Hydrodynamique du plateau continental aquitain et influence sur les épisodes à Dinophysis dans le Bassin d'Arcachon

Des épisodes à Dinophysis affectent périodiquement l'exploitation des fruits de mer dans le Bassin d'Arcachon. Le réseau de surveillance interne au Bassin d'Arcachon montre que Dinophysis est advecté de l'océan ouvert. Le but de cette étude est de déterminer l'origine de Dinophysis. Des campagnes en mer sur le plateau continental Aquitain ont permis d'identifier une zone propice au développement de Dinophysis au large de Capbreton. Les épisodes à Dinophysis dans le bassin d'Arcachon se produisent suite à des vents d'Ouest qui induisent des courants vers le Sud d'après la littérature. L'étude des données hydrodynamiques acquises pendant les campagnes met en évidence un processus complexe et nouveau suite aux vents d'Ouest: de forts courants le long de la côte vers le Nord capables de transporter Dinophysis de Capbreton jusqu'au Bassin d'Arcachon. Un travail de modélisation a permis de reproduire ce courant et d'étudier son mécanisme particulier lié coin Sud-Est du Golfe de Gascogne.AbstractBORDEAUX1-Bib.electronique (335229901) / SudocSudocFranceF

Spring-neap tidal and circadian variability in the distribution of two groups of Pseudo-nitzschia species in an upwelling influenced estuary

High-resolution physical and biological measurements were carried out in the Ría de Pontevedra (NW Spain) in late spring during the ‘HABIT Pontevedra 2007’ survey, which utilized high vertical resolution instruments. Cell maxima of P. delicatissima (6 x 105 cells L-1) and P. seriata (2 x 106 cells L-1) groups were observed during the first half of the cruise during downwelling and a significant decrease in cell numbers occurred during subsequent upwelling conditions. The effect of tidal (both semidiurnal and spring-neap) and event driven (upwelling-downwelling cycle) variability were evident. The observed sequence of events suggests that Pseudo-nitzschia populations were advected from the shelf. The circadian variability was regulated by tidal forcing and Pseudo-nitzschia spp. maxima were observed at low tide. From results presented here we conclude that the magnitude of spring-neap tidal and circadian variability has to be considered when designing and implementing harmful algal bloom monitoring programmesEn prens

Rapid Enzyme-linked Immunosorbent Assay for Detection of the Algal Toxin Domoic Acid

Domoic acid (DA) is a potent toxin produced by bloom-forming phytoplankton in the genus Pseudo-nitzschia, which is responsible for causing amnesic shellfish poisoning (ASP) in humans. ASP symptoms include vomiting, diarrhea, and in more severe cases confusion, loss of memory, disorientation, and even coma or death. This paper describes the development and validation of a rapid, sensitive, enzyme linked immunosorbent assay test kit for detecting DA using a monoclonal antibody. The assay gives equivalent results to those obtained using standard high performance liquid chromatography, fluorenylmethoxycarbonyl high performance liquid chromatography, or liquid chromatography—mass spectrometry methods. It has a linear range from 0.1–3 ppb and was used successfully to measure DA in razor clams, mussels, scallops, and phytoplankton. The assay requires approximately 1.5 h to complete and has a standard 96-well format where each strip of eight wells is removable and can be stored at 4°C until needed. The first two wells of each strip serve as an internal control eliminating the need to run a standard curve. This allows as few as 3 or as many as 36 duplicate samples to be run at a time enabling real-time sample processing and limiting degradation of DA, which can occur during storage. There was minimal cross-reactivity in this assay with glutamine, glutamic acid, kainic acid, epi- or iso-DA. This accurate, rapid, cost-effective, assay offers environmental managers and public health officials an effective tool for monitoring DA concentrations in environment samples

Modelling of Gymnodinium mikimotoï blooms along the French Atlantic coast: geographical and vertical distributions

In order to study the occurrence of Gymnodinium mikimotoï bloom on the French Atlantic coast, a three-dimensional model of primary production was set up. The biological model was coupled to a hydrodynamic model previously developed at Ifremer, by the intermediary of transport, diffusion and heat fluxes. The cycles of three limiting elements for the phytoplankton growth were modelised: nitrogen, phosphorus and silicon. The second phase of the study aimed at reproducing the summer dinoflagellate blooms. In this new approach a model of the species Gymnodinium mikimotoï was coupled with the previous biomass model which provides the physical and chemical environments. The study focuses on the results obtained by this specific sub-model. The parametrisation was based on some physiological studies reported from laboratory cultures and on parameters existing in the literature. Consistent with the observations, the model reproduces the sub-surface cell concentrations, in the zone of minimal turbulence. The formulation retained for the temperature effect on the growth rate leads to a strong influence of temperature on the onset of the bloom and the mortality rate controls the vertical distribution. Nevertheless, as formulated here, the model underestimates the cell density.Afin d'étudier les processus de formation des blooms estivaux du dinoflagellé Gymnodinium mikimotoi; un modèle de la production primaire sur le plateau continental atlantique français a été développé. Un modèle biologique a été couplé au modèle physique tridimensionnel développé à I'lfremer, par l'intermédiaire du transport, de la diffusion et des flux de chaleur. Le modèle biologique décrit les cycles de l'azote, du phosphore et du silicium au travers du réseau trophique. Un modèle spécifique de I'espèce Gymnodinium mikimotoi'a ensuite été introduit. La nouveauté dans cette approche consiste à introduire un modèle de dynamique simple, pour une espèce phytoplanctonique particulière, dans un modèle tridimensionnel physico-biologique de biomasse globale. L'étude présentée ici montre les résultats issus de ce sous modèle. La paramétrisation spécifique à cette espèce est fondée sur une étude bibliographique et sur des expériences en laboratoire. Une des originalités de l'étude réside dans la formulation du taux de mortalité en fonction de la turbulence et de la densité cellulaire. La distribution verticale en subsurface des concentrations en Gymnodinium mikimotoï est assez bien reproduite et l'étude est prometteuse. Les maximums de densité cellulaire simulés pour Gymnodinium mikimotoi'se situent en sub-surface, au niveau de la pycnocline, correspondant à la zone de turbulence minimale. La comparaison avec les mesures de terrain montre que le modèle reproduit correctement la distribution spatiale de cette espèce le long des côtes; néanmoins, il sous-estime les niveaux de concentrations maximales observés. Le choix retenu pour représenter le rôle de la température sur le taux de croissance conduit à un effet prépondérant sur le déclenchement du bloom. Le taux de mortalité contrôle par la suite la distribution verticale

Modelling of Gymnodinium mikimotoï blooms along the French Atlantic coast: geographical and vertical distributions

In order to study the occurrence of Gymnodinium mikimotoï bloom on the French Atlantic coast, a three-dimensional model of primary production was set up. The biological model was coupled to a hydrodynamic model previously developed at Ifremer, by the intermediary of transport, diffusion and heat fluxes. The cycles of three limiting elements for the phytoplankton growth were modelised: nitrogen, phosphorus and silicon. The second phase of the study aimed at reproducing the summer dinoflagellate blooms. In this new approach a model of the species Gymnodinium mikimotoï was coupled with the previous biomass model which provides the physical and chemical environments. The study focuses on the results obtained by this specific sub-model. The parametrisation was based on some physiological studies reported from laboratory cultures and on parameters existing in the literature. Consistent with the observations, the model reproduces the sub-surface cell concentrations, in the zone of minimal turbulence. The formulation retained for the temperature effect on the growth rate leads to a strong influence of temperature on the onset of the bloom and the mortality rate controls the vertical distribution. Nevertheless, as formulated here, the model underestimates the cell density

Hydrodynamic conditions associated with the formation, maintenance and dissipation of a phytoplankton thin layer in a coastal upwelling system

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Phytoplankton assemblages and characterization of a Dinophysis acuminata population during an upwelling-downwelling cycle

The distributions of Dinophysis acuminata, its potential prey Myrionecta rubra, and the microplankton populations associated with them, were studied in Ria de Pontevedra (NW Spain) during a 2 wk cruise that covered an upwelling-downwelling cycle, and during intensive sampling over 21 h at the end of the cruise. Special attention was focused on the characterization and physiological condition of D. acuminata. There was vertical segregation between a phytoplankton assemblage that was dominated by upwelling-promoted diatoms and another assemblage that was dominated by small dinoflagellates, located in the warmer surface layer (0 to 5 m) where D. acuminata was observed. High spatio-temporal variability was observed in the frequency of cells containing starch granules (indicating photosynthetic activity) and digestive vacuoles (indicating heterotrophic feeding); this pattern corresponded with the apparent availability of M rubra cells. Populations of D. acuminata and M rubra have their own niches and distinct responses to physical forcing, but both are located in common water masses and occasionally meet. Changes in vacuolation of D. acuminata were followed by a substantial increase (similar to 35 %) in cellular volume. D. acuminata did not exhibit daily migratory behaviour, and expressed a high division rate (0.51 d(-1)) under downwelling conditions. This work sheds new light on the relation between D. acuminata populations and its potential prey, and on its ecophysiology; it also questions previous assumptions about the environment that is suitable for its development

Essai de détermination d'une typologie des sédiments côtiers en fonction de l'apparition d'eaux colorées

The study of different chemical parameters characterizing the coastal sediment, showed a possible relation between, respectively, high levels in organic matter and total copper, and the "red tide"  phenomenon.L'étude de différents paramètres caractérisant la composition chimique du sédiment côtier, a montré l'existence d'une relation possible entre les teneurs élevées en matière organique totale et en cuivre total, avec le phénomène "eaux colorées"