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Understanding the factors that sculpt fish gut microbiome is challenging, especially in natural populations characterized by high environmental and host genomic complexity. Yet, closely related hosts are valuable models for deciphering the contribution of host evolutionary history to microbiome assembly, through the underscoring of phylosymbiosis and co-phylogeny patterns. Here, we hypothesized that the recent allopatric speciation ofHarpagiferacross the Southern Ocean (1.2–0.8 Myr) will promote the detection of robust phylogenetic congruence between the host and its microbiome.We characterized the gut mucosa microbiome of 77 individuals from four field-collected species of the plunderfishHarpagifer(Teleostei, Notothenioidei), distributed across three biogeographic regions of the Southern Ocean. We found that seawater physicochemical properties, host phylogeny and geography collectively explained 35% of the variation in bacterial community composition inHarpagifergut mucosa. The core microbiome ofHarpagiferspp. gut mucosa was characterized by a low diversity, mostly driven by selective processes, and dominated by a singleAliivibriotaxon detected in more than 80% of the individuals. Almost half of the core microbiome taxa, includingAliivibrio, harbored co-phylogeny signal at microdiversity resolution withHarpagiferphylogeny. This suggests an intimate symbiotic relationship and a shared evolutionary history withHarpagifer.The robust phylosymbiosis signal emphasizes the relevance of theHarpagifermodel to understanding the contribution of fish evolutionary history to the gut microbiome assembly. We propose that the recent allopatric speciation ofHarpagiferacross the Southern Ocean may have generated the diversification ofAliivibriointo patterns recapitulating the host phylogeny.ImportanceAlthough challenging to detect in wild populations, phylogenetic congruence between marine fish and its microbiome is critical, as it allows highlighting potential intimate associations between the hosts and ecologically relevant microbial symbionts.Through a natural system consisting of closely related fish species of the Southern Ocean, our study provides foundational information about the contribution of host evolutionary trajectory on gut microbiome assembly, that represents an important yet underappreciated driver of the global marine fish holobiont. Notably, we unveiled striking evidence of co-diversification betweenHarpagiferand its microbiome, demonstrating both phylosymbiosis of gut bacterial communities, and co-phylogeny of specific bacterial symbionts, in patterns that mirror the host diversification. Considering the increasing threats that fish species are facing in the Southern Ocean, understanding how the host evolutionary history could drive its microbial symbiont diversification represents a major challenge to better predict the consequences of environmental disturbances on microbiome and host fitness.

19 pages, 3 figures, 2 tables, supplementary information https://doi.org/10.1007/s10661-023-11066-3.-- Data availability: All genetic data, as well as photographs of voucher specimens, can be publicly accessed and downloaded on boldsystems.org, under the “INTGS” project (Intertidal fauna from the Gerlache Strait). Occurrence data can be found on the Global Biodiversity Information Facility (GBIF, B121 dataset) using the following link: https://doi.org/10.15468/56bv6z. Additional data, tables and figures are also provided as Supplementary materials. The specimens used in this study are hosted at the Université Libre de Bruxelles (ULB, Brussels, Belgium) – Laboratoire de Biologie Marine, The underexplored intertidal ecosystems of Antarctica are facing rapid changes in important environmental factors. Associated with temperature increase, reduction in coastal ice will soon expose new ice-free areas that will be colonized by local or distant biota. To enable detection of future changes in faunal composition, a biodiversity baseline is urgently required. Here, we evaluated intertidal faunal diversity at 13 locations around the Gerlache Strait (western Antarctic Peninsula), using a combination of a quadrat approach, morphological identification and genetic characterization. Our data highlight a community structure comprising four generally distributed and highly abundant species (the flatworm Obrimoposthia wandeli, the bivalve Kidderia subquadrata, and the gastropods Laevilitorina umbilicata and Laevilitorina caliginosa) as well as 79 rarer and less widely encountered species. The most abundant species thrive in the intertidal zone due to their ability to either survive overwinter in situ or to rapidly colonize this zone when conditions allow. In addition, we confirmed the presence of multiple trophic levels at nearly all locations, suggesting that complex inter-specific interactions occur within these communities. Diversity indices contrasted between sampling locations (from 3 to 32 species) and multivariate approaches identified three main groups. This confirms the importance of environmental heterogeneity in shaping diversity patterns within the investigated area. Finally, we provide the first genetic and photographic baseline of the Antarctic intertidal fauna (106 sequences, 137 macrophotographs), as well as preliminary insights on the biogeography of several species. Taken together, these results provide a timely catalyst to assess the diversity and to inform studies of the potential resilience of these intertidal communities, This work was supported by the ‘Refugia and Ecosystem Tolerance in the Southern Ocean’ project (RECTO; BR/154/A1/RECTO) funded by the ‘Belgian Science Policy Office’ (BELSPO). [...] The B121 expedition was funded by the Federation Wallonia-Brussels, the Fund for Scientific Research (FNRS), the Research Foundation – Flanders (FWO), the Leopold 3 Fund for the exploration and conservation of Nature and the Royal Belgian Society for Zoology. David Bauman was funded by the Belgian American Educational Foundation (BAEF) and the European Union's Horizon 2020 research and innovation programme under the Marie Skłodowska-Curie grant agreement No. 895799. Henrik Christiansen was funded by the BELSPO project COPE (B2/191/P1/COPE). Blanca Figuerola received funding from the Beatriu de Pinós program (2019-BP-00183), funded by the Secretary of Universities and Research (Government of Catalonia) and the European Union's Horizon 2020 program under the Marie Skłodowska-Curie grant agreement No. 801370. Peter Convey was supported by NERC core funding to the BAS ‘Biodiversity, Evolution and Adaptation’ Team, With the institutional support of the ‘Severo Ochoa Centre of Excellence’ accreditation (CEX2019-000928-S)

The Antarctic marine environment, although rich in life, is predicted to experience rapid and significant effects from climate change. Despite a revolution in the approaches used to document biodiversity, less than one percent of Antarctic marine invertebrates are represented by DNA barcodes and we are at risk of losing biodiversity before discovery. The ease of sequencing mitochondrial DNA barcodes has promoted this relatively ‘universal’ species identification system across most metazoan phyla and barcode datasets are currently readily used for exploring questions of species-level taxonomy. Here we present the most well-sampled phylogeny of the direct-developing, Southern Ocean nudibranch mollusc, Doris kerguelenensis to date. This study sampled over 1000 new Doris kerguelenensis specimens spanning the Southern Ocean and sequenced the mitochondrial COI gene. Results of a maximum likelihood phylogeny and multiple subsequent species delimitation analyses identified 27 new species in this complex (now 59 in total). Using rarefaction techniques, we infer more species are yet to be discovered. Some species were only collected from southern South America or the sub-Antarctic islands, while at least four species were found spanning the Polar Front. This is contrary to dispersal predictions for species without a larval stage such as Doris kerguelenensis. Our work demonstrates the value of increasing geographic scope in sampling and highlights what could be lost given the current global biodiversity crisis.

Aim In the context of intensifying threats of climate change on marine communities, ecological models are widely applied for conservation strategies, though polar studies remain scarce given the limited number of datasets available. Correlative (e.g. species distribution models, SDM) and mechanistic (e.g. dynamic energy budget models, DEB) modelling approaches are usually used independently in studies. Using both approaches in integrative, hybrid models could help to better estimate the species potential ecological niche, as mechanistic and correlative models complement each other very well, giving more insights into species potential response to fast-changing environmental conditions. Location The study focusses on the Baie du Morbihan, a silled basin located in the east of the Kerguelen Islands (sub-Antarctic). Methods A hybrid, correlative-mechanistic model was implemented to predict the response of the endemic sea urchin Abatus cordatus (Verrill, 1876). We compared the performances of classic and integrated approaches to predict A. cordatus distribution according to two dates representing seasonal contrasts. Two integrated approaches were studied and performed by either (1) including the spatial projection of the DEB model as an input layer inside the SDM ('integrated SDM-DEB') or (2) using a Bayesian procedure to use DEB model outputs as priors of the SDM ('integrated Bayesian' approach). Results Results show higher performances of 'integrated Bayesian' approaches to evaluate A. cordatus potential ecological niche compared with 'classic' and 'integrated SDM-DEB' methods. The influence of environmental conditions on model predictions is further captured with these Bayesian procedures and better highlights the environmental influence on the species-predicted distribution. Model performance is good for the different simulations, and uncertainty in predictions is well-highlighted. Main conclusions The good performances of 'integrated Bayesian' approaches to estimate species potential ecological niche opens perspectives for future applications to a broad panel of natural examples, noteworthy for decision-making and conservation management purposes.

17 pages; International audience; Kelp forests dominated by Macrocystis pyrifera are widely distributed in coastal waters from boreal, temperate and subantarctic regions. This widespread distribution may result in regional differences in food web structure and functioning. In temperate northern regions, where most studies on kelp forest benthic food webs have been conducted, kelp grazing is a well-documented phenomenon and can lead to the overgrazing of M. pyrifera by sea urchins when their predators (e.g., sea otters) are absent. In contrast, little is known about their counterparts in subantarctic areas. The present study aimed to reconstruct the benthic food web of a kelp forest dominated by M. pyrifera in a subantarctic environment using stable isotope analysis. Stable carbon (δ13C), nitrogen (δ15N) and sulfur (δ34S) isotope ratios were measured from food sources (macrophytobenthos, suspended particulate organic matter SPOM, and sediment) and consumers (sponges, bivalves, gastropods, sedentary and mobile polychaetes, arthropods and echinoderms) which were sampled in a kelp forest of the Kerguelen archipelago. Mixing models highlighted two interconnected trophic pathways which were either supported by SPOM and resuspended macrophytobenthos detritus (bentho-pelagic), or by live micro/macrophytobenthos (phytobenthos-based). No major prey were highlighted for several consumers, indicating the existence of potential supplementary trophic pathways. No consumer relying primarily on living M. pyrifera was highlighted by the mixing models. The investigated kelp forest is hence a complex ecosystem supporting multiple trophic pathways, and direct consumption of M. pyrifera is limited. Nonetheless, M. pyrifera and other macrophytobenthos species may constitute a pool of detritus supporting several trophic pathways.

The western Antarctic Peninsula is facing rapid environmental changes and many recent publications stress the need to gain new knowledge regarding ecosystems responses to these changes. In the framework of the Belgica 121 expedition, we tested the use of a nimble vessel with a moderate environmental footprint as an approach to tackle the urgent needs of the Southern Ocean research community in terms of knowledge regarding the levels of marine biodiversity in shallow areas and the potential impacts of retreating glaciers on this biodiversity in combination with increasing tourism pressure. We discuss the strengths and drawbacks of using a 75’ (23 m) sailboat in this research framework, as well as its sampling and environmental efficiency. We propose that the scientific community considers this approach to 1) fill specific knowledge gaps and 2) improve the general coherence of the research objectives of the Antarctic scientific community in terms of biodiversity conservation and the image that such conservation conveys to the general public.

23 pages; International audience; The Southern Ocean is undergoing rapid environmental changes that are likely to have a profound impact on marine life, as organisms are adapted to sub-zero temperatures and display specific adaptations to polar conditions. However, species ecological and physiological responses to environmental changes remain poorly understood at large spatial scale owing to sparse observation data. In this context, correlative ecological niche modeling (ENMc) can prove useful. This approach is based on the correlation between species occurrences and environmental parameters to predict the potential species occupied space. However, this approach suffers from a series of limitations amongst which extrapolation and poor transferability performances in space and time. Mechanistic ecological niche modeling (ENMm) is a process-based approach that describes species functional traits in a dynamic environmental context and can therefore represent a complementary tool to understand processes that shape species distribution in a changing environment. In this study, we used both ENMc and ENMm projections to model the distribution of the Antarctic echinoid Sterechinus neumayeri. Both models were projected according to present (2005–2012) and future IPCC scenarios RCP 4.5 and 8.5 for (2050–2099). ENMc and ENMm projections are congruent and predict suitable current conditions for the species on the Antarctic shelf, in the Ross Sea and Prydz Bay areas. Unsuitable conditions are predicted in the northern Kerguelen Plateau and South Campbell Plateau due to observed lower food availability and higher sea water temperatures compared to other areas. In contrast, the two models diverge under future RCP 4.5 and 8.5 scenarios. According to ENMm projections, the species would not be able to grow nor reach sexual maturity over the entire ocean, whereas the Antarctic shelf is still projected as suitable by the ENMc. This study highlights the complementarity and relevance of EMN approaches to model large scale distribution patterns and assess species sensitivity and potential response to future environmental conditions.

18 pages; International audience; 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.

Species inventories are essential to the implementation of conservation policies to mitigate biodiversity loss and maintain ecosystem services and their value to the society. This is particularly topical with respect to climate change and direct anthropogenic effects on Antarctic biodiversity, with the identification of the most at-risk taxa and geographical areas becoming a priority. Identification tools are often neglected and considered helpful only for taxonomists. However, the development of new online information technologies and computer-aided identification tools provides an opportunity to promote them to a wider audience, especially considering the emerging generation of scientists who apply an integrative approach to taxonomy. This paper aims to clarify essential concepts and provide convenient and accessible tools, tips and suggested systems to use and develop knowledge bases (KBs). The software Xper3 was selected as an example of a user-friendly KB management system to give a general overview of existing tools and functionalities through two applications: the 'Antarctic Echinoids' and 'Odontasteridae Southern Ocean (Asteroids)' KBs. We highlight the advantages provided by KBs over more classical tools, and future potential uses are highlighted, including the production of field guides to aid in the compilation of species inventories for biodiversity conservation purposes., 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)., info:eu-repo/semantics/published

20 pages; International audience; 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 proposed MPAs and support current proposals of Conservation of Antarctic Marine Living Resources for the creation of Antarctic MPAs.

The Avilés Canyons System (ACS) is located in the South of the Bay of Biscay (Northern Spain, Cantabrian Sea) and covers a total of 3,390 km2. It is composed of three canyons, reaching the abyssal plain at 4700 m depth. The mixing of diverse water masses generates gyres and upwellings that contribute to the enrichment in nutrient concentration at different depth and favour the settlement of benthic communities. The ACS has been declared Site of Community Importance (SCI: C ESZZ12003) within the Natura 2000 Network and recognized as a Vulnerable Marine Ecosystem where echinoderms play an important ecological role in benthic communities and habitats. The aim of the present study is to inventory and review the echinoid fauna collected during the INDEMARES project in the ACS, compare the new findings with previous studies Official Spanish Checklist (IEEM: “Inventario Español de Especies Marinas”, 2017, 2020) and update our knowledge of the diversity and distribution of echinoid species. During the surveys carried out within the project LIFE + INDEMARES-Avilés Canyons System (2010–2012), a total of 287 specimens of echinoids were sampled at 35 stations and depth ranging between 510 and 1476 m. Twelve species of echinoids were identified, the most frequent being Araeosoma fenestratum (Thomson, 1872) (48.57%), Cidaris cidaris (Linnaeus, 1758) (42.85%) and Phormosoma placenta Thomson, 1872 (28.57%). One species should be considered as a new record in Spanish waters, Gracilechinus affinis (Mortensen, 1903) and the species Echinocardium flavescens expands its known bathymetric range (from 325 to 552 m). This research has been funded by the LIFE+INDEMARES ACS project coordinated by the Biodiversity Foundation of the Ministry of Agriculture, Food and Environment and the European Union's LIFE programme. It was also supported by the Spanish Ministry of Environment through a management agreement with the Spanish Institute of Oceanography (IEO) and University of Malaga. Also, we want to recognize the effort of Dr. Francisco Sánchez and Dr. Alberto Serrano, who provide the opportunity to fund this study through the Transferring Office of the Málaga University under contract nº:2013/0032460–80625/47.6006.

International audience; The Groupe Français du Crétacé and GroupeFrançais d’étude du Jurassique are pleased to joinand offer this thematic issue as a tribute to ourcolleague and friend, Professor Jacques Rey, for hisremarkable career as a specialist of stratigraphy.Jacques Rey was a pioneer in Sequence Stratigraphy.Jacques Rey passed away at home, in Toulouse, onMarch 5th, 2018. He had carried out his academic careerat Paul Sabatier University of Toulouse. He beganas a teacher in 1962 until he retired in 2002. Duringthese forty years, he successively passed all academicdegrees: laboratory assistant (1964), assistantlecturer (1967), lecturer (1975) and professor (1979), jumping up to the exceptional level (1993). Since2002, he was professor emeritus.

Sea stars (Echinodermata: Asteroidea) are a key component of Southern Ocean benthos, with 16% of the known sea star species living there. In temperate marine environments, sea stars commonly play an important role in food webs, acting as keystone species. However, trophic ecology and functional role of Southern Ocean sea stars are still poorly known, notably due to the scarcity of large-scale studies. Here, we report 24332 trophic marker (stable isotopes and elemental contents of C, N and S of tegument and/or tube feet) and biometric (arm length, disk radius, arm to disk ratio) measurements in 2456 specimens of sea stars. Samples were collected between 12/01/1985 and 08/10/2017 in numerous locations along the Antarctic littoral and Subantarctic islands. The spatial scope of the dataset covers a significant portion of the Southern Ocean (Latitude: 47.717° South to 86.273° South; longitude: 127.767° West to 162.201° East; depth: 6 to 5338 m). The dataset contains 133 distinct taxa, including 72 currently accepted species spanning 51 genera, 20 families and multiple feeding guilds / functional groups (suspension feeders, sediment feeders, omnivores, predators of mobile or sessile prey). For 505 specimens, mitochondrial CO1 genes were sequenced to confirm and/or refine taxonomic identifications, and those sequences are already publicly available through the Barcode of Life Data System. This number will grow in the future, as molecular analyses are still in progress. Overall, thanks to its large taxonomic, spatial, and temporal extent, as well as its integrative nature (combining genetic, morphological and ecological data), this dataset can be of wide interest to Southern Ocean ecologists, invertebrate zoologists, benthic ecologists, and environmental managers dealing with associated areas. Please cite this data paper in research products derived from the dataset, which is freely available without copyright restrictions.

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. ispartof: BIODIVERSITY DATA JOURNAL vol:9 ispartof: location:Bulgaria status: published

International audience; La végétation marine des îles Kerguelen, inventaire de la flore et première analyse de ses affinités biogéographiques.Conçu comme une base de référence indispensable à la gestion et à la conservation de la flore marine dans l’aire marine protégée des Terres australes françaises (réserve naturelle nationale des Terres australes françaises), l’inventaire de la flore marine des îles Kerguelen a été mis à jour sur la base d’un examen approfondi de la littérature et des bases de données scientifiques, du premier rapport de l’expédition Ross, en 1840, jusqu’aux travaux les plus récents. Ce travail a aussi pour objectif de constituer un point de départ pour de futures investigations utilisant les outils de la systématique moléculaire, et pour le suivi des effets du changement global sur les écosystèmes marins subantarctiques. Après un bref historique des campagnes scientifiques menées, une liste de 166 espèces a été établie (103 Rhodophyta, 35 Chlorophyta et 28 Ochrophyta [Phaeophyceae]). Les travaux récents ont montré l’existence de divergences récurrentes entre la taxinomie actuelle, établie sur des caractères morphologiques et la délimitation moléculaire des espèces, préconisant une révision de la systématique des macroalgues. Une première analyse des affinités biogéographiques de la flore marine des îles Kerguelen a été cependant réalisée et les résultats préliminaires se sont révélés en partie congruents avec les grandes régions actuellement reconnues dans l’océan Austral, suggérant l’importance du phénomène de dispersion sur de longues distances pour expliquer les motifs de distribution observés.; Conceived as a baseline for the management and conservation of the marine protected area of the French Southern Territories (réserve naturelle nationale des Terres australes françaises), the checklist of marine macroalgae of the Kerguelen Islands was updated based on an extensive review of the literature and scientific databases, from the first report of the Ross expedition, in 1840, to the most recent works. This work was also conceived as a starting point for forthcoming investigations using molecular systematics tools and for monitoring the effects of global change on sub-Antarctic marine ecosystems. After a brief history of scientific campaigns, a list of 166 species was established (103 Rhodophyta, 35 Chlorophyta and 28 Ochrophyta [Phaeophyceae]). Molecular systematics studiess have shown the existence of recurrent discrepancies between the established, morphology-based taxonomy and molecular species delimitation, calling for a revision of systematics. Nevertheless, a first analysis of biogeographical affinities of the marine flora of the Kerguelen Islands is carried out and preliminary results are partially congruent with the main regions currently recognized in the Southern Ocean suggesting the importance of long-distance dispersal to explain the observed distribution patterns.

One of the current challenges in today’s ecology research is to understand and quantify the effects of climate changes on biodiversity. In order to detect possible trends in biodiversity patterns, it is necessary to conduct long-term observations in various and representative environments. This is always challenging, even more difficult in marine habitats and in the Southern Ocean in particular. Since 2012, a submarine observatory of the coastal benthos has been in operation in the Kerguelen Islands. Eight contrasting sites are monitored using photo and video surveys, loggers, and settlement plots. To quantify potential changes, several photographic analysis techniques are also complemented by scuba diving and ROV (Remotely Operated Vehicle) observations. Investigator scientists have developed and improved new protocols that will be carried out in the long term by the staff of the National Natural Reserve of the French Southern Territories. In order to provide reliable support of species identification, the Proteker program supported by IPEV, French Polar Institute, is currently developing several field guides that should improve the identification of the main taxa being monitored. In light of their abundance in coastal environments of the Kerguelen Islands, and because they are among the most visible invertebrates and the easiest of organisms to consider for monitoring surveys, we first focused on echinoderms. Results of this first study are presented here. For each echinoderm species, a spreadsheet provides the species name with synonymies, a description of diagnostic features, the recorded distribution, as well as three different types of illustrations: (i) living specimens in their environment, which is useful for scuba divers, (ii) fresh collected specimens out of water, and (iii) specimens fixed in ethanol. Therefore, species can be identified alive while diving, but also after sampling in the field, and after several years in the laboratory. An assessment of Kerguelen’s coastal echinoderms is also given.

The species of the genus Aequiyoldia Soot-Ryen, 1951, previously known as Yoldia, are common, soft-substratum, sareptid bivalves. In the Southern Ocean, Aequiyoldia eightsii (Jay, 1839) was originally described from the Antarctic Peninsula and has also been reported in southern South America. The species A. woodwardi (Hanley, 1960) was reported for the Falkland/Malvinas Islands and Tierra del Fuego, but this taxon has been recently synonymised within the broadly distributed A. eightsii. Aequiyoldia has received little attention across its distribution in the Southern Ocean, and although its taxonomy and systematics remain uncertain, all the species have been grouped under a single and broadly distributed unit: A. eightsii. Nevertheless, preliminary mtDNA comparisons demonstrated a marked genetic divergence (>7%) between A. eightsii populations from South America and Antarctic Peninsula. In order to further understand the diversity and biogeography of Aequiyoldia, we analyzed A. eightsii populations from different provinces of the Southern Ocean including South America (SA), the Falkland/Malvinas Islands (FI), the Antarctic Peninsula (AP), and Kerguelen Islands (KI). Individuals were characterized according to typical diagnostic morphological measurements and phylogenetic relationships were reconstructed based on mtDNA (cytochrome c oxidase subunit I). Patterns of genetic divergence of nucDNA intergenic transcribed spacers (ITS1, ITS2) were also estimated. The statistical analysis of external diagnostic characteristics revealed two morphotypes: (1) individuals with the morphology recorded for the nominal FI species, A. woodwardi, and (2) individuals from SA, AP, and KI, with the morphology recorded for A. eightsii. However, phylogenetic reconstructions based on mtDNA and nucDNA suggest the presence of at least five lineages within A. eightsii including: one lineage in Kerguelen Island, two lineages in the Antarctic Peninsula, one lineage in South America, and the last one restricted to the Falkland/Malvinas Islands. Such results are evidence that the Antarctic Polar Front represents an historical biogeographic barrier for this group and that after the separation of these lineages, they followed independent evolutionary pathways in different provinces of the Southern Ocean. Estimates of divergence time suggest that KI separated from other Aequiyoldia lineages close to the middle Miocene. Following this, the separation between the AP and SA lineages occurred at the end of the Miocene around 7.5 Ma. Finally, Aequiyoldia diversified during the Pliocene in Antarctic Peninsula (∼4.5 Ma) and South America (∼3.0 Ma). Individuals from FI exhibited morphological differences, and 4% of divergence from South American individuals, suggesting that A. woordwardi could be revalidated. Similarly, the marked molecular divergence between the KI and the rest of the recorded lineages also support the validity of A. kerguelensis (Thiele, 1931).

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., info:eu-repo/semantics/published

Daily weather regimes are defined around the Kerguelen Islands (Southern Ocean) based on daily 500 hPa geopotential height anomalies derived from the ERA5 ensemble reanalysis over the period 1979-2018. Ten regimes are retained as significant. Their occurrences are highly consistent across reanalysis ensemble members. Regimes show weak seasonality and non-significant long-term trends in their occurrences. Their sequences are usually short (1-3 days), with extreme persistence values above 10 days. Seasonal regime frequency is mostly driven by the phase of the Southern Annular Mode over Antarctica, mid-latitude dynamics over the Southern Ocean like the Pacific South American mode, and to a lesser extent, tropical variability, with significant but weaker relationships with El Niño Southern Oscillation. At the local scale over the Kerguelen Islands, regimes have a strong influence on measured atmospheric and oceanic variables, including minimum and maximum air temperature, mostly driven by horizontal advections, sea water temperature recorded 5 m below the surface, wind speed and sea level pressure. Relationships are weaker for precipitation amounts. Regimes also modify regional contrasts between observational sites in Kerguelen, highlighting strong exposure contrasts. The regimes allow improving our understanding of weather and climate variability and interactions in this region; they will be used in future work to assess past and projected long-term circulation changes in the southern mid-latitudes.

14 pages; International audience; Irregular urchins exclusively live in marine soft bottom habitats, dwelling either upon or inside sediments and selectively picking up sediment grains and organic particles, or swallowing bulk sediment to feed on the associated organic matter. The exact food source and dietary requirements of most irregular echinoids, however, remain incompletely understood. The schizasterid species Abatus cordatus (Verrill, 1876) is a sub-Antarctic spatangoid that is endemic to the Kerguelen. The feeding behaviour of A. cordatus was investigated using simultaneously metabarcoding and stable isotope approaches. Comparison of ingested and surrounding sediments by metabarcoding revealed a limited selective ingestion of prokaryotes and eukaryotes by the urchin. Compared to surrounding sediments, the gut content had (i) higher carbon and nitrogen concentrations potentially due to selective ingestion of organic matter and/or the sea urchin mucus secretion and (ii) δ15N enrichment due to the selective assimilation of lighter isotope in the gut. Feeding experiments were performed using 13C and 15 N-enriched sediments in aquariums. The progression of stable isotope enrichment in proximal and distal parts of the digestive track of A. cordatus revealed that all particles are not similarly transported likely due to siphon functioning. Ingestion of water with associated dissolved and particulate organic matter should play an important role in urchin nutrition. A. cordatus had a gut resident time fluctuating between 76 and 101 h and an ingestion rate of 36 mg dry sediment h−1 suggesting that dense populations of the species may play a key ecological role through bioturbation in soft bottom shallow-water habitats of the Kerguelen Islands.

International audience; Members of the trochoidean genus Margarella (Calliostomatidae) are broadly distributed across Antarctic and sub-Antarctic ecosystems. Here we used novel mitochondrial and nuclear gene sequences to clarify species boundaries and phylogenetic relationships among seven nominal species distributed on either side of the Antarctic Polar Front (APF). Molecular reconstructions and species-delimitation analyses recognized only four species: M. antarctica (the Antarctic Peninsula), M. achilles (endemic to South Georgia), M. steineni (South Georgia and Crozet Island) and the morphologically variable M. violacea (=M. expansa, M. porcellana and M. pruinosa), with populations in southern South America, the Falkland/Malvinas, Crozet and Kerguelen Islands. Margarella violacea and M. achilles are sister species, closely related to M. steineni, with M. antarctica sister to all these. This taxonomy reflects contrasting biogeographic patterns on either side of the APF in the Southern Ocean. Populations of Margarella north of the APF (M. violacea) showed significant genetic variation but with many shared haplotypes between geographically distant populations. By contrast, populations south of the APF (M. antarctica, M. steineni and M. achilles) exhibited fewer haplotypes and comprised three distinct species, each occurring across a separate geographical range. We hypothesize that the biogeographical differences may be the consequence of the presence north of the APF of buoyant kelps – potential long-distance dispersal vectors for these vetigastropods with benthic-protected development – and their near-absence to the south. Finally, we suggest that the low levels of genetic diversity within higher-latitude Margarella reflect the impact of Quaternary glacial cycles that exterminated local populations during their maxima.