficient cells (rho(assim NO3) /rho(assim NH4) = 0.54-0.72), whereas in N-sufficient cells, both N sources were equally preferred (rho(assim NO3) /rho(assim NH4) =0.90-1.00). The comparison of uptake and assimilation rates highlighted the ability of A. minutum to significantly store in 1 h nitrate and ammonium in amounts sufficient to supply twice the daily N requirements of the slowest-growing N-deficient cells. Nitrogen uptake kinetic parameters of A. minutum and their ecological implications are discussed.
Janvier 2007 - Biofilm composition and mercury availability as key complementary factors for mercury accumulation in fish (Curimata cyprinoides) from a disturbed Amazonian freshwater system
Auteurs : Dominique Y., Maury-brachet R., Muresan B., Vigouroux R., Richard S., Cossa D., Mariotti A., Boudou A.
Environmental Toxicology and Chemistry, 26:45-52 (162 Ko)
The Petit-Saut hydroelectric reservoir was filled in 1994 on the Sinnamary River in French Guiana (Amazonian basin). Flooding of the equatorial rain forest led to anoxia in most of the water column and enhanced mercury methylation in the reservoir hypolimnion. We selected the benthivorous/omnivorous fish species Curimata cyprinoides to investigate total mercury and methylmercury (MeHg) bioavailability and bioaccumulation capacities in the reservoir and downstream in the Sinnamary River. Mercury concentrations in the dorsal skeletal muscle were 10-fold higher in fish from the downstream zone. Stomach contents and stable nitrogen and carbon isotope ratios showed that biofilms and the associated invertebrate communities represented important food sources at the two sites. The d13C measurements indicated that biofilms in the flooded forest zone of the reservoir consist of endogenous primary producers; downstream, they are based on exogenous organic matter and microorganisms, mainly from the anoxic layers of the reservoir. Total mercury and MeHg concentrations in the biofilms and associated invertebrates were much higher at the downstream site compared to concentrations at the reservoir. Our results clearly show the importance of MeHg export from the anoxic layers of this tropical reservoir. We conclude that differences between biofilm composition and MeHg concentrations in the ingested food could explain the marked differences observed between mercury levels in fish.
Keywords : Mercury, Fish, Amazonian hydroelectric reservoir, Biofilms
Janvier 2007 - Marine water quality assessment using transplanted oyster larvae
Auteurs : Françoise Quiniou (Ifremer) , G. Damiens (UMR 1112 INRA-UNSA R.O.S.E) , M. Gnassia Barelli (Gnassia-Barelli) , A. Geffard (EA 2069 URVVC, Faculté des Sciences Exactes et Naturelles de REIMS) , C. Mouneyrac (Centre d'Etude et de Recherche sur les écosystèmes aquatiques (CEREA), Faculté des Sciences Nantes) , H. Budzinski (LPTC Université de Bordeaux I) , Michèle Romeo (UMR 1112 INRA-UNSA R.O.S.E)
Active bio-monitoring in terms of biornarkers was attempted using Crassostrea gigas larvae produced in the laboratory and transplanted using special containers to two sites at the entrance (A) and inner part (P) of the harbour of Arcachon (French Atlantic Coast). The larvae were kept in the medium for 48 h. Their physiological status and their biomarker levels : acetylcholinesterase AChE, catalase CAT and glutathione S-transferase GST activities were determined together with metallothionein Wand Thiobarbituric Acid Reactive Substances TBARS concentrations. Copper and PAH (polycyclic aromatic hydrocarbon) concentrations were determined in the exposed larvae and in the sediments collected under the containers. Cadmium, lead and zinc could be also analyzed in the sediments. Toxicity tests demonstrate that the larvae are in better physiological conditions in A compared to P. Larvae transplanted in the inner harbour (P) present relatively high GST activity (869.1 +/- 39.3 nmol min(-1) mg protein(-1)), TBARS (2.74 +/- 0.19 nmol mg protein(-1)), compared to those exposed at the harbour entrance (A). Copper measured in the sediments (65 +/- 1 mg kg(-1) d.w.) collected under the cages at P is higher than at A. Larvae placed in A present higher total PAH concentrations compared to the inner part. The data tend to reveal a lower copper and higher PAH contamination in A than in P. Therefore larvae, developing in the natural medium, show different responses according to their immersion sites. These responses, obtained within 48 h, may be related to the chemical contamination of the environment and may be used for seawater quality assessment in future studies. (c) 2006 Elsevier Ltd. All rights reserved.
Keywords : Crassostrea gigas larvae, Active bio monitoring, Biomarkers, Trace metals, PAHs
Contact : Françoise. Quiniou@ifremer.fr
Janvier 2007 - Two-or three-layered box-models versus fine 3D models for coastal ecological modelling? A comparative study in the English Channel (Western Europe)
Auteurs : Alain Ménesguen (a), Philippe Cugier (a), Sophie Loyer (b), Alice Vanhoutte-Brunier (a) ,Thierry Hoch (c), Jean-François Guillaud (a), Francis Gohin (a)
a) Ifremer, Ecosystem Dynamics Department, BP 70, 29280, Plouzané, France
b) ATLANTIDE, Technopôle Brest Iroise, Site du Vernis, CS 23866, 29238 Brest Cedex 3, France
c) UMR ENVN-INRA Gestion de la santé animale, BP 40706, 44307 Nantes Cedex 3, France
The general trend in ecosystem modelling is to improve the spatial resolution by shifting from rough box-models to fine 3D models. Despite the continuous speeding-up of computing, 3D models involving numerous state variables may remain intractable, especially for parameter calibration, when processes with long half-life periods (i.e, from years to decades) are introduced, such as the behaviour of organic matter in sediment and population dynamics of benthic species. In these cases, a first approach can be provided by fast-running box-models, if they take into account the most crucial hydrodynamic properties of the system. In a macrotidal shelf sea such as the English Channel, the long-term horizontal transport can be summarized by the tidal residual circulation, and the vertical stratification can be sketched by a two- or three-layered integral model. This paper compares the results obtained in the English Channel area by the same biogeochemical equations of pelagic primary production, coupled to 1) a two-layered box-model 2) a three-layered box-model (i.e., with an intermediate cline layer between surface and bottom ones) and 3) a fine-gridded 3D model. Comparison is focused firstly on thermal stratification and summer dinoflagellate blooms in the north-western Channel and secondly on the haline stratification and the sequence of blooms obtained in the eutrophicated Seine river plume. Comparison shows that box-models act as low-pass filters which reproduce correctly the weekly mean time-course, but greatly reduce the variance locally observed in a tide-oscillating plume region. As far as global characteristics are concerned, such as the annual primary production, or the percentage of variation in annual production after reducing the nutrient loadings, the box and 3D models gave very similar results. This conclusion reinforces the usefulness of using box-models as a first approach in long-term processes, for which a long transient phase is expected before reaching the annual periodic solution.
Contacts : Alain.Menesguen@ifremer.fr et auteurs
Janvier 2007 - Small scale retentive structures and Dinophysis
Auteurs : Hongqin Xie, Pascal Lazure, Patrick Gentien
Journal of Marine System, Volume 64, Issues 1-4, January 2007, Pages 173-188
Despite its rarity, Dinophysis acuminata is in terms of economic impact, the first toxic algal species along the coasts of Western Europe. It is observed at low levels (< 20 cell l- 1) all the year round but toxic events occur mainly in late spring and summer. D. acuminata ecophysiology is largely unknown due to the inability to culture it. Therefore, standard biomass models based on inorganic nutrition are largely inadequate. Presently, any progress in describing the conditions of population growth of this species will be a step forward to prediction of harmful events at the coast. This species has been observed at increased, albeit low cell densities in retentive eddies located in pycnocline layers. A concentration build-up of one species results from the balance between growth and loss processes, one of the latter being dispersal. The scales of interest for a D. acuminata population are of the order of 10 nautical miles on the horizontal and duration of 10 days, for a reported achievable growth rate of 0.6 day- 1. A three dimensional (3D) hydrodynamical model of the Bay of Biscay has been elaborated to reproduce hydrological structures over the last decade. We attempt here to relate the existence of retentive structures revealed from simulations under realistic forcing conditions and the toxic coastal events recorded in the 10-year time series of the French plankton monitoring network database. The eddies in the coastal area appear to be directly related with the Dinophysis coastal events and they may be a potential effective tool to predict those.
Keywords: Dinophysis; Prediction; Rare species; Eddy; 3D hydrodynamical model; Bay of Biscay