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This dataset relates to the biodiversity census carried out during the Belgica 121 (B121) expedition to the Western Antarctic Peninsula from February to March 2019. One of the aims of the campaign was to explore the surroundings of the Gerlache Strait and to carry out a detailed biodiversity census focusing on inter- and subtidal shallow-water areas using both classic descriptive marine ecology methods as well as state-of-the art techniques (habitat mapping, genetics, trophic ecology). The biodiversity census was carried out onboard a nimble research vessel, RV Australis. This dataset will offer access to the raw data on biodiversity occurrences, obtained using a range of methods described in this data paper., info:eu-repo/semantics/inPress

info:eu-repo/semantics/published

Macroalgae play a structuring role in benthic ecosystems, which makes it very important to monitor their cover rates and study their community structures and changes in time. Such studies are usually led by autonomous divers and often do not generate sufficient data to provide enough material for strategically-sound conservation plans. This paper describes the dataset generated in the framework of the evaluation of the potential of a complementary data acquisition method: annotating videos transects obtained using an underwater Remotely Operated Vehicle (ROV). The focus was on Cystoseira brachycarpa ,together with the abundance of several other macroalgae species, which could be identified using the ROV images after validation through specimen identification. Furthermore, in order to allow future uses, such as monitoring the status of colonisation of the invasive algae Caulerpa cylindracea ,the ROV was sent to some deeper transects on sedimentary habitats (40 m) below the Posidonia meadows lower limits. The project, while providing some interesting insights on using a ROV as a tool to study marine biodiversity, generated a dataset for the distribution of 19 macroalgae on both standardised and new transects in the Bay of Calvi (Katz et al. 2021). The observed species of macroalgae included: Acetabularia acetabulum ,Amphiroa rigida ,Caulerpa prolifera ,Caulerpa cylindracea ,Codium bursa ,Colpomenia sinuosa ,Corallinales (order), Cystoseira brachycarpa ,Cystoseira crinita ,Cystoseira spinosa ,Cystoseira zosteroides ,Dictyota (genus), Flabellia petiolata ,Halopteris (genus), Halopteris scoparia ,Jania (genus), Osmundaria volubilis ,Padina pavonica and Peyssonnelia squamaria .The videos also showed that the invasive algae Caulerpa cylindracea has spread between 2016 and 2019 and that more focused studies should be held in the Bay to assess the actual reach and possible impacts of this invasion. Finally, our ROV video transects have also underlined the significant presenc, info:eu-repo/semantics/published

Background This dataset relates to the biodiversity census carried out during the Belgica 121 (B121) expedition to the Western Antarctic Peninsula from February to March 2019. One of the aims of the campaign was to explore the surroundings of the Gerlache Strait and to carry out a detailed biodiversity census focusing on inter- and subtidal shallow-water areas using both classic descriptive marine ecology methods, as well as state-of-the art techniques (habitat mapping, genetics, trophic ecology). The biodiversity census was carried out onboard a nimble research vessel, RV Australis. This dataset will offer access to the raw data on biodiversity occurrences, obtained using a range of methods described in this data paper. New information New raw biodiversity data for a poorly-sampled region (Western Antarctic Peninsula) with a special focus on shallow ecosystems., SCOPUS: ar.j, info:eu-repo/semantics/published

Species distribution modelling studies the relationship between species occurrence records and their environmental setting, providing a valuable approach to predicting species distribution in the Southern Ocean (SO), a challenging region to investigate due to its remoteness and extreme weather and sea conditions. The specificity of SO studies, including restricted field access and sampling, the paucity of observations and difficulties in conducting biological experiments, limit the performance of species distribution models. In this review, we discuss some issues that may influence model performance when preparing datasets and calibrating models, namely the selection and quality of environmental descriptors, the spatial and temporal biases that may affect the quality of occurrence data, the choice of modelling algorithms and the spatial scale and limits of the projection area. We stress the importance of evaluating and communicating model uncertainties, and the most common evaluation metrics are reviewed and discussed accordingly. Based on a selection of case studies on SO benthic invertebrates, we highlight important cautions to take and pitfalls to avoid when modelling the distribution of SO species, and we provide some guidelines along with potential methods and original solutions that can be used for improving model performance., SCOPUS: ar.j, info:eu-repo/semantics/published

The potential for biological colonization of Antarctic shores is an increasingly important topic in the context of anthropogenic warming. Successful Antarctic invasions to date have been recorded exclusively from terrestrial habitats. While non-native marine species such as crabs, mussels and tunicates have already been reported from Antarctic coasts, none have as yet established there. Among the potential marine invaders of Antarctic shallow waters is Halicarcinus planatus (Fabricius, 1775), a crab with a circum-Subantarctic distribution and substantial larval dispersal capacity. An ovigerous female of this species was found in shallow waters of Deception Island, South Shetland Islands in 2010. A combination of physiological experiments and ecological modelling was used to assess the potential niche of H. planatus and estimate its future southward boundaries under climate change scenarios. We show that H. planatus has a minimum thermal limit of 1°C, and that its current distribution (assessed by sampling and niche modelling) is physiologically restricted to the Subantarctic region. While this species is presently unable to survive in Antarctica, future warming under both ‘strong mitigation’ and ‘no mitigation’ greenhouse gas emission scenarios will favour its niche expansion to the Western Antarctic Peninsula (WAP) by 2100. Future human activity also has potential to increase the probability of anthropogenic translocation of this species into Antarctic ecosystems., SCOPUS: ar.j, info:eu-repo/semantics/published

One important aspect of marine plastic pollution is that small particles are ubiquitously present in seawater and can transport a large variety of co-contaminants. The sorption-desorption kinetics of these co-contaminants sorbed to microplastics (MPs) are not fully understood, partially due to the lack of any standardised procedures between studies. The present work aims at describing a new and efficient method to investigate the sorption of co-contaminants onto different types of particles using proven radiotracer techniques. This work provides recommendations as well as a thorough description of the materials, conditions and procedures required to optimise the adsorption of polychlorinated biphenyl (PCB) onto particles. Details of the controlled experimental conditions, such as the volume of the container, the concentration of particles, and specifics of the radiotracer are provided. In addition, a thorough description of the novel filtration methodology specific to these radiotracer techniques is presented, for the first time in the literature. To validate the efficiency of the method, we examined the partition coefficients (Kd) of ¹⁴C-PCB153 onto virgin MP (10-29 µm polyethylene beads) and onto natural sediment particles that are similarly sized (1-17.8 µm) in seawater. After 40 h, plastic particles adsorbed 25.7% of ¹⁴C-PCB153 while sediment particles adsorbed 89.3% of the same compound. Results suggest that in this scenario, polyethylene MP particles may be less effective transport vectors of ¹⁴C-PCB153 than natural sediment particles. • Details of experimental conditions, such as the volume of the container, and the concentration of particles and of radiotracer, were defined • A thorough description of the filtration methodology specific to radiotracer techniques is presented • Results highlight that virgin polyethylene MPs may be less effective transport vectors of ¹⁴C-PCB153 than natural sediment particles., SCOPUS: ar.j, info:eu-repo/semantics/published

Among tools that are used to fill knowledge gaps on natural systems, ecological modelling has been widely applied during the last two decades. Ecological models are simple representations of a complex reality. They allow to highlight environmental drivers of species ecological niche and better understand species responses to environmental changes. However, applying models to Southern Ocean benthic organisms raises several methodological challenges. Species presence datasets are often aggregated in time and space nearby research stations or along main sailing routes. Data are often limited in number to correctly describe species occupied space and physiology. Finally, environmental datasets are not precise enough to accurately represent the complexity of marine habitats. Can we thus generate performant and accurate models at the scale of the Southern Ocean ?What are the limits of such approaches ?How could we improve methods to build more relevant models ?In this PhD thesis, three different model categories have been studied and their performance evaluated. (1) Mechanistic physiological models (Dynamic Energy Budget models, DEB) simulate how the abiotic environment influences individual metabolism and represent the species fundamental niche. (2) Species distribution models (SDMs) predict species distribution probability by studying the relationship between species presences and the environment. They represent the species realised niche. (3) Dispersal lagrangian models predict the drift of propagules in water masses. Results show that physiological models can be developed for marine Southern Ocean species to simulate the metabolic variations in link with the environment and predict population dynamics. However, more data are necessary to highlight detailed physiological contrasts between populations and to accurately evaluate models. Results obtained for SDMs suggest that models generated at the scale of the Southern Ocean and future simulations are not relevant, give, Doctorat en Sciences, info:eu-repo/semantics/nonPublished

Mixoplankton are protist plankton that are capable of phototrophy and phagotrophy. These organismsare increasingly recognised not just as freaks of nature, but as a substantial part of marineplankton. Most existing plankton models still assume a strict dichotomy between phototrophsand heterotrophs. Few models consider mixoplanktonic activity as a synergism of the two trophicmodes. Many different mixoplankton functional types exist on a gradient between heterotrophy andphototrophy. The cryptophyte (Teleaulax)-Mesodinium-Dinophysis (TMD) complex is a specificpredator-prey interaction of different types of mixoplankton and a good example of the complexityof mixoplankton interaction and trophodynamics. The specialist non-constitutive mixoplankton(SNCM) Mesodinium acquires its chloroplasts strictly from a specific constitutive mixoplankton(CM) cryptophyte, while the harmful algal bloom (HAB) species Dinophysis acquires its third-handchloroplasts exclusively from Mesodinium.The generic NPZ-style protist model developed here shows that mixoplankton displays dynamicsthat are distinctly different from strict heterotrophs and autotrophs in terms of growth and theway they shape their environment. In addition, there is a clear niche separation between differentmixoplankton types (general non-constitutive mixoplankton (GNCM), SNCM and CM) according tonutrient, prey and light resource availabilities indicating a niche separation of each type. Thus,considering the different mixoplankton functional types in specialised multi-organism relationshipsas they are found in the TMD-complex may be important for their understanding and accurateprediction of growth and biomass development. Currently, none of the many models of Dinophysiscapture the biological dependencies. Results from a nitrogen-based TMD model suggest thatthe timing and quantity of prey availability is crucial for the bloom dynamics of Mesodinium andDinophysis. Some CMs may only feed when phosphate is the limiting nutrient, Le mixoplancton inclut les protistes planctoniques capables de phototrophie et de phagotrophie.Ces organismes sont de plus en plus reconnus comme une partie importante du plancton marin.Toutefois, la plupart des modèles mathématiques planctoniques existants supposent encoreune stricte dichotomie entre les organismes phototrophes et hétérotrophes et peu de modèlesconsidèrent l’activité mixoplanctonique comme une synergie entre les deux modes trophiques.De nombreux types fonctionnels mixoplanctoniques différents existent dans un gradient entrel’hétérotrophie et la phototrophie. Le complexe cryptophyte (Teleaulax)-Mesodinium-Dinophysis(TMD) est une interaction prédateur-proie spécifique entre différents types de mixoplancton et unbon exemple de la complexité des interactions et des relations trophodynamiques du mixoplancton.Mesodinium, mixoplancton spécialiste non constitutif (SNCM), ne peut acquérir ses chloroplastesque de cryptophytes (mixoplancton constitutif (CM)) spécifiques (tel que Teleaulax), tandis quel’espèce Dinophysis, responsable d’efflorescences algales nuisibles, acquiert ses chloroplastesexclusivement de Mesodinium. Le modèle générique de protistes, de type NPZ, développé dansce travail montre que le mixoplancton présente une dynamique nettement différente de celle deshétérotrophes et autotrophes strictes en termes de croissance et de la façon dont ils façonnentleur environnement. En outre, il existe une séparation de niches claire entre les différents typesde mixoplancton (mixoplancton généraliste non-constitutif (GNCM), SNCM et CM) en fonction dela disponibilité en lumière, en nutriments et en proies. En conséquence, la prise en compte desdifférents types fonctionnels du mixoplancton dans des relations multi-organismes spécialisées,telles qu’on les trouve dans le complexe TMD, peut être importante pour leur compréhension et laprédiction précise de leur croissance et biomasse. Actuellement, aucun des modèles existants deDinophysis ne rend compte de ces, Doctorat en Sciences agronomiques et ingénierie biologique, info:eu-repo/semantics/nonPublished

n a rapidly changing world, we need to know which areas warrant protection from current and forthcoming threats. This is hard to do objectively in the vast Southern Ocean. However, identifying where predators go also tells us where their prey can be found. If multiple predator species and their diverse prey are found in the same place, then this indicates an area of high ecological significance. We assembled Southern Ocean predator tracking data to produce a database of over 4000 individual animal tracks from 17 species. Statistical spatial models used these data to project the at-sea movements for all known colonies of each predator species across the entire Southern Ocean. These projections were combined across all species to provide an integrated map of those areas important to many different predators. These areas of ecological significance were scattered around the Antarctic continental shelf and in two oceanic regions, one extending from the Antarctic Peninsula into the Scotia Arc, and another surrounding the sub-Antarctic islands in the Southern Indian Ocean. Existing and proposed marine protected areas (MPAs) are mostly within these important habitats, suggesting they are currently in the right places. Yet, when using IPCC climate model projections to account for how areas of important habitat are likely to move by 2100, the same MPAs may not remain perfectly aligned with important predator habitats. Dynamic MPAs are therefore needed to ensure continued protection of Southern Ocean ecosystems and their resources in the face of growing demand by the current and future generations.

Southern Ocean ecosystems are under pressure from resource exploitation and climate change. Mitigation requires the identification and protection of Areas of Ecological Significance (AESs), which have so far not been determined at the ocean-basin scale. Here, using assemblage-level tracking of marine predators, we identify AESs for this globally important region and assess current threats and protection levels. Integration of more than 4,000 tracks from 17 bird and mammal species reveals AESs around sub- Antarctic islands in the Atlantic and Indian Oceans and over the Antarctic continental shelf. Fishing pressure is disproportionately concentrated inside AESs, and climate change over the next century is predicted to impose pressure on these areas, particularly around the Antarctic continent. At present, 7.1% of the ocean south of 40°S is under formal protection, including 29% of the total AESs. The establishment and regular revision of networks of protection that encompass AESs are needed to provide long-term mitigation of growing pressures on Southern Ocean ecosystems.

Studying the influence of changing environmental conditions on Antarctic marine benthic invertebrates is strongly constrained by limited access to the region, which poses difficulties to performing long-term experimental studies. Ecological modelling has been increasingly used as a potential alternative to assess the impact of such changes on species distribution or physiological performance.

A founding principle of the Antarctic Treaty is that, in the interests of all humankind, Antarctica should continue to be used exclusively for peaceful purposes and should not become the scene or object of international discord. From many standpoints, Antarctica is considered as a sanctuary, and plays a pivotal role in the global system. From an ecological point of view, Antarctica and the surrounding Southern Ocean harbor exceptional levels of biodiversity. Its ecosystems are, however, facing rapid climatic and environmental changes, and the scientific community, embodied by the Scientific Committee on Antarctic Research (SCAR), have identified the urgent need to understand the potential responses of these ecosystems. Such questions are extremely complex, as biodiversity, here defined as “the variability among living organisms from all sources, including inter alia, terrestrial, marine and other aquatic ecosystems and the ecological complexes of which they are part; this includes diversity within species, between species and of ecosystems” (Convention on Biological Diversity, 1992), can vary at many different spatio-temporal scales and levels of biological organization, from molecules to entire ecosystems.

Significant environmental changes have already been documented in the Southern Ocean (e.g. sea water temperature increase and salinity drop) but its marine life is still incompletely known given the heterogeneous nature of biogeographic data. However, to establish sustainable conservation areas, understanding species and communities distribution patterns is critical. For this purpose, the ecoregionalization approach can prove useful by identifying spatially explicit and well-delimited regions of common species composition and environmental settings. Such regions are expected to have similar biotic responses to environmental changes and can be used to define priorities for the designation of Marine Protected Areas. In the present work, a benthic ecoregionalization of the Southern Ocean is proposed based on echinoids distribution data and abiotic environmental parameters. Echinoids are widely distributed in the Southern Ocean, they are taxonomically and ecologically well diversified and documented. Given the heterogeneity of the sampling effort, predictive spatial models were produced to fill the gaps in between species distribution data. A first procedure was developed using Gaussian Mixture Models (GMM) to combine individual species models into ecoregions. A second, integrative procedure was implemented using the Generalized Dissimilarity Models (GDM) to model and assemble species distributions. Both procedures were compared to propose benthic ecoregions at the scale of the entire Southern Ocean., SCOPUS: ar.j, info:eu-repo/semantics/published

The Kerguelen Islands are part of the French Southern Territories, located at the limit of the Indian and Southern oceans. They are highly impacted by climate change, and coastal marine areas are particularly at risk. Assessing the responses of species and populations to environmental change is challenging in such areas for which ecological modelling can constitute a helpful approach. In the present work, a DEB-IBM model (Dynamic Energy Budget – Individual-Based Model) was generated to simulate and predict population dynamics in an endemic and common benthic species of shallow marine habitats of the Kerguelen Islands, the sea urchin Abatus cordatus. The model relies on a dynamic energy budget model (DEB) developed at the individual level. Upscaled to an individual-based population model (IBM), it then enables to model population dynamics through time as a result of individual physiological responses to environmental variations. The model was successfully built for a reference site to simulate the response of populations to variations in food resources and temperature. Then, it was implemented to model population dynamics at other sites and for the different IPCC climate change scenarios RCP 2.6 and 8.5. Under present-day conditions, models predict a more determinant effect of food resources on population densities, and on juvenile densities in particular, relative to temperature. In contrast, simulations predict a sharp decline in population densities under conditions of IPCC scenarios RCP 2.6 and RCP 8.5 with a determinant effect of water warming leading to the extinction of most vulnerable populations after a 30-year simulation time due to high mortality levels associated with peaks of high temperatures. Such a dynamic model is here applied for the first time to a Southern Ocean benthic and brooding species and offers interesting prospects for Antarctic and sub-Antarctic biodiversity research. It could constitute a useful tool to support conservation studies in th, SCOPUS: ar.j, info:eu-repo/semantics/published

Benthic life in the Southern Ocean (SO) features unique life history traits and species assemblages, but the origin and evolution of many of these taxonomic groups is still unclear. Sea stars (Asteroidea) are a diversified and abundant component of benthic ecosystems in the SO, in which they can play key ecological roles. Former studies suggest that the diversity of the entire class is still poorly known and underestimated, hampering the assessment of the origin and evolution of the class in the SO. In the present study, we analyse spatial patterns of SO sea star diversity using an occurrence database of ~14,000 entries. The biogeographic analysis is coupled with the exploration of an extensive molecular phylogeny based on over 4,400 specimen sequences to inform, support and/or question the observed diversity patterns. We show that the current taxonomy of SO asteroids needs revision and that their diversity has generally been overlooked and misinterpreted. Molecular results highlight the recent diversification of most studied taxa, at genus and species levels, which supports an evolutionary scenario referring to successive invasion and exchange events between the SO and adjacent regions, and clade diversification during periods of rapid environmental changes driven by the succession of glacial cycles. Our work advocates for employing, and endorsing the use of extensive genetic barcode libraries for biodiversity studies., SCOPUS: ar.j, info:eu-repo/semantics/published

Species distribution modelling (SDM) has been increasingly applied to Southern Ocean case studies over the past decades, to map the distribution of species and highlight environmental settings driving species distribution. Predictive models have been commonly used for conservation purposes and supporting the delineation of marine protected areas, but model predictions are rarely associated with extrapolation uncertainty maps. In this study, we used the Multivariate Environmental Similarity Surface (MESS) index to quantify model uncertainty associated to extrapolation. Considering the reference dataset of environmental conditions for which species presence-only records are modelled, extrapolation corresponds to the part of the projection area for which one environmental value at least falls outside of the reference dataset. Six abundant and common sea star species of marine benthic communities of the Southern Ocean were used as case studies. Results show that up to 78% of the projection area is extrapolation, i.e. beyond conditions used for model calibration. Restricting the projection space by the known species ecological requirements (e.g. maximal depth, upper temperature tolerance) and increasing the size of presence datasets were proved efficient to reduce the proportion of extrapolation areas. We estimate that multiplying sampling effort by 2 or 3-fold should help reduce the proportion of extrapolation areas down to 10% in the six studied species. Considering the unexpectedly high levels of extrapolation uncertainty measured in SDM predictions, we strongly recommend that studies report information related to the level of extrapolation. Waiting for improved datasets, adapting modelling methods and providing such uncertainy information in distribution modelling studies are a necessity to accurately interpret model outputs and their reliability., SCOPUS: ar.j, info:eu-repo/semantics/published

An integrative approach is crucial in discrimination of species, especially for taxa that are difficult to identify based on morphological characters. In this study, we combine genetics and morphology to assess the diversity of Pterasteridae, a sea star family diversified in deep-sea and polar environments. Because of their derived anatomy and the frequent loss of characters during preservation, Pterasteridae are a suitable case for an integrative study. The molecular identification of 191 specimens (mostly from the Southern Ocean) suggests 26–33 species in three genera (Diplopteraster, Hymenaster and Pteraster), which match the morphological identification in 54–62% of cases. The mismatches are either different molecular units that are morphologically indistinguishable (e.g. Pteraster stellifer units 2 and 4) or, conversely, nominal species that are genetically identical (e.g. Hymenaster coccinatus/densus/praecoquis). Several species are shared between the Northern and Southern Hemispheres (e.g. Pteraster jordani/affinis). In conclusion, the taxonomic status of some groups is confirmed, but for others we find the need to re-evaluate the taxonomy at both genus and species levels. This work significantly increases the DNA barcode library of the Southern Ocean species and merges taxonomic information into an identification key that could become a baseline for future studies (pterasteridae-so.identificationkey.org)., SCOPUS: ar.j, info:eu-repo/semantics/published

Species distribution models (SDMs) are increasingly used in ecological and biogeographic studies by Antarctic biologists, including for conservation and management purposes. During the modelling process, model calibration is a critical step to ensure model reliability and robustness, especially in the case of SDMs, for which the number of selected environmental descriptors and their collinearity is a recurring issue. Boosted regression trees (BRT) was previously considered as one of the best modelling approach to correct for this type of bias. In the present study, we test the performance of BRT in modelling the distribution of Southern Ocean species using different numbers of environmental descriptors, either collinear or not. Models are generated for six sea star species with contrasting ecological niches and wide distribution ranges over the entire Southern Ocean. For the six studied species, overall modelling performance is not affected by the number of environmental descriptors used to generate models, BRT using the most informative descriptors and minimizing model overfitting. However, removing collinear descriptors also helps reduce model overfitting. Our results confirm that BRTs may perform well and are relevant to deal with complex and redundant environmental information for Antarctic biodiversity distribution studies. Selecting a limited number of non-collinear descriptors before modelling may generate simpler models and facilitate their interpretation. The modelled distributions do not differ noticeably between the different species despite contrasting species ecological niches. This unexpected result stresses important limitations in using SDMs for broad scale spatial studies, based on limited, spatially aggregated data, and low-resolution descriptors., SCOPUS: ar.j, info:eu-repo/semantics/published

The uptake of CO2 by the ocean is causing major changes in its chemistry. These changes are likely to have detrimental effects on many organisms with a severe impact on calcifying species. With future OA, marine organisms will be submitted to hypercapnia (increased pCO2) and acidosis (decreased pH). Skeleton production and maintenance could be impacted due to the increased energetic cost to calcify in less favourable conditions and direct corrosive effect of undersaturated seawater resulting in dissolution of calcium-carbonate unprotected structures. Postmetamorphic echinoderms (juveniles and adults) endoskeleton is made of high magnesium-calcite, one of the most soluble form of CaCO3. Because of their low metabolism and their heavily calcified skeleton, echinoderms were designated as species particularly at risk under OA. However, the effects of OA on calcification and on skeleton maintenance vary among closely related taxa. Hypotheses explaining these contrasted tolerance to OA were stated: (1) regulation of the acid-base balance, which occurs in some echinoderms taxa and not others, plays a major role; (2) populations living in highly fluctuating habitats are adapted or selected, which may confer them a better resistance to acidified conditions. The goal of this thesis was to evaluate these hypotheses using a comparative approach in asteroids (two species) and regular euechinoids (five species). The chosen species differ by their ability to regulate their acid-base physiology and by the amplitude of fluctuations in their habitats. The impacts of OA on corrosion and mechanical properties of their skeletal elements as well as, in selected species, the expression of biomineralization-related genes were investigated. All samples were obtained from individuals exposed to acidified conditions during long-term aquarium experiments or in situ exposures (CO2 vents).Bending and compression mechanical tests analysed by Weibull statistics and expression of biomineralization, Depuis la Révolution Industrielle, la concentration en dioxyde de carbone (CO2) atmosphérique augmente continuellement. Les océans absorbent en partie ce CO2, ce qui induit une diminution de la concentration en ions carbonate ainsi qu’une augmentation de la concentration en protons, processus connus sous le nom d’acidification des océans (AO). Ces changements sont susceptibles d'avoir des effets néfastes sur une variété d'organismes marins qui seront soumis à l’hypercapnie (augmentation de la pCO2) et à l’acidose (diminution du pH). De plus, la calcification fait l’objet d’une attention particulière étant donné la remontée des horizons de saturation en carbonate de calcium dans les océans. La production ainsi que le maintien du squelette pourraient être limités en raison de l'augmentation du coût énergétique de la calcification dans des conditions moins favorables. Cependant, les effets de l’AO sur la calcification et sur le maintien du squelette varient selon les taxons voire au sein d’un même taxon. Des hypothèses ont donc été émises quant aux mécanismes sous-tendant ces différences. Une meilleure résistance face à l’AO pourrait aller de pair avec (1) une capacité à réguler le pH des fluides extracellulaires, (2) une préadaptation due à l’occupation d’habitats fortement fluctuants.Les échinodermes post-métamorphiques (juvéniles et adultes), espèces marines clés, possèdent une biologie générale assez semblable et sont constitués d’un endosquelette composé de calcite hautement magnésienne, une des formes les plus solubles de carbonate de calcium. En raison de leur faible métabolisme et de leur squelette fortement calcifié, les échinodermes ont été désignés comme des espèces particulièrement vulnérables sous l’effet de l’AO. Toutefois, de récentes études montrent que le squelette de certaines espèces d’échinodermes au stade adulte n’est pas affecté lorsque les organismes sont soumis à de bas pH d’eau de mer. L'objectif principal de la présente thèse était d’évaluer l, Doctorat en Sciences, info:eu-repo/semantics/nonPublished

The Southern Ocean (SO) is among the regions on Earth that are undergoing regionally the fastest environmental changes. The unique ecological features of its marine life make it particularly vulnerable to the multiple effects of climate change. A network of Marine Protected Areas (MPAs) has started to be implemented in the SO to protect marine ecosystems. However, considering future predictions of the Intergovernmental Panel on Climate Change (IPCC), the relevance of current, static, MPAs may be questioned under future scenarios. In this context, the ecoregionalization approach can prove promising in identifying well-delimited regions of common species composition and environmental settings. These so-called ecoregions are expected to show similar biotic responses to environmental changes and can be used to define priority areas for the designation of new MPAs and the update of their current delimitation. In the present work, a benthic ecoregionalization of the entire SO is proposed for the first time based on abiotic environmental parameters and the distribution of echinoid fauna, a diversified and common member of Antarctic benthic ecosystems. A novel two-step approach was developed combining species distribution modeling with Random Forest and Gaussian Mixture modeling from species probabilities to define current ecoregions and predict future ecoregions under IPCC scenarios RCP 4.5 and 8.5. The ecological representativity of current and proposed MPAs of the SO is discussed with regard to the modeled benthic ecoregions. In all, 12 benthic ecoregions were determined under present conditions, they are representative of major biogeographic patterns already described. Our results show that the most dramatic changes can be expected along the Antarctic Peninsula, in East Antarctica and the sub-Antarctic islands under both IPCC scenarios. Our results advocate for a dynamic definition of MPAs, they also argue for improving the representativity of Antarctic ecoregions in pr, SCOPUS: ar.j, info:eu-repo/semantics/published