Sophie Bestley

Extreme weather events (EWEs) are increasing in both intensity and frequency globally. For long-lived, slow-reproducing marine predators, repeated or sequential EWE-driven breeding failures can have population-level consequences. We quantified effects of EWEs on reproductive output and identified temporal windows of vulnerability during breeding in three sentinel species across 14 colonies with varying population trajectories in Tasmania, Australia. Using long-term breeding datasets and daily weather records, we found that Australian fur seals ( Arctocephalus pusillus doriferus ), short-tailed shearwaters ( Ardenna tenuirostris ), and shy albatross ( Thalassarche cauta ) exhibited species- and colony-specific vulnerabilities. Storm surges reduced pup production in a low-lying fur seal colony, extreme rainfall lowered shearwater breeding success, and albatross productivity declined with exposure to extreme heat, rainfall, and wave events. These results highlight the importance of identifying critical extreme weather thresholds and periods of vulnerability to inform ecological forecasting. Proactive, climate-informed management strategies tailored to specific colonies are needed to enhance the resilience of vulnerable populations under accelerating climate change.

Animal‐borne conductivity-temperature-depth (CTD) and fluorescence sensors deployed on Southern Ocean elephant seals ( Mirounga leonina ) provide essential hydrographic and biogeochemical observations in remote Southern Ocean regions where shipboard and autonomous sampling is sparse. For these data to be fully integrated into the Global Ocean Observing System, their accuracy and consistency with established autonomous observing standards must be assessed. Here we present a dedicated field intercomparison of 20 CTD Satellite Relay Data Loggers (SRDLs), including nine equipped with Valeport Hyperion fluorometers, conducted against a shipboard SeaBird SBE 911plus CTD and an ECO FLBB fluorometer during a 2025 East Antarctic research voyage. Hyperion fluorometers systematically underestimated the ECO fluorometer by a consistent factor across deployments. We therefore recommend applying a single gain correction of 1.7±0.6 to Hyperion fluorescence measurements to align seal‑borne fluorescence with ECO fluorometers commonly used on biogeochemical Argo (BGC‑Argo) floats and other autonomous platforms. After application of this gain correction, established BGC-Argo delayed-mode physiological correction schemes can be applied to obtain more accurate chlorophyll estimates and improve cross-platform comparability. CTD temperature and salinity showed linear pressure‑dependencies comparable to previous SRDL sensor assessments, with mean (±1 standard deviation, s.d.) biases of 0.006±0.026˚C km ^-1 for temperature and 0.006±0.028 psu km ^-1 for salinity. If uncorrected, these pressure dependencies introduce additional uncertainty into delayed-mode adjustments (±0.04˚C and ±0.05 psu at 1000 m). Together, these results highlight the value of routine at‑sea calibration for improving CTD and fluorescence sensor accuracy and enhancing interoperability between seal‑borne, ship-based and autonomous oceanographic observations across the Southern Ocean.

Regional differences in southern elephant seal (Mirounga leonina) population trends have long been hypothesised to reflect environmental variation affecting prey availability. By integrating census counts, demographic data, and locally relevant winter sea-ice conditions, we provide new evidence quantifying the suspected link between seal numbers and regional sea-ice cover in the Southern Ocean. We developed an integrated population model using annual abundance and capture–mark–recapture data from 1980–2023, accounting for observation error and temporal random effects. Population breeding probability varied annually (50-65% on average). To assess how environmental conditions influence reproductive dynamics, we tested the effect of winter sea-ice cover within the known foraging range of adult females. We compared two covariate structures and a null model, incorporating one-year-lagged (B-COV1) and same-year (C-COV0) sea-ice conditions. Covariate models confirmed a negative relationship (βB-COV1 = -0.0103 to βC-COV0 = -0.0345), indicating that reduced population breeding probability was associated with higher-than-average sea-ice cover. Estimates of the total population size (N) mirrored the observed decrease in seal numbers. N was used to project historical scenarios representing persistently ’best’, ’neutral’, and ’worst’ case sea-ice cover conditions over the full timeseries. The scenario-specific intrinsic growth rates ranged from a slow decrease under the best-case scenario (r = –0.495%) to a substantially stronger decline under the worst-case scenario (r = –3.126%), with the neutral scenario closely matching the observed population trend (r ≈ –2%). These comparisons emphasise how local-regional scale habitat conditions can alter long-term population trajectories at magnitudes relevant to species recovery

East Antarctic coastal polynyas—semi-permanent areas of ice-free ocean—are vital for sea ice production, Antarctic Bottom Water formation, and global heat redistribution. The Dibble Polynya has pronounced sea-ice production, yet the shelf water properties there and its offshore influence have been unclear. Here we show Dense Shelf Water outflow from the polynya that ventilates a lighter variety of local bottom water. Hydrographic records suggest Dense Shelf Water formation has persisted for 50 years, consistent with satellite-derived sea-ice production since the 1990s. Since the 2010s, the downstream cross-slope salinity gradient within bottom water has weakened and the Antarctic Slope Front has been modified, following a sharp decline in sea-ice production in the neighbouring Mertz Polynya after 2010 icescape changes. We infer that reduced denser Antarctic Bottom Water formation upstream weakens the slope current barrier, promoting outflow of not-so-dense shelf water from the Dibble Polynya that efficiently ventilates the abyssal basin.

Foraging behavior and success are a function of prey abundance and distribution in marine environments. Oceanographic processes shape prey spatial structuring, leading to some areas of high heterogeneity and others of high homogeneity, causing marine predators to exhibit different at‐sea behaviors. Our study investigated foraging success and effort of adult female southern elephant seals dispersing west or east of the Kerguelen Plateau. We quantified drift dive data and dive metric data for 153 seals, focusing on timing and spatial patterns in seal buoyancy change and its relationship with seal dive behavior. We assessed whether differences were linked to differing responses to forage quality. Overall, buoyancy changes indicated elephant seals had similar foraging success in both homogeneous (west) and heterogeneous (east) environments around the Kerguelen Plateau. Seals to the east dived deeper, with shorter hunting times and higher descent rates, probably related to higher mesoscale activity, while those to the west had lower descent rates and focused on shallower prey. Both groups responded to changes in forage quality by increasing ascent/descent rate in high‐quality areas. These results suggest that these seals behave as predicted by the marginal value theorem and in so doing adapt foraging behavior to efficiently exploit profitable prey patches.

Marine megafauna species are affected by a wide range of anthropogenic threats. To evaluate the risk of such threats, species’ vulnerability to each threat must first be determined. We build on the existing threats classification scheme and ranking system of the International Union for Conservation of Nature (IUCN) Red List of Threatened Species by assessing the vulnerability of 256 marine megafauna species to 23 at‐sea threats. The threats we considered included individual fishing gear types, climate‐change‐related subthreats not previously assessed, and threats associated with coastal impacts and maritime disturbances. Our ratings resulted in 70 species having high vulnerability ( v > 0.778 out of 1) to at least 1 threat, primarily drifting longlines, temperature extremes, or fixed gear. These 3 threats were also considered to have the most severe effects (i.e., steepest population declines). Overall, temperature extremes and plastics and other solid waste were rated as affecting the largest proportion of populations. Penguins, pinnipeds, and polar bears had the highest vulnerability to temperature extremes. Bony fishes had the highest vulnerability to drifting longlines and plastics and other solid waste; pelagic cetaceans to 4 maritime disturbance threats; elasmobranchs to 5 fishing threats; and flying birds to drifting longlines and 2 maritime disturbance threats. Sirenians and turtles had the highest vulnerability to at least one threat from all 4 categories. Despite not necessarily having severe effects for most taxonomic groups, temperature extremes were rated among the top threats for all taxa except bony fishes. The vulnerability scores we provide are an important first step in estimating the risk of threats to marine megafauna. Importantly, they help differentiate scope from severity, which is key to identifying threats that should be prioritized for mitigation.

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.

Antarctic sea ice is one of the largest biomes on Earth providing a critical habitat for ice algae. Measurements of primary production in Antarctic sea ice remain scarce and an observation‐based estimate of primary production has not been revisited in over 30 years. We fill this knowledge gap by presenting a newly compiled circumpolar data set of particulate and dissolved organic carbon from 362 ice cores, sampled between 1989 and 2019, to estimate sea‐ice net community production using a carbon biomass accumulation approach. Our estimate of 26.8–32.9 Tg C yr ⁻¹ accounts for at least 15%–18% of the total primary production in the Antarctic sea‐ice zone, less than a previous observation‐based estimate (63–70 Tg C yr ⁻¹ ) and consistent with recent modeled estimates. The results underpin the ecological significance of sea‐ice algae as an early season resource for pelagic food webs.

Climate change could irreversibly modify Southern Ocean ecosystems. Marine ecosystem model (MEM) ensembles can assist policy making by projecting future changes and allowing the evaluation and assessment of alternative management approaches. However, projected changes in total consumer biomass from the Fisheries and Marine Ecosystem Model Intercomparison Project (FishMIP) global MEM ensemble highlight an uncertain future for the Southern Ocean, indicating the need for a region‐specific ensemble. A large source of model uncertainty originates from the Earth system models used to force FishMIP models, particularly future changes to lower trophic level biomass and sea‐ice coverage. To build confidence in regional MEMs as ecosystem‐based management tools in a changing climate that can better account for uncertainty, we propose the development of a Southern Ocean Marine Ecosystem Model Ensemble (SOMEME) contributing to the FishMIP 2.0 regional model intercomparison initiative. One of the challenges hampering progress of regional MEM ensembles is achieving the balance of global standardised inputs with regional relevance. As a first step, we design a SOMEME simulation protocol, that builds on and extends the existing FishMIP framework, in stages that include: detailed skill assessment of climate forcing variables for Southern Ocean regions, extension of fishing forcing data to include whaling, and new simulations that assess ecological links to sea‐ice processes in an ensemble of candidate regional MEMs. These extensions will help advance assessments of urgently needed climate change impacts on Southern Ocean ecosystems.

Climate change could irreversibly modify Southern Ocean ecosystems. Marine ecosystem model (MEM) ensembles can assist policy making by projecting future changes and allowing the evaluation and assessment of alternative management approaches. However, projected future changes in total consumer biomass from the Fisheries and Marine Ecosystem Model Intercomparison Project (FishMIP) global MEM ensemble highlight an uncertain future for the Southern Ocean, indicating the need for a region-specific ensemble. A large source of model uncertainty originates from the Earth system models (ESMs) used to force FishMIP models, particularly future changes to lower trophic level biomass and sea ice coverage. To build confidence in regional MEMs as ecosystem-based management tools in a changing climate that can better account for uncertainty, we propose the development of a Southern Ocean Marine Ecosystem Model Ensemble (SOMEME) contributing to the FishMIP 2.0 regional model intercomparison initiative. One of the challenges hampering progress of regional MEM ensembles is achieving the balance of global standardised inputs with regional relevance. As a first step, we design a SOMEME simulation protocol, that builds on and extends the existing FishMIP framework, in stages that include: detailed skill assessment of climate forcing variables for Southern Ocean regions, extension of fishing forcing data to include whaling, and new simulations that assess ecological links to sea-ice processes in an ensemble of candidate regional MEMs. These extensions will help advance assessments of urgently needed climate change impacts on Southern Ocean ecosystems.