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We studied the influence of the distribution of prey and hydrographic fronts on the spatial distribution of foraging Brunnich's guillemots (Uria lomvia) in Storfjorden, southeastern Svalbard in late July 1992. Two large breeding colonies, comprising a total of 540,000 individuals, were located adjacent to the study area, and large numbers of Brunnich's gullemots from these colonies foraged within the area, as well as to the south, outside of Storfjorden. Within the study area, most guillemots foraged on the west side of the fjord, coincident with a weak subsurface front between warm Atlantic water, which penetrated Storfjorden from the south, and cold Arctic water. Food samples from the guillemots collected in the study area contained primarily crustaceans (Parathemisto spp. and Thysanoessa inermis) and polar cod Boreogadus saida. Acoustic observations of prey were differentiated into two classes of signals, which we interpreted as originating from aggregated and dispersed organisms. The numbers of foraging guillemots were strongly correlated with the strength of echoes of the aggregated type, whereas correlations with dispersed echoes were consistently weaker. The distribution of foraging guillemots showed no significant correlations with either horizontal or vertical gradients of physical properties of the water column. Our finding that guillemots respond differently to aggregated and dispersed prey has important implications both for the interpretation of past work on the foraging ecology of marine birds, and for the management of fisheries.

We used five transects radiating from the South Orkney Islands to describe the distribution and abundance of marine birds during three days in late summer 1983. We found elevated numbers of birds at most crossings of steep physical gradients (fronts), but species were not equally attracted to each front. Our data suggest that the fronts around the South Orkney Islands, especially the Weddell-Scotia Confluence, provide important foraging habitat for birds. Albatrosses and fulmars appeared to aggregate preferentially near fronts overlying the insular slope, whereas Chinstrap Penguins were most abundant over the shelf. © 1992 Springer-Verlag.

The purpose of the present study was to determine the link between planktivorous little auks (Alle alle) and their soil fertilization, the concentration of total, and different forms of phosphorus in the surface layer of the High Arctic soils and the vascular plant composition of the tundra vegetation. Samples of the surface soil layer (0–10 cm) were collected along three pairs of transects (affected and unaffected by little auks) at different locations in Spitsbergen (Svalbard). The surface layer of soils affected by little auks was characterized by a significantly higher mean concentration of Ptot (1.02–1.44 g kg−1) compared to those not affected by seabirds (0.58–0.77 g kg−1). The mean concentration of different forms of P was also generally higher in soils affected by seabirds (i.e., labile P: 0.13–0.34 g kg−1, moderately labile P: 0.31–0.90 g kg−1, stable P: 0.27–0.39 g kg−1) than in unaffected soils (labile P: 0.04–0.18 g kg−1, moderately labile P: 0.30–0.37 g kg−1, stable P: 0.12–0.24 g kg−1); however, the differences were not always significant, most likely due to the high heterogeneity of specific environmental conditions at the local scale such as soil type, soil chemical composition, and vegetation type. Vascular plant cover was significantly and positively related to the concentration of the P forms studied in the soil. The phosphorus gradient significantly altered the composition of the vascular plants and explained 58.4% of its variation. Little auks are an important source of soil phosphorus in terrestrial ecosystems in the High Arctic that significantly affect the cover and composition of vascular plants. [ABSTRACT FROM AUTHOR]

Colonial seabirds have adopted certain strategies to minimize breeding losses during fledging. This review focuses on the most numerous high-Arctic auks: Little Auk Alle alle and Brünnich's Guillemot Uria lomvia. Colonies of Little Auks are usually situated farther from the sea than cliff-nesting guillemots. On departing the nest, Little Auk chicks are more advanced and can fly, while guillemot chicks, lacking flight feathers, jump from the cliff ledges and glide to the sea. Little Auk chicks lose weight before departure, thus improving their flight efficiency. In both species, fledglings have strong legs and a thick layer of feathers on the underside to prevent injury from hard landings. Some chicks reach the sea on foot. The fathers care for their fledglings, with whom they are in vocal contact. On land, chicks are hunted by Arctic foxes Vulpes lagopus and gulls Larus sp. When attacked by gulls at sea, young auks dive. In the air, however, only young Little Auks perform a characteristic nose-diving manoeuvre to confuse the predator. Guillemot parents can effectively counteract gull attacks on their young, while Little Auk parents do not directly defend their chicks. Unlike Little Auks, several adult guillemots usually accompany chicks during gliding and landing at sea. Adult guillemots gather near the colony during the fledging period and call loudly, thus indicating a safe landing place. In both species, fledging is highly synchronized and condensed into a few days and night-time hours, thus causing a swamping effect that reduces total losses among fledglings. [ABSTRACT FROM AUTHOR]

The Chukchi Sea pelagic ecosystem continues to undergo dramatic oceanographic changes associated with reductions in sea ice and increasing temperatures over the last decades. Impacts of these changes on polar cod (Boreogadus saida), an ice-associated pelagic fish that constitutes a key energetic link between lower and upper trophic levels, remain uncertain. Here, we use 4 years (2016–2019) of high-resolution acoustic and oceanographic data from the Chukchi Ecosystem Observatory to characterize temporal patterns in polar cod densities and identify its environmental drivers in years with contrasting sea ice and temperature conditions. Polar cod densities were 2–16 times greater with peaks occurring 14–60 days earlier in years with early sea ice retreat and higher water temperatures (2017 and 2019). The variance to mean relationship showed a decrease in variance for larger abundances in warmer years. Increased densities occurring earlier in the summer are attributed to a combination of earlier and increased transport of polar cod eggs and larvae from spawning areas, enhanced local primary and secondary production, and increased growth rates of fish due to higher temperatures. Earlier sea ice retreat and increases in temperature could temporarily benefit polar cod production in the NE Chukchi Sea but potential changes in prey quality, mismatch between polar cod and its prey, and increased competition with boreal fish species could have detrimental effects on polar cod populations with further warming. Such effects on polar cod populations could propagate through pelagic Arctic food webs impacting higher trophic levels and human communities. [ABSTRACT FROM AUTHOR]

The Antarctic krill, Euphausia superba, is a major component of the Southern Ocean's ecosystem. Limited high-resolution data on the relative importance of oceanographic processes on the behavioral responses of krill at traditional predator foraging grounds constitutes a major obstacle in the understanding of krill-environment coupling and ecosystem-based management of this resource. Aggregation structures of krill and predator interactions were investigated using active acoustic data collected by WBAT echosounders deployed on moorings in two hydrographically different sites in Bransfield Strait. Near Nelson Island, water flows from the northwest to southeast while Deception Island is influenced by stronger net current velocities from the southwest to northeast. Krill aggregations were identified and then classified in three clusters using a swarm-identification algorithm and hierarchical clustering using aggregation morphological characteristics: acoustic density, mean depth, center of mass, inertia, equivalent area, aggregation index, and proportion occupied. A total of 693 and 736 aggregations were detected at the mooring sites close to Nelson and Deception Islands. The three aggregation categories ranged from high to low densities, evenness, and dispersion and were distributed throughout the water column. Krill aggregation density distribution and mean thickness are influenced by krill mean depth, current velocities and direction. The majority of observed predator dive profiles occurred over the aggregation type with highest krill densities at both Nelson and Deception Islands, and within the first 25 m of the water column. The heterogeneity of krill aggregations potentially impacts predator foraging strategies and predator–krill interactions in the hydrodynamically active Bransfield Strait. [ABSTRACT FROM AUTHOR]

The use of combined conventional and stable isotope analyses (SIA) to study the diet of seabirds has become very frequent. Unfortunately, information on the trophic ecology of immature seabirds remains scarce because the sampling of tissues to perform SIA is often very limited due to the difficulty to capture these birds. The koilin membrane, which covers the regurgitated pellet casts of some seabirds, could offer an interesting non-intrusive alternative tissue to perform SIA. In this two-year study of the diet of imperial cormorants in southern Patagonia, we (1) compare the diets of breeding and non-breeding birds through conventional pellet analysis; (2) describe the diet of breeding adults and chicks through a combined method of pellet analysis and whole blood SIA; and finally, (3) compare SIA values of breeding adults obtained from blood with those obtained from koilin membranes. We found that immature individuals incorporated abundant invertebrate taxons, compared with breeding adults which relied mainly on fish. Younger and inexperienced individuals, which are not under the constraint to feed chicks, are feeding on more predictable, but lower trophic and less energetic prey. By comparing the stable isotope values of koilin and blood in breeding adults, a correlated interannual difference between the two seasons was found. Under the light of our results, the koilin offers an encouraging alternative to blood in the study of trophic ecology, particularly for ages or stages in which capture is not possible. [ABSTRACT FROM AUTHOR]

Historical climate change and human exploitation are thought to have played important roles in shaping population dynamics of sub-Antarctic marine predators, such as king penguins (Aptenodytes patagonicus) and Antarctic fur seals (Arctocephalus gazelle). For example, Antarctic fur seals on the sub-Antarctic South Georgia Island were nearly hunted to extinction by humans before the early 1900s. However, records of occupation history pre- and post-anthropogenic stress are often sporadic and challenging to interpret. In this study, we investigated paleoecological proxies in sediment cores from South Georgia Island to examine past marine predator population dynamics in the face of climate change and exploitation pressure. Sediment cores representing 1854 CE to present were collected from two sites on South Georgia Island in the South Atlantic and analyzed for geochemical (total carbon, total nitrogen, δ13C and δ15N values) and biological (e.g., seal hairs, penguin feathers) proxies. Proxies in both cores indicated the onset of the recovery of penguin and fur seal populations in the early to mid-1900s, following the cessation of hunting. Additionally, our results suggest marked increases in both penguin and seal populations beginning around 1950 CE. Between the 1950s and 2019, 97% of South Georgia Island's glaciers retreated associated with recent climatic warming. This warming increased the availability of local breeding areas for king penguins, which likely explains the population rise during that time. This study deepens our understanding of the response of sub-Antarctic marine predator populations to past climate change and human exploitation, which may aid in predicting future ecosystem responses to environmental disturbance. [ABSTRACT FROM AUTHOR]

Despite the exclusion of the Southern Ocean from assessments of progress towards achieving the Convention on Biological Diversity (CBD) Strategic Plan, the Commission for the Conservation of Antarctic Marine Living Resources (CCAMLR) has taken on the mantle of progressing efforts to achieve it. Within the CBD, Aichi Target 11 represents an agreed commitment to protect 10% of the global coastal and marine environment. Adopting an ethos of presenting the best available scientific evidence to support policy makers, CCAMLR has progressed this by designating two Marine Protected Areas in the Southern Ocean, with three others under consideration. The region of Antarctica known as Dronning Maud Land (DML; 20°W to 40°E) and the Atlantic sector of the Southern Ocean that abuts it conveniently spans one region under consideration for spatial protection. To facilitate both an open and transparent process to provide the vest available scientific evidence for policy makers to formulate management options, we review the body of physical, geochemical and biological knowledge of the marine environment of this region. The level of scientific knowledge throughout the seascape abutting DML is polarized, with a clear lack of data in its eastern part which is presumably related to differing levels of research effort dedicated by national Antarctic programmes in the region. The lack of basic data on fundamental aspects of the physical, geological and biological nature of eastern DML make predictions of future trends difficult to impossible, with implications for the provision of management advice including spatial management. Finally, by highlighting key knowledge gaps across the scientific disciplines our review also serves to provide guidance to future research across this important region. [ABSTRACT FROM AUTHOR]

Southern Ocean myctophid fish (Family Myctophidae) are an important conduit of energy through foodwebs and between the surface layers and mesopelagic depths. Species that reside in both pelagic and near-bottom environments of continental shelves, such as Gymnoscopelus nicholsi and Gymnoscopelus bolini, may also be important in benthopelagic coupling, although their ecology and role in such processes remain unresolved. Here, we examined inter-annual variation in the depth of occurrence, biomass and population dynamics of benthopelagic G. nicholsi on the South Georgia shelf (100–350 m) using bottom trawl data collected between 1987 and 2019. Gymnoscopelus nicholsi was a regular component of the local benthopelagic community, particularly northwest of South Georgia, but was patchily distributed. It appeared to enter a benthopelagic phase at ~ 3 years, with annual growth and recruitment of year classes between ~ 3 and 5 years. However, transition of cohorts into the benthopelagic zone was not annual. There was clear inter-annual variation in G. nicholsi biomass and depth of occurrence. Shallower depth of occurrence was significantly (P < 0.05) correlated with years of warmer summer sea surface temperatures, suggesting that inter-annual variation in local environmental conditions has an important influence on its migration behaviour and ecology. Our data also suggest that Antarctic krill is an important dietary component of the older G. nicholsi cohorts (~ 5 years) in the benthopelagic zone. We note that Gymnoscopelus bolini is rare in bottom trawl catches between 100 and 350 m, although Antarctic krill appears to dominate its diet from the available data. Our study provides important information on understudied myctophid species in a poorly investigated region of the water column that is relevant for Southern Ocean ecosystem studies, particularly in relation to understanding trophic connectivity between the pelagic and near-bottom realms. [ABSTRACT FROM AUTHOR]

Nearshore fish communities comprise a fundamental component of Arctic marine ecosystems and serve as an important subsistence resource. As changing climate conditions affect Arctic waters, nearshore fish communities may also shift; however, how these communities will respond to climate change is not well understood. This study summarizes trends from a long-term (2001–2018) nearshore fish sampling program near Prudhoe Bay, Alaska, in the central Beaufort Sea. Abundance data (n = 1.78 million fish) from daily sampling (July–August) at four fixed sampling locations showed distinct shifts in fish community metrics. Since 2001, annual species richness has significantly increased by approximately one species per decade (p = 0.0167) while water temperature has warmed by approximately 1.4 °C. Results from non-metric multidimensional scaling (nMDS) and Permutational Analysis of Variance (PERMANOVA) models indicated that species composition based on biweekly catch data has significantly changed across years with distinct variations among sample locations and throughout the season. Salinity and water temperature were significantly related to multivariate species composition; specifically, the abundances of five species changed significantly over time. The species that increased in response to observed changes in the aquatic environment appear to be eurythermic and/or euryhaline generalist species such as Broad Whitefish Coregonus nasus and Saffron Cod Eleginus gracilis. Such patterns of altered species compositions demonstrate that continued long-term changes in environmental conditions will likely favor generalist species, potentially causing substantial shifts within the Arctic nearshore ecosystem with impacts on important subsistence resources. [ABSTRACT FROM AUTHOR]

Allometric relationships between body properties of animals are useful for a wide variety of purposes, such as estimation of biomass, growth, population structure, bioenergetic modelling and carbon flux studies. This study summarizes allometric relationships of zooplankton and nekton species that play major roles in polar marine food webs. Measurements were performed on 639 individuals of 15 species sampled during three expeditions in the Southern Ocean (winter and summer) and 2374 individuals of 14 species sampled during three expeditions in the Arctic Ocean (spring and summer). The information provided by this study fills current knowledge gaps on relationships between length and wet/dry mass of understudied animals, such as various gelatinous zooplankton, and of animals from understudied seasons and maturity stages, for example, for the krill Thysanoessa macrura and larval Euphausia superba caught in winter. Comparisons show that there is intra-specific variation in length–mass relationships of several species depending on season, e.g. for the amphipod Themisto libellula. To investigate the potential use of generalized regression models, comparisons between sexes, maturity stages or age classes were performed and are discussed, such as for the several krill species and T. libellula. Regression model comparisons on age classes of the fish E. antarctica were inconclusive about their general use. Other allometric measurements performed on carapaces, eyes, heads, telsons, tails and otoliths provided models that proved to be useful for estimating length or mass in, e.g. diet studies. In some cases, the suitability of these models may depend on species or developmental stages. [ABSTRACT FROM AUTHOR]

Polar cod and saffron cod are dominant components of the fish community in the Chukchi Sea and are ecologically important forage fishes linking plankton to upper-level consumers. In 2017, we conducted a study as part of the Arctic Integrated Ecosystem Research Program to characterize the distribution, abundance, and growth of polar cod and saffron cod early life history stages (ELHS) in late spring and late summer in the Chukchi Sea. Ship-based plankton tows showed that polar cod and saffron cod larvae were centered in Kotzebue Sound in the late spring. By late summer, polar cod juveniles were most abundant in the offshore areas of the northern Chukchi Sea, whereas saffron cod were distributed nearshore in the southern Chukchi Sea around Cape Lisburne. Empirical fish collections were paired with an individual-based biophysical transport model to examine connectivity and relate changes in seasonal distribution to potential environmental variables. Modeled drift trajectories and growth in spring for polar cod and saffron cod matched well with empirical observations, especially along the northern coastline of Kotzebue Sound, offshore of Point Hope/Cape Lisburne. Given the coherence between modeled and observed distributions, Kotzebue Sound is likely a source of gadid ELHS in the nearshore areas of the Chukchi Sea and offshore of Cape Lisburne/Point Hope, although it is not the likely source of polar cod over Hanna Shoal in the late summer. This is the first study to examine seasonal distribution, abundance, and growth of polar cod and saffron cod in the US Arctic and provides data necessary to evaluate the impacts of climate change on forage fishes in the Arctic. [ABSTRACT FROM AUTHOR]

The decline of eastern Bering Sea snow (Chionoecetes opilio) and Tanner (Chionoecetes bairdi) crab has coincided with loss of spring sea ice extent and northward contraction of the 'cold pool,' a layer of cold (< 2 °C) summer bottom water. We measured temperature-associated growth and lipid storage of lab-reared Tanner crab, as well as the fatty acid content of field-collected juvenile Chionoecetes spp. Field collections occurred during a cold, high sea ice year (2012) and a warm, low ice year (2014), representative of cold and warm climate stanzas in the southeastern Bering Sea. Lab-reared Tanner crab maintained the lowest growth rates but highest lipids under cold conditions (2 °C). In the field, crabs contained higher fatty acids per wet weight (mg g−1) during 2012 than during 2014. Water column-integrated chlorophyll a (chla, an indicator of phytoplankton biomass) from large particles (> 10 µm) such as diatoms was elevated in the colder year particularly over the central middle shelf. During the cold year, crab storage of diatom-sourced fatty acids (16:1n-7 to 16:0, r2 = 0.72) as well as a station-specific relationship between large size-fraction integrated chla and crab total fatty acids (r2 = 0.5) points to the potential importance of diatoms to juvenile crab nutrition. Our results suggest that continued warming and loss of sea ice across the Bering Sea may reduce juvenile crab lipid storage through both direct thermal effects as well as through the reduction of large-size phytoplankton delivered to the benthos. [ABSTRACT FROM AUTHOR]

The influence of climate on the dynamics of Arctic gadids is of increasing interest, particularly as research and survey effort expands in the Pacific Arctic. Understanding species-specific thermal tolerance may inform models of species distribution and projections of available habitat and also clarify implications of warming for ecological communities. Analyzing shifts in species distribution in warm and cold periods, this study considers the effects of a warming climate on the distribution of two keystone Arctic gadids (polar cod, saffron cod) and two commercially important sub-Arctic gadids (walleye pollock, Pacific cod). Shifts in distribution were used to derive temperature tolerance thresholds and to project how these species might react to a warming Arctic. Significant shifts were noted in comparisons of warm (2002–2005, 2014–2016, 2017–2018) and cold (2006–2013) periods. Sub-Arctic species expanded and contracted their range as environmental conditions shifted. In contrast, Arctic species appeared constrained, such that population densities increased or decreased within the same core geographic area. Additionally, species with a demersal life history were able to tolerate a wider range of thermal conditions. These results provide important insights on relative thermal tolerance of each species, differential influence of temperature on pelagic versus demersal life histories, and depth as thermal refuge. This study demonstrates both the need to understand the spatial response of fish to changing ocean conditions in polar regions and the utility of distributional analyses to inform that effort. [ABSTRACT FROM AUTHOR]

In high-latitude marine ecosystems, traditional net sampling is constrained to the ice-free season, resulting in an incomplete understanding of ecosystem structure and dynamics. Using 4 years of continuous acoustic and environmental measurements from a NE Chukchi Sea subsurface mooring, we assessed fish and zooplankton abundance and behavior relative to environmental factors over a wide range of temporal scales. We applied wavelet analysis to these high-resolution, multi-year, concurrent, and co-located datasets to identify temporal scales of variability in environmental conditions and density and vertical distribution metrics for pelagic fish and zooplankton. Biological variability occurs mainly at distinct diel (24-h), seasonal (3–6-month), and annual (9–12-month) scales. Diel patterns are present throughout the year but are strongest in autumn when day-night cycles are pronounced. Seasonal variability in zooplankton metrics (3–4 months) is mainly associated with sea ice patterns that may also regulate the onset of primary production. Seasonal variations in fish metrics are associated most closely with salinity patterns (~ 3 months) and slower changes in water temperature (~ 6 months). Annual cycles in biological characteristics are influenced by year-round variations in water temperature, sea ice concentration, light irradiance, and wind. Wind and salinity-associated variability in biological metrics was observed at scales of 6–28 days. Scale-dependent biological and environmental associations vary through time and emphasize the importance of high-resolution long-term studies for comprehensive ecosystem characterizations. Our results identify necessary scales of observation in Arctic monitoring programs for improved prediction and detection of biological responses to rapidly changing environments. [ABSTRACT FROM AUTHOR]

To monitor the rapid changes occurring in Arctic ecosystems and predict their direction, basic information about the current number and structure of the main components of these systems is necessary. Using boat-based surveys, we studied the numbers and distribution of seabirds foraging in Hornsund (SW Spitsbergen) during three summer seasons. The average number of seabirds foraging concurrently in the whole fjord was estimated at 28,000. Little Auks Alle alle were the most numerous, followed by Northern Fulmars Fulmarus glacialis, Brünnich's Guillemots Uria lomvia and Black-legged Kittiwakes Rissa tridactyla. The pelagic zone was exploited by some 75% of the birds. Their density was the highest (> 400 ind. km−2) in the tidewater glacier bays, where kittiwakes were predominant, and the lowest in the coastal glacier bays. The seabirds in Hornsund daily consumed c. 12.7 tons of food, i.e. c. 0.2% of the summer mesozooplankton and fish standing stocks available in the fjord. This food consisted primarily of copepods, amphipods and molluscs (c. 70%), whereas fish made up < 15%. More than 50% of this biomass was ingested by pursuit divers, while surface feeders took c. 29% and benthophages c. 13%. About three-quarters of the food biomass was taken from the pelagic zone. This paper describes, for the first time in quantitative terms, the structure and function of a seabird community foraging in an Arctic fjord. It also provides a baseline for future studies on climate-induced changes in the importance of seabirds in the Arctic food web. [ABSTRACT FROM AUTHOR]

As Arctic seas rapidly change with increased ocean temperatures and decreased sea ice extent, traditional Arctic marine mammal distributions may be altered, and typically temperate marine mammal species may shift poleward. Extant and seasonal odontocete species on the continental shelves of the Bering and Chukchi Seas include killer whales (Orcinus orca), sperm whales (Physeter microcephalus), beluga whales (Delphiapterus leucas), harbor porpoises (Phocoena phocoena), and Dall's porpoises (Phocoenoides dalli). Newly documented, typically temperate odontocete species include Risso's dolphins (Grampus griseus) and Pacific white-sided dolphins (Lagenorhynchus obliquidens). Until recently, recording constraints limited sampling rates, preventing the acoustic detection of many of these high frequency-producing (> 22 kHz) species in the Arctic seas. Using one of the first long-term datasets to record frequencies up to 50 kHz in these waters, clicks, buzzes, and whistles have been detected, classified, and paired with environmental data to explore which variables best parameterize habitat preference. Typically temperate species were associated temporally with cold Bering Sea Climate Regimes in tandem with negative Pacific Decadal Oscillations. Typically Arctic species' strongest explanatory variables for distribution were largely species and site specific. Regardless of species, however, the environmental cues (e.g. percent ice cover or zooplankton community structure) marine mammals use for locating viable habitat space are ones that will change as temperatures increase. This 10-year dataset documents the current state and tracks recent dynamics of odontocetes and their habitats along the Pacific Arctic Corridor to contribute to ongoing discussions about future Arctic conditions. [ABSTRACT FROM AUTHOR]

We studied positive associations among seabirds and marine mammals at South Georgia on research cruises during the Austral winters of 1985, 1991 and 1993 and found statistically significant differences. We collected data on abundance and distribution, providing a critical reference for sub-Antarctic conservation in anticipation of future environmental changes. We found significant changes in the abundance of 29% of species surveyed and a consequent change in species diversity. We postulate that the resulting altered community composition may have previously unanticipated population effects on the component species, due to changes in positive interactions among species which use each other as cues to the presence of prey. We found a near threefold reduction in spatial overlap among vertebrate predators, associated with warming sea temperatures. As the strength and opportunity for positive associations decreases in the future, feeding success may be negatively impacted. In this way, environmental changes may disproportionately impact predator abundances and such changes are likely already underway, as Southern Ocean temperatures have increased substantially since our surveys. Of course the changes we describe are not solely due to changing sea temperature or any other single cause—many factors are important and we do not claim to have removed these from consideration. Rather, we report previously undocumented changes in positive associations among species, and argue these changes may continue into the future, given near-certain continued increases in climate-related changes. [ABSTRACT FROM AUTHOR]

Marine microbial communities undergo drastic changes during the seasonal cycle in high latitude seas. Despite the dominance of microbial biomass in the oceans, comprehensive studies on the seasonal changes of microbial plankton during the complete winter period are lacking. To study the seasonal variation in abundance of the microbial community, water samples were collected weekly in the Northern Baltic Sea from October to May. During ice cover from mid-January to April, samples from the sea ice and the underlying water were taken in addition to the water column samples. Abundances of bacteria, virus-like particles, nanoflagellates, and chlorophyll a concentrations were measured from sea ice, under-ice water, and the water column, and examined in relation to environmental conditions. All studied organisms had clear seasonal changes in abundance, and the sea-ice microbial community had an independent wintertime development compared to the water column. Bacteria were observed to have a key role in the biotic interactions in both ice and the water column, and the dormant period during the cold-water months (October–May) was limited to before ice formation. Our results provide the first insights into the temporal dynamics of bacteria and viruses during the whole cold-water season (October–May) in coastal high latitude seas, and demonstrate that changes in the environmental conditions are likely to affect bacterial dynamics and have implications on trophic interactions. [ABSTRACT FROM AUTHOR]

Polar cod (Boreogadus saida) is the most abundant fish in the US Arctic (US Chukchi and Beaufort seas), where commercial fishing is currently prohibited because data to assess the sustainability of potential fisheries are lacking. Using data from fisheries oceanographic surveys in the US Chukchi Sea during 2012 and 2013 (August–September), we examined drivers of distribution and abundance, and assessed the current status and dynamics of polar cod. We estimated age structure, abundance, biomass, natural mortality, and reproductive potential using data from these surveys, combined with available estimates of biological parameters from the literature. High densities of age-0 polar cod were observed in the northeastern Chukchi Sea, while older polar cod (age-1+) were more widely distributed throughout the survey area. Results indicate that temperature is an important driver for the distribution of both age-0 and age-1+ polar cod with age-0 polar cod less likely to be present in warmer waters (≥ 8 °C), which supports past research on drivers of fish and other ectotherm species distribution. Estimates of egg production and early survival suggest that the numbers of mature polar cod present in the survey area during summer are unlikely to produce the observed high abundances of age-0 polar cod in the US Chukchi Sea. This could imply that either mature polar cod migrate to the Chukchi Sea to spawn in the winter, that age-0 fish are advected from outside the study area, or that adult polar cod abundance is underestimated. Additional systematic surveys and further research are needed to resolve the origins of age-0 polar cod, identify nursery areas, and estimate early life survival. [ABSTRACT FROM AUTHOR]

Characterizing the condition of fish in dynamic seasonal environments requires an understanding of their energy allocation strategies. Both polar cod (Boreogadus saida) and saffron cod (Eleginus gracilis) are important mid-trophic fish in Alaska Arctic waters, and changes in their lipid allocation could have important implications for their overwintering survival as well as their energetic value for predators. We used a combination of laboratory and field approaches to describe allometric relationships in lipid storage of polar cod and we then explored spatial patterns in field-caught juvenile gadid condition during 2012 and 2013. Lipid density in wild juvenile Arctic gadids increased with size leading into the first overwintering period, but age-1 + fish showed a reduction in lipid density with size prior to the 2nd overwintering period. Using the residuals from the underlying allometry of total lipid and fatty acid density in each species, we were able to develop a condition metric which was then explored in relation to spatial patterns in large Calanus glacialis copepodite (stages C3 and older) abundance and thermal conditions measured in the field. Fatty acid biomarkers from the total lipid pool indicated that polar cod have a higher reliance on calanoid copepods than saffron cod. Collectively, these data suggest polar cod and saffron cod will likely respond differently to regional warming depending upon the shift in the zooplankton communities, such that the energetic contribution of these fish to higher trophic levels could be transformed with future ocean warming. [ABSTRACT FROM AUTHOR]

Previous work found that an earlier ice breakup favors the recruitment of juvenile polar cod (Boreogadus saida) by enabling early hatchers to survive and reach a large size by late summer thanks to a long growth season. We tested the hypothesis that, in addition to a long growth season, an earlier ice breakup provides superior feeding conditions for young polar cod by enhancing microalgal and zooplankton production over the summer months. Ice cover and surface chlorophyll a were derived from satellite observations, and zooplankton and juvenile cod biomass were estimated by hydroacoustics in ten regions of the Canadian Arctic over a period of 11 years. Earlier breakups resulted in earlier phytoplankton blooms. Zooplankton backscatter in August increased with earlier breakup and bloom, and plateaued at chlorophyll a > 1 mg m−3. Juvenile cod biomass in August increased with an earlier breakup, and plateaued at a zooplankton backscatter > 5 m2 nmi−2, supporting the hypothesis that higher food availability promotes the growth and survival of age-0 fish in years of early ice melt. However, there was little evidence that late summer biomass of either zooplankton or age-0 polar cod benefitted from ice breakup occurring prior to June. On average, zooplankton standing stock was similar in the Southern Beaufort Sea and the North Water-Lancaster Sound polynya complex, but juvenile cod biomass was higher in the Beaufort Sea. Intense avian predation could explain the lower biomass of juvenile cod in the polynya complex, confirming its reputation as a biological hotspot for energy transfer to higher trophic levels. [ABSTRACT FROM AUTHOR]

The current information about the diet composition of the rock shag (Phalacrocorax magellanicus) in the SW Atlantic coast comes mainly from conventional pellet or stomach content analysis from a few locations situated in northern Patagonia (Chubut Province, Argentina). In this work, we studied the diet of breeding rock shags over several years at a colony from southern Patagonia (Ría Deseado, Santa Cruz Province, Argentina) using a combined technique of conventional diet assessment (pellet analysis) and stable isotope analysis of carbon and nitrogen. Our results confirm the importance of benthic prey and the low inter-annual variability in the diet of the rock shag. These results coincide with previous research in relation to the exploitation of slow moving, predictable, but low-energy density prey. The stable isotope mixing models, which was informed with prior data obtained from pellet analysis, allowed for the detection of subtle differences between the diet of adults and chicks, consisting in the incorporation of higher proportions of cephalopods, an energy-rich prey, in the diet of chicks. By comparing our results with the diet of the red-legged cormorant, which breeds in sympatry in the Ría Deseado Estuary and whose diet composition is strongly pelagic, we suspect a certain level of trophic resource partitioning between these rock shag and red-legged cormorant. [ABSTRACT FROM AUTHOR]

The survival of the planktonic stages of marine fishes is widely considered to be a bottleneck in recruitment success and is a period when fishes are highly sensitive to changes in their environment. In high latitude areas that are forecasted to experience warming temperatures, it is critical to determine a baseline of ichthyoplankton assemblages to detect how the ecosystem may change in response to shifting conditions. This study used ichthyoplankton data from the eastern Chukchi Sea in the summers of 2010–2015 to assess temporal and spatial variation in assemblage structure. Larval densities were examined in relation to oceanographic conditions at depth and corresponding water masses. Additionally, the standard lengths of polar cod (Boreogadus saida), a key trophic link in Arctic food webs, were assessed for size-at-catch relationships. In 2010 and 2011, years of widespread presence of warm, low salinity bottom water masses such as Alaska Coastal Water, yellowfin sole (Limanda aspera) and longhead dab (Limanda proboscidea) dominated the assemblages. In 2012 and 2013, the increased presence of colder, more saline Winter Water coincided with a shift to polar cod-dominated assemblages. In 2014 and 2015, water masses were less spatially defined and different assemblages, characterized by Arctic sand lance (Ammodytes hexapterus) and saffron cod (Eleginus gracilis), were detected than previous years. The greatest range in sizes of polar cod was observed in 2014, as well as the highest number of juveniles and age-1 individuals were collected. The biophysical patterns identified here support the strong connection between interannual oceanographic conditions and ichthyoplankton assemblages which reflect the importance of continuous, multi-year surveys to document assemblage changes in the Arctic. [ABSTRACT FROM AUTHOR]

We performed stable carbon (δ13C) and nitrogen (δ15N) isotope analyses of 12 ancient Adélie penguin (Pygoscelis adeliae) chick mummies recovered from abandoned colonies in the Ross Sea region, Antarctica, to investigate isotopic variation and fractionation over time. We also examined latitudinal variation in penguin diet to address if the modern dietary pattern (an increase in krill as dominant prey to the north) in this region has existed in the past or if this is a recent phenomenon. The ancient mummies range in age from > 48,000 14C years before present (BP) to ~ 500 calendar years BP. Feather, skin, bone, and toenail samples were analyzed from each individual where available. Identical analyses were performed on five modern mummified Adélie penguin chick carcasses and breast feathers of ten recently dead chicks from each of two active colonies, Cape Hallett and Adélie Cove. We found significantly lower δ15N values in Cape Hallett modern chicks as compared to those from Adélie Cove, indicating an entire trophic-level difference in modern diet that agrees with other studies in this region. The ancient mummies exhibited consistent isotopic fractionation of δ13C among the four different tissues through time. Variation in δ15N and δ13C values was greater in bone and skin than in feather or toenail, but δ15N in all four tissues indicated similar dietary trends with latitude as occurs in this region today. These results provide insight into the dietary variability of Adélie penguins across the Ross Sea region and a framework for similar analyses with other avian species. [ABSTRACT FROM AUTHOR]

The physical environments of high-latitude systems are rapidly changing. For example, the Chukchi Sea has experienced increased water temperatures, advection from the Bering Sea, declines in sea-ice concentration, earlier spring ice retreat, and delayed fall ice formation. This physical restructuring is expected to impact ecosystem structure and function. In this study, a series of bio-oceanographic research surveys were conducted in the summers of 2010, 2011, and 2012 to characterize the physical environment and to examine the influence of physical forcing on zooplankton community distribution and abundance. Results revealed yearly advection from the Bering Sea influenced zooplankton community structure, but this influence became less apparent in the northeastern Chukchi due to changes in current speeds and patterns. Decreased advection and later ice retreat in colder years resulted in zooplankton communities that exhibited more diversity, had higher abundances of the lipid-rich copepod Calanus glacialis, and were less closely related to water masses advected from the south. These findings suggest more localized processes are influencing zooplankton community structure in the Chukchi Sea. Increased inflow of water into the Chukchi is predicted with increased warming in the Arctic and changes in food-web structure and function are likely to result. [ABSTRACT FROM AUTHOR]

The climate regime in the eastern Bering Sea has recently been dominated by a pattern of multi-year stanzas, in which several successive years of minimal sea-ice formation and warm summer temperatures (e.g., 2002-2005, 2014-2017) alternate with several years of relatively extensive sea-ice formation and cold summer temperatures (e.g., 2006-2013). This emerging climate pattern may be forcing long-term changes in the spatial distributions of the Bering Sea's marine fauna. The National Marine Fisheries Service's Alaska Fisheries Science Center recently conducted two bottom trawl surveys covering the entire Bering Sea shelf from the Alaska Peninsula to the Bering Strait. The first, in the summer of 2010, was conducted during a cold year when the majority of the continental shelf was covered by a pool of cold (< 2 °C) water. The second, in the summer of 2017, was during a warmer year with water temperatures above the long-term survey mean. These two surveys recorded significantly different spatial distributions for populations of several commercially important fish species, including walleye pollock (Gadus chalcogrammus), Pacific cod (Gadus macrocephalus), and several flatfish species, as well as jellyfishes. Population shifts included latitudinal displacement as well as variable recruitment success. The large-scale distributional shifts reported here for high-biomass species raise questions about long-term ecosystem impacts, and highlight the need for continued monitoring. They also raise questions about our management strategies for these and other species in Alaska's large marine ecosystems. [ABSTRACT FROM AUTHOR]

Changing environmental conditions in the Pacific Arctic are expected to affect ice-adapted marine food webs. As such, understanding ringed seal (Pusa hispida) dive and haul-out behavior is vital to understanding if and how these environmental changes affect seal foraging behavior. Working with Alaska Native subsistence hunters, we tagged 14 adult and 20 subadult ringed seals with satellite-linked data recorders in Kotzebue Sound, Alaska, during late-September and October 2007-2009. Information about dive and haul-out behavior in the Bering and Chukchi seas was collected for 12-297 days. We analyzed indices of dive depth, duration, and rate, and haul-out probability using a model selection framework for adults during fall (late-September-November) and winter (December-March) and for subadults during fall, winter, and also spring (April-June). We found differences by season and time of day, but not by sex. Where subadults and adults occurred together, they dove to similar depths; although subadults were commonly located in deeper waters where they generally dove deeper than adults. Both age classes dove longer during winter and subadults tended to make a few more (~3.5) dives per hour than adults. Both age classes hauled out less and dove deeper, longer, and more frequently during midday than at other times of day. We suspect that seals dive deeper during midday because their prey migrates deeper. Dive and haul-out behaviors of ringed seals are influenced by a combination of factors, including prey distribution and abundance, sea ice, and seal diving physiology. [ABSTRACT FROM AUTHOR]

Fatty acids (FAs), the main components of lipids, are crucial for energy storage and other physiological functions in animals and plants. Dietary FAs are incorporated and conserved in consumer tissues in predictable patterns and can be analyzed to determine the composition of an individual’s diet. This study measured the variation in FA profiles of polar cod (Boreogadus saida) across multiple years (2010-2013) over a wide geographic area in the Beaufort and Chukchi seas. Polar cod are important prey of marine mammals, sea birds, and fishes, providing a crucial link between primary producers and higher trophic-level predators. Spatial and temporal variations in FA profiles of this important forage fish species provide insight into the transfer of lipids through the Arctic ecosystem, and inform diet studies of higher trophic-level predators on polar cod that utilize trophic mixing models based on prey FA data. FA profiles of polar cod differed between the Beaufort and Chukchi seas, and among collection years. High lipid content and elevated levels of long-chain FAs in Chukchi Sea specimens relative to the Beaufort Sea may indicate more favorable feeding conditions over the years sampled, and higher energy density for Chukchi Sea polar cod as prey. FA data provide a useful metric for examining spatial and temporal variation in the quality of prey available to higher trophic-level consumers. [ABSTRACT FROM AUTHOR]

Ice decline is believed to benefit the pelagic food chain in Arctic shelf ecosystems, but the impacts of ice decline are usually difficult to detect owing to the overlap of ice decline with natural variability. To evaluate the responses of zooplankton communities to sea ice reduction in the Chukchi Sea, we combined zooplankton samples collected in the early summers of 2003, 2008, 2010, and 2012 and compared the inter-annual changes in the subregions with various physical and biological characteristics. Three geographically separate communities were identified by a hierarchical cluster analysis. The Bering Sea water influenced the central (CCS) and south (SCS) Chukchi Sea communities, which had total abundances that were approximately ten times higher than that of the north (NCS) Chukchi Sea community, and the inter-annual variability was dramatic. The SCS and CCS shared dominant taxa of Calanus glacialis, Pseudocalanus spp., barnacle larvae (nauplii and cypris), and Oikopleura vanhoffeni, while Pacific and neritic species were recognized as the dominant species in only the SCS. The inter-annual variations in the dominant species assemblages can be explained by the variability in oceanic circulation and the counteractions between copepods and barnacle larvae. Despite the numerical fluctuations, an increase in the average abundances in the Pacific-influenced region and the summer establishment of the C. glacialis population are proposed to be the most pronounced responses to ice decline. The NCS, which is governed by cold Arctic water, was characterized by low abundances and a constant dominant taxa assemblage. This area was also characterized by the presence of the high Arctic species Calanus hyperboreus and a lack of barnacle larvae. The total abundance of the NCS doubled from 2003 to 2008, while the community structure remained consistent. These results indicate that sea ice reduction has a positive effect on the zooplankton community, but heterogeneity is the main obstacle to the detection of the zooplankton community in the Western Arctic Ocean. [ABSTRACT FROM AUTHOR]

The recent increasing of atmospheric turbulence has had considerable impact on the oceanic environment and ecosystems of the Arctic. To understand its effect on phytoplankton community structure, a Eulerian fixed-point observation (FPO) was conducted on the Chukchi shelf in fall 2013. Temporal and vertical distributions of the phytoplankton community were inferred from algal pigment signatures. A strong wind event (SWE) occurred during the observation term, and significant convection supplied nutrients from the bottom layer to the surface. Before the SWE, pigment composition in the warmer, less saline, and nutrient-poor surface waters was diverse with low concentration of chlorophyll-a (chla). Vertical mixing induced by the SWE weakened the stratification and brought sufficient nutrients to enhance diatom-derived pigment concentrations (e.g., fucoxanthin and chlc3), suggesting increases in diatoms. We also developed a model to predict the distribution of major phytoplankton pigment/chla ratios using a profiling multi-wavelength fluorometer (Multi-Exciter) with higher spatio-temporal resolution. The Multi-Exciter also captured changes in pigment composition with environmental changes at the FPO site and at four observation sites 16 km from the location of the FPO. Furthermore, we investigated the change in grazing rates of the major Arctic copepod Calanus glacialis copepodid stage five to assess the interaction between primary and secondary producers during the fall bloom. Increased diatom biomass caused a significant increase in the grazing rate on microphytoplankton (> 20 µm) and a decrease on nanophytoplankton (2-20 µm), indicative of a strong cascade effect because of the reduction of microzooplankton due to the grazing from C. glacialis. We conclude that SWEs during fall might affect food webs via the alternation of seasonal succession of phytoplankton community structure. [ABSTRACT FROM AUTHOR]

Climate change in the Arctic is expected to have drastic effects on marine primary production sources by shifting ice-associated primary production to an overall greater contribution from pelagic primary production. This shift could influence the timing, amount, and quality of algal material reaching the benthos. We determined the contribution of sea ice particulate organic matter (iPOM) to benthic-feeding invertebrates by examining concentrations and stable carbon isotope values (expressed as δ13C values) of three fatty acids (FAs) prominent in diatoms: 16:4(n-1), 16:1(n-7), and 20:5(n-3). Our underlying assumption was that diatoms make up the majority in sea ice algal communities compared with phytoplankton communities. According to the FA concentrations, subsurface deposit feeders consumed the most iPOM and suspension feeders the least. Conversely, there were little differences in δ13C values of FAs between deposit and suspension feeders, but the higher δ13C values of 16:1(n-7) in omnivores indicated greater consumption of iPOM. We suggest that omnivores accumulate the ice algal FA biomarker from their benthic prey, which in turn may feed on ice algae from a deposited sediment pool. The dissimilar results between FA concentrations and isotope values suggest that the FAs used here may not be sufficiently source specific and that other unaccounted production sources, such as bacteria, may also contribute to the FA pool. We propose that FA isotope values are a more indicative biomarker than FA concentrations, with a further need for more specific ice algal biomarkers to resolve the question of ice algal contributions to the Arctic benthic food web. [ABSTRACT FROM AUTHOR]

Movements of brown skuas ( Catharacta antarctica lonnbergi) originating from two populations in the southern Indian Ocean were studied during the nonbreeding period using geolocation. A total of 33 individuals were equipped resulting in 34 annual tracks recovered from 50 deployments. Brown skuas varied extensively in their post-breeding movements, from true long range migrations to reach distant wintering zones, to short movements in the vicinity of breeding grounds. Overall, brown skuas migrated northward to overwinter in different areas in the southern hemisphere; individuals remained in the Indian Ocean, except two that overwintered in the Benguela Current (Atlantic Ocean). Wintering grounds were generally situated in productive dynamic upwelling waters or frontal systems. Brown skuas avoided the less productive area of the South Subtropical Gyre in the Central Indian Ocean. Individuals clearly differed in migratory strategies, targeting areas in a continuum from the sub-Antarctic to the tropics. Inter-individual differences were not sex-dependent. The migration dates varied between sexes with females leaving the breeding sites earlier and returning later compared to males. The duration of migration depended on wintering area and sex. Males had shorter migrations than females, regardless of the wintering area. Isotopic signatures clearly indicated that birds moulted in the wintering area and during migration. The low δ N values of feathers that grew in mixed subtropical-sub-Antarctic waters suggest that skuas fed on low trophic level prey in these areas. The origin and consequences of such strong inter-individual variation in migratory strategies requires further investigation. [ABSTRACT FROM AUTHOR]

An increasing number of boreal marine species are expected to invade the warming Arctic Ocean with the potential to displace endemic species. We provide first evidence that Pacific sand lance ( Ammodytes hexapterus) is expanding its range in the Canadian Arctic Archipelago, a region far outside the species temperate-boreal traditional range south of the Bering Strait. To the best of our knowledge, supported by local Inuit knowledge, the species was not present in the area until the present decade. We observed an increasing density of larval Pacific sand lance with time over the 2011-2016 period, suggesting that environmental conditions are becoming increasingly favorable for the species to reproduce in the Central Canadian Arctic. The northward distribution change of Pacific sand lance is occurring earlier than predicted by current models and could trigger abrupt shifts in Arctic marine food webs if the boreal invader displaces polar cod, a key prey species for top predators in Arctic marine ecosystems. [ABSTRACT FROM AUTHOR]

Marine ecological indicators can be used to assess the condition of the pelagic ecosystems. The bloom onset provides a warning bell for possible changes in trophic interactions and biogeochemical processes. However, depicting the phenology of phytoplankton blooms at high latitudes, where long-term observations are sparse or unavailable, is not a straightforward task. A data-interpolating empirical orthogonal function algorithm was applied to daily satellite-retrieved chlorophyll- a images to produce a long-term (1998-2014) and cloud-free data set over the North Water (NOW) polynya. The seasonal bloom was modeled using a multi-Gaussian approach from which a baseline of phenological characteristics was extracted. The correlation analysis highlights the influence of environmental factors, such as sea surface temperature, cloud fraction, wind stress, and sea-ice concentration, in modulating the bloom start date, its duration, and amplitude. The year-to-year variability in bloom onset appears to be controlled by a delicate balance between oceanographic and meteorological conditions. Blooms last longer during years characterized by a longer open-water period and are shorter during those characterized by greater sea-ice coverage. Noteworthy is the decrease in phytoplankton bloom amplitude over the 17 years examined. Collectively, these outcomes depict the NOW as a climate-sensitive region in which the pelagic marine ecosystem seems to be going toward a decline in chlorophyll- a concentrations. Satellite time series are still too short to differentiate between inter-annual variability, inter-decadal variability, and climate change signal. Should these changes persist; however, the NOW may no longer act as a productive regional oasis supporting thriving populations of zooplankton and top predators. [ABSTRACT FROM AUTHOR]

Our long-term study on top predator (seabirds and marine mammals) distribution in polar marine ecosystems aims at detecting possible temporal and spatial population changes, especially in the context of global changes in temperature and ice cover. Quantitative data on the seabird distribution were collected in the northern Greenland Sea and Fram Strait onboard the icebreaker RV Polarstern between 1988 and 2014, applying 30-min transect counts from the bridge, without width limitation ( n = 7320). A drastic decrease in numbers by a factor of seven was detected for the ivory gull Pagophila eburnea from 2007 on. These data confirm the decrease of ivory gull previously detected in North Canada and North Greenland, leading to the conclusion that the species is 'endangered' or 'near threatened'. These changes are discussed in relation to the decreasing Arctic pack ice coverage leading to the opening of the Northwest and Northeast Passages in 2007, at the time the year with the lowest ice coverage ever recorded. On the other hand, the decrease was even stronger for Ross's gull Rhodostethia rosea after 1993, apparently reflecting changes in migratory habits. The third high Arctic gull, Sabine's gull Xema sabini, was only tallied in very low numbers, without any clear temporal evolution in numbers. [ABSTRACT FROM AUTHOR]

The ivory gull ( Pagophila eburnea) is a high-Arctic species considered endangered in most parts of its breeding range. Ivory gulls must cope with not only the reduction in sea ice cover triggered by climate change but also increasing contaminant loads due to changes in global contaminant pathways and the release of previously stored pollutants from melting snow and ice. This top predator may be affected by biomagnification processes of a variety of compounds with concentrations dramatically increasing from water to higher trophic levels. The objective of this study was therefore to assess the contaminant bioaccumulation of this species in four colonies located on Barentsøya, Svalbard, in link with its trophic behaviour. To that end, contaminants, including organochlorines (OCs), brominated flame retardants (BFRs), and perfluorinated alkyl substances (PFASs), were determined in the blood (plasma and whole blood) of ivory gulls sampled over several years. Carbon- and nitrogen-stable isotopes were also determined in different tissues (feathers, plasma and red blood cells, or whole blood) to infer the trophic level (δN) and feeding habitat (δC) during both the breeding and moulting periods. The most quantitatively abundant contaminants found in the ivory gull were p, p′-DDE (dichlorodiphenyldichloroethylene), ΣPCB (polychlorobiphenyl), and PFOS (perfluorooctane sulphonate). Several compounds including most of the PFASs, trans-nonachlor, cis-nonachlor, and BDE-28 were correlated with nitrogen values. This study highlighted variability in trophic behaviour among individuals during the breeding and the moulting periods. Overall, similar feeding habitats and strategies were used between breeding sites which was echoed by similar contaminant levels. [ABSTRACT FROM AUTHOR]

The humpback whale ( Megaptera novaeangliae) makes annual migrations from Antarctic feeding grounds to tropical breeding grounds. The extent to which it feeds during migration is unknown, but thought to be very low. Whether an animal feeds during migration is likely dependent on prey availability and on the ease with which it can capture the available prey. This study used digital tags (DTAGs) and concurrent prey sampling to measure how changes in the depth and type of prey influenced the lunge feeding rates and the amount of energy consumed by migrating humpback whales. Whales targeting krill lunged at significantly higher rates than whales targeting fish; however, the depth of the prey did not influence lunge rate. The observed lunge rates when feeding on krill, to the best of our knowledge, are higher than any previously reported rates of whales feeding. Estimates of the energetic content of the prey ingested revealed that whales may consume between 1.2 and 3.4 times their daily energy requirements per day while feeding on krill during migration, but less when feeding on fish. This suggests that whales may begin to restock energy supplies prior to reaching the Antarctic. Determining how often this high rate of energy intake occurs along the migratory route will assist with understanding the contribution of migratory energy intake to annual energy budgets. [ABSTRACT FROM AUTHOR]

Picophytoplankton are important primary producers in oligotrophic waters and sensitive to environmental changes. However, little is known about their ecophysiology in the northern Bering Sea with complex water masses. The distribution of picophytoplankton with their optical physiological features and physicochemical characteristics as well as water masses were investigated on the northern Bering Sea Shelf during the summer of 2008. Flow cytometry and statistical analysis including Pearson correlation analysis and cluster analysis were the main methods used. Synechococcus and picoeukaryotes were the primary existing picophytoplankton assemblages, with their respective abundances ranging from 0 to 2.69 × 10 and 0.47 × 10 to 13.20 × 10 cells l and peaking at water depths of 10-30 m with surface light levels of 30-50 %. Larger Synechococcus cells contained larger amounts of chlorophyll a (Chl a) and phycoerythrin. Low temperature, high nutrient concentrations and a high N/P value (>7) might limit cell abundance of picoeukaryotes, as shown by their close relationships. With an increase of temperature and oligotrophic freshwater input, smaller picophytoplankton would thrive and the cellular Chl a (Chl a/cell) increase with higher contribution to total Chl a. Seven water types with different physicochemical and biological characteristics were differentiated using the mini-ecosystem (a descriptor of a composite of parameters defining a composite water type community, including temperature, salinity, macronutrients and community abundance of picophytoplankton) as an indicator. They are Alaska Coastal Water, Bering Shelf Surface Water, 20-40 m of Bering Shelf Water, Bering Shelf Cold Water, Anadyr Water, Anadyr-Bering Shelf Water (Bering Sea Water) and Cold Pool. [ABSTRACT FROM AUTHOR]

Although the Arctic cod ( Boreogadus saida) has a pan-Arctic distribution, little is known about its occurrence in near-shore waters where this species is the principal prey for seabirds, marine mammals and other fish. Published research describes the scyphomedusa Cyanea capillata as an Arctic cod predator, and this paper presents observations from long-term investigations using active hydroacoustics that suggest the Arctic cod avoided C. capillata in two small bays of Cornwallis Island (Canadian High Arctic archipelago). Distribution patterns in echograms suggested that features such as boundary layer fronts restricted jellyfish movements and Arctic cod were often abundant on the side of fronts where C. capillata were absent. Thus, habitat partitioning allowed Arctic cod to share habitat with its predator, albeit exceptions to this sharing occurred when jellyfish abundance was high and Arctic cod were displaced. Thus, if a warmer Arctic triggers an increase in C. capillata abundance, it is possible that small-scale aspects of Arctic cod distribution could be affected. This in turn could have significant ripple effects within the Arctic food web, an additional and previously unrecognized consequence of climate change. [ABSTRACT FROM AUTHOR]

The ivory gull Pagophila eburnea is an Arctic seabird species whose distribution is tightly coupled to the availability of sea ice. During the last decades, strong declines have been reported for breeding colonies in Canada and Greenland, which are usually located on nunataks or remote coastal islands. Here, we report the observation of a colony of ivory gulls breeding on a gravel-covered iceberg 70 km off Northeast Greenland in August 2014. It concerned approximately 60 adults, including two ringed individuals, and many chicks. This represents an unusual breeding site for the species, to be compared with a few cases of colonies on gravel-covered sea ice. Breeding on an offshore iceberg may be advantageous since it provides ultimate protection from predators. Furthermore, the proximity to the productive North East Water polynya may have been attractive to these gulls. As a consequence of this and previous observations, colony surveys should not solely focus on inland and coastal breeding habitats, but should be extended towards the ocean. [ABSTRACT FROM AUTHOR]

People that the author would like to thank for their assistance in the creation of the 2015 issues of the journal "Polar Biology" are mentioned, including J. Aalto, P. Bartels, and A. Barbosa.

Phenology, the study of stages within the life cycles of plants and animals, has served as a proxy for weather and climate throughout human history, but has only recently become its own field of environmental science. Phenological constraints are particularly demanding in avian species because of the necessity of matching chick provisioning with high food abundance, while allocating time for migration. Within avian species, seabird phenology is of particular interest because many seabird species exhibit colonial breeding behaviour. Penguins, representing roughly 90 % of the biomass in the Southern Ocean, are well studied in the context of population dynamics, prey abundance, and phenology. Here I review the annual cycles of Pygoscelis penguins, a genus including gentoo ( Pygoscelis papua), chinstrap ( Pygoscelis antarctica), and Adélie ( Pygoscelis adeliae) penguins, to better understand what is known about their phenology, what causes known changes, and how their phenology influences fitness. Major differences exist between species, particularly in relation to winter migration, incubation shifts, and the timing of breeding. Even with the numerous studies examining phenology in Pygoscelis penguins, large gaps in our understanding of plasticity in the annual cycle remain. In particular, certain phases are neglected because they are logistically difficult to record or have erroneously been ignored. In addition, temporally, large gaps exist in our understanding of phenology, where studies have not been updated in over 20 years at a particular field site. Because phenology does vary greatly between years, depending on the colony, when possible, researchers should strive to update phenological records by recording the dates of phases each year. [ABSTRACT FROM AUTHOR]

Despite being an essential part of the marine food web during periods of ice cover, sea ice algae have not been studied in any detail in the Bering Sea. In this study, we investigated the diversity, abundance and ultimate fate of ice algae in the Bering Sea using sea ice, water and sub-ice sediment trap samples collected during two spring periods in 2008 and 2009: ice growth (March-mid-April) and ice melt (mid-April-May). The total ice algal species inventory included 68 species, dominated by typical Arctic ice algal diatom taxa. Only three species were determined from the water samples; we interpret the strong overlap in species as seeding of algal cells from the sea ice. Algal abundances in the ice exceeded 10 cells l in the bottom 2-cm layer and were on average three orders of magnitude higher than in the water column. The vertical flux of algal cells beneath the ice during the period of ice melt (>10 cells m day) exceeded export during the ice growth period by one order of magnitude; the vertical flux during both periods can only be sustained by the release of algae from the ice. Differences in the relative species proportions of algae among sample types indicated that the fate of the released ice algae was species specific, with some taxa contributing to seeding in the water column, while other taxa were preferentially exported. [ABSTRACT FROM AUTHOR]

Polar bears in the Beaufort (SB) and Chukchi (CS) Seas experience different environments due primarily to a longer history of sea ice loss in the Beaufort Sea. Ecological differences have been identified as a possible reason for the generally poorer body condition and reproduction of Beaufort polar bears compared to those from the Chukchi, but the influence of exposure to other stressors remains unknown. We use molecular technology, quantitative PCR, to identify gene transcription differences among polar bears from the Beaufort and Chukchi Seas as well as captive healthy polar bears. We identified significant transcriptional differences among a priori groups (i.e., captive bears, SB 2012, SB 2013, CS 2013) for ten of the 14 genes of interest (i.e., CaM, HSP70, CCR3, TGFβ, COX2, THRα, T-bet, Gata3, CD69, and IL17); transcription levels of DRβ, IL1β, AHR, and Mx1 did not differ among groups. Multivariate analysis also demonstrated separation among the groups of polar bears. Specifically, we detected transcript profiles consistent with immune function impairment in polar bears from the Beaufort Sea, when compared with Chukchi and captive polar bears. Although there is no strong indication of differential exposure to contaminants or pathogens between CS and SB bears, there are clearly differences in important transcriptional responses between populations. Further investigation is warranted to refine interpretation of potential effects of described stress-related conditions for the SB population. [ABSTRACT FROM AUTHOR]

The Chukchi Sea shelf is a complex transition zone between the Pacific and Arctic Oceans, on which climate variation may have a profound impact. We examined summer zooplankton community structure of the western Chukchi Sea in Alaskan and Russian waters during 2004, 2009, 2010 and 2012 within the ongoing Russian-American Long-term Census of the Arctic program. The four study years were very different both in water mass properties and in zooplankton community structure. A 'warm' year with an early ice retreat and highest water temperatures occurred in 2004, whereas the years 2009-2012 were 'cold' with a later-than-average ice retreat and colder average water temperatures during the sampling period. The extent and prominence of different water masses (Bering Sea-Anadyr Water, Alaska Coastal Current, Siberian Coastal Current, Resident Chukchi Water) within the Chukchi Sea varied between years, which was in turn reflected within the zooplankton communities. Community structure was highly correlated with water mass properties, with bottom temperature being the most significant factor influencing communities. The 'cold' summers of 2009-2012 had nearly twice the biomass and abundance of zooplankton compared with the 'warm' summer of 2004. Biomass was dominated by the large copepod Calanus glacialis believed to originate from the Bering Sea, and abundance was dominated by small shelf species of copepods, such as Pseudocalanus spp., Acartia spp. and Oithona similis. We discuss the implications of the inter-annual variability of planktonic communities within the Chukchi Sea and the possible effects of longer-term climate change. [ABSTRACT FROM AUTHOR]

The species composition of Arctic zooplankton differs greatly from that of the zooplankton of the North Pacific and Bering Sea. Particularly with greater warming from sea-ice retreat, the reproduction of North Pacific species transported into the Chukchi Sea and beyond may lead to changes in the Arctic pelagic ecosystem. We report the egg production and hatching of the Pacific copepod Neocalanus flemingeri in the Chukchi Sea based on shipboard experiments performed in September 2013. The reproductive capability of N. flemingeri observed in the Chukchi Sea resembled that reported in the Pacific, with the exception of a lower hatching success. Only 7.5 % of N. flemingeri eggs hatched compared with 93 % in Pacific experiments. Low hatching success is considered to be caused by failures of fertilization. The potential recruitment number for N. flemingeri suggests that it is unlikely to establish expatriate Arctic populations in the near future. [ABSTRACT FROM AUTHOR]

Drake Passage, extending from the southern tip of South America to the northern Antarctic Peninsula, is a dynamic oceanographic region with well-defined habitats delineated by the three strong frontal jets of the Antarctic Circumpolar Current (ACC). Here, we describe seabird species distribution patterns across Drake Passage and test the hypothesis that species assemblages broadly reflect physical characteristics of the hydrographic fronts. Strip-transect seabird surveys were conducted between Tierra del Fuego and the South Shetland Islands (700 km track line) during January-March (austral summer) over 14 years (48 crossings). Locations of the latitudinally variable fronts were assessed using in situ shipboard data on sea surface temperature and salinity; areas of high variance were used to indicate frontal features. We quantified five distinct species assemblages that correspond to biogeographic regions and relate to the positions of the Sub-Antarctic Front, Polar Front and ACC Southern Front. Dense seabird concentrations coincided with regions characterized by highly variable sea surface temperature and salinity, suggesting that associated species assemblages reflect the mesoscale hydrographic surface as indicated by sea surface conditions. [ABSTRACT FROM AUTHOR]