Explore the vast range of titles available.

Determining the links between the behavioural and population responses of wild species to environmental variations is critical for understanding the impact of climate variability on ecosystems. Using long-term data sets, we show how large-scale climatic anomalies in the Southern Hemisphere affect the foraging behaviour and population dynamics of a key marine predator, the king penguin. When large-scale subtropical dipole events occur simultaneously in both subtropical Southern Indian and Atlantic Oceans, they generate tropical anomalies that shift the foraging zone southward. Consequently the distances that penguins foraged from the colony and their feeding depths increased and the population size decreased. This represents an example of a robust and fast impact of large-scale climatic anomalies affecting a marine predator through changes in its at-sea behaviour and demography, despite lack of information on prey availability. Our results highlight a possible behavioural mechanism through which climate variability may affect population processes. Understanding how organisms respond to short-term climate variations will help predict the impact of future global change. Here, Bost et al . show that large-scale climatic anomalies coincide with changes in the foraging behaviour and populations dynamics of king penguins in the Southern hemisphere.

Large-scale breeding failures, such as offspring die-offs, can disproportionately impact wildlife populations that are characterized by a few large colonies. However, breeding monitoring—and thus investigations of such die-offs—is especially challenging in species with long reproductive cycles. We investigate two unresolved dramatic breeding failures that occurred in consecutive years (2009 and 2010) in a large king penguin Aptenodytes patagonicus colony, a long-lived species with a breeding cycle lasting over a year. Here we found that a single period, winter 2009, was likely responsible for the occurrence of breeding anomalies during both breeding seasons, suggesting that adults experienced poor foraging conditions at sea at that time. Following that unfavorable winter, the 2009 breeding cohort—who were entering the late stage of chick-rearing—immediately experienced high chick mortality. Meanwhile, the 2010 breeding cohort greatly delayed their arrival and egg laying, which would have otherwise started not long after the winter. The 2010 breeding season continued to display anomalies during the incubation and chick-rearing period, such as high abandonment rate, long foraging trips and eventually the death of all chicks in winter 2010. These anomalies could have resulted from either a domino-effect caused by the delayed laying, the continuation of poor foraging conditions, or both. This study provides an example of a large-scale catastrophic breeding failure and highlights the importance of the winter period on phenology and reproduction success for wildlife that breed in few large colonies.

Understanding the factors that drive the dynamics of populations of long‐lived species presents a unique challenge for conservation management. Here, we investigated long-term change in the body condition of adult northern rockhopper penguins Eudyptes moseleyi at Amsterdam Island, southern Indian Ocean, which hosts 5–10% of the global population of this endangered species. Analysis of a long‐term dataset (1994–2016), concurrent to the population's rapid decline, revealed no trend in adult northern rockhopper penguin body condition over time at the stages considered in this study, i.e. breeding and moulting. However, body condition varied between years and sexes and part of this variation was explained by environmental factors. Males were on average in better condition than females whatever the stage and individuals on average were in better condition during the moulting compared to the breeding period. The environmental conditions [sea surface temperature anomaly (SSTa), Subtropical Indian Ocean Dipole (SIOD) and Southern Annular Mode (SAM)] appeared to impact non-linearly the body condition. Overall, females were in better condition for negative values of SAM, SIOD and SSTa. The body condition of males exhibited similar but less complex and more significant patterns, with decreasing body condition for increasing SAM, SIOD and SSTa. The absence of long-term trends in male and female body condition suggests that the very low reproductive output and declining population since 1997 is probably not the result of environmental conditions during pre-breeding and pre-moult and necessitates further research into possible drivers during the breeding season.

Aim Climate change will likely lead to a significant redistribution of biodiversity in marine ecosystems. We examine the potential redistribution of a community of marine predators by comparing current and future habitat distribution projections. We examine relative changes among species, indicative of potential future community‐level changes and consider potential consequences of these changes for conservation and management. Location Southern Indian Ocean. Methods We used tracking data from 14 species (10 seabirds, 3 seals and 1 cetacean, totalling 538 tracks) to model the habitat selection of predators around the Prince Edward Islands. Using random forest classifiers, we modelled habitat selection as a response to a static environmental covariate and nine dynamic environmental covariates obtained from eight IPCC‐class climate models. To project the potential distribution of the predators in 2071–2100, we used climate model outputs assuming two greenhouse gas emission scenarios: RCP 4.5 and RCP 8.5. Results Analogous climates are projected to predominantly shift to the southeast and southwest. Species’ potential range shifts varied in direction and magnitude, but overall shifted slightly to the southwest. Despite the variable shifts among species, current species co‐occurrence patterns and future projections were statistically similar. Our projections show that at least some important habitats will shift out of national waters and marine protected areas by 2100, but important habitat area will increase in the Convention on the Conservation of Antarctic Marine Living Resources Area. Predicted areas of common use among predators decreased north of the islands and increased to the south, suggesting that multiple predator species may use southerly habitats more intensively in the future. Consequently, Southern Ocean management authorities could implement conservation actions to partially offset these shifts. Main conclusions Overall, we predict that marine predator biodiversity in the southern Indian Ocean will be redistributed, with ecological, conservation and management implications.

In the Antarctic Circumpolar Current region of the Southern Ocean, the massive phytoplankton blooms stemming from islands support large trophic chains. Contrary to islands, open ocean seamounts appear to sustain blooms of lesser intensity and, consequently, are expected to play a negligible role in the productivity of this area. Here we revisit this assumption by focusing on a region of the Antarctic Circumpolar Current zone which is massively targeted by marine predators, even if no island fertilizes this area. By combining high resolution bathymetric data, Lagrangian analyses of altimetry-derived velocities and chlorophyll a observations derived from BGC-Argo floats and ocean color images, we reveal that the oligotrophic nature of the study region considered in low chlorophyll a climatological maps hides in reality a much more complex environment. Significant (chlorophyll a in excess of 0.6 mg/m3) phytoplankton blooms spread over thousands of kilometers and have bio-optical signatures similar to the ones stemming from island systems. By adopting a Lagrangian approach, we demonstrate that these moderate blooms (i) originate at specific sites where the Antarctic Circumpolar Current interacts with seamounts, and (ii) coincide with foraging areas of five megafauna species. These findings underline the ecological importance of the open ocean subantarctic waters and advocate for a connected vision of future conservation actions along the Antarctic Circumpolar Current.

Oceanic frontal zones have been shown to deeply influence the distribution of primary producers and, at the other extreme of the trophic web, top predators. However, the relationship between these structures and intermediate trophic levels is much more obscure. In this paper we address this knowledge gap by comparing acoustic measurements of mesopelagic fish concentrations to satellite-derived fine-scale Lagrangian Coherent Structures in the Indian sector of the Southern Ocean. First, we demonstrate that higher fish concentrations occur more frequently in correspondence with strong Lagrangian Coherent Structures. Secondly, we illustrate that, while increased fish densities are more likely to be observed over these structures, the presence of a fine-scale feature does not imply a concomitant fish accumulation, as other factors affect fish distribution. Thirdly, we show that, when only chlorophyll-rich waters are considered, front intensity modulates significantly more the local fish concentration. Finally, we discuss a model representing fish movement along Lagrangian features, specifically built for mid-trophic levels. Its results, obtained with realistic parameters, are qualitatively consistent with the observations and the spatio-temporal scales analysed. Overall, these findings may help to integrate intermediate trophic levels in trophic models, which can ultimately support management and conservation policies.

One of the largest sectors of the Southern Ocean is the Indian Sector, which plays an important role in regulating the Earth’s climate and supports a diverse ecosystem. To understand how climate change impacts the environment in this sector, ocean observations are collected via various platforms, including conventional ship-based technologies, autonomous instruments (e.g., animal-borne sensors, autonomous underwater vehicles, and profiling floats), satellites, and other remote sensing methods. However, the harsh environment, remoteness, and natural obstacles such as sea ice and clouds limit year-round ocean observations by vessel and satellite, respectively. This incomplete data coverage makes predicting future scenarios a challenge. Here, led by the Regional Working Group for the Indian Sector of the Southern Ocean in the Southern Ocean Observing System, we examined the status of multidisciplinary ocean observations in the Indian Sector. Our review covers oceanography, sea ice, biogeochemistry, air–sea flux, pelagic and benthic biology, and direct anthropogenic pressures. We also address seasonal and spatial gaps, along with platform biases. Furthermore, we explore the synergies between modelling and observations, highlighting how models can test hypotheses, address observational gaps, and, in turn, benefit from improved observational data. Finally, we provide recommendations for enhancing the observing system in the Indian Sector of the Southern Ocean to better understand its current state and anticipated future changes.

Sub‐mesoscale fronts—with scales from 1 to 50 km are ubiquitous in satellite images of the world oceans. They are known to generate strong vertical velocities with significant impacts on biogeochemical fluxes and pelagic ecosystems. Here, we use a unique data set, combining high‐resolution behavioral and physical measurements, to determine the effects of sub‐mesoscale structures on the foraging behavior of 12 instrumented female southern elephant seals. These marine mammals make long voyages (several months over more than 2000 km), diving and feeding continuously in the Antarctic Circumpolar Current. Our results show that elephant seals change their foraging behavior when crossing sub‐mesoscale fronts: They forage more and at shallower depths inside sub‐mesoscale fronts compared to nonfrontal areas, and they also reduce their horizontal velocity likely to concentrate on their vertical diving activity. The results highlight the importance of sub‐mesoscale fronts in enhancing prey accessibility for upper trophic levels, and suggest that trophic interactions are stimulated in these structures.

The manuscript assesses the current and expected future global drivers of Southern Ocean (SO) ecosystems. Atmospheric ozone depletion over the Antarctic since the 1970s, has been a key driver, resulting in springtime cooling of the stratosphere and intensification of the polar vortex, increasing the frequency of positive phases of the Southern Annular Mode (SAM). This increases warm air-flow over the East Pacific sector (Western Antarctic Peninsula) and cold air flow over the West Pacific sector. SAM as well as El Niño Southern Oscillation events also affect the Amundsen Sea Low leading to either positive or negative sea ice anomalies in the west and east Pacific sectors, respectively. The strengthening of westerly winds is also linked to shoaling of deep warmer water onto the continental shelves, particularly in the East Pacific and Atlantic sectors. Air and ocean warming has led to changes in the cryosphere, with glacial and ice sheet melting in both sectors, opening up new ice free areas to biological productivity, but increasing seafloor disturbance by icebergs. The increased melting is correlated with a salinity decrease particularly in the surface 100 m. Such processes could increase the availability of iron, which is currently limiting primary production over much of the SO. Increasing CO 2 is one of the most important SO anthropogenic drivers and is likely to affect marine ecosystems in the coming decades. While levels of many pollutants are lower than elsewhere, persistent organic pollutants (POPs) and plastics have been detected in the SO, with concentrations likely enhanced by migratory species. With increased marine traffic and weakening of ocean barriers the risk of the establishment of non-indigenous species is increased. The continued recovery of the ozone hole creates uncertainty over the reversal in sea ice trends, especially in the light of the abrupt transition from record high to record low Antarctic sea ice extent since spring 2016. The current rate of change in physical and anthropogenic drivers is certain to impact the Marine Ecosystem Assessment of the Southern Ocean (MEASO) region in the near future and will have a wide range of impacts across the marine ecosystem.