Etude de l’impact de la température sur la dynamique de croissance des coraux d’eau froide de l’Océan Atlantique
Etude de l’impact de la température sur la dynamique de croissance des coraux d’eau froide de l’Océan Atlantique.
Description et objectifs scientifiques :
Comme leurs analogues tropicaux, les coraux d’eau froide sont des ingénieurs qui créent des récifs et habitats complexes servant de refuge pour une large diversité d’organismes dans les environnements profonds du monde entier. Comme ils contribuent aussi à fixer le dioxyde de carbone et archivent les conditions (paléo)environnementales dans leur squelette, ils constituent des écosystèmes de haute valeur écologique. Les récifs de coraux d’eau froide sont aujourd'hui confrontés à de graves menaces anthropiques, particulièrement dans les canyons sous marins, lié aux activités de pêche nondurables (e.g., le chalutage), à la pollution (par les hydrocarbures, l'exploitation minière desfonds marins, les plastiques) et aux changements climatiques (augmentation de la température, acidification des océans, désoxygénation) (Chapron et al., 2018). De récents travaux montrent que les coraux Méditerranéens, vivant dans des eaux à 13-14°C, sontparticulièrement exposés aux effets de la température, au travers d’une perturbation dumicrobiote, des flux de carbone organique, de la nutrition et de la biominéralisation dusquelette, pouvant aboutir à la mort dans certaines conditions (Chapron et al., 2021). Dans les canyons sous-marins de l’Atlantique, les coraux vivent à de plus faibles températures qu’enMéditerranée (8-12°C), mais les impacts des changements globaux sont tout de même attendus jusqu’à 2000 m de profondeur (Wijffels et al., 2016).
Master. La croissance des coraux est déterminée au niveau microscopique grâce à des techniques de marquage-recapture combinée à des analyses sclérochronologiques (Lartaud et al., 2013; 2017). Le marquage consiste en l’incorporation d’un fluorochrome, la calcéine, dans le squelette, qui permet de suivre la croissance à fine échelle. Une évaluation macroscopique sera également réalisée, en combinant les approches classiques (allongement linéaire, taux de bourgeonnement ; Lartaud et al., 2017).
Des expérimentations in situ dans le canyon de Lampaul (Océan Atlantique) permettront également de déterminer le taux de croissance en milieu naturel. L’ensemble des résultats sera intégré avec de précédentes données pour cette espèce soumise à d’autres gammes de températures et comparé aux réponses observées pour les populations de Méditerranée, afin de mieux définir les conditions de résilience pour cette espèce.
Matériel analytique :
Préparation de sections fines du squelette des coraux élevés en aquariums et récoltés in situ, microscopie optique, analyse d’images, traitement statistique des données. L’ensemble du
matériel est disponible au sein du laboratoire d’accueil ou sur la plateforme d’imagerie (BioPic) de l’Observatoire Océanologique de Banyuls.
Références bibliographiques :
Chapron, L., Peru, E., Engler, A., Ghiglione, J. F., Meistertzheim, A. L., Pruski, A. M., Purser, A., Vétion, G., Galand, P. E., & Lartaud, F. (2018). Macro- and microplastics affect cold-water
corals growth, feeding and behaviour. Scientific Reports, 8(1), 1–8.
https://doi.org/10.1038/s41598-018-33683-6
Encadrants :
Mathilde CHEMEL (LECOB, OOB)
Franck LARTAUD (LECOB, OOB)
Lieu du stage :
LECOB UMR822, Observatoire Océanologique de Banyuls, Sorbonne Université – CNRS, 66650 Banyuls-sur-Mer.
Biodiversity and connectivity of deep-sea hydrothermal vent communities of the West Pacific
from 01/04/2021 au 06/30/2021
supervisor : Stéphane Hourdez
General information :
Deep-sea hydrothermal communities are host to a relatively small number of very specialized taxa that are only found near active hydrothermal vents. Community composition varies among biogeographic provinces in the world. In the West Pacific, the complex geological history has led to similar-looking communities amongst different regions. The goal of this research line is to use molecular barcode approaches (a fragment of mitochondrial CoxI gene) to compare the species composition of each community, determine whether larval exchange takes place (connectivity) and whether our estimation of biodiversity is skewed by the presence of cryptic species.
These data will have important repercussions in our understanding and in the management and conservation of these unique ecosystems and the species that inhabit them. This is especially important in the West Pacific, where deep-sea mining is planned in the upcoming years. The produced data will be made accessible on public databases such as GenBank use by other researchers in the world.
The assessment of the uncertainty of the hydrodynamical SYMPHONIE2015 model and its implications for Lagrangian dispersal studies
PhD student: Elise VISSENAEKENS (2019-2021)
Supervisor (ASR): Katell Guizien
To provide good management advice, connectivity in coastal areas must be fully understood. The common thread of this thesis is the analysis of the uncertainty of the SYMPHONIE2015 model and its effect on larval dispersal simulations. In the first chapter, the robustness of the model to the violation of the assumptions was tested. This was done by calculating six relative and absolute statistical indicators during and outside of wind, wave and stratification events. The results showed that the model performance is not affected by these events. In the second chapter, the instantaneous error was calculated. Then, the cumulative error distributions were compared to each other in space and time. Over time, intraseasonal differences in error distributions were smaller than interseasonal differences. In space, eight groups of error distributions could be formed. No relationship was found between model performance and stratification, water depth, resolution and slope. However, a strong correlation between current velocity and error distributions was found. In chapter three, instantaneous error was added as noise to the Lagrangian dispersion simulations and compared to the initial run to assess the effect of model error on connectivity. The median difference in transfer rate between analyzes with and without noise is zero for most areas. However, the relative transfer rate difference can vary from -100% to 100%. Knowing the uncertainties in the dispersion simulations can help to use them for management advice.
Analysis of boundary layer flow modification in coral forests : canopy effect quantification
Scientific supervisor: GUIZIEN Katell, DR2 HDR CNRS (Tel : 04 68 88 73 19, e-mail: This email address is being protected from spambots. You need JavaScript enabled to view it.),
Hosting laboratory: Laboratoire d’Ecogéochimie des Environnements Benthiques (UMR8222), Observatoire Océanologique de Banyuls S/ Mer, 1 avenue Pierre Fabre, 66650 Banyuls S/ Mer, France
Short description of the internship:
When ocean beds are covered by large obstacles, the classical boundary layer structure is significantly modified. The wakes produced by these obstacles create strong spatial variations in the flow, over a region (embedded within the boundary layer) known as the roughness sublayer (Ghisalberti 2009). Long-lived hard and soft coral species that are able to develop dense patches with a complex, three-dimensional structure form an animal forest canopy (sensu Rossi et al 2017), similar to trees in terrestrial systems (Ghisalberti and Nepf, 2002). Aside from the shelter provided by this canopy to other organisms, the animal forest can significantly modify the local physical and biogeochemical environment (reviewed in Guizien and Ghisalberti, 2017). Flow velocity profiles were measured with a high-resolution Doppler profiler across the 2 meters above the bottom in locations covered by soft corals at differents population densities. In shallow locations, the flow was dominated by waves (oscillatory flow) and in deep locations, by current (steady flow). The objective of the internship is to analyse the near-bottom flow velocity profile measurements with various signal processing methods developping customed Matlab routines in order to quantify the animal forest canopy effect on the flow (steady and unsteady) and test wether it can be related to any animal forest descriptors (height, population density). In the case of steady flows, canopy descriptors as established for atmospherical urban canopies will be considered (Mac Donald, 2000).
Facilities for the intern:
Computing facilities and Matlab software.
Bibliographical references:
- Mac Donald RW. Modelling the mean velocity profile in the urban canopy layer. Boundary Layer Meteorology 2000 ; 97:25-45.
- Ghisalberti M Obstructed shear flows: similarities across systems and scales. J. Fluid Mech. 2009 ; 641:51-61.
- Ghisalberti M, Nepf H. The structure of the shear layer in flows over a rigid and flexible canopies. J. Geophys. Res. Oceans. 2002 ; 107(C2): 3011-1-11.
- Guizien K., Ghisalberti M. (2017) Living in the Canopy of the Animal forest: Physical and Chemical Aspects. In Marine Animal Forests. The Ecology of Benthic Biodiversity Hotspots. S. Rossi, L. Bramanti, A. Gori, C. Orejas Saco del Valle (Eds) . Springer. ISBN: 978-3-319-17001-5 (Online).
- Rossi S, Bramanti L, Gori A, Orejas C. (2017) An Overview of the Animal Forests of the World. In Marine Animal Forests. The Ecology of Benthic Biodiversity Hotspots. S. Rossi, L. Bramanti, A. Gori, C. Orejas Saco del Valle (Eds) . Springer. ISBN: 978-3-319-17001-5 (Online).
Diversity of bacterioplankton communities in ecosystems influenced by freshwater from glacial origin in sub-Antarctic and Antarctic zones
PhD student : Claudia MATURANA (2019-2021)
Supervisor (ASR): Pierre Galand (LECOB)
Co-supervisor: Camila Fernandez (LOMIC)
General information:
The southern Patagonia of Chile concentrates one of the largest reserves of fresh water in the world, which makes it a key region for the development of anthropogenic and productive activities. The coast of the Antarctic Peninsula is characterized by being very vulnerable to climate change and being an area of high biodiversity and biomass production, presenting diverse and complex ecosystems that harbor rich marine communities controlled by local and regional oceanographic processes. For the sub-Antarctic and Antarctic zones, a decrease in ice cover is predicted, which will affect the marine and coastal systems, transforming its structure and altering the dominant species, their functioning and productivity levels. Regarding the structure of bacterial communities in bodies of waters of high latitudes with the entrance of fresh water from glaciers, different studies have reported presence of the three domains of life Bacteria, Archaea and Eukarya. Studies carried out in fjords of the southern Patagonia of Chile, suggest that the melting of glaciers would favour the development of microorganisms adapted to cold and low salinity during a scenario of high discharge, generating in this way changes in the structure of the normal microbial community and possible changes in the trophic web.
The Yendegaia fjord is characterized for being a low nutrient system and for presenting l
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