Sara Labrousse

The sea ice zone plays important ecological roles in Antarctica, influencing phytoplankton bloom timing, which cascades through the food web, and providing habitat for many species. Weddell seals...

Extreme episodic changes in Antarctic continental shelf regions, such as glacier calving or iceberg grounding, can fundamentally reshape regional sea-ice conditions. Weddell seals are obligate sea-ice predators and so may reflect ecosystem change around the Antarctic shoreline. From 2006 to 2024, the movements and diving behaviour of 35 female Weddell seals were studied using biotelemetry. Following the calving of the Mertz Glacier Tongue in February 2010, five females expanded into the previously unused Commonwealth Bay, where they undertook between 0.05 and 65.3% of their dives. This shift coincided with the establishment of persistent land-fast ice in the region (2019–2024), absent prior to calving (2006–2009). Residency times were positively associated with land-fast ice persistence. Although generalized additive mixed models detected no significant overall effect of calving on dive depth, dive duration, hunting time or hunting depth when averaged across the study area, all behavioural variables displayed pronounced spatial heterogeneity. This suggests that calving primarily altered the spatial distribution of diving and foraging behaviour rather than inducing uniform behavioural shifts. By contrast, this glacier calving event caused catastrophic breeding failures in seabirds, whereas even the resulting drastic sea-ice changes remained within the behavioural and spatial flexibility of Weddell seals.

Sous la banquise Antarctique : écologie alimentaire des éléphants de mer des îles Kerguelen, influence des paramètres océanographiques et de glace de mer: Les mammifères marins de l'Océan Austral sont des éléments essentiels des écosystèmes marins antarctiques et des sentinelles de l’état des océans polaires. Comprendre comment les conditions océanographiques déterminent leurs habitats préférentiels est essentiel pour identifier de quelle façon et dans quelle région ces mammifères acquièrent les ressources nécessaires à leur déplacement, leur croissance, leur reproduction et donc leur survie. Les éléphants de mer du Sud (Mirounga leonina) se déplacent dans l’océan austral à l’échelle des bassins océaniques pour s’alimenter en plongeant en moyenne à 500 m et jusqu’à 2000 m de profondeur. En fonction de leur colonie d’origine, de leur sexe, et de leur âge, ils exploitent des régions radicalement différentes de l’océan austral, mettant ainsi en œuvre des stratégies alimentaires diversifiées. Les éléphants de mer de Kerguelen utilisent deux zones préférentiellement: la zone du Front Polaire ou la zone Antarctique couverte par la banquise. Dans cette thèse, les stratégies alimentaires des voyages post-mue Antarctiques de 46 mâles et femelles éléphants de mer de Kerguelen ont été étudiées. Une série temporelle de 11 années (2004-2014) de données de déplacement, de plongées et de données hydrologiques a été analysée pour déterminer le rôle des paramètres océanographiques et de glaces de mer impliqués dans l’acquisition des ressources alimentaires des éléphants de mer en Antarctique. L’influence de la variabilité spatio-temporelle et interannuelle de la glace de mer associée à la position des mâles et des femelles ainsi que le rôle des polynies côtières sur les stratégies alimentaires des mâles en hiver ont été examinés.

The Southern Ocean around Antarctica is one of the fastest changing regions on the planet and an emerging resource frontier for fisheries. Here, we present the Antarctic Ecosystem Value Index created by merging ecosystem information across food web trophic levels, from phytoplankton to fish and penguins, to quantify the ecological value of marine areas around the Antarctic continent. We find that coastal polynyas - areas of reduced sea-ice - have Index values 31–72% higher than surrounding areas, suggesting that these areas are biologically valuable hot spots for a number of ice-dependent Antarctic Species. Using output from an Earth system model to generate future projections of the Index, we find that high-value locations, often within polynyas, are likely to continue to be valuable throughout the 21st century despite environmental changes. The Antarctic Ecosystem Value Index indicates that penguins lose importance as their habitat becomes increasingly unsuitable, so protecting high-value habitat areas may be critical for these species. This study also shows that while many high-value Index areas are within existing or proposed Marine Protected Areas, there are several opportunities for adopting additional protection, particularly in East Antarctica and the Amundsen Sea.

Extreme episodic changes in Antarctic continental shelf icescapes—such as glacier calving or iceberg grounding—can reshape regional sea and icescapes. Grounded icebergs may block or enable sea ice advection, altering sea ice phenology and affecting nutrient and light cycles. These changes can shift phytoplankton bloom timing with repercussions throughout the food web. Ice-dependent species may lose or gain foraging habitats, affecting their reproductive rates and breeding success. Weddell seals, as resident polar predators, can act as sentinel species for detecting ecosystem changes caused by such events. Changes in seal movement ecology likely reflect changes in prey structure and distribution. From 2006 to 2024, the movements and diving behaviour of 34 female Weddell seals were studied using biotelemetry. Following the calving of the Mertz Glacier Tongue in February 2010, seals spent more time in Commonwealth Bay (from 0.9% to 13% of their post-calving dive locations), consistent with earlier formation of landfast ice (February 2019–2024) and its persistence post-calving. Landfast ice persisted in Commonwealth Bay from May onwards, although it was absent before the calving event (2006-2009). In Commonwealth Bay and west of Pointe Géologie Archipelago, seals also dived deeper after calving than before, suggesting changes in foraging strategies.

Over the last 20 years (2004 to 2025), a French-Australian research and ocean observing collaboration has collected >400,000 temperature-salinity profiles providing broad coverage within the Indian Sector of the Southern Ocean. The collaboration is the cornerstone of the emerging global Animal-Borne Oceanographic Sensors (AniBOS) network, from which the data are freely available to the operational, ocean and climate research, and public communities. These data are a primary source of information for the study of ocean properties in this remote region, enabling major advances in knowledge of dense water formation, glacial ice shelf melting, frontal structure and recent trends driven by climate change in the Southern Ocean. The data have also provided key observations of biological processes, redefining our understanding of the ecology of seals in the Southern Ocean and providing a detailed picture of how they utilise their dynamic ocean-ice environment. The two-fold delivery of essential oceanographic and ecological observations makes this a flagship program, one which has enabled a step-change in our understanding of coupling between physics and biology. Sustaining the observations delivered by AniBOS is critical within the context of a rapidly changing Southern Ocean, for detecting change and anticipating consequences for these unique coupled systems.

Dispersal is a ubiquitous phenomenon that affects the dynamics of the population and the evolution of natural populations; however, it is challenging to measure in most species. Furthermore, the influence of informed dispersal behaviors, referring to the nonrandom selection of breeding habitats by individuals, on species' responses to rapid global change is substantial but difficult to comprehend. Here, we present a modeling framework to assess the dispersal characteristics and behaviors of a metapopulation when observations provide information on its neutral genetic structure for a restricted sampling of locations. Our mechanistic‐statistical model couples a deterministic model capturing the spatio‐temporal dynamics of four genetic clusters across all breeding colonies by integrating demographic processes with genetic projections, with a probabilistic observation model describing the probability to sample an individual from a given genetic cluster. We apply this new framework to the emperor penguin, a species living in Antarctica and currently experiencing habitat loss. The model estimates the species' dispersal distance, rates of emigration, and behaviors associated with dispersal (informed or random). By incorporating these estimations with satellite censuses of breeding colonies, we can identify environmental and demographic factors that influence the dispersal of emperor penguins. Finally, we provide new global population forecasts for emperor penguins that can inform conservation actions in Antarctica.

Like many polar animals, emperor penguin populations are challenging to monitor because of the species' life history and remoteness. Consequently, it has been difficult to establish its global status, a subject important to resolve as polar environments change. To advance our understanding of emperor penguins, we combined remote sensing, validation surveys and using Bayesian modelling, we estimated a comprehensive population trajectory over a recent 10-year period, encompassing the entirety of the species’ range. Reported as indices of abundance, our study indicates with 81% probability that there were fewer adult emperor penguins in 2018 than in 2009, with a posterior median decrease of 9.6% (95% credible interval (CI) −26.4% to +9.4%). The global population trend was −1.3% per year over this period (95% CI = −3.3% to +1.0%) and declines probably occurred in four of eight fast ice regions, irrespective of habitat conditions. Thus far, explanations have yet to be identified regarding trends, especially as we observed an apparent population uptick toward the end of time series. Our work potentially establishes a framework for monitoring other Antarctic coastal species detectable by satellite, while promoting a need for research to better understand factors driving biotic changes in the Southern Ocean ecosystem.