Description: Cyanobacterial microbial mats are highly structured communities commonly found in Antarctic inland waters including melt streams. These benthic microbial associations comprise a large number of microorganisms with different metabolic capacities, impacting nutrient dynamics where established. The denitrification process is a feasible nitrogen loss pathway and a biological source of nitrous oxide, a potent greenhouse gas that also promotes ozone depletion. Potential denitrifiers from five microbial mats were characterized using a PCR-DGGE (denaturing gradient gel electrophoresis) approach. Molecular markers encoding for key enzymes in the denitrification process ( nir K, nir S and nos Z) were used. Fingerprints were obtained for the five sampled mats and compared for two successive years. Distance analysis showed that despite the sampled year, the denitrifying genetic potential was similar between most of the sites when represented in Euclidean space. The number of dominant denitrifiers detected for each sample ranged between 6 and 18 for nir K, 4–10 for nir S and 6–17 for nos Z. The seventy-two sequenced phylotypes showed 80–98 % identity to previously reported environmental sequences from water column, sediments and soil samples. These results suggest that Antarctic microbial mats have a large denitrification potential, previously uncharacterized and composed by both site-specific and common phylotypes belonging mainly to Alpha -, Beta - and Gammaproteobacteria .

Description: The rough-legged buzzard, a circumpolar avian predator, is usually defined as rodent specialist in the tundra but as a generalist in the boreal zone, leaving open the question of where the shift in feeding strategy occurs. Here, we investigated the diet and breeding biology of buzzards as well as abundance of their possible prey during 5 years in the low-Arctic shrub tundra on the Nenetsky Ridge, Russia. We employed three complementary methods to assess the diet of this Arctic predator—pellet dissection, identification of prey remains on nests, and stable isotope analysis—to overcome their respective limitations. We documented fluctuations in abundances of the likely prey, namely rodents, ptarmigans, and hares. Nesting density of buzzards changed substantially over the years, but did not track the abundance cycle of the rodents. The number of buzzard fledglings was relatively low (1.08 ± 0.3) and did not change according to the density of rodents. In the year when rodents were at their lowest abundance, diet analyses of nestlings documented a shift from rodents to alternative prey, with a decrease in the proportion of tundra voles and an increase in proportion of hares, ptarmigans, and ducks. Here, we argue that buzzards may adopt different feeding strategies along the gradient from generalists to specialists. While the rough-legged buzzard is usually considered a small rodent specialist, our study shows that it can shift to alternative prey where or when rodents are scarce and when alternative prey are sufficiently abundant to provide subsistence for breeding.

Description: Photosynthetic carbon allocations into different macromolecular classes provide important clues regarding physiological conditions of phytoplankton and the nutritional status of potential grazers. The productivity experiments for photosynthetic carbon allocations were conducted at three light depths (100, 30, and 1 %) for nine different stations in the northern Bering Sea as an important gateway into the western Arctic Ocean, using the 13 C isotope tracer technique to determine the major controlling factors and physiological conditions of phytoplankton. The photosynthetic carbon allocations into different macromolecular classes [Low molecular weight metabolites (LMWM), lipids, proteins, and polysaccharides] of primary producers were determined based on the productivity experiments. LMWM and polysaccharides had similar vertical patterns whereas lipids and proteins had reverse vertical patterns at all the stations, which is consistent with other results under different light depths. The overall average allocations were 37.9 (SD = ± 18.8 %), 26.6 (SD = ± 17.4 %), 26.5 (SD = ± 20.7 %), and 9.1 % (SD = ± 7.8 %), for LMWM, lipids, proteins, and polysaccharides, respectively. Based on a general pattern of macromolecular production in the northern Bering Sea, phytoplankton was in a physiologically transitional phase from an unlimited status to a nitrogen-deficient condition during our cruise period, 2007. However, more in situ field measurements for macromolecular production under a variety of environmental conditions will improve the understanding of the physiological responses of phytoplankton to the ongoing environmental changes in the Arctic Ocean.

Description: Single-celled bacterial grazers are key components of marine ecosystems, and at times represent the dominant eukaryotes in the Arctic Ocean. Among these are small, phylogenetically diverse stramenopiles, known almost exclusively from their 18S rRNA gene sequences. Marine stramenopiles (MAST) have been found in the upper waters of the world ocean and in all Arctic seas. In particular, three sub-clades of MAST-1, MAST-1A, 1B and 1C co-occur in Arctic waters, but ecological and distributional details are lacking. Here, we have updated phylogenies of the MAST-1 clade to test whether there are Arctic-specific MAST-1 ecotypes. In addition, taking advantage of samples collected over 2 years as part of several Arctic cruises leading up to and during the International Polar Year, we applied sub-clade-specific probes and fluorescent in situ hybridization to describe the distribution of the three sub-clades in the Canadian Arctic. The three groups were found principally in the euphotic zone; however, evidence of Arctic ecotypes remains elusive. Some environment-specific separation among sub-clades was detected, with MAST-1C reaching significantly greater concentrations near the marginal ice zone, while MAST-1A and MAST-1B were associated with ice-covered and open-water stations, respectively. MAST-1B appeared to be able to persist at greater depths. Changing ice cover and mixing regimes are therefore expected to have an impact on the concentrations and distribution of these sub-clades, with possible downstream consequences on the marine food webs.

Description: Knowledge about the protist diversity of the Pacific sector of the Southern Ocean is scarce. We tested the hypothesis that distinct protist community assemblages characterize large-scale water masses. Therefore, we determined the composition and biogeography of late summer protist assemblages along a transect from the coast of New Zealand to the eastern Ross Sea. We used state of the art molecular approaches, such as automated ribosomal intergenic spacer analysis and 454-pyrosequencing, combined with high-performance liquid chromatography pigment analysis to study the protist assemblage. We found distinct biogeographic patterns defined by the environmental conditions in the particular region. Different water masses harbored different microbial communities. In contrast to the Arctic Ocean, picoeukaryotes had minor importance throughout the investigated transect and showed very low contribution south of the Polar Front. Dinoflagellates, Syndiniales, and small stramenopiles were dominating the sequence assemblage in the Subantarctic Zone, whereas the relative abundance of diatoms increased southwards, in the Polar Frontal Zone and Antarctic Zone. South of the Polar Front, most sequences belonged to haptophytes. This study delivers a comprehensive and taxon detailed overview of the protist composition in the investigated area during the austral summer 2010.

Description: The marble notothen, Notothenia rossii , is widely distributed around the waters of sub-Antarctic islands in the Southern Ocean and is exposed to different temperatures that range from −1.5 to 8 °C. This study investigates whether the different environmental conditions experienced by N. rossii at different latitudes in the Southern Ocean affect the levels of its blood serum antifreeze glycoprotein (AFGP). N. rossii specimens were collected from four localities, including the Ob’ Seamount in the Indian Ocean sector, and South Georgia Island, South Shetland Islands and Dallman Bay in the Atlantic Ocean sector. Serum AFGP activity was determined in terms of thermal hysteresis, i.e. the difference between the equilibrium melting and non-equilibrium freezing points (f.p.s.). Among the four populations, the Ob’ Seamount specimen had the lowest serum AFGP activity (0.44 °C) and concentration (4.88 mg/mL), and the highest non-equilibrium f.p. (−1.39 °C). These results are consistent with the warmer, ice-free waters around the Ob’ Seamount. The other three higher latitude populations have 2–3 times greater serum AFGP activity and concentration, and much lower non-equilibrium f.p.s. In contrast, the physiological profiles of serum AFGP size isoforms revealed that all N. rossii populations, including the Ob’ Seamount specimen, possess an extensive complements of AFGP proteins. Isoform variation was observed, especially in the large size isoforms (AFGPs 1–5), when compared to AFGP of the high Antarctic Dissostichus mawsoni. The lower levels of AFGP and the absence of some of the large isoforms are likely responsible for higher non-equilibrium f.p.s. of the Ob’ seamount specimen.

Description: Knowledge about parasitism in harbour porpoises and their health status around Greenland is scarce. This study provides knowledge about the poorly studied cetacean in its rapidly changing environment. Parasites and pathological findings in 20 harbour porpoises ( Phocoena phocoena ) hunted in waters around West Greenland are presented. Carcasses were dissected, and parasitological, histological and bacteriological investigations were carried out. Protozoa ( Sarcocystis sp.), Nematoda ( Halocercus invaginatus , Stenurus minor , Anisakis simplex sensu lato (s.l.), Crassicauda sp.), Trematoda ( Campula oblonga ) and Cestoda ( Phyllobothrium delphini , Monorygma grimaldii ) were found. Parasitic infection of the peribullar cavity and lung with pseudaliid nematodes was found in most animals. Sixty per cent of the porpoises were infected with stomach worms, and trematodes were present in liver and pancreas of 90 and 30 % of the porpoises, respectively. Crassicauda sp. was isolated from perimuscular fascia in 45 % of the animals. This is the first record of tetraphyllidean merocercoids in harbour porpoises. M. grimaldii and P. delphini were found in blubber layer of 15 % and abdominal cavity of 50 % of the porpoises. Bronchopneumonia, gastritis, cholangitis, pancreatitis and panniculitis were almost exclusively associated with parasitic infection and usually mild. Compared with a previous study of Greenlandic porpoises from 1995, a significant increase in severity of parasitic infections and the emergence of new parasite species were observed, most likely associated with changes in diet, influenced by increasing sea temperatures and receding ice cover.

Description: Previous work in our laboratory showed that levels of oxidized proteins and/or lipids increase in heart ventricles of icefishes but not red-blooded notothenioids in response to exposure to their critical thermal maxima (CTMax). However, neither icefishes nor red-blooded fishes up-regulate their antioxidant defenses in response to exposure to CTMax, suggesting notothenioids may have lost the ability to alter antioxidant levels in response to stress during their evolution at cold temperature. Alternatively, exposure to CTMax may have been too short a thermal stress to induce increases in antioxidant levels. To address this question, the icefish Chionodraco rastrospinosus and the red-blooded notothenioid Notothenia coriiceps were maintained at either 0 ºC or 4 °C for 1 week. Levels of oxidized proteins and lipids, as well as transcript abundance and maximal activity of the antioxidants superoxide dismutase and catalase, were quantified in heart ventricle and pectoral adductor muscle. Although previous studies showed that the production of reactive oxygen species increases in response to warming in notothenioids, neither levels of oxidized proteins, lipids nor antioxidant activity increased in any tissue of either species in response to exposure to 4 °C. This suggests that notothenioids do not incur oxidative damage during prolonged, moderate warming.

Description: In the twentieth century, red fox ( Vulpes vulpes ) expanded into the Canadian Arctic, where it competes with arctic fox ( Vulpes lagopus ) for food and shelter. Red fox dominates in physical interactions with the smaller arctic fox, but little is known about competition between them on the tundra. On Hershel Island, north Yukon, where these foxes are sympatric, we focused on natal den choice, a critical aspect of habitat selection. We tested the hypothesis that red fox displaces arctic fox from dens in prey-rich habitats. We applied an approach based on model comparisons to analyse a 10-year data set and identify factors important to den selection. Red fox selected dens in habitats that were more prey-rich in spring. When red foxes reproduced, arctic fox selected dens with good springtime access, notably many burrows unblocked by ice and snow. These provided the best refuge early in the reproductive season. In the absence of red foxes, arctic foxes selected dens offering good shelter (i.e. large isolated dens). Proximity to prey-rich habitats was consistently less important than the physical aspects of dens for arctic fox. Our study shows for the first time that red foxes in the tundra select dens associated primarily with prey-rich areas, while sympatric arctic foxes do not. These results fit a model of red fox competitively interfering with arctic fox, the first detailed study of such competition in a true arctic setting.

Description: Polar cod was shown to form dense under-ice winter aggregations at depth in the Amundsen Gulf (southeastern Beaufort Sea). In this paper, we verify the premises of the aggregation mechanism by determining the distribution and habitat characteristics of polar cod prior to the formation of winter aggregations. Multifrequency split-beam acoustic data collected in October–November 2003 revealed that polar cod split into two distinct layers. Age-0 polar cod formed an epipelagic layer between 0 and ~60 m depth without any clear large-scale biomass trend. In contrast, adult polar cod tended to distribute into an offshore mesopelagic layer between ~200 and 400 m that shoaled into a denser (1–37 g m −2 ) benthopelagic layer on sloping bottoms (between 150 and 600-m isobaths) along the Mackenzie shelf and into the Amundsen Gulf basin. Concentrations peaked in the Amundsen Gulf where estimated total biomass reached ~250 kt. Both age-0 and adult polar cod distributed in the warmer waters (〉−1.4 °C). We hypothesise that polar cod concentration over slopes is governed by the combined actions of (1) local currents concentrating both depth-keeping zooplankton and polar cod at the shelf-break and basin slopes and (2) trophic association with these predictable topographically trapped aggregations of zooplankton prey. During freeze-up, these slope concentrations of polar cod are thought to constitute the main source of the observed dense under-ice winter aggregations. The hypothesis of active short-distance displacements combined with prevailing mean currents is retained as the likely aggregation mechanism.