1,721,043 research outputs found
Habitat constraints and self-thinning shape Mediterranean red coral deep population structure: implications for conservation practice
No full textThe Mediterranean red coral, Corallium rubrum, is one of the most precious corals worldwide. Below 50 m depth, C. rubrum populations are generally characterised by large and sparse colonies, whereas shallow populations (above 50 m depth) show high densities of small colonies. We show here instead that populations dwelling between 80 and 170 m depth exhibited a continuous range of population density (from 2 to 75 colonies per 0.25 m2), with less than 1% of variance explained by water depth. An inverse relationship between maximum population density and mean colony height was found, suggesting that self-thinning processes may shape population structure. Moreover, demographically young populations composed of small and dense colonies dominated along rocky vertical walls, whereas mature populations characterised by large and sparsely distributed colonies were found only in horizontal beds not covered by sediment. We hypothesise that, in the long term, shallow protected populations should resemble to present deep populations, with sparsely distributed large colonies. Since the density of red coral colonies can decay as a result of self-thinning mechanisms, we advise that future protection strategies should be based also on a measure of red coral spatial coverage instead of population densit
Connectivity of rocky habitat invertebrate populations in the Gulf of Lion
No full textConnectivity has an important role for populations persistence in fragmented areas as it enables recolonization after local disturbance and compensate low local larval retention rates in sink populations. For most marine benthic invertebrates, which exhibit a complex bentho-pelagic life cycle, connectivity arises from dispersal during the pelagic larval phase.
In the seascape of the Gulf of Lion, rocky habitat is fragmented and separated by large sandy areas. Objective of this study is to quantify the potential connectivity among populations of sessile or sedentary benthic invertebrates inhabiting rocky habitat of the Gulf of Lion based on numerical simulations of larval dispersal, which integrate numerical simulations of ocean currents and larval traits affecting larval dispersal. To achieve this objective, the work is organized around three axis, forming the 3 chapters of the thesis.
In the first chapter, a review based on literature has been carried out collecting data on the traits affecting larval dispersal, mainly period and duration of spawning, Pelagic Larval Duration (PLD), larval size and larval motility behavior. The review includes all species building up the biodiversity of 4 hard-bottom assemblages of the Gulf of Lion. Each assemblage is designated according to the gorgonian (Octocorallia, Alcyonacea) which dominated the assemblage in terms of biomass: Paramuricea clavata (Plexauridae), Corallium rubrum (Coralliidae), Eunicella cavolinii (Gorgoniidae) and Eunicella singularis (Gorgoniidae). Gorgonians are of particular interest as they are among the main structural species of the Mediterranean hard-bottom communities due to their three-dimensional structures that create an habitat for small epifauna and refuge for several vagile species, determining the increase of the biodiversity of hard substrates. The inventory of existing knowledge clearly evidenced a lack of information about larval traits affecting larval dispersal (information available on less than 25 % of species) especially for the motility behavior.
The second chapter presents new data about experimental quantification of the free-fall speed of Eunicella singularis larvae, in order to increase the information on larval traits of a benthic species abundant in the rocky habitat of the Gulf of Lion. The free-fall speed was quantified using a particle tracking routine applied to video recordings of the passive motility behavior of Eunicella singularis larvae.
In the third chapter larval dispersal simulations in the Gulf of Lion were performed with a Lagrangian larva tracking model, integrating ocean currents and some larval traits, such as spawning areas, spawning period and Pelagic Larval Duration (PLD), according to the review made in chapter 1 for benthic invertebrate inhabiting rocky habitat (larval dispersal simulations are summarized in the form of connectivity matrices).
This thesis was carried out at the Laboratoire d'Ecogéochimie des Environnements Benthiques (LECOB, UMR 8222), at the Observatoire Océanologique de Banyuls sur Mer, which is a joint laboratory of the Université Pierre et Marie Curie (UPMC) and the Centre National de la Recherche Scientifique (CNRS)
Les ondes longues internes : génération et interaction avec la houle
No full textEconomical activities at sea have been moving from the coast towards the continental margins where baroclinic motion, sometimes of large amplitude, are to be faced. These are long internal waves of which we present two aspects in this report. In the first part, the generation of long linear internal wave by the external tide interacting with the continental step is examined. Importance of the oblique incidence of the tide and earth rotation have been settled within a two-layer long wave model. This model has been validated bearing the comparison with in-situ data from the Malin Shelf (Scotland). In the second part, the interaction between long internal waves and surface waves has been studied. Indeed, the surface signature of internal waves can be observed on SAR images. Firstly, experiments of interaction between an external solitary wave and short monochromatic surface waves have been carried out, in order to take into account the scale difference that exists between long internal wave and wind waves. Large phase shift have been measured on the short wave train, in good agreement with the predictions of a theoretical model based on WKBJ technique developped in this report. This model also gives short wave amplitude modulations through the wave action conservation, but this was not tested experimentally. Lastly, experiments of interaction between an internal solitary wave and short surface waves in a stratified medium revealed that phase shifts were too small to be neasured. It also showed that wave action conservation, as obtained theoretically for the first set of experiments, did not apply to describe the short wave amplitude modulations.L’activité économique maritime s’étant éloignée de la côte pour se rapprocher du bord du talus continental, les exploitants se trouvent confrontés à des mouvements baroclines qui peuvent être de grandes amplitudes, les ondes longues internes. Dans ce mémoire, on présente donc deux aspects concernant les ondes longues internes. Dans une première partie, la génération des ces ondes lors de l’interaction de la marée externe avec le talus continental a été étudié. Il a été montré grâce à un modèle linéaire d’ondes longues en bi-couche que l’incidence oblique de la marée ainsi que la rotation terrestre n’étaient pas à négliger. Le modèle a été validé en le comparant à des mesures in-situ réalisées sur le Malin Shelf (Ecosse). Dans la seconde partie, nous nous sommes intéressés à l’interaction de ces ondes longues internes avec la houle de surface. En effet, sur les images de SAR, on peut observer la signature des ondes internes laissée en surface. Une première étude expérimentale d’interaction entre une onde solitaire de surface et une onde courte monochromatique barotrope a été menée simulant la différence d’échelle existant entre une onde longue interne et des vagues de vent. Des déphasages importants de l’onde courte ont été mesurés, en bon accord avec ceux prédits par un modèle théorique utilisant la technique WKB également présenté dans ce mémoire. Ce modèle a aussi conduit à estimer les modulations d’amplitude de l’onde courte à travers la conservation de l’action d’onde mais ce point n’a pu être testé expérimentalement. Enfin, des expériences d’interaction entre une onde solitaire interne et une onde courte externe ont été menées en milieu stratifié. Les modulations de la phase se sont avérées trop faibles pour être mesurées, et celles de l’amplitude ne sont pas décrites par la conservation de l’action d’onde établie théoriquement pour le cas de la première série d’expériences
Towards a spatialized approach to marine spatial planning : case study for sessile invertebrate populations in the Gulf of Lion
No full textLa planification spatiale marine est un enjeu d’avenir pour la conservation des ressources marines, mais notre compréhension de l’agencement spatial des zones de conservation et des zones d'aménagement pour favoriser la persistance des populations n’est pas si claire. L’étude des échelles spatiales structurant la distribution des espèces et des processus influençant la dynamique et la persistance des populations marines est donc essentielle pour une approche spatialisée de l'organisation des espaces marins. Ce travail de thèse s’est donc organisé autour de deux objectifs : (i) appréhender les échelles locales et régionales structurant la distribution spatiale des invertébrés sessiles dans les habitats naturels et artificiels (partie 2 et partie 3) et (ii) évaluer comment l’intégration de la connectivité fonctionnelle associée à la dispersion larvaire dans un réseau hybride d’habitats naturels et d’habitats artificiels influencent les schémas prospectifs spatialisés d'extension de la conservation dans le golfe du Lion. Les approches choisies combinent des outils de modélisation et des inventaires à haute résolution d'invertébrés sessiles communs sur les habitats naturels et sur les récifs artificiels. La partie 2 examine la distribution spatiale régionale de 5 espèces de gorgones en utilisant un modèle de niche écologique, à partir de prédicteurs hydrologiques et géomorphologiques (courants de fond, température de surface, turbidité, profondeur, pente, rugosité, orientation des parois). La structuration spatiale de 4 des 5 espèces de gorgones peut s’expliquer par ces facteurs. Dans la partie 3, les effets de facteurs locaux (forme, profondeur et durée d'immersion) et régionaux (zone géographique) ont été évalués en examinant les assemblages de cinq espèces aux traits d'histoire de vie contrastés. Le positionnement géographique a été prévalent sur les facteurs locaux dans la colonisation des RA. L'approche multi spécifique réalisée dans les parties 2 et 3 a montré d’importances différentes du rôle de la dispersion et des facteurs abiotiques sur la structuration spatiale (locale et régionale) des espèces. Dans la partie 4, un schéma prospectif d'extension de la conservation a été simulé pour évaluer l'intégration de la connectivité fonctionnelle au sein du réseau de substrats rocheux naturels et avec l’ajout du réseau des récifs artificiels. Le réseau d'aires marines protégées est fortement modifié quand la connectivité fonctionnelle au sein de l’habitat naturel rocheux fragmenté est prise en compte. Le réseau des récifs artificiels, ajoutant des points relais dans le réseau des habitats naturels, modifie le schéma prospectif. Ces résultats soulignent l’importance d’intégrer la connectivité fonctionnelle dans la planification spatiale marine et le potentiel impact de l’installation ou du démantèlement de récifs artificiels.Marine spatial planning is a future issue for the conservation of marine resources, but our understanding of the spatial arrangement of conservation zones and management zones to promote the persistence of populations is not so clear. The study of spatial scales structuring the distribution of species and processes influencing the dynamics and persistence of marine populations is therefore essential for a spatialized approach to the organization of marine spaces. This thesis work is therefore organized around two objectives: (i) to understand the local and regional scales structuring the spatial distribution of sessile invertebrates in natural and artificial habitats (part 2 and part 3) and (ii) to evaluate how the he integration of functional connectivity associated with larval dispersal in a hybrid network of natural habitats and artificial habitats influences the spatialized prospective schemes of conservation extension in the Gulf of Lion. The chosen approaches combine modelling tools and high-resolution inventories of common sessile invertebrates on natural habitats and on artificial reefs. Part 2 examines the regional spatial distribution of 5 gorgonian species using an ecological niche model, based on hydrological and geomorphological predictors (bottom currents, surface temperature, turbidity, depth, slope, roughness, wall orientation). The spatial structuring of 4 of the 5 species of gorgonians can be explained by these factors. In part 3, the effects of local (shape, depth and duration of immersion) and regional (geographical area) factors were evaluated by examining the assemblages of five species with contrasting life history traits. Geographical positioning prevailed over local factors in AR colonization. The multi-specific approach carried out in parts 2 and 3 showed different importance of the role of dispersal and abiotic factors on the spatial structuring (local and regional) of species. In Part 4, a prospective conservation extension design was simulated to assess the integration of functional connectivity within the natural hard bottom and with the addition of the artificial reef network. The network of marine protected areas is strongly modified when the functional connectivity within the fragmented rocky natural habitat is taken into account. The network of artificial reefs, adding stepping stone in the network of natural habitats, modifies the prospective design. These results highlight the importance of integrating functional connectivity into marine spatial planning and the potential impact of installing or dismantling artificial reefs
Influence de l'hydrodynamisme sur la dynamique des communautés benthiques pré-littorales et leur environnement géochimique
No full textBenthic sedimentary environments host micro- and macro-organisms which are the main agents of early diagenesis, a key step to sustain a recycled primary production in coastal areas. Nearshore soft-bottom habitats undergo intense but highly variable hydrodynamical stresses due to the dissipation of the energy accumulated by the ocean and brought by the rivers. Thus, elements recycling at the water-sediment interface is controlled by hydrodynamical conditions which regulate vertical fluxes across the interface as well as horizontal redistribution of particulate, including living organisms, and dissolved matter. Moreover, hydrodynamical conditions may also affect the diversity and abundance of benthic macrofauna assemblages depending on their reproductive behaviour. Indeed, while most micro-organisms have a direct reproductive cycle in the sediment, most macrofauna species have a complex life cycle with a pelagic larval stage enabling distant colonisation possibilities as a result of larval dispersal by the circulation. Herein, I present mechanistic models that I developped to describe the influence of hydrodynamical forcings on the dynamics of nearshore benthic invertebrates communities and their geochemical environment. Chapter 1 describes my contribution to the description of the main hydrodynamical processes of the microtidal nearshore area, focussing on its boundary layer dissipative role at fixed and mobile interfaces (shoreline, sea bottom, river mouth). Chapter 2 presents my investigations on the role of hydrodynamics on benthic macrofauna communities structuring, including larval dispersal, recruitment failures and benthic stages spatial redistribution. Chapter 3 presents my investigations on the role of hydrodynamics on the geochemical dynamics at the water-sediment interface, including sediment dynamics and dissolved fluxes in the wave-current-organisms interaction. Chapter 4 presents on future investigations aiming at coupling explicitly biogeochemical cycles with species life cycles in integrated ecosystem models for the nearshore area
Accuracy of solitary wave generation by a piston wave maker
No full textInternational audienceA new experimental procedure to generate solitary waves in a flume using a piston type wave maker is derived from Rayleigh's (1876, [18]) solitary wave solution. Resulting solitary waves fordimensionless amplitudes £ ranging from 0.05 to 0.5 are as pure as the ones generated using Goring's (1978, [7]) procedure which is based on Boussinesq (1871a, [1]) solitary wave, with trailing waves of amplitude lower than 3 % of the main pulse amplitude. In contrast with Goring's procedure, the new procedure results in very little loss of amplitude in the initial stage of the propagation of the solitary waves. We show that solitary waves generated using this new procedure are more rapidly established. This is attributed to the better description of the outskirts decay coefficient in a solitary wave given by Rayleigh's solution rather than by a Boussinesq expression. Two other generation procedures based on first-order (KdV) and second order shallow water theories are also tested. Solitary waves generated by the latter are of much lower quality than those generated with Rayleigh or Boussinesq-based procedures
Modulations d’amplitude dans l’interaction onde solitaire interne-houle
No full textInternational audienc
Etude expérimentale de la dégradation de la matière organique sous différents scénarios de turbulences instationnaires
No full textDans les environnements côtiers, les écoulements turbulents instationnaires tels que les vagues, la houle et la marée sont fréquents et vont modifier l épaisseur de la couche limite diffusive qui contrôle les flux d oxygène à l interface eau-sédiment. L oxygène joue un rôle primordial dans les processus de minéralisation et d oxydation de la matière organique dans les sédiments superficiels. Un système expérimental à grille oscillante a été développé dans le but d étudier ces processus sous hydrodynamique contrôlée. Ce mésocosme permet de (1) contrôler le flux diffusif à l interface eau-sédiment de 36 carottes de sédiments avec l oscillation de la grille, produisant une turbulence purement diffusive ; (2) simuler des dynamiques d épaisseur de la couche limite diffusive à différentes échelles de temps en contrôlant facilement l intensité de la turbulence et (3) étudier la dynamique transitoire de l oxygène à haute fréquence au cours d expériences de dégradation de la matière organique avec des épaisseurs de couche limite diffusive instationnaire. Deux expériences de dégradation de la matière organique ont été réalisées avec des scénarios hydrodynamiques différents: une expérience (enrichissement protéique) simulant une mortalité de consommateurs dans un système fermé de type lagunaire avec une réoxygénation progressive par des turbulences courtes et une autre expérience (enrichissement glucidique) simulant un apport végétal d origine terrestre dans un système ouvert tel qu une zone côtière soumise à la houle, avec 4 périodes journalières de forte houle. Durant ces expériences, la dynamique de l oxygène, de la matière organique et des variables biotiques (microfaune et méiofaune) ont été mesurés. Ces expériences ont permis d étudier expérimentalement la dynamique de la matière organique et des populations sous différentes dynamiques transitoires de l oxygène pour compléter les modèles de diagénèse précoce sous des écoulements instationnaires. D une expérience à l autre, la demande sédimentaire totale en oxygène a évolué en fonction du temps, de la profondeur et de l oxygène disponible. Les affinités globales et spécifiques à l oxygène montrent que la demande sédimentaire totale en oxygène reflète la dynamique des communautés microbiennes aérobies dans l expérience avec enrichissement glucidique. Ainsi, ce mésocosme à grille oscillante est un outil prometteur pour étudier le couplage entre la dynamique des communautés microbiennes et les fluctuations hydrodynamiques, qui peuvent se produire dans les eaux côtières avec des périodes et intensités différentes (marées, vagues, seiches...).In shallow environments, frequent unsteady flows such as tides, waves or wind-driven currents modulate the diffusive boundary layer thickness that controls the exchange of electron acceptors for mineralization and oxidation processes in surficial sediment. An oscillating grid mesocosm was developed in order to study organic matter degradation under controlled unsteady turbulence. The ability of this oscillating grid mesocosm is to (1) produce homogenous control of diffusive flux at sediment-water interface of 36 sediment cores with an oscillating grid ; (2) simulate diffusive boundary layer thickness dynamics at different time scales by easy control of turbulence intensity and (3) study transient oxygen dynamics along organic matter mineralization under unsteady diffusive boundary layer thickness. Two experiments of organic matter degradation were investigated under different hydro- dynamics : firstly, an experiment (protein enrichment) simulating a mortaly of consumers in a closed system (i.e. lagoon) with a progressive sediment reoxygenation by short turbulences and secondly, an experiment (carbohydrates enrichment) simulating a terrestrial vegetal input in an open system under waves (i.e. coastal zone), with 4 daily periods of high turbulence. During these experiments, oxygen, organic matter and biotic (microfauna and meiofauna) dynamics were measured. Moreover, these experiments were investigated to study experimentally organic matter and microbial population dynamics under different oxygen transients to complete early diagenesis model under unsteady flows. For each experiment, total sedimentary oxygen demande was oscillated with time, depth and oxygen supply. Oxygen global affinity and oxygen specific affinity were calculated and show that sedimentary oxygen demand reflects aerobic microbial community dynamics in carbohydrates enrichment experiment. To conclude, oscillating grid mesocosm is a promising tool to carry out benchmark expe- riments to investigate the coupling between microbial community dynamics and hydrodynamic fluctuations, which occurs in coastal waters with different periods and intensities (tides, waves, seiches)PARIS-BIUSJ-Biologie recherche (751052107) / SudocSudocFranceF
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
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