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The marine coastal region makes up just 10% of the total area of the global ocean but contributes nearly 20% of its total primary production and over 80% of fisheries landings. Unicellular phytoplankton dominate primary production. Climate variability has had impacts on various marine ecosystems, but most sites are just approaching the age at which ecological responses to longer term, unidirectional climate trends might be distinguished. All five marine pelagic sites in the US Long Term Ecological Research (LTER) network are experiencing warming trends in surface air temperature. The marine physical system is responding at all sites with increasing mixed layer temperatures and decreasing depth and with declining sea ice cover at the two polar sites. Their ecological responses are more varied. Some sites show multiple population or ecosystem changes, whereas, at others, changes have not been detected, either because more time is needed or because they are not being measured.

We evaluated annual and regional variation in the dietary niche ofPygoscelispenguins including the sea ice-obligate Adélie penguin (Pygoscelis adeliae), and sea ice-intolerant chinstrap (Pygoscelis antarcticus) and gentoo (Pygoscelis papua) penguins, three species that nest throughout the western Antarctic Peninsula (AP) to test thesea ice trophic interaction hypothesis, which posits that penguin breeding populations with divergent trends, i.e., declining or increasing, are reliant on differing food webs. Our study relies on values of naturally occurring carbon (13C/12C, δ13C) and nitrogen (15N/14N, δ15N) stable isotopes as integrated proxies of penguin food webs measured over three years at three different breeding colonies. At Anvers Island in the north, where reductions in sea ice and changes in breeding population trends among sympatric sea ice-obligate (Adélie) and sea ice-intolerant (chinstrap and gentoo) penguins have been most notable, our analyses show that all three species ofPygoscelispenguins became more similar isotopically over the reproductive period. By late chick-rearing at Anvers Island, crèched chicks at 5-weeks-old for all species occupied similar trophic positions. Isotopic mixing models indicated that the proportions of prey provisioned by adult penguins to 5-week-old chicks at Anvers Island were generally similar across species within years, consisting primarily of Antarctic krill (Euphausia superba). Crèched Adélie chicks had higher δ13C and δ15N values at Avian and Charcot Islands, southern breeding colonies where sea ice is more prominent and populations of Adélie penguins have increased or remain stable. Trophic position increased with latitude, while the proportions of prey provisioned by Adélie penguin adults to chicks at southern breeding colonies included species typical of high Antarctic marine food webs, especially crystal krill (Euphausia crystallorophias). A Bayesian metric for dietary niche width, standard ellipse area (SEA-B), indicated thatPygoscelispenguins with greater population changes in the north had more variability in dietary niche width than stable populations further south. Our results lend insight on marine food web drivers ofPygoscelispenguin reproduction at the regional scale and question the long-standing paradigm that Antarctic krill are the only food web component critical to penguin reproductive survival in this region of the Southern Ocean.

Ecosystems across the United States are changing in complex and unpredictable ways and analysis of these changes requires coordinated, long‐term research. This paper is a product of a synthesis effort of the U.S. National Science Foundation funded Long‐Term Ecological Research (LTER) network addressing the LTER core research area of “populations and communities.” This analysis revealed that each LTER site had at least one compelling “story” about what their site would look like in 50–100 yr. As the stories were prepared, themes emerged, and the stories were group into papers along five themes: state change, connectivity, resilience, time lags, and cascading effects. This paper addresses the cascading effects theme and includes stories from the Bonanza Creek (boreal), Kellogg Biological Station (agricultural and freshwater), Palmer (Antarctica), and Harvard Forest (temperate forest) LTER sites. We define cascading effects very broadly to include a wide array of unforeseen chains of events that result from a variety of actions or changes in a system. While climate change is having important direct effects on boreal forests, indirect effects mediated by fire activity—severity, size, and return interval—have large cascading effects over the long term. In northeastern temperate forests, legacies of human management and disturbance affect the composition of current forests, which creates a cascade of effects that interact with the climate‐facilitated invasion of an exotic pest. In Antarctica, declining sea ice creates a cascade of effects including declines in Adèlie and increases in Gentoo penguins, changes in phytoplankton, and consequent changes in zooplankton populations. An invasion of an exotic species of lady beetle is likely to have important future effects on pest control and conservation of native species in agricultural landscapes. New studies of zebra mussels, a well‐studied invader, have established links between climate, the heat tolerance of the mussels, and harmful algal blooms. Collectively, these stories highlight the need for long‐term studies to sort out the complexities of different types of ecological cascades. The diversity of sites within the LTER network facilitates the emergence of overarching concepts about trophic interactions as an important driver of ecosystem structure, function, services, and futures.

Principal Investigators from several sites within the Long Term Ecological Research (LTER) program offer their insights about how long-term research has been effectively sustained from periods ranging from 20 to 40 years. The sites are: Hubbard Brook (New Hampshire), Konza Prairie (Kansas), Niwot Ridge (Colorado), Arctic (Alaska), Palmer Station (Antarctica), and Georgia Coastal Ecosystems (Georgia). The main themes discussed include: the importance of a strong foundation and common vision, creating a culture of collaboration and cooperation, showing the relevance of research to societal needs, managing conflict resolution, encouraging innovation, facilitating an exchange of ideas, working to build collaborations, willingness to adopt new management structures, and careful attention to transitions in leadership. The conclusion summarizes themes based on this chapter as well as other chapters in the book.

Climate‐induced range overlap can result in novel interactions between similar species and potentially lead to competitive exclusion. The West Antarctic Peninsula (WAP) is one of the most rapidly warming regions on Earth and is experiencing a poleward climate migration from a polar to subpolar environment. This has resulted in a range expansion of the ice‐intolerant gentoo penguins (Pygoscelis papua) and a coincident decrease in ice‐obligate Adélie penguins (P. adeliae) near Palmer Station, Anvers Island, WAP. Ecologically similar species that share a limited prey resource must occupy disparate foraging niches in order to co‐exist. Therefore, we determined the extent of foraging and dietary niche segregation between Adélie and gentoo penguins during the austral breeding season near Palmer Station. This research was conducted across six breeding seasons, from 2009 to 2014, which allowed us to investigate niche overlap in the context of interannual resource variability. Using biotelemetry and diet sampling, we found substantial overlap in the diets of Adélie and gentoo penguins, who primarily consumed Antarctic krill (Euphausia superba); however, our results showed that Adélie and gentoo penguins partitioned this shared prey resource through horizontal segregation of their core foraging areas. We did not find evidence that Antarctic krill were a limiting resource during the breeding season or that climate‐induced sympatry of Adélie and gentoo penguins resulted in competition for prey or caused the subsequent differing population trajectories. This apparent absence of resource competition between Adélie and gentoo penguins throughout this study implies that current population trends in this region are governed by other biological and physical factors. Our results highlight the importance of understanding the mechanistic processes that influence top predator populations in the context of climate‐driven ecosystem shifts.

Adélie penguins (Pygoscelis adeliae) are responding to ocean–climate variability throughout the marine ecosystem of the western Antarctic Peninsula (WAP) where some breeding colonies have declined by 80%. Nuclear and mitochondrial DNA (mtDNA) markers were used to understand historical population genetic structure and gene flow given relatively recent and continuing reductions in sea ice habitats and changes in numbers of breeding adults at colonies throughout the WAP. Genetic diversity, spatial genetic structure, genetic signatures of fluctuations in population demography and gene flow were assessed in four regional Adélie penguin colonies. The analyses indicated little genetic structure overall based on bi-parentally inherited microsatellite markers (FST=-0.006–0.004). No significant variance was observed in overall haplotype frequency (mtDNAΦST=0.017;P=0.112). Some comparisons with Charcot Island were significant, suggestive of female-biased philopatry. Estimates of gene flow based on a two-population coalescent model were asymmetrical from the species’ regional core to its northern range. Breeding Adélie penguins of the WAP are a panmictic population and hold adequate genetic diversity and dispersal capacity to be resilient to environmental change.

We herein review the modeling approach of Pinkerton et al. (2016, Ecol. Modelling), who tested the hypothesis that fishery depletion of large, neutrally buoyant Antarctic toothfish (Dissostichus mawsoni) was implicated in the recent increase in the southern Ross Sea population of Adelie penguins (Pygoscelis adeliae). Toothfish are a trophic competitor of penguins for Antarctic silverfish (Pleuragramma antarctica) in the southern Ross Sea, hence Ainley et al. (2013) and Lyver et al. (2014) proposed that the effect of the removal of toothfish was through predation release of silverfish. Pinkerton et al. concluded that predation release could not provide sufficient energy to sustain the observed penguin population growth. Critically, however, they failed to consider certain spatial and size-by-depth aspects of diet overlap, and mechanisms associated with population dynamics that could cause the population growth through predation release. In order to effectively test the prey release hypothesis, we suggest a strong inference path that incorporates what we know about population dynamics in penguins and Ross Sea food webs into life history parameterizations of penguins, toothfish and silverfish population dynamics models.

Foraging strategies in gentoo penguins (Pygoscelis papua) have been well studied (e.g. Croxall et al. 1988, Robinson & Hindell 1996, Lescroël et al. 2004, Takahashi et al. 2008, Xavier et al. 2017). The general consensus is this largest member of the three pygoscelid penguins displays both nearshore benthic and pelagic foraging tactics to consume combinations of crustaceans and fish. In a recent study, Carpenter-Kling et al. (2017) reported that gentoos at sub-Antarctic Marion Island displayed a novel foraging strategy that consisted of alternating typical lengthy foraging trips with much shorter nearshore afternoon trips. They suggest the latter foraging behaviour may be a response to suboptimal feeding conditions caused by local environmental change. This novel discovery reinforces the fact that, despite considerable study, not all foraging tactics in penguins have been documented. In this paper, we describe what we believe to be, yet another undocumented foraging tactic employed by gentoos.

Motivation The BioTIME database contains raw data on species identities and abundances in ecological assemblages through time. These data enable users to calculate temporal trends in biodiversity within and amongst assemblages using a broad range of metrics. BioTIME is being developed as a community-led open-source database of biodiversity time series. Our goal is to accelerate and facilitate quantitative analysis of temporal patterns of biodiversity in the Anthropocene. Main types of variables included The database contains 8,777,413 species abundance records, from assemblages consistently sampled for a minimum of 2 years, which need not necessarily be consecutive. In addition, the database contains metadata relating to sampling methodology and contextual information about each record. Spatial location and grain BioTIME is a global database of 547,161 unique sampling locations spanning the marine, freshwater and terrestrial realms. Grain size varies across datasets from 0.0000000158 km2 (158 cm2) to 100 km2 (1,000,000,000,000 cm2). Time period and grain BioTIME records span from 1874 to 2016. The minimal temporal grain across all datasets in BioTIME is a year. Major taxa and level of measurement BioTIME includes data from 44,440 species across the plant and animal kingdoms, ranging from plants, plankton and terrestrial invertebrates to small and large vertebrates. Software format .csv and .SQL., Global Ecology and Biogeography, 27 (7), ISSN:1466-822X, ISSN:1466-8238

Reproductive timing in many taxa plays a key role in determining breeding productivity , and is often sensitive to climatic conditions . Current climate change may alter the timing of breeding at different rates across trophic levels, potentially resulting in temporal mismatch between the resource requirements of predators and their prey . This is of particular concern for highertrophic-level organisms, whose longer generation times confer a lower rate of evolutionary rescue than primary producers or consumers. However, the disconnection between studies of ecological change in marine systems makes it difficult to detect general changes in the timing of reproduction5 . Here, we use a comprehensive meta-analysis of 209 phenological time series from 145 breeding populations to show that, on average, seabird populations worldwide have not adjusted their breeding seasons over time (−0.020 days yr−1 ) or in response to sea surface temperature (SST) (−0.272 days °C−1 ) between 1952 and 2015. However, marked between-year variation in timing observed in resident species and some Pelecaniformes and Suliformes (cormorants, gannets and boobies) may imply that timing, in some cases, is affected by unmeasured environmental conditions. This limited temperature-mediated plasticity of reproductive timing in seabirds potentially makes these top predators highly vulnerable to future mismatch with lower-trophic-level resources Fil: Keogan, Katharine. University of Edinburgh; Reino Unido Fil: Daunt, Francis. Centre for Ecology & Hydrology; Reino Unido Fil: Wanless, Sarah. Centre for Ecology & Hydrology; Reino Unido Fil: Phillips, Richard A.. British Antarctic Survey; Reino Unido Fil: Walling, Craig A.. University of Edinburgh; Reino Unido Fil: Agnew, Philippa. Oamaru Blue Penguin Colony; . Oamaru Blue Penguin Colony; Nueva Zelanda Fil: Ainley, David G.. HT Harvey and Associates; Estados Unidos Fil: Anker-Nilssen, Tycho. Norwegian Institute For Nature Research; Noruega Fil: Ballard, Grant. Point Blue Conservation Science; Estados Unidos Fil: Barrett, Robert T.. Uit The Arctic University Of Norway; Noruega Fil: Barton, Kerry J.. Landcare Research; Nueva Zelanda Fil: Bech, Claus. Norges Teknisk-naturvitenskapelige Universitet; Noruega Fil: Becker, Peter. Institut Fur Vogelforschung "vogelwarte Helgoland"; Alemania Fil: Berglund, Per-Arvid. University of Agricultural Sciences. Institute of Marine Research, Department of Aquatic Resources; Suecia Fil: Bollache, Loïc. Universite de Bourgogne; Francia Fil: Bond, Alexander L.. Memorial University Of Newfoundland; Canadá Fil: Bouwhuis, Sandra. Institut Fur Vogelforschung "vogelwarte Helgoland"; Alemania Fil: Bradley, Russell W.. Point Blue Conservation Science; Estados Unidos Fil: Burr, Zofia M.. The University Centre In Svalbard; Noruega Fil: Camphuysen, Kees. University of Utrecht; Países Bajos Fil: Catry, Paulo. Ispa - Instituto Universitário; Portugal Fil: Chiaradia, Andre. Monash University; Australia. Phillip Island Nature Park; Australia Fil: Christensen-Dalsgaard, Signe. Norwegian Institute for Nature Research; Noruega Fil: Cuthbert, Richard. Royal Society For The Protection Of Birds; Reino Unido Fil: Dehnhard, Nina. Universiteit Antwerp; Bélgica Fil: Descamps, Sébastien. Norwegian Polar Institute; Noruega Fil: Diamond, Tony. University Of New Brunswick; Canadá Fil: Divoky, George. Friends of Cooper Island; Estados Unidos Fil: Drummond, Hugh. Universidad Nacional Autónoma de México; México Fil: Dugger, Katie M.. United States Geological Survey; Estados Unidos Fil: Dunn, Michael J.. British Antarctic Survey; Reino Unido Fil: Emmerson, Louise. Australian Antarctic Division; Australia Fil: Erikstad, Kjell Einar. Norwegian Polar Institute; Noruega Fil: Fort, Jérôme. Université de la Rochelle; Francia Fil: Fraser, William. Polar Oceans Research Group; Estados Unidos Fil: Genovart, Meritxell. Consejo Superior de Investigaciones Cientificas. Instituto Mediterraneo de Estudios Avanzados; España Fil: Gilg, Olivier. Universite de Bourgogne; Francia. Groupe de Recherches En Ecologie Arctique; Fil: González-Solís, Jacob. Universidad de Barcelona; España Fil: Granadeiro, José Pedro. Universidade de Lisboa; Portugal Fil: Grémillet, David. University Of Cape Town; Sudáfrica Fil: Hansen, Jannik. University Aarhus; Dinamarca Fil: Hanssen, Sveinn A.. Norwegian Institute For Nature Research; Noruega Fil: Harris, Mike. Centre for Ecology & Hydrology; Reino Unido Fil: Hedd, April. Environment Canada; Canadá Fil: Hinke, Jefferson. National Oceanic And Atmospheric Administration; Estados Unidos Fil: Igual, José Manuel. Consejo Superior de Investigaciones Cientificas. Instituto Mediterraneo de Estudios Avanzados; España Fil: Jahncke, Jaime. Point Blue Conservation Science; Estados Unidos Fil: Jones, Ian. Memorial University Of Newfoundland; Canadá Fil: Kappes, Peter J.. Oregon Cooperative Fish And Wildlife Research Unit; Estados Unidos Fil: Lang, Johannes. Groupe de Recherche en Ecologie Arctique; Francia Fil: Langset, Magdalene. Norwegian Institute For Nature Research; Noruega Fil: Lescroël, Amélie. Géosciences Montpellier; Francia Fil: Lorentsen, Svein-Håkon. Norwegian Institute For Nature Research; Noruega Fil: Lyver, Phil O'B.. Landcare Research; Nueva Zelanda Fil: Mallory, Mark. Acadia University; Canadá Fil: Moe, Børge. Norwegian Institute For Nature Research; Noruega Fil: Montevecchi, William A.. Memorial University Of Newfoundland; Canadá Fil: Monticelli, David. University Of Coimbra, Marine And Environmental Sciences Center; Portugal Fil: Mostello, Carolyn. Massachusetts Division Of Fisheries And Wildlife; Estados Unidos Fil: Newell, Mark. Centre for Ecology & Hydrology; Reino Unido Fil: Nicholson, Lisa. Halfmoon Biosciences; Australia Fil: Nisbet, Ian. I. C. T. Nisbet & Company; Estados Unidos Fil: Olsson, Olof. Stockholms Universitet; Suecia Fil: Oro, Daniel. Consejo Superior de Investigaciones Cientificas. Instituto Mediterraneo de Estudios Avanzados; España Fil: Pattison, Vivian. Laskeek Bay Conservation Society; Canadá Fil: Poisbleau, Maud. Universiteit Antwerp; Bélgica Fil: Pyk, Tanya. Deakin University; Australia Fil: Quintana, Flavio Roberto. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina Fil: Ramos, Jaime A.. University Of Coimbra, Marine And Environmental Sciences Center; Portugal Fil: Ramos, Raül. Universidad de Barcelona; España Fil: Reiertsen, Tone Kirstin. Norwegian Polar Institute; Noruega Fil: Rodríguez, Cristina. Universidad Nacional Autónoma de México; México Fil: Ryan, Peter. University Of Cape Town; Sudáfrica Fil: Sanz-Aguilar, Ana. Consejo Superior de Investigaciones Cientificas. Instituto Mediterraneo de Estudios Avanzados; España Fil: Schmidt, Niels M.. University Aarhus; Dinamarca Fil: Shannon, Paula. National Audubon Society Seabird Restoration Program; Estados Unidos Fil: Sittler, Benoit. Groupe de Recherche en Ecologie Arctique; Francia Fil: Southwell, Colin. Australian Antarctic Division; Australia Fil: Surman, Christopher. Halfmoon Biosciences; Australia Fil: Svagelj, Walter Sergio. Universidad Nacional de Mar del Plata; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mar del Plata. Instituto de Investigaciones Marinas y Costeras. Universidad Nacional de Mar del Plata. Facultad de Ciencias Exactas y Naturales. Instituto de Investigaciones Marinas y Costeras; Argentina Fil: Trivelpiece, Wayne. Bolinas; Estados Unidos Fil: Warzybok, Pete. Point Blue Conservation Science; Estados Unidos Fil: Watanuki, Yutaka. Hokkaido University; Japón Fil: Weimerskirch, Henri. Centre National de la Recherche Scientifique; Francia Fil: Wilson, Peter R.. Landcare Research; Nueva Zelanda Fil: Wood, Andrew G.. British Antarctic Survey; Reino Unido Fil: Phillimore, Albert B.. University of Edinburgh; Reino Unido Fil: Lewis, Sue. University of Edinburgh; Reino Unido

The western Antarctic Peninsula is experiencing dramatic climate change as warm, wet conditions expand poleward and interact with local physics and topography, causing differen- tial regional effects on the marine ecosystem. At local scales, deep troughs (or canyons) bisect the continental shelf and act as conduits for warm Upper Circumpolar Deep Water, with reduced sea- sonal sea ice coverage, and provide a reservoir of macro- and micronutrients. Shoreward of many canyon heads are Adelie penguin breeding colonies; it is hypothesized that these locations reflect improved or more predictable access to higher biological productivity overlying the canyons. To synoptically assess the potential impacts of regional bathymetry on the marine ecosystem, 4 major canyons were identified along a latitudinal gradient west of the Antarctic Peninsula using a high- resolution bathymetric database. Biologicalphysical dynamics above and adjacent to canyons were compared using in situ pigments and satellite-derived sea surface temperature, sea ice and ocean color variables, including chlorophyll a (chl a) and fucoxanthin derived semi-empirically from remote sensing reflectance. Canyons exhibited higher sea surface temperature and reduced sea ice coverage relative to adjacent shelf areas. In situ and satellite-derived pigment patterns indicated increased total phytoplankton and diatom biomass over the canyons (by up to 22 and 35%, respectively), as well as increases in diatom relative abundance (fucoxanthin:chl a). While regional heterogeneity is apparent, canyons appear to support a phytoplankton community that is conducive to both grazing by krill and enhanced vertical export, although it cannot compensate for decreased biomass and diatom relative abundance during low sea ice conditions.

Evidence of climate change-driven shifts in plant and animal phenology have raised concerns that certain trophic interactions may be increasingly mismatched in time, resulting in declines in reproductive success. Given the constraints imposed by extreme seasonality at high latitudes and the rapid shifts in phenology seen in the Arctic, we would also expect Antarctic species to be highly vulnerable to climate change-driven phenological mismatches with their environment. However, few studies have assessed the impacts of phenological change in Antarctica. Using the largest database of phytoplankton phenology, sea-ice phenology, and Adelie penguin breeding phenology and breeding success assembled to date, we find that while a temporal match between penguin breeding phenology and optimal environmental conditions sets an upper limit on breeding success, only a weak relationship to the mean exists. Despite previous work suggesting that divergent trends in Adelie penguin breeding phenology are apparent across the Antarctic continent, we find no such trends. Furthermore, we find no trend in the magnitude of phenological mismatch, suggesting that mismatch is driven by interannual variability in environmental conditions rather than climate change-driven trends, as observed in other systems. We propose several criteria necessary for a species to experience a strong climate change-driven phenological mismatch, of which several may be violated by this system. This article is protected by copyright. All rights reserved.

The fledging mass of penguin chicks can be an indicator of food availability and environmental conditions at a penguin colony. For the period 1989 to 2011, we analyzed predictor variables of environmental and food resource factors acting on multiple spatial scales near Palmer Station, Antarctica, that may influence the interannual variability in Adelie penguin chick fledg- ing mass (CFM). To understand the influence of parental Adelie penguin diet on CFM, we mod- eled the energy density and krill demographics of penguin diet samples. We found a weak but sig- nificant positive relationship between the proportion of immature krill in adult penguin diets and CFM, which may indicate that krill recruitment and prey availability to adults influences CFM. However, the impact of large-scale climate and local weather outweighed the impact of parental diet characteristics on CFM. CFM was negatively associated with a positive Antarctic Oscillation (or Southern Annular Mode) and increased westerly winds and was positively associated with increased air temperature. The mechanistic relationship between climate, local weather, and CFM could include direct and indirect impacts, such as increased thermo-regulative costs for unattended chicks, decreased chick feeding frequency, and smaller meal mass for chicks driven by the geophysical transport of krill by climate and wind events.

Adelie penguins (Pygoscelis adeliae) are important predators of krill (Euphausia spp.) and Antarctic silverfish (Pleuragramma antarctica) during summer, are a key indicator of the status of the Southern Ocean ecosystem, and are therefore a focal species for the Committee for the Conservation of Antarctic Marine Living Resources (CCAMLR) Ecosystem Monitoring Program. The ability to monitor the population size of species potentially affected by Southern Ocean fisheries, i.e., the Adelie penguin, is critical for effective management of those resources. However, for several reasons, direct estimates of population size are not possible in many locations around Antarctica. In this study, we combine high-resolution (0.6 m) satellite imagery with spectral analysis in a supervised classification to estimate the sizes of Adelie penguin breeding colonies along Victoria Land in the Ross Sea and on the Antarctic Peninsula. Using satellite images paired with concurrent ground counts, we fit a generalized linear mixed model with Poisson errors to predict the abundance of breeding pairs as a function of the area of current-year guano staining identified in the satellite imagery. Guano-covered area proved to be an effective proxy for the number of penguins residing within. Our model provides a robust, quantitative mechanism for estimating the breeding population size of colonies captured in imagery and identifies terrain slope as a significant component influencing apparent nesting density. While our high-resolution satellite imagery technique was developed for the Adelie penguin, these principles are directly transferrable to other colonially nesting seabirds and other species that aggregate in fixed localities.

An inverse food-web model for the western Antarctic Peninsula (WAP) pelagic food web was constrained with data from Palmer Long Term Ecological Research (PAL-LTER) project annual austral summer sampling cruises. Model solutions were generated for 2 regions with Adelie penguin Pygoscelis adeliae colonies presenting different population trends (a northern and a southern colony) for a 12 yr period (1995�2006). Counter to the standard paradigm, comparisons of carbon flow through bacteria, microzooplankton, and krill showed that the diatomkrilltop predator food chain is not the dominant pathway for organic carbon exchanges. The food web is more complex, including significant contributions by microzooplankton and the microbial loop. Using both inverse model results and network indices, it appears that in the northern WAP the food web is dominated by the microbial food web, with a temporal trend toward its increasing importance. The dominant pathway for the southern WAP food web varies from year to year, with no detectable temporal trend toward dominance of microzooplankton versus krill. In addition, sensitivity analyses indicated that the northern colony of Adelie penguins, whose population size has been declining over the past 35 yr, appears to have sufficient krill during summer to sustain its basic metabolic needs and rear chicks, suggesting the importance of other processes in regulating the Adelie population decline.

The extent, duration, and seasonality of sea ice and glacial discharge strongly influence Antarctic marine ecosystems. Most organisms' life cycles in this region are attuned to ice seasonality. The annual retreat and melting of sea ice in the austral spring stratifies the upper ocean, triggering large phytoplankton blooms. The magnitude of the blooms is proportional to the winter extent of ice cover, which can act as a barrier to wind mixing. Antarctic krill, one of the most abundant metazoan populations on Earth, consume phytoplankton blooms dominated by large diatoms. Krill, in turn, support a large biomass of predators, including penguins, seals, and whales. Human activity has altered even these remote ecosystems. The western Antarctic Peninsula region has warmed by 7°C over the past 50 years, and sea ice duration has declined by almost 100 days since 1978, causing a decrease in phytoplankton productivity in the northern peninsula region. Besides climate change, Antarctic marine systems have been greatly altered by harvesting of the great whales and now krill. It is unclear to what extent the ecosystems we observe today differ from the pristine state.

Pygoscelis penguins are experiencing general population declines in their northernmost range whereas there are reported increases in their southernmost range. These changes are coincident with decadal-scale trends in remote sensed observations of sea ice concentrations (SIC) and sea surface temperatures (SST) during the chick-rearing season (austral summer). Using SIC, SST, and bathymetry, we identified separate chick-rearing niche spaces for the three Pygoscelis penguin species and used a maximum entropy approach (MaxEnt) to spatially and temporally model suitable chick-rearing habitats in the Southern Ocean. For all Pygoscelis penguin species, the MaxEnt models predict significant changes in the locations of suitable chick-rearing habitats over the period of 1982-2010. In general, chick-rearing habitat suitability at specific colony locations agreed with the corresponding increases or decreases in documented population trends over the same time period. These changes were the most pronounced along the West Antarctic Peninsula where there has been a rapid warming event during at least the last 50 years.

The population size of Antarctic minke whales Balaenoptera bonaerensis has been changing simultaneously with profound changes in the physics, i.e., mesopredator habitat features, of the Southern Ocean. Although the two trends may not be related, distinguishing among the factors responsible requires a better understanding of minke whale habitat preferences. For the first time at a large geographic scale, i.e., between 140° E and 35° W, we use data not constrained by vessels needing to avoid sea ice to model the habitat affinities of this pagophilic mesopredator. Using Maxent, we modeled minke whale proximity to the Antarctic Shelf Break Front (ASBF) and the southern boundary of Antarctic Circumpolar Current (sbACC), as well as association with sea ice, given that global climate change is altering the positions or intensity of these features. We also included water depth and chlorophyll (proxy for productivity) as variables. Minke whale presence data were gathered using strip and line census on 55 cruises on board icebreakers during late spring and summer, 1976–2005. The most important variable was distance to ASBF, followed by water depth and sea-ice concentration. That is, found principally in waters south of the sbACC during summer, minke whales were most abundant near the outer edge of the continental shelf (shallow depth), including areas heavily covered by sea ice. We propose that as the sbACC moves south and sea ice disappears, as projected by global climate models, minke whale habitat will shrink, and likely intra- and inter-specific competition will increase.

Adelie penguins (Pygoscelis adeliae), carabeater seals (Lobodon carcinophagus), humpback (Megaptera novaeangliae), and minke whales (Balaenoptera bonaernsis) are found in the waters surrounding the Western Antarctic Peninsula. Each species relies primarily on Antarctic krill (Euphausia superba) and has physiological constraints and foraging behaviors that dictate their ecological niches. Understanding the degree of ecological overlap between sympatric krill predators is critical to understanding and predicting the impacts on climate-driven changes to the Antarctic marine ecosystem. To explore ecological relationships amongst sympatric krill predators, we developed ecological niche models using a maximum entropy modeling approach (Maxent) that allows the integration of data collected by a variety of means (e.g. satellite-based locations and visual observations). We created spatially explicit probability distributions for the four krill predators in fall 2001 and 2002 in conjunction with a suite of environmental variables. We find areas within Marguerite Bay with high krill predator occurrence rates or biological hot spots. We find the modeled ecological niches for Adelie penguins and crabeater seals may be affected by their physiological needs to haul-out on substrate. Thus, their distributions may be less dictated by proximity to prey and more so by physical features that over time provide adequate access to prey. Humpback and minke whales, being fully marine and having greater energetic demands, occupy ecological niches more directly proximate to prey. We also find evidence to suggest that the amount of overlap between modeled niches is relatively low, even for species with similar energetic requirements. In a rapidly changing and variable environment, our modeling work shows little indication that krill predators maintain similar ecological niches across years around Marguerite Bay. Given the amount of variability in the marine environment around the Antarctic Peninsula and how this affects the local abundance of prey, there may be consequences for krill predators with historically little niche overlap to increase the potential for interspecific competition for shared prey resources.

In accord with the hypotheses driving the Southern Ocean Global Ocean Ecosystems Dynamics (SO GLOBEC) program, we tested the hypothesis that the winter foraging ecology of a major top predator in waters off the Western Antarctic Peninsula (WAP), the Adelie penguin (Pygoscelis adeliae), is constrained by oceanographic features related to the physiography of the region. This hypothesis grew from the supposition that breeding colonies in the WAP during summer are located adjacent to areas of complex bathymetry where circulation and upwelling processes appear to ensure predictable food resources. Therefore, we tested the additional hypothesis that these areas continue to contribute to the foraging strategy of this species throughout the non-breeding winter season. We used satellite telemetry data collected as part of the SO GLOBEC program during the austral winters of 2001 and 2002 to characterize individualpenguinforaginglocations inrelation tobathymetry, seaicevariability withinthe pack ice, and wind velocity and divergence (as a proxy for potential areas with cracks and leads). We also explored differences between males and females in core foraging area overlap. Ocean depth was the most influential variable in the determination of foraging location, with most birds focusing their effort on shallow (o200 m) waters near land and on mixed-layer (200-500 m) waters near the edge of deep troughs. Within-ice variability and wind (as a proxy for potential areas with cracks and leads) were not foundtobe influentialvariables, which islikelybecause of the low resolution satellite imagery and model outputs that were available. Throughout the study period, all individuals maintained a core foraging area separated from other individuals with very little overlap. However, from a year with light sea ice to one with heavy ice cover (2001-2002), we observed an increase in the overlap of individual female foraging areas with those of other birds, likely due to restricted access to the water column, reduced prey abundance, or higher prey concentration. Male birds maintained separate core foraging areas with the same small amount of overlap, showing no difference in overlap between the years. While complex bathymetry was an important physical variable influencing the Adelie penguin's foraging, the analysis of sea icedata ofa higher resolution than was availablefor thisstudymayhelpelucidate therole ofsea icein affecting Adelie penguin winter foraging behavior within the pack ice.

Waters off the western Antarctic Peninsula (i.e., the eastern Bellingshausen Sea) are unusually complex owing to the convergence of several major fronts. Determining the relative influence of fronts on occurrence patterns of top-trophic species in that area, therefore, has been challenging. In one of the few ocean-wide seabird data syntheses, in this case for the Southern Ocean, we analyzed ample, previously collected cruise data, Antarctic-wide, to determine seabird species assemblages and quantitative relation- ships to fronts as a way to provide context to the long-term Palmer LTER and the winter Southern Ocean GLOBEC studies in the eastern Bellingshausen Sea. Fronts investigated during both winter (April– September) and summer (October–March) were the southern boundary of the Antarctic Circumpolar Current (ACC), which separates the High Antarctic from the Low Antarctic water mass, and within which are embedded the marginal ice zone and Antarctic Shelf Break Front; and the Antarctic Polar Front, which separates the Low Antarctic and the Subantarctic water masses. We used clustering to determine species’ groupings with water masses, and generalized additive models to relate species’ densities, biomass and diversity to distance to respective fronts. Antarctic-wide, in both periods, highest seabird densities and lowest species diversity were found in the High Antarctic water mass. In the eastern Bellingshausen, seabird density in the High Antarctic water mass was lower (as low as half that of winter) than found in other Antarctic regions. During winter, Antarctic-wide, two significant species groups were evident: one dominated by Ade´ lie penguins (Pygoscelis adeliae) (High Antarctic water mass) and the other by petrels and prions (no differentiation among water masses); in eastern Bellingshausen waters during winter, the one significant species group was composed of species from both Antarctic-wide groups. In summer, Antarctic- wide, a High Antarctic group dominated by Ade´ lie penguins, a Low Antarctic group dominated by petrels, and a Subantarctic group dominated by albatross were evident. In eastern Bellingshausen waters during summer, groups were inconsistent. With regard to frontal features, Antarctic-wide in winter, distance to the ice edge was an important explanatory factor for nine of 14 species, distance to the Antarctic Polar Front for six species and distance to the Shelf Break Front for six species; however, these Antarctic-wide models could not successfully predict spatial relationships of winter seabird density (individual species or total) and biomass in the eastern Bellingshausen. Antarctic-wide in summer, distance to land/Antarctic continent was important for 10 of 18 species, not a surprising result for these summer-time Antarctic breeders, as colonies are associated with ice-free areas of coastal land. Distance to the Shelf Break Front was important for 8 and distance to the southern boundary of the ACC was important for 7 species. These summer models were more successful in predicting eastern Bellingshausen species density and species diversity but failed to predict total seabird density or biomass. Antarctic seabirds appear to respond to fronts in a way similar to that observed along the well-studied upwelling front of the California Current. To understand fully the seabird patterns found in this synthesis, multi-disciplinary at-sea investigations, including a quantified prey field, are needed.

On 20 and 22 January 2007, we observed macaroni penguins (Eudyptes chrysolophus) on Avian Island, Antarctica, approximately 1° south of the Antarctic Circle along the Western Antarctic Peninsula (WAP) near Adelaide Island, a new high-latitude observational record for the species within this region of the continent. Additionally, we report several extra-limital sightings of macaroni penguins over the last decade at relatively lower latitudes along the WAP near Anvers Island, including observations of breeding attempts. Although vagrancy cannot be ruled out as a possible causal factor in our observations, we hypothesize that a climate-induced shift in the species’ bio-geographic range may be in progress. In this context, our observations are similar to the well-documented range shifts and eventual establishment of breeding populations by other sub-Antarctic penguin species along the WAP, over the last three decades, in response to regional climate warming. We highlight that the few observations reported here do not provide conclusive evidence for any putative causal mechanism explaining the presence of macaroni penguins at locations outside their natural geographic range. However, our observations are important for developing a better understanding of the natural history of the species along the WAP.

Factors that control variability in energy density of Antarctic krill (Euphausia superba) populations, and the consequences of this variability for growth and fledging mass of Adelie penguin (Pygoscelis adeliae) chicks, were investigated using an individual-based energetics model. Lipid content as a function of sex/maturity stage and season was used to calculate the energy density of krill ingested by chicks. Simulations tested the influence of variability in krill size-class distribution, sex-ratio, length-at-maturity, and the timing of spawning on krill population energy density and penguin chick fledging mass. Of the parameters included in simulations, variability in the timing of krill spawning had the greatest influence on predicted Adelie penguin fledging mass, with fledging mass decreasing from 3.30 to 2.92 kg when peak spawning was shifted from early December to early March. Adelie penguin chicks that fledge from colonies along the western Antarctic Peninsula (wAP) and survive to recruit into the breeding population are 0.117 kg heavier than those that do not survive to breed. Thus, it appears that small differences in fledging mass potentially have significant implications for Adelie penguin chick survivorship. Therefore, the timing of krill spawning may have important consequences for Adelie penguins, and other top-predator species, that may time critical activities to coincide with a period of dependable prey availability with maximum energy density.

We assess the response of pack ice penguins, Emperor (Aptenodytes forsteri) and Adelie (Pygoscelis adeliae), to habitat variability and, then, by modeling habitat alterations, the qualitative changes to their populations, size and distribution, as Earth's average tropospheric temperature reaches 28C above preindustrial levels (ca. 1860), the benchmark set by the European Union in efforts to reduce greenhouse gases. First, we assessed models used in the Intergovernmental Panel on Climate Change Fourth Assessment Report (AR4) on penguin performance duplicating existing conditions in the Southern Ocean. We chose four models appropriate for gauging changes to penguin habitat: GFDL-CM2.1, GFDL-CM2.0, MIROC3.2(hi-res), and MRI-CGCM2.3.2a. Second, we analyzed the composited model ENSEMBLE to estimate the point of 28C warming (2025-2052) and the projected changes to sea ice coverage (extent, persistence, and concentration), sea ice thickness, wind speeds, precipitation, and air temperatures. Third, we considered studies of ancient colonies and sediment cores and some recent modeling, which indicate the (space/time) large/centennial- scale penguin response to habitat limits of all ice or no ice. Then we considered results of statistical modeling at the temporal interannual-decadal scale in regard to penguin response over a continuum of rather complex, meso- to large-scale habitat conditions, some of which have opposing and others interacting effects. The ENSEMBLE meso/decadal-scale output projects a marked narrowing of penguins' zoogeographic range at the 28C point. Colonies north of 708 S are projected to decrease or disappear: ;50% of Emperor colonies (40% of breeding population) and ;75% of Adelie colonies (70% of breeding population), but limited growth might occur south of 738 S. Net change would result largely from positive responses to increase in polynya persistence at high latitudes, overcome by decreases in pack ice cover at lower latitudes and, particularly for Emperors, ice thickness. Adelie Penguins might colonize new breeding habitat where concentrated pack ice diverges and/or disintegrating ice shelves expose coastline. Limiting increase will be decreased persistence of pack ice north of the Antarctic Circle, as this species requires daylight in its wintering areas. Adelies would be affected negatively by increasing snowfall, predicted to increase in certain areas owing to intrusions of warm, moist marine air due to changes in the Polar Jet Stream.

Baleen whales and Adelie penguins in the near-shore waters around the Antarctic Peninsula forage principally on Antarctic krill. Given the spatial overlap in the distribution of these krill predators (particularly humpback whales) and their dependence on krill, the goals of this paper are to determine if the inter-annual community structure and relative abundance of baleen whales around Anvers Island is related to krill demography and abundance, and if the potential exists for inter-specific interactions between Adelie penguins and baleen. We use whale sightings and prey data from both net tows and Adelie penguin stomach samples to correlate the abundance of humpback whales with krill demography and abundance from 1993 to 2001. We find significant relationships between whale abundance and the size–frequency distribution of krill targeted by Adelie penguins, as well as the foraging success of Adelie penguins. These findings suggest both krill predators share common prey preferences in the upper portions of the water column around Anvers Island. These findings highlight the need for better knowledge of baleen whale foraging ecology and inter-specific interactions with penguins, as sea ice and krill populations around the Antarctic Peninsula are affected by rapid changes in climate.

We consider how Antarctic seals may respond to changes in climate, realizing that anthropogenic alteration of food webs will influence these responses. The species considered include the ice-obligate - crabeater (Lobodon carcinophaga), Weddell (Leptonychotes weddellii), Ross (Ommataphoca rossii) and leopard (Hydrurga leptonyx) seal - and the ice-tolerant Antarctic fur seal (Arctocephalus gazella) and southern elephant seal (Mirounga leonina). The data analysed are from long-term censuses of Weddell seals in McMurdo Sound (1997–2006), and of Weddell, fur and elephant seals at Arthur Harbour, Antarctic Peninsula (1974–2005). After considering their responses to recent changes in environmental features, as well as projected and current changes to their habitat our conclusions are that the distribution and abundance of 1) crabeater and Weddell seals will be negatively affected by changes in the extent, persistence and type of annual sea ice, 2) Ross and leopard seal will be the least negatively influenced by changes in pack ice characteristics, although, as may be the case for crabeater and Weddell, population size and distribution may be altered through changes in food web dynamics, and 3) southern elephant and fur seals will respond in ways opposite to the pack ice species, but could also be influenced most immediately by changes in their food resources due to factors other than climate.

A key hypothesis guiding the US Southern Ocean Global Ocean Ecosystems Dynamics (US SO GLOBEC) program is that deep across-shelf troughs facilitate the transport of warm and nutrient-rich waters onto the continental shelf of the Western Antarctic Peninsula, resulting in enhanced winter production and prey availability to top predators. We tested aspects of this hypothesis during austral winter by assessing the distribution of the resident pack-ice top predators in relation to these deep across-shelf troughs and by investigating associations between top predators and their prey. Surveys were conducted July–August 2001 and August–September 2002 in Marguerite Bay, Antarctica, with a focus on the main across-shelf trough in the bay, Marguerite Trough. The common pack-ice seabird species were snow petrel ( Pagodroma nivea , 1.2 individuals km −2 ), Antarctic petrel ( Thalassoica antarctica , 0.3 individuals km −2 ), and Adelie penguin ( Pygoscelis adeliae , 0.5 individuals km −2 ). The most common pack-ice pinniped was crabeater seal ( Lobodon carcinophagus ). During both winters, snow and Antarctic petrels were associated with low sea-ice concentrations independent of Marguerite Trough, while Adelie penguins occurred in association with this trough. Krill concentrations, both shallow and deep, also were associated with Adelie penguin and snow petrel distributions. During both winters, crabeater seal occurrence was associated with deep krill concentrations and with regions of lower chlorophyll concentration. The area of lower chlorophyll concentrations occurred in an area with complex bathymetry close to land and heavy ice concentrations. Complex or unusual bathymetry via its influence on physical and biological processes appears to be one of the keys to understanding how top predators survive during the winter in this Antarctic region.

The Southern giant petrel (Macronectes gigan- teus) is declining over much of its range and currently is listed as vulnerable to extinction by the International Union for the Conservation of Nature (IUCN). Island-speciWc breeding colonies near Palmer Station, Antarctica, have been monitored for over 30 years, and because this popula- tion continues to increase, it is critically important to con- servation. In austral summer 2004, six diseased giant petrel chicks were observed in four of these colonies. Diseased chicks were 6-9 weeks old and had multiple proliferative nodules on their bills and skin. One severely aVected chick was found dead on the nest and was salvaged for necropsy. Histopathological examination of nodules from the dead chick revealed epithelial cell hyperplasia and hypertrophy with numerous eosinophilic intracytoplasmic inclusions (Bollinger bodies). A poxvirus was isolated from multiple nodules. Poxviral infection has not been reported in this species, and the reason for its emergence and its potential impact on the population are not yet known.

Climate-driven sympatry may lead to competition for food resources between species. Rapid warming in the West Antarctic Peninsula (WAP) is coincident with increasing gentoo penguin and decreasing Adélie penguin populations, suggesting that competition for food may exacerbate the Adélie penguin decline. On fine scales, we tested for foraging competition between these species during the chick-rearing period by comparing their foraging behaviors with the distribution of their prey, Antarctic krill. We detected krill aggregations within the horizontal and vertical foraging ranges of Adélie and gentoo penguins and found that krill selected for habitats that balance the need to consume food and avoid predation. In overlapping Adélie and gentoo penguin foraging areas, four gentoo penguins switched foraging behavior by foraging at deeper depths, a strategy which limits competition with Adélie penguins. This suggests that climate-driven sympatry does not necessarily result in competitive exclusion of Adélie penguins by gentoo penguins. Contrary to a recent theory, which suggests that increased competition for krill is one of the major drivers of Adélie penguin population declines, we suggest that declines in Adélie penguins along the WAP are more likely due to direct and indirect climate impacts on their life histories.

Micronektonic fishes and invertebrates were sampled with 32 midwater trawls at nine sites along the Western Antarctic Peninsula (WAP) in the austral fall (March–April) of 2010. Study sites were located within four hypothesized hydrographic regions: near Joinville Island in Region I, at Croker Passage, near Anvers Island, and near Renaud Island in Region II, within Marguerite Bay and the Marguerite Trough in Region III, and near Charcot Island in Region IV. A total of 62 taxa representing 12 taxonomic groups of pelagic invertebrates and 9 families of fish were captured, but assemblages were dominated by only a few species. The most numerically abundant taxa were the euphausiids, Thysanoessa macrura, Euphausia superba, and E. crystallorophias, combining to contribute nearly 79% of the total catch. Biomass dominants included E. superba, which contributed more than 44% of the total catch, the notothenioid Pleuragramma antarctica, and the salp, Salpa thompsoni. A comparison of total catches among sites revealed that the largest volumetric abundances and biomasses were captured at the Marguerite Bay site. Cluster analysis of abundance data identified distinct multispecies assemblages at Joinville Island in Region I, Croker Passage in Region II, Marguerite Bay in Region III, and Charcot Island in Region IV. A fifth distinct assemblage included samples from sites near Anvers and Renaud Island in Region II, and from the Marguerite Trough in Region III. Assemblages at Joinville Island and Croker Passage were both dominated by E. superba and S. thompsoni, but hydrographic conditions at Joinville Island favored a neritic assemblage, underscored by substantial numbers of P. antarctica. The assemblage at Croker Passage was more oceanic in nature with major inputs from the myctophid, Electrona antarctica and the hyperiid amphipod, Themisto gaudichaudii. Marguerite Bay and Charcot Island were well-mixed assemblages with strong representation by both neritic and oceanic fauna. The mid-peninsula assemblage was oceanic in character, being overwhelmingly dominated by Thysanoessa macrura and T. gaudichaudii. Pleuragramma antarctica were captured at five sites: Joinville Island, Croker Passage, Marguerite Bay, and the two sites near Charcot Island. They were completely absent at the two sites near Anvers Island, at Renaud Island, and in the Marguerite Trough. One fish was captured in Croker Passage. The majority of fish captured in Marguerite Bay were larger than 150 mm standard length (SL), with very few fish of smaller size present. If resident populations of Pleuragramma reproduce and recruit locally rather than being sustained by larval advection, those populations will be highly susceptible to local disappearance. This may be the causative factor behind the absence of Pleuragramma from the mid-peninsula region. Continued warming and subsequent sea ice reductions may not only cause Pleuragramma population collapses in the Marguerite Bay and Charcot Island regions, but may also change the character of the faunal assemblages along the WAP to those of an oceanic system.

Exceptional sea ice conditions occurred in the West Antarctic Peninsula (WAP) region from September 2001 to February 2002, resulting from a strongly positive atmospheric pressure anomaly in the South Atlantic coupled with strong negative anomalies in the Bellingshausen–Amundsen and southwest Weddell Seas. This created a strong and persistent north-northwesterly flow of mild and moist air across the WAP. In situ, satellite, and NCEP–NCAR Reanalysis (NNR) data are used to examine the profound and complex impact on regional sea ice, oceanography, and biota. Extensive sea ice melt, leading to an ocean mixed layer freshening and widespread ice surface flooding, snow–ice formation, and phytoplankton growth, coincided with extreme ice deformation and dynamic thickening. Sea ice dynamics were crucial to the development of an unusually early and rapid (short) retreat season (negative ice extent anomaly). Strong winds with a dominant northerly component created an unusually compact marginal ice zone and a major increase in ice thickness by deformation and over-rafting. This led to the atypical persistence of highly compact coastal ice through summer. Ecological effects were both positive and negative, the latter including an impact on the growth rate of larval Antarctic krill and the largest recorded between-season breeding population decrease and lowest reproductive success in a 30-yr Adélie penguin demographic time series. The unusual sea ice and snow cover conditions also contributed to the formation of a major phytoplankton bloom. Unexpectedly, the initial bloom occurred within compact sea ice and could not be detected in Sea-Viewing Wide Field-of-View Sensor (SeaWiFS) ocean color data. This analysis demonstrates that sea ice extent alone is an inadequate descriptor of the regional sea ice state/conditions, from both a climatic and ecological perspective; further information is required on thickness and dynamics/deformation.

The sea-ice zone of the Antarctic exhibits high rates of primary productivity and large interannual variability in plankton and biogeochemical properties, influenced by variations in the timing, extent and duration of sea-ice advance and retreat. In the past decade several interdisciplinary research programs conducted investigations in the sea ice zones of the West Antarctic Peninsula (WAP) and Ross Sea. In this article we synthesize results of these investigations to provide an overview of water-column processes influenced by regional-scale sea-ice dynamics. Primary production (PP) off the WAP varies by nearly an order of magnitude from year-to-year, and its interannual variability is related to the amount of open water within the annual ice pack. The annual sedimentation at 170 m averages about 2% of the overlying PP but is not related to interannual variations in the ice or PP. Rather the interannual variations in sedimentation are related to stocks of krill and salps. Plankton foodwebs in the Ross Sea and WAP exhibit similar annual PP but differ greatly in quantitative foodweb structure. Foodwebs of the WAP are dominated by krill grazing of spring-summer diatom blooms, whereas in the Ross Sea the extensive and early (November) bloom of Phaeocystis antarctica is not grazed and ∼50% sinks as ungrazed cells. Foodweb reconstructions from inverse models suggest that some functional characteristics of foodwebs in the two regions are quite similar in spite of taxonomic contrasts. Relatively high rates of microbial processing and nutrient recycling characterize both systems, even during years in the WAP when PP differs by an order of magnitude. These similarities indicate broad functional similarities across contrasting foodweb composition in the sea-ice zone.

Simultaneous, but contrary, decadal-scale changes in population trajectories of two penguin species in the western Pacific and Ross Sea sectors of the Southern Ocean, during the early/mid-1970s and again during 1988–89, correspond to changes in weather and sea ice patterns. These in turn are related to shifts in the semi-annual and Antarctic oscillations. Populations of the two ecologically dissimilar penguin species - Adélie Pygoscelis adeliae and emperor Aptenodytes forsteri - have been tallied annually since the 1950s making these the longest biological datasets for the Antarctic. Both species are obligates of sea ice and, therefore, allowing for the demographic lags inherent in the response of long-lived species to habitat or environmental variation, the proximate mechanisms responsible for the shifts involved changes in coastal wind strength and air and sea temperatures, which in turn affected the seasonal formation and decay of sea ice and polynyas. The latter probably affected such rates as the proportion of adults breeding and ultimately the reproductive output of populations in ways consistent with the two species' opposing sea ice needs. Corresponding patterns for the mid-1970s shift were reflected also in ice-obligate Weddell seal Leptonychotes weddelli populations and the structure of shallow-water sponge communities in the Ross Sea. The 1988–89 shift, by which time many more datasets had become available, was reflected among several ice-frequenting vertebrate species from all Southern Ocean sectors. Therefore, the patterns most clearly identified in the Pacific Sector were apparently spread throughout the high latitudes of the Southern Ocean.

A primary research objective of the Palmer Long Term Ecological Research (LTER) program has been to identify and understand the factors that regulate the demography of Adélie penguins (Pygoscelis adeliae). In this context, our work has been focused on variability in the marine environment on which this species depends for virtually all aspects of its life history (Ainley, 2002). As we show here, however, there are patterns evident in the population dynamics of Adélie penguins that are better explained by variability in breeding habitat quality rather than by variability in the marine system. Interactions between the geomorphology of the terrestrial environment that, in turn, affect patterns of snow deposition, drive breeding habitat quality.

The West Antarctic Peninsula (WAP) is home to large breeding colonies of the ice-dependent Antarctic Adélie penguin (Pygoscelis adeliae). Although the entire inner continental shelf is highly productive, with abundant phytoplankton and krill populations, penguin colonies are distributed heterogeneously along the WAP (Ducklow et al., 2013, in this issue). This ecological conundrum targets a long-standing question of interest: what environmental factors structure the locations of Adélie penguin "hot spots" throughout the WAP? - See more at: http://tos.org/oceanography/archive/26-3_schofield.html#sthash.KsdW5rk4.dpuf

The distribution of seabirds and pinnipeds and their relationship to physical oceanographic variables were investigated as part of the US Southern Ocean Global Ocean Ecosystem Dynamics field program along a study grid centered around Marguerite Bay on the west Antarctic Peninsula during late fall (April–May) and winter (July–August), 2001. Sea-ice conditions during the cruises provided an opportunity to compare the relationship among physical oceanographic variables and species distributions before and after the development of pack ice. During the fall cruise before pack ice development, both sea-ice-affiliated species and open-water-affiliated were observed in the area. The most common ice-affiliated species observed at this time were snow petrel ( Pagodroma nivea , 0.7 individuals km −2 ) and Antarctic petrel ( Thalassoica antarctica , 0.2 individuals km −2 ) and the most common open-water-affiliated species were blue petrel ( Halobaena caerulea , 0.4 individuals km −2 ), cape petrel ( Daption capense , 0.2 individuals km −2 ), and southern fulmar ( Fulmarus glacialoides , 0.1 individuals km −2 ). In addition, Antarctic fur seals ( Arctocephalus gazella , 0.1 individuals km −2 ) and crabeater seals ( Lobodon carcinophagus , 0.4 individuals km −2 ) were observed in low numbers. Akaike's information criterion was used to assess competing models that predicted predator distributions based on physical oceanographic variables proposed to structure predator distribution in previous research. These analyses indicated that predator distributions were primarily associated with water-mass structure and variability in bottom depth during the fall cruise. Crabeater seal, snow petrel, Antarctic petrel, and southern fulmar had higher densities in Inner Shelf Water, particularly near Alexander Island where a coastal current was present. Blue petrel, kelp gull ( Larus dominicanus ), and southern giant petrel ( Macronectes giganteus ) were positively associated with variability in bottom depth in April–May, suggesting that hydrographic processes influenced by bathymetry may have been important in structuring bird distributions. After the development of pack ice, during July and August, only sea-ice-affiliated species, including snow petrel (1.0 individuals km −2 ), Antarctic petrel (0.1 individuals km −2 ), Adelie penguin ( Pygoscelis adeliae , 0.4 individuals km −2 ), and crabeater seal (0.3 individuals km −2 ), were observed. Seabirds were primarily associated with sea-ice characteristics (e.g. sea-ice concentration, sea-ice type) rather than the water-column environment later in the winter. Results from this study suggest that the timing and extent of sea-ice development in the fall may influence over-winter predation by seabirds and pinnipeds on zooplankton and fish on the western Antarctic Peninsula. Delays in sea-ice development may allow seabirds and pinnipeds access to biologically important areas such as the Inner Shelf Water for a longer period of time thereby increasing predation on zooplankton and fish.

Crabeater seals are abundant pack-ice predators that feed almost exclusively on krill. They have a circumpolar distribution and are generally sighted hauled out on ice floes alone or in pairs. Here we report our observations of a sighting of 150–200 crabeater seals, which were synchronised in their diving and surfacing behaviour, along with a summary of similar observations from western Antarctica of large groups of crabeater seals in synchronous dive cycles. We report on the low frequency of sightings of such groups during Antarctic pack-ice seal surveys in eastern (Greater) Antarctica. We examine plausible hypotheses to explain these observations, and suggest this behaviour is likely to represent some form of cooperative foraging behaviour, whereby a net advantage in individual energy intake rates is conferred to each seal. Current research on crabeater seal foraging using satellite-linked dive recorders is unlikely to provide sufficiently fine-scale data to examine this hypothesis. Nor will this approach indicate if a seal is foraging with conspecifics. The use of remote or animal-borne camera systems is more likely to provide an insight into fine-scale foraging tactics, as well as the possible, occasional use of cooperative foraging strategies.

The mechanisms by which variability in sea ice cover and its effects on the demography of the Antarctic krill Euphausia superba cascade to other ecosystem components such as apex preda- tors remain poorly understood at all spatial and temporal scales, yet these interactions are essential for understanding causal links between climate change, ecosystem response and resource monitor- ing and management in the Southern Ocean. To address some of these issues, we examined the long- term foraging responses of Adelie penguins Pygoscelis adeliae near Palmer Station, western Antarc- tic Peninsula, in relation to ice-induced changes in krill recruitment and availability. Our results suggest that (1) there is a direct, causal relationship between variability in ice cover, krill recruitment, prey availability and predator foraging ecology, (2) regional patterns and trends detected in this study are consistent with similar observations in areas as far north as South Georgia, and (3) large- scale forcing associated with the Antarctic Circumpolar Wave may be governing ecological inter- actions between ice, krill and their predators in the western Antarctic Peninsula and Scotia Sea regions. Another implication of our analyses is that during the last 2 decades in particular, krill pop- ulations have been sustained by strong age classes that emerge episodically every 4 to 5 yr. This raises the possibility that cohort senescence has become an additional ecosystem stressor in an envi- ronment where ice conditions conducive to good krill recruitment are deteriorating due to climate warming. In exploring these interactions, our results suggest that at least 1 'senescence event' has already occurred in the western Antarctic Peninsula region, and it accounts for significant coherent decreases in krill abundance, predator populations and predator foraging and breeding perfor- mance. We propose that krill longevity should be incorporated into models that seek to identify and understand causal links between climate change, physical forcing and ecosystem response in the western Antarctic Peninsula region.

Background Sexual segregation in vertebrate foraging niche is often associated with sexual size dimorphism (SSD), i.e., ecological sexual dimorphism. Although foraging behavior of male and female seabirds can vary markedly, differences in isotopic (carbon, δ13C and nitrogen, δ15N) foraging niche are generally more pronounced within sexually dimorphic species and during phases when competition for food is greater. We examined ecological sexual dimorphism among sympatric nesting Pygoscelis penguins asking whether environmental variability is associated with differences in male and female pre-breeding foraging niche. We predicted that all Pygoscelis species would forage sex-specifically, and that higher quality winter habitat, i.e., higher or lower sea ice coverage for a given species, would be associated with a more similar foraging niche among the sexes. Results P2/P8 primers reliably amplified DNA of all species. On average, male Pygoscelis penguins are structurally larger than female conspecifics. However, chinstrap penguins were more sexually dimorphic in culmen and flipper features than Adelie and gentoo penguins. Adelies and gentoos were more sexually dimorphic in body mass than chinstraps. Only male and female chinstraps and gentoos occupied separate δ15N foraging niches. Strong year effects in δ15N signatures were documented for all three species, however, only for Adelies, did yearly variation in δ15N signatures tightly correlate with winter sea ice conditions. There was no evidence that variation in sex-specific foraging niche interacted with yearly winter habitat quality. Conclusion Chinstraps were most sexually size dimorphic followed by gentoos and Adelies. Pre-breeding sex-specific foraging niche was associated with overall SSD indices across species; male chinstrap and gentoo penguins were enriched in δ15N relative to females. Our results highlight previously unknown trophic pathways that link Pygoscelis penguins with variation in Southern Ocean sea ice suggesting that each sex within a species should respond similarly in pre-breeding trophic foraging to changes in future winter habitat.