![]() | Dynamique et réponse fonctionnelle des foraminifères et de la macrofaune benthiques en zone ostréicole dans les pertuis charentais Auteur(s) : Bouchet, Vincent Éditeur(s) : Université d'Angers Résumé : In oyster farming areas, organic matter fluxes toward sediment is increased. Pacific oysters (Crassostrea gigas) reject organic-rich faeces and pseudofaeces as a result of filtration process. Organic matter can be consumed by benthic fauna, but in excess it can entails the reduction of benthic faunal species richness, abundance and biomass. Organic matter degradation also induces hypoxic (or anoxic) conditions in the sediment, and production of ammonia and sulfides in toxic concentrations. The main objective of this study is to assess the effects of oyster farming on benthic intertidal ecosystems in the Pertuis Charentais. Benthic macrofauna, living (stained) foraminifera, and physicochemical characteristics of the water column and sediment were used as indicators to evaluate these effects. A multidisciplinary approach was conducted across the Pertuis Charentais at 3 different spatial scales: an oyster trestle (micro-scale), an oyster culture area (meso-scale) and various sites across the Pertuis Charentais (macro-scale). The study was also realised at 4 different temporal scales: some months for the spatial micro-scale, every two weeks for 2 years at meso-scale and once per season during one year at macro-scale. In this study, I found that oyster farming enriches sediment in fine particles, organic matter (up to 12 %), particulate organic carbon (15-20 µg mg 1) and leads to high microphytobenthic biomass. Moreover, the association of seasonnal warming (during spring and summer), remineralisation of accumulated organic matter and short-term hypoxic conditions leads to sulfides and ammonium production. Consequently, the benthic biodiversity decreases and the population dynamic is disturbed. The population dynamic disturbance is characterised by fast abundance rises followed by high mortality rates. In these conditions, tolerant benthic macrofaunal (Cirratulidae, Spionidae and Capitellidae) and foraminiferal (Ammonia tepida and Cribroelphidium gunteri) species are promoted. AMBI index confirms "medium" ecological quality of oyster farming areas. On the contrary, across the control sites, sensible species are maintained (Amphipods, Rosalina cf. vilardeboana). Comparison of oyster farming techniques shows that on-bottom culture is less disturbing for benthic ecosystem than off-bottom culture. Axial tomodensitometry, an innovative method, was used to describe in 3D the sedimentary column organisation. I show that oyster farming modifies the sedimentary column functioning. Indeed, the macrofaunal diversity decrease leads to the modification of the functional diversity of assemblages. Thus, the vertical distribution of living foraminifera is limited in oyster farming areas, because their distribution is tightly related to macrofaunal bioturbating modes. Dans les zones ostréicoles, les flux de matière organique sont importants, l'huître Crasssotrea gigas rejetant sous forme de pseudo-fécès et de fécès de grandes quantités de matière organique. De ce fait, bien que cette matière organique puisse être consommée par la faune benthique, sa surabondance peut provoquer une réduction de la richesse spécifique, de l'abondance et de la biomasse et provoquer sur le plan des processus biogéochimiques des déplétions en oxygène et l'apparition de substances comme l'ammonium et les sulfures dont les concentrations peuvent devenir toxiques. L'objectif principal de cette étude était donc de déterminer l'impact de l'ostréiculture, grâce à plusieurs indicateurs, sur le compartiment benthique d'un écosystème littoral comme les pertuis charentais. Pour évaluer ces effets, la macrofaune benthique et les foraminifères vivants benthiques ont été utilisés en association avec des mesures des paramètres physico-chimiques de la colonne d'eau et du sédiment. Une approche pluridisciplinaire a ainsi été menée dans les pertuis charentais à trois échelles spatiales différentes : à l'échelle d'une table ostréicole (micro-échelle), à l'échelle d'un site ostréicole (méso-échelle) et à l'échelle des pertuis charentais (macro-échelle). Dans les trois cas, un suivi dans le temps a été associé à une étude de distribution spatiale, quelques mois à micro-échelle, tous les quinze jours pendant deux années à méso-échelle et une fois par saison pendant une année à macro-échelle. Ces différentes approches ont permis d'avoir une vision pertinente de la dynamique et de la réponse fonctionnelle de la faune benthique aux changements induits par la présence de l'ostréiculture. La présence des cultures ostréicoles dans les pertuis charentais enrichit les sédiments en particules fines, en matière organique (12 %), en carbone organique particulaire (15-20 µg mg-1) et favorise une production microphytobenthique élevée. Pendant la période chaude de l'année printemps-été, la reminéralisation de la matière organique accumulée associée à des hypoxies temporaires a favorisé la production de sulfures et d'ammonium. Dans les stations soumises à l'ostréiculture, la diversité des assemblages diminue. La dynamique des espèces est caractérisée par des augmentations rapides des abondances suivies d'épisodes de mortalité. Les espèces tolérantes de la macrofaune benthique (Cirratulidae, Spionidae et Capitellidae) et des foraminifères vivants benthiques (Ammonia tepida et Cribroelphidium gunteri) sont favorisées. Le calcul de l'indice AMBI confirme la qualité écologique moyenne de ces sites. Au contraire, dans la station témoin, les espèces sensibles sont favorisées (Amphipodes, Rosalina cf. vilardeboana). La comparaison de la technique de culture sur table et de culture à plat a montré que la culture des huîtres à plat est moins perturbante pour le milieu. L'étude de la bioturbation a montré l'influence qui existe entre le mode de bioturbation des différents groupes de la macrofaune et la répartition verticale des foraminifères vivants dans la colonne sédimentaire. La diminution de la diversité des assemblages de la macrofaune dans les zones soumises à l'ostréiculture modifient la diversité fonctionnelle de ces assemblages et affectent le fonctionnement de la colonne sédimentaire, limitant la répartition verticale des foraminifères dans ces zones. Droits : info:eu-repo/semantics/openAccess http://archimer.ifremer.fr/doc/2007/these-2582.pdf http://archimer.ifremer.fr/doc/00000/2582/ | Partager |
![]() | Influence of the mode of macrofauna-mediated bioturbation on the vertical distribution of living benthic foraminifera: First insight from axial tomodensitometry Auteur(s) : Bouchet, Vincent Sauriau, Pierre-guy Debenay, J.p. Mermillod-blondin, F Schmidt, S Amiard, J.c. Dupas, B Éditeur(s) : Elsevier Résumé : We investigated the influence of bioturbation by macrofauna on the vertical distribution of living (stained) benthic foraminifera in marine intertidal sediments. We investigated the links between macrofaunal bioturbation and foraminiferal distribution, by sampling from stations situated on a gradient of perturbation by oyster-farming, which has a major effect on benthic faunal assemblages. Sediment cores were collected on the French Atlantic coast, from three intertidal stations: an oyster farm, an area without oysters but affected by oyster biodeposits, and a control station. Axial tomodensitometry (CT-scan) was used for three-dimensional visualization and two-dimensional analysis of the cores. Biogenic structure volumes were quantified and compared between cores. We collected the macrofauna, living foraminifera, shells and gravel from the cores after scanning, to validate image analysis. We did not investigate differences in the biogenic structure volume between cores. However, biogenic structure volume is not necessarily proportional to the extent of bioturbation in a core, given that many biodiffusive activities cannot be detected on CT-scans. Biodiffusors and larger gallery-diffusors were abundant in macrofaunal assemblage at the control station. By contrast, macrofaunal assemblages consisted principally of downward-conveyors at the two stations affected by oyster farming. At the control station, the vertical distribution of biogenic structures mainly built by the biodiffusor Scorbicularia plana and the large gallery-diffusor Hediste diversicolor was significantly correlated with the vertical profiles of living foraminifera in the sediment, whereas vertical distributions of foraminifera and downward-conveyors were not correlated at the station affected by oyster farming. This relationship was probably responsible for the collection of foraminifera in deep sediment layers (> 6 cm below the sediment surface) at the control station. As previously suggested for other species, oxygen diffusion may occur via the burrows built by S. plana and H. diversicolor, potentially increasing oxygen penetration and providing a favorable microhabitat for foraminifera in terms of oxygen levels. By contrast, the absence of living foraminifera below 6 cm at the stations affected by oyster farming was probably associated with a lack of biodiffusor and large gallery-diffusor bioturbation. Our findings suggest that the effect of macrofaunal bioturbation on the vertical distribution of foraminiferal assemblages in sediments depends on the effects of the macrofauna on bioirrigation and sediment oxidation, as deduced by Eh values, rather than on the biogenic structure volume produced by macrofauna. The loss of bioturbator functional diversity due to oyster farming may thus indirectly affect infaunal communities by suppressing favorable microhabitats produced by bioturbation. Journal of Experimental Marine Biology and Ecology (0022-0981) (Elsevier), 2009-03 , Vol. 371 , N. 1 , P. 20-33 Droits : 2009 Elsevier B.V. All rights reserved. http://archimer.ifremer.fr/doc/2009/publication-6146.pdf DOI:10.1016/j.jembe.2008.12.012 http://archimer.ifremer.fr/doc/00000/6146/ | Partager Voir aussi Macrofauna Living foraminifera Interspecific interaction CT scan Bioturbating modes Biogenic structures Télécharger |
![]() | Effects of short-term environmental disturbances on living benthic foraminifera during the Pacific oyster summer mortality in the Marennes-Oléron Bay (France) Auteur(s) : Bouchet, Vincent Debenay, Vincent Sauriau, Pierre-guy Radford Knoery, Joel Soletchnik, Patrick Éditeur(s) : Elsevier Résumé : 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. Marine Environmental Research (0141-1136) (Elsevier), 2007-09 , Vol. 64 , N. 3 , P. 358-383 Droits : 2007 Elsevier Ltd All rights reserved http://archimer.ifremer.fr/doc/2007/publication-2586.pdf DOI:10.1016/j.marenvres.2007.02.007 http://archimer.ifremer.fr/doc/00000/2586/ | Partager Voir aussi Marennes Oléron bay Aquaculture Crassostrea gigas Intertidal Ammonium Hypoxia Organic matter Living benthic foraminifera Télécharger |
![]() | First report of Quinqueloculina carinatatriata (Wiesner, 1923) (foraminifera) along the french atlantic coast (Marennes-Oléron bay and ile de Ré) Auteur(s) : Bouchet, Vincent Debenay, Jean-pierre Sauriau, Pierre-guy Éditeur(s) : Cushman Foundation for Foraminiferal Research Résumé : Large populations of the living benthic foraminifera Quinqueloculina carinatastriata (Wiesner, 1923) are reported for the first time from intertidal mudflats of the French Atlantic coast (Marennes-Oléron Bay and Ile de Ré). Maximum abundance of living specimens was recorded in early autumn. The species was previously described from the Adriatic and Tyrrhenian Seas (central Mediterranean Sea) and reported from the Eastern Mediterranean and Red Seas, as well as tropical and subtropical regions. A survey of available literature to trace records of the species in muddy shallow habitats along the western coasts of Europe and Africa reveals that the species is unrecorded from the Western Mediterranean Sea and is unknown in the eastern Atlantic Ocean from the Ivory Coast to Denmark, including the British Isles. This supports the hypothesis that the species has been accidentally introduced outside its natural range as a probable result of mariculture trade and/or shipping activities. This is the first report of a successful introduction of a non-indigenous benthic foraminifera to the Atlantic coast of Europe. The Journal of Foraminiferal Research (0096-1191) (Cushman Foundation for Foraminiferal Research), 2007-07 , Vol. 37 , N. 3 , P. 204-212 Droits : Cushman Foundation for Foraminiferal Research http://archimer.ifremer.fr/doc/2007/publication-2587.pdf DOI:10.2113/gsjfr.37.3.204 http://archimer.ifremer.fr/doc/00000/2587/ | Partager |
![]() | Foraminiferal assemblages: tools for assessment of shrimp pond conditions Auteur(s) : Debenay, Jean-pierre Della Patrona, Luc Herbland, Alain Goguenheim, Hemitti Peignon, Jean-marie Éditeur(s) : PSIC 11 - 11th Pacific Science Inter-Congress : Pacific Countries and their Ocean: Facing Local and Global Changes / 2nd Symposium on French Research in the Pacific. March 2 - 6, 2009 Tahiti, French Polynesia. Résumé : Meiofauna is a functional group made of small benthic metazoans 45 to 500µm in size. Although protista, foraminifera living in this kind of environment are often put in to the meiofauna. Meiofauna has been studied in New Caledonia for its double role as biological indicator for monitoring pond health status and as shrimp forage. Suitability of EOM (easily oxidized material), SOD(sediment oxygen demand),as new biochemical tools for monitoring shrimp pond health was assessed in an environmental survey aiming to assess the role of the water/sediment interface in the occurrence of the summer syndrome vibriosis. EOM, SOD and redox were correlated with shrimp survivals. Lowest meiofauna biomass and abundance were concomitantly found in the most polluted station. Proportion of abnormal tests over exceeding the one found in areas subjected to natural ecological stress were collected and were positively related to EOM and SOD and negatively to redox. Shrimp pond dominant species are common to estuaries and lagoons. But foraminifera abnormal behaviour indicates specific shrimp pond conditions Droits : info:eu-repo/semantics/openAccess http://archimer.ifremer.fr/doc/00198/30876/29244.pdf http://archimer.ifremer.fr/doc/00198/30876/ | Partager |
![]() | Peuplements actuels et thanatocénoses à Soritidae et Peneroplidae des Keys de Floride (USA) Auteur(s) : Levy, A Éditeur(s) : Gauthier-Villars Résumé : In the sedimentary areas surrounding the Florida Keys, Soritidae and Peneroplidae are very well represented. These benthic foraminifera are generally attached to seagrasses or algae and more rarely to carbonate deposits. The colouring of their protoplasm results from the nature of endosymbiotic algae. The principal species represented are: Androsina lucasi (never recorded before in Florida) which lives only in the margino-littoral biotopes where the salinity is highly variable; Archaias angulatus and Amphisorus hemprichii which live in the biotopes of the littoral platform but also in those of the interior margin of the bay where the variations of salinity are weak; Cyclorbiculina compressa and Peneroplis proteus which live for the main part in the littoral biotopes of the oceanic platform where the salinity is normal and quite constant; five other species of secondary importance take the number of taxa observed alive in the Keys area up to ten. Moreover, if the comparison of the biocenoses and thanatocenoses emphasizes their comparative similitude, knowledge of the biocenoses permits a better understanding of their adaptation to present-day environments. Oceanologica Acta (0399-1784) (Gauthier-Villars), 1991 , Vol. 14 , N. 5 , P. 515-524 Droits : info:eu-repo/semantics/openAccess http://archimer.ifremer.fr/doc/00103/21379/18979.pdf http://archimer.ifremer.fr/doc/00103/21379/ | Partager |
![]() | Premières observations sur la morphologie et les processus sédimentaires récents de l'Éventail celtique Auteur(s) : Auffret, Gérard-andré Zaragosi, S Voisset, Michel Droz, Laurence Loubrieu, Benoit Pelleau, Pascal Savoye, R Bourillet, Jean-francois Éditeur(s) : Elsevier Résumé : During the SEDIFAN 1 cruise we surveyed the bathymetry and the acoustic properties of the surface sediment of the Celtic Deep Sea Fan. We also collected Kullenberg cores in order to study recent sedimentary processes. From the bathymetry survey it is relatively easy to recognize the main areas of modern fan. The upper fan included a large sedimentary ridge which constitutes the right levee of the prominent meandering Whittard valley. After its confluence with the Shamrock valley the course of the Whittard valley is abruptly deflected to the south. At a short distance to the south the valley divides into two upper-fan channels, the Celtic channel to the west being the deeper one. This point constitutes the centre of a radiating pattern which is developed on a 150 degrees quadrant and a radius of about 100 km. The acoustic imagery displays contrasted features, related to change in lithology within the first metre beneath the sea bottom and to the sea floor roughness. The Austell ridge exhibits a contrasted pattern of elongated areas with high and low acoustic backscattering levels. This pattern is related to the development of abyssal dunes, the amplitude of which is of metric order. Particularly remarkable is a lobe-shaped low back-scattering area in the western part of the middle fan, also noteworthy are a lineated facies to the west and a braided facies to the east of the fan. The laminated silty-clayey sequences deposited on the Whittard ridge and on the Trevelyan levee were deposited during the deglaciation. We interpret these as turbidity currents overflow deposits from the Whittard valley. At the end of isotopic stage 3 and during stage 2, the English Channel was a large plain flooded by the Channel River. During this period a broad delta developed at 100 m below the present-day depth and a wide spectrum of material was bound to be supplied to the deep sea and contributed particularly to the deposition of the Whittard ridge silty-clayey sequences. The stage 2 deposits are characterized by rhythmic levels enriched in monosulfides. These types of deposits are common in areas affected by fluvial discharges. Excluding the sedimentary ridge and the channel levees the surface deposits sampled with the Kullenberg corer are sandy. These sands are deposited in various contexts on the interfluve between the western and eastern channels and at channel mouths. They were emplaced during high sea level stands as a result of high energy gravity processes. The precise sources of these sands have not yet been identified, however benthic foraminifers from included ooze pebbles have living depths of between 500 and 1 000 m. The gravity processes which eroded this marry ooze may have been triggered on the upper slope. The Celtic shelf is presently a high energy platform where the conjunction of storms and spring tides call lead to enhanced sediment transport from near-shore to the deep sea. The relict or palimpsest deposits of the glacial delta also constitute a large reservoir of sandy material which can also be subject to reworking. Le programme Enam 2 (European North Atlantic Margin) concerne l'étude des processus sédimentaires quaternaires du Spitzberg au golfe de Gascogne. Dans le cadre de ce programme, la reconnaissance de l'Éventail profond celtique était l'objectif de la campagne Sedifan 1 au cours de laquelle nous avons établi la morphologie de l'éventail et obtenu une image acoustique des fonds sédimentaires. La morphologie permet de mettre en évidence une organisation en éventail. On note aussi le développement remarquable d'une ride sédimentaire au niveau de l'éventail supérieur. Les sédiments prélevés révèlent la présence de dépôts sableux, témoins d'une activité récente qui pourrait être liée à l'importance de l'hydrodynamisme sur les Grands Bancs de la plate-forme celtique. Oceanologica Acta (0399-1784) (Elsevier), 2000 , Vol. 23 , N. 1 , P. 109-116 Droits : 2000 Ifremer/CNRS/IRD/Editions scientifiques et medicales Elsevier SAS http://archimer.ifremer.fr/doc/2000/publication-525.pdf DOI:10.1016/S0399-1784(00)00116-X http://archimer.ifremer.fr/doc/00000/525/ | Partager Voir aussi Paléoclimat Turbidité Sédiment Quaternaire Eventail profond Palaeoclimate Turbidity Sediment Quaternary Deep sea fan Télécharger |