Description: Stresses on Antarctic ecosystems result from environmental change, including extreme events, and from (other) human impacts. Consequently, Antarctic habitats are changing, some at a rapid pace while others are relatively stable. A cascade of responses from molecular through organismic to the community level are expected. The differences in biological complexity and evolutionary histories between both polar regions and the rest of the planet suggest that stresses on polar ecosystem function may have fundamentally different outcomes from those at lower latitudes. Polar ecosystem processes are therefore key to informing wider ecological debate about the nature of stability and potential changes across the biosphere. The main goal of AnT-ERA is to facilitate the science required to examine changes in biological processes in Antarctic and sub-Antarctic marine-, freshwater and terrestrial ecosystems. Tolerance limits, as well as thresholds, resistance and resilience to environmental change will be determined. AnT-ERA is classified into three overlapping themes, which represent three levels of biological organisation: (1) molecular and physiological performance, (2) population processes and species traits, (3) ecosystem function and services.

Description: Polar oceans are poorly monitored despite the important role they play in regulating Earth’s climate system. Marine mammals equipped with biologging devices are now being used to fill the data gaps in these logistically difficult to sample regions. Since 2002, instrumented animals have been generating exceptionally large data sets of oceanographic CTD casts (〉500,000 profiles), which are now freely available to the scientific community through the MEOP data portal (http://meop.net). MEOP (Marine Mammals Exploring the Oceans Pole to Pole) is a consortium of international researchers dedicated to sharing animal-derived data and knowledge about the polar oceans. Collectively, MEOP demonstrates the power and cost-effectiveness of using marine mammals as data-collection platforms that can dramatically improve the ocean observing system for biological and physical oceanographers. Here, we review the MEOP program and database to bring it to the attention of the international community.

Description: Resource selection studies in ecology are commonly undertaken at a population-level, yet long-term individual-level studies are undoubtedly important. We compared the travelling- and dive behaviour characteristics of 22 adult male southern elephant seals (Mirounga leonina) tracked from King George Island / Isla 25 de Mayo (KGI) at the Antarctic Peninsula, with data obtained from 28 migrations performed by 17 adult males tracked from sub-Antarctic Marion Island (MI). The population-level home ranges of seals were similar in size for their two-dimensional home ranges (95% kernel density estimate: MI = 2.19 million km²; KGI = 2.1 million km²). However, Marion Island elephant seals typically performed deeper dives (MI = 605 ± 427 m; KGI = 444 ± 282 m), resulting in substantial differences between the total water volumes used when incorporating dive depths into population-level home range estimates (three-dimensional 95% kernel density estimate: MI = 1.4 million km³; KGI = 0.67 million km³). We further investigated the relative influences of population of origin, individual-level behavioural variability, estimated seafloor depths and migration type (i.e. post-moulting vs post-breeding migrations) on the three-dimensional home ranges of study animals. We found no statistically significant support for consistent individual-level differences in three-dimensional home range sizes between populations, but rather that individual-level variability explained most of the data variance, followed by other drivers (e.g. migration time and seafloor depth). These results highlight the need for continued broad-scale long-term individual-level monitoring in this species to inform population-level resource use and habitat requirements.

Description: Fidelity to foraging sites and foraging strategies is potentially beneficial to individuals using habitats with patchily distributed resources, as in a number of marine mammal species. We assessed inter-annual and long term (up to eight year) patterns in the spatial distribution and diving strategies used by southern elephant seals (Mirounga leonina) from sub-Antarctic Marion Island, instrumented with satellite-relay data loggers over multiple foraging migrations. We calculated inter-annual three-dimensional (3D) kernel density (KD) range overlaps for seals tracked over at least two post-moult foraging migrations in order to assess overlap for both the water depths and temperatures targeted during foraging migrations. We used intra-class correlation coefficients from linear mixed effects models to calculate intra- and inter-individual variance for a series of track and dive metrics. A repeatability index was ultimately derived for individual metrics, where higher values (between 0.5 and 1) indicate individually unique consistent behaviours, since greater variance occurs between, and not within, individual behaviours. Individual seals displayed high levels of fidelity to vertical depth layers where mean overlap for 95% 3D KD homerange estimates were 52.6% (inter-annual) and 34.3% (multi-year). Similarly, high levels of fidelity to temperature zones were evident where mean overlap for 95% 3D KD homerange estimates were 48% (inter-annual) and 35% (multi-year). Repeatability index values ranged between 0.38 and 0.57 for all metrics tested, indicating that the variance between individuals tested was generally not substantially more than within individuals. This study is the first to show that southern elephant seals display high levels of foraging niche fidelity in terms of spatial areas used, vertical depth layers targeted, as well as preferred in situ thermal conditions. Such observed inter-migration stability in habitat use patterns likely confers long-term energetic advantages to individual seals, despite little evidence for individually unique behaviours between these seals. While previous studies suggested likely inter-sex and inter-age-class avoidance of intra-specific competition in southern elephant seals, the apparent lack of individually unique foraging strategies reported here indicates that there is little individual level avoidance of intra-specific competition.

Description: Long-term fidelity to foraging areas may have fitness benefits to individuals, particularly in unpredictable environments. However, such strategies may result in short-term energetic losses and delay responses to fast environmental changes. We used satellite tracking data and associated diving data to record the habitat use of nine individual southern elephant seals over 34 winter migrations. By assessing overlap in two- and three-dimensional home ranges we illustrate strong long-term (up to 7-year) fidelity to foraging habitat. Furthermore, a repeatability statistic and hierarchical clustering exercise provided evidence for individual specialization of foraging migration strategies.We discuss the possible influences of stable long-term foraging migration strategies on the adaptability of individual elephant seals to rapid environmental change. Our results further illustrate the need for more long-term longitudinal studies to quantify the influence of individual-level site familiarity, fidelity and specialization on population-level resource selection and population dynamics.

Description: The region around the sill of the Filchner Trough outflow (77°S, 36°W) is considered a hot spot, both in terms of biology and physical oceanography. The factors contributing to this oceanic area of enhanced food availability and its relation to physical processes are not yet understood. Animal-borne satellite telemetry of southern elephant seal males, instrumented at King George Island / Isla 25 de Mayo aims to describe the seals' preferred foraging depths around the Filchner Trough in order to elucidate the vertical distribution of prey in relation to the oceanographic features on-site. Recent deployments (2010) represent a follow-up study of an ARGOS satellite telemetry project on elephant seals in 2000. Adult males travelled deep into the winter pack ice of the Weddell Sea along the western continental shelf break until they reached the region of the sill of the Filchner Trough outflow, where they remained in a localized 100 km wide shelf-slope area for several months. The re-instrumentation aims to investigate if males continue to travel to similar areas. The trilateral, long-term observation study of scientists from South Africa, Argentina and Germany is based on a synoptic approach for Marion Island and King George Island / Isla 25 de Mayo.

Description: The potential effects of ocean warming on marine predators are largely unknown, though the impact on the distribution of prey in vertical space may have far reaching impacts on diving predators such as southern elephant seals. We used data from satellite-tracked southern elephant seals from Marion Island to investigate the relationship between their dive characteristics (dive depths, dive durations and time-at-depth index values) and environmental variables (temperature at depth, depth of maximum temperature below 100 m, frontal zone and bathymetry) as well as other demographic and behavioural variables (migration stage, age-class, track day and vertical diel strategy). While other variables, such as bathymetry and vertical diel strategy also influenced dive depth, our results consistently indicated a significant influence of temperature at depth on dive depths. This relationship was positive for all groups of animals, indicating that seals dived to deeper depths when foraging in warmer waters. Female seals adjusted their dive depths proportionally more than males in warmer water. Dive durations were also influenced by temperature at depth, though to a lesser extent. Results from time-at-depth indices showed that both male and female seals spent less time at targeted dive depths in warmer water, and were presumably less successful foragers when diving in warmer water. Continued warming of the Southern Ocean may result in the distribution of prey for southern elephant seals shifting either poleward and/or to increasing depths. Marion Island elephant seals are expected to adapt their ranging and diving behaviour accordingly, though such changes may result in greater physiological costs associated with foraging.