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In the Kerguelen Islands, the multiple effects of climate change are expected to impact coastal marine habitats. Species distribution models (SDM) can represent a convenient tool to predict the biogeographic response of species to climate change but biotic interactions are not considered in these models. Nevertheless, new species interactions can emerge in communities exposed to environmental changes and the structure of biotic interactions is directly related to the potential resilience of ecosystems. Trophic interaction studies can help predict species vulnerability to environmental changes using carbon (δ13C) and nitrogen (δ15N) stable isotope ratios to generate trophic models. Using new available data inputs, we generated robust SDM and trophic interaction models to assess the potential response and sensitivity of three echinoid species to future worst-case scenarios of environmental change in the Kerguelen Plateau region. The two modelling approaches provide contrasting insights into the potential responses of each species to future environmental changes with both approaches identifying Abatus cordatus to be particularly vulnerable due to its narrow ecological niche and endemism to near-shore areas. Coupling insights gained from trophic niche ecology with species distribution modelling represents a promising approach that can improve our understanding and ability to predict the potential responses of species to future habitat changes.

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ContextEnvironmental changes are now vastly documented for large areas of the Southern Ocean. The response of marine organisms and ecosystem processes to these changes are still not well understood. In this framework, insights in resilience, thresholds and tipping points for species, communities and ecosystems are of paramount importance. Addressing these endpoints is however highly complex, and requires robust, interdisciplinary and collaborative research networks to progressively reach a holistic understanding.By design, the vERSO project was intended to forge ahead and identify key areas of research in this respect, and in line with the SCAR priorities. Building on the experience gathered by its long-term partners and taking advantage of the overlap period with another BELSPO-funded project (rECTO), the vERSO developments were intentionally novel and ambitious (in experimental, field and integration facets).ObjectivesThe goal of the vERSO project was to assess the impact of the main stressors driven by global change on benthic Antarctic ecosystems using an integrated multiscale approach including different representative size classes of the benthos. Two principal regions with current contrasting responses to global change have been considered, namely the Western Antarctic Peninsula and the East Antarctic. To reach this goal, researches on connectivity and adaptation, trophic ecology and sensitivity and resilience were conducted by all partners and integrated using state of the art modelling techniques.Results and conclusionsvERSO has globally reached its proposed objectives, paving the way for its sister project, rECTO. vERSO members have participated in 11 expeditions to the Antarctic. Specific efforts were devoted to involving several consortium partners in the fieldwork to optimize the exchange of know-how and crosslinkages using the obtained results. This is reflected in the authorships of the papers and datasets published so far. Most of the experimental wor, info:eu-repo/semantics/published

L’augmentation de la concentration en CO2 dans l’atmosphère, principalement due auxactivités anthropiques, induit une augmentation de la pCO2 dans les eaux de surface océaniques quiengendre des modifications substantielles au sein du système des carbonates, un phénomène connusous le nom d’acidification des océans. Les échinides seraient particulièrement sensibles àl’acidification des océans dû au fait que ce sont des organismes osmoconformes et qu’ils édifient unsquelette constitué de calcite magnésienne, une des formes les plus solubles de carbonate decalcium. Les cidaroïdes, un clade basal d’échinides, possèdent une physiologie acide-base particulièrepar rapport à celle des autres échinides, les euéchinoïdes. Ils possèdent un pH extracellulaire bas,une pCO2 extracellulaire élevée et une alcalinité similaire à celle de l’eau de mer ;leur liquidecoelomique est donc sous-saturé par rapport à la calcite magnésienne. Ils édifient des piquantsprimaires constitués d’une couche de minéral externe, le cortex, qui, à maturité, est dépourvud’épiderme, laissant le minéral en contact direct avec l’eau de mer. La couche corticale est ensuitecolonisée par un biofilm et des épibiontes. Etonnamment, les cidaroïdes ont déjà survécu à la crised’acidification survenue au Permien-Trias et, à l’heure actuelle, certains membres de ce clade viventsous l’horizon de saturation du minéral qui forme leur squelette. Les cidaroïdes sont donc un modèleintéressant pour l’étude des mécanismes permettant aux organismes marins de faire face àl’acidification des océans. L’objectif de la présente thèse est d’étudier les caractéristiquesmorphologiques et physiologiques qui permettent aux cidaroïdes de résister aux faibles valeurs depH de l’eau de mer. Différents aspects seront abordés :(1) l’impact de l’acidification des océans surla dissolution et les propriétés mécaniques du squelette des cidaroïdes ;(2) la morphogenèse et lespropriétés du cortex en relation avec sa résistance à l’acidification des, Doctorat en Sciences, info:eu-repo/semantics/nonPublished

Evolution and population genetic structure of marine species across the Caribbean Sea are shaped by two complex factors: the geological history and the present pattern of marine currents. Characterizing and comparing the genetic structures of codistributed species, such as host–parasite associations, allow discriminating the relative importance of environmental factors and life history traits that influenced gene flow and demographic events. Using microsatellite and Cytochrome Oxidase I markers, we investigated if a host–parasite pair (the heart urchin Meoma ventricosa and its parasitic pea crab Dissodactylus primitivus) exhibits comparable population genetic structures in the Caribbean Sea and how the observed patterns match connectivity regions from predictive models and other taxa. Highly contrasting patterns were found: the host showed genetic homogeneity across the whole studied area, whereas the parasite displayed significant differentiation at regional and local scales. The genetic diversity of the parasitic crabs (both in microsatellites and COI) was distributed in two main groups, Panama–Jamaica–St Croix on the one hand, and the South-Eastern Caribbean on the other. At a smaller geographical scale, Panamanian and Jamaican parasite populations were genetically more similar, while more genetic differentiation was found within the Lesser Antilles. Both species showed a signature of population expansion during the Quaternary. Some results match predictive models or data from previous studies (e.g. the Western-Eastern dichotomy in the parasite) while others do not (e.g. genetic differentiation within the Lesser Antilles). The sharp dissimilarity of genetic structure of these codistributed species outlines the importance of population expansion events and/or contrasted patterns of gene flow. This might be linked to differences in several life history traits such as fecundity (higher for the host), swimming capacity of larval stages (higher for the parasite), and, SCOPUS: ar.j, info:eu-repo/semantics/published

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In some long-living symbiotic species, movements between hosts are not limited to offspring since adult parasites can move from one individual host to another one. Host-switching may be driven by different parameters such as (1) mating strategies of symbionts, (2) foraging for resources or (3) avoiding overcrowded or diseased/dead host. Symbiotic marine crustaceans are suitable models to understand what underlies host-switching behavior. In this study, we investigated host desertion by the parasitic pea crab Dissodactylus primitivus associated with the echinoid host Meoma ventricosa. Mark-recapture field experiments, during which crabs were almost always found on their host in heterosexual combinations, suggest that host desertion occurs less frequently when 2 crabs (compared to 3) share the same host. During laboratory experiments with high crab density, the proportion of crabs leaving an echinoid was low when the 2 genders of crabs were present on the host, compared to 1 gender only (males or females). This suggests that host desertion is mostly driven by intersex selection and the search for a mate and, to a lesser extent, by competition between crabs. However, both field and laboratory experiments showed evidence that when they switch host, most crabs remained for a while in the sediment underneath their host. We propose that this behavior, associated with the aggregative behavior of their hosts, would allow the crabs to solve the trade-off between staying on their hosts (therefore suffering overcrowding and sub-optimal mate search) and moving too far from the host (therefore suffering loss of food source and high predation risk)., SCOPUS: ar.j, info:eu-repo/semantics/published

The Southern Ocean ecosystem at the Antarctic Peninsula has steep natural environmental gradients, e.g. in terms of water masses and ice cover, and experiences regional above global average climate change. An ecological macroepibenthic survey was conducted in three ecoregions in the north-western Weddell Sea, on the continental shelf of the Antarctic Peninsula in the Bransfield Strait and on the shelf of the South Shetland Islands in the Drake Passage, defined by their environmental envelop. The aim was to improve the so far poor knowledge of the structure of this component of the Southern Ocean ecosystem and its ecological driving forces. It can also provide a baseline to assess the impact of ongoing climate change to the benthic diversity, functioning and ecosystem services. Different intermediate-scaled topographic features such as canyon systems including the corresponding topographically defined habitats ‘bank’, ‘upper slope’, ‘slope’ and ‘canyon/deep’ were sampled. In addition, the physical and biological environmental factors such as sea-ice cover, chlorophyll-a concentration, small-scale bottom topography and water masses were analysed. Catches by Agassiz trawl showed high among-station variability in biomass of 96 higher systematic groups including ecological key taxa. Large-scale patterns separating the three ecoregions from each other could be correlated with the two environmental factors, sea-ice and depth. Attribution to habitats only poorly explained benthic composition, and small-scale bottom topography did not explain such patterns at all. The large-scale factors, sea-ice and depth, might have caused large-scale differences in pelagic benthic coupling, whilst small-scale variability, also affecting larger scales, seemed to be predominantly driven by unknown physical drivers or biological interactions., SCOPUS: ar.j, info:eu-repo/semantics/published

Echinoids are common members of Antarctic zoobenthos, and different groups can show important trophic diversity. As part of the ANT-XXIX/3 cruise of RV Polarstern, trophic plasticity of sea urchins was studied in three neighbouring regions (Drake Passage, Bransfield Strait and Weddell Sea) featuring several depth-related habitats offering different trophic environments to benthic consumers. Three families with contrasting feeding habits (Cidaridae, Echinidae and Schizasteridae) were studied. Gut content examination and stable isotopes ratios of C and N suggest that each of the studied families showed a different response to variation in environmental and food conditions. Schizasteridae trophic plasticity was low, and these sea urchins were bulk sediment feeders relying on sediment-associated organic matter in all regions and/or depth-related habitats. Cidaridae consumed the most animal-derived material. Their diet varied according to the considered area, as sea urchins from Bransfield Strait relied mostly on living and/or dead animal material, while specimens from Weddell Sea fed on a mixture of dead animal material and other detritus. Echinidae also showed important trophic plasticity. They fed on various detrital items in Bransfield Strait, and selectivity of ingested material varied across depth-related habitats. In Weddell Sea, stable isotopes revealed that they mostly relied on highly 13C-enriched food items, presumably microbially reworked benthic detritus. The differences in adaptive strategies could lead to family-specific responses of Antarctic echinoids to environmental and food-related changes., SCOPUS: ar.j, info:eu-repo/semantics/published

Increasing atmospheric carbon dioxide concentration alters the chemistry of the oceans towards more acidic conditions. Polar oceans are particularly affected due to their low temperature, low carbonate content and mixing patterns, for instance upwellings. Calcifying organisms are expected to be highly impacted by the decrease in the oceans' pH and carbonate ions concentration. In particular, sea urchins, members of the phylum Echinodermata, are hypothesized to be at risk due to their high-magnesium calcite skeleton. However, tolerance to ocean acidification in metazoans is first linked to acid–base regulation capacities of the extracellular fluids. No information on this is available to date for Antarctic echinoderms and inference from temperate and tropical studies needs support. In this study, we investigated the acid–base status of 9 species of sea urchins (3 cidaroids, 2 regular euechinoids and 4 irregular echinoids). It appears that Antarctic regular euechinoids seem equipped with similar acid–base regulation systems as tropical and temperate regular euechinoids but could rely on more passive ion transfer systems, minimizing energy requirements. Cidaroids have an acid–base status similar to that of tropical cidaroids. Therefore Antarctic cidaroids will most probably not be affected by decreasing seawater pH, the pH drop linked to ocean acidification being negligible in comparison of the naturally low pH of the coelomic fluid. Irregular echinoids might not suffer from reduced seawater pH if acidosis of the coelomic fluid pH does not occur but more data on their acid–base regulation are needed. Combining these results with the resilience of Antarctic sea urchin larvae strongly suggests that these organisms might not be the expected victims of ocean acidification. However, data on the impact of other global stressors such as temperature and of the combination of the different stressors needs to be acquired to assess the sensitivity of these organisms to global cha, SCOPUS: ar.j, FLWIN, info:eu-repo/semantics/published