Polar Biology

The Western Antarctic Peninsula (WAP) has experienced significant changes in seawater temperature over the past 50 years. This warming affects seawater and sea ice microbial cycling of organic matter, where viral features could play a crucial role in sympagic sea ice melting environments. However, there is a lack of information about the sea ice viral abundances and processes (e.g. lysis rates and carbon release from microorganisms). To gain knowledge of sea ice viral, microbial, and chemical characteristics, we collected four different sea ice samples and their surrounding surface seawater during the Austral summer of 2019 north of the WAP. In each sample, we assessed viral and microbial abundances and environmental parameters. In the sea ice, we also measured viral-driven mortality rates on prokaryotes and protists and the consequent release of organic carbon. The viral and microorganism abundances in the sea ice were higher (4.5 ± 1.9 × 10⁶ viruses mL⁻¹; 1.5 ± 0.7 × 10⁶ prokaryotes mL⁻¹, 9.4 ± 5.0 × 10² protists mL⁻¹) than in the surrounding surface seawater (1.7 × 10⁶ viruses mL⁻¹, 0.4 × 10⁶ prokaryotes mL⁻¹, 7.1 × 10² protists mL⁻¹). Furthermore, viral lytic production on prokaryotes (4.5 ± 0.8 × 10⁵ mL⁻¹day⁻¹) and protists (1.9 ± 1.0 × 10⁴ mL⁻¹ day⁻¹) in sympagic environments had a higher viral impact on carbon release by protist (1.5 ± 1.1 µg C L⁻¹ day⁻¹) than by prokaryotes (0.3 ± 0.1 µg C L⁻¹ day⁻¹). Our results suggest that, after sea ice melting, viral abundances and activities may influence the functioning of the microbial food web by increasing the release of dissolved organic matter, affecting biogeochemical cycles and microbial communities in the underlying surface waters.

Living specimens of the macroalga Palmaria decipiens were collected from 100 m depth, representing a new confirmed depth record, considerably exceeding the previous record of 42 m depth. Previous deeper collections (below conventional SCUBA depths) have relied on dredge/grab samples or drop camera surveys. Remote techniques cannot conclusively prove that macroalgae are living at these depths, as algae detach from shallower substrata, e.g., through ice scouring, and drift to depths below their growth limit. This, combined with a low rate of decay of macroalgae around Antarctica, requires validation that algal samples from depth have grown in situ. Estimates of macroalgal biomass, energy fluxes, and the potential energy fixation may need adjusting to consider the deeper growing depths particularly with glacial retreat along the Antarctic Peninsula revealing areas of rocky substrata for macroalgal colonisation. The confirmed extension of depth where macroalgae can grow will have implications for assessments of benthic productivity and food webs in Antarctica.

Polar bears ( Ursus maritimus ) in the southern Beaufort Sea experience long annual periods when preferred seal prey are scarce or are unavailable. Consumption of bowhead whale ( Balaena mysticetus ) carcasses from native Alaskan subsistence hunting is increasingly common for onshore polar bears, yet the energetic consequences of this consumption remain unclear. We use data on bears captured repeatedly over periods that encompassed autumn and winter, combined with calculations, to show that adult female bears likely consume an average of at least 4 seal equivalents during both autumn and winter periods and that considerable variation in energy intake exists across individual bears. We further show that subsistence-caught whale carcasses provide an upper threshold of > 4000 seal equivalents, which could potentially meet mean consumption needs of ~ 80% of the southern Beaufort Sea bear subpopulation during autumn and winter periods. Finally, we modify an existing model to show that observed mass changes over autumn and winter could substantially alter spring foraging habitat choice by females with cubs and the chance that a female with reduced energy reserves would abort a pregnancy or abandon cubs in favor of increasing her own survival; these behaviors could potentially influence population vital rates. Our study highlights the importance of mass dynamics over the autumn and winter months, points to the need for additional data on foraging and energetics over this period, and indicates that the recent declines in polar bear body condition in some subpopulations could have complex effects on reproduction.

In Kongsfjorden (Spitsbergen), we quantified the zonation of visually dominant macroalgal taxa and of detached macroalgae from underwater videos taken in summer 2009 at six transects between 2 and 138 m water depth. For the first time, we provide information on the occurrence of deep water red algae below the kelp forest and of detached macroalgae at water depth > 30 m. The presence and depth distribution of visually dominant red algae were especially pronounced at the outer fjord, decreased with proximity to the glacial front and they were absent at the innermost locations. Deepest crustose coralline red algae and foliose red algae were observed at 72 and 68 m, respectively. Brown algae were distributed along the entire fjord axis at 2–32 m. Green algae were only present at the middle to inner fjord and at areas influenced by physical disturbance at water depths of 2–26 m. With proximity to the inner fjord the depth distribution of all macroalgae became shallower and only extended to 18 m depth at the innermost location. Major recipients of detached macroalgae were sites at the shallower inner fjord and at the middle fjord below the photic zone at depths to 138 m. They may either fuel deep water secondary production, decompose or support carbon sequestration. Univariate and community analyses of macroalgal classes including detached macroalgae across transects and over depths reveal a considerable difference in community structure between the outermost sites, the central part and the inner fjord areas, reflecting the strong environmental gradients along glacial fjords.

Changes to Pacific walruses (Odobenus rosmarus divergens) habitat and foraging behavior may affect exposure to both toxic and essential trace elements in walrus tissue. This study measured the trace element concentrations of silver (Ag), arsenic (As), cadmium (Cd), cobalt (Co), copper (Cu), nickel (Ni), total (THg) and methyl mercury (MeHg), selenium (Se), lead (Pb), and zinc (Zn) in walrus skeletal muscle sampled during 2009–2015. Females had significantly higher concentrations of THg (p = 0.021), MeHg (p = 0.037), Cd (p = 0.021), Cu (p = 0.003), and Se (p = 0.001) compared to males. Females with no calf had significantly higher concentrations of Cd compared to females with a calf (p = 0.001) and pregnant females and females with a calf had significantly lower Se concentrations compared to females with a yearling or no calf (p < 0.05). Bering Sea males had significantly higher Ni concentrations (p = 0.001) and significantly lower Se (p = 0.006) and Zn concentrations (p = 0.001) compared to other locations. THg, MeHg, and As tissue concentrations decreased with age (p < 0.01), suggesting these toxic elements are not accumulating in this tissue while Cd increased with age (p < 0.05). The narrower range in ele- ment concentrations among pregnant and nursing females may indicate less variation in prey species, and coupled with the reproductive needs for essential elements, suggests they may be more vulnerable to changes in prey availability compared to other walruses.

Arctic climate change is leading to an advance of plant phenology (the timing of life history events) with uncertain impacts on tundra ecosystems. Although the lengthening of the growing season is thought to lead to increased plant growth, we have few studies of how plant phenology change is altering tundra plant productivity. Here, we test the correspondence between 14 years of Salix arctica phenology data and radial growth on Qikiqtaruk–Herschel Island, Yukon Territory, Canada. We analysed stems from 28 individuals using dendroecology and linear mixed-effect models to test the statistical power of growing season length and climate variables to individually predict radial growth. We found that summer temperature best explained annual variation in radial growth. We found no strong evidence that leaf emergence date, earlier leaf senescence date, or total growing season length had any direct or lagged effects on radial growth. Radial growth was also not explained by interannual variation in precipitation, MODIS surface greenness (NDVI), or sea ice concentration. Our results demonstrate that at this site, for the widely distributed species S. arctica, temperature—but not growing season length—influences radial growth. These findings challenge the assumption that advancing phenology and longer growing seasons will increase the productivity of all plant species in Arctic tundra ecosystems.

The summer climate in Maritime Antarctica is characterised by high humidity and cloudiness with slightly above zero temperatures. Under such conditions, photosynthetic activity is temperature-limited and plant communities are formed by a few species. These conditions could prevent the operation of the photoprotective xanthophyll (VAZ) cycle as low irradiance reduces the excess of energy and low temperatures limit enzyme activity. The VAZ cycle regulates the dissipation of the excess of absorbed light as heat, which is the main mechanism of photoprotection in plants. To test whether this mechanism operates dynamically in Antarctic plant communities, we characterised pigment dynamics under natural field conditions in two representative species: the moss Polytrichum juniperinum and the grass Deschampsia antarctica . Pigment analyses revealed that the total VAZ pool was in the upper range of the values reported for most plant species, suggesting that they are exposed to a high degree of environmental stress. Despite cloudiness, there was a strong conversion of violaxanthin (V) to zeaxanthin (Z) during daytime. Conversely, the dark-induced enzymatic epoxidation back to V was not limited by nocturnal temperatures. In contrast with plants from other cold ecosystems, we did not find any evidence of overnight retention of Z or sustained reductions in photochemical efficiency. These results are of interest for modelling, remote sensing and upscaling of the responses of Antarctic vegetation to environmental challenges.

Over decades, persistent organic pollutants (POPs) and trace metals like mercury (Hg) have reached the remotest areas of the world such as Antarctica by atmospheric transport. Once deposited in polar areas, low temperatures, and limited solar radiation lead to long environmental residence times, allowing the toxic substances to accumulate in biota. We investigated the load of polychlorinated biphenyls (PCBs) and dichlorodiphenyltrichloroethane (DDTs) and metabolites (DDEs, DDDs) in embryos from failed eggs of the smallest seabird breeding in Antarctica, the Wilson's storm-petrel ( Oceanites oceanicus ) at King George Island (Isla 25 de Mayo). We compared samples of different developmental stages collected in 2001, 2003, and 2014 to 2016 to investigate changes in pollutant concentrations over time. We detected eight PCBs including the dioxin-like (dl) congeners PCB 105 and 118 (ΣPCBs: 59-3403 ng g ⁻¹ ww) as well as 4,4’-DDE, and 4,4’-DDD (ΣDDX: 19-1035 ng g ⁻¹ ww) in the embryos. Samples from the years 2001 and 2003 showed higher concentrations of PCBs than those from 2014 to 2016. Concentrations of DDX was similar in both time intervals. Furthermore, we determined Hg concentrations in egg membranes from 1998 to 2003, and 2014 to 2016. Similar to PCBs, Hg in egg membranes were higher in 1998 than in 2003, and higher in 2003 than in the years 2014 to 2016, suggesting a slow recovery of the pelagic Antarctic environment from the detected legacy pollutants. Embryos showed an increase in pollutant concentrations within the last third of their development. This finding indicates that contaminant concentrations may differ among developmental stages, and it should be taken into account in analyses on toxic impact during embryogenesis.

The main target of this paper is to improve the knowledge of the species composition of sea stars in Patagonian Argentine deep sea reaching depths of 2062 m. In addition, these results offer us the opportunity to analyze the possible connections between Argentinian marine fauna and adjacent Antarctic areas that have become a topic of interest in the past few years. This work is based on Atlantic Projects’ surveys carried out on an atypical and especially vulnerable marine ecosystems (canyons created from craters collapse by gas leaks). These are profusely impacted by frequent fishing activities, being one of the most important and international fishing grounds, where 887 records (1878 specimens) of 41 species of asteroids were collected in 217 stations ranging from 219 to 2062 m in depth. Seven of those species are proposed as new records: (Diplasterias octoradiata (Studer 1885), Plutonaster bifrons (Wyville Thomson, 1873), Radiaster elegans Perrier, 1881, Anseropoda antarctica Fisher, 1940, Pillsburiaster calvus Mah, 2011, Paralophaster lorioli (Koehler, 1907), Pteraster flabellifer Mortensen 1933). After refining the database built from literature and open-access databases such as OBIS and AntBIF, the new Argentinian asteroids deep-water checklist contains 2198 records from 64 asteroids species including the 7 new records proposed. Most of these 64 species (89.06%) are present in Antarctic-adjacent waters, and after the study of their occurrences at traditional biogeographic entities, our results support the hypothesis that Argentinian waters (in the case of the class Asteroidea) should be considered part of the sub-Antarctic entity.

Despite the ecological importance of leopard seals (Hydrurga leptonyx) as apex marine predators, little is known about their reproductive biology. To address this paucity, we reviewed leopard seal birth and pup records and applied a standardised age-class classification system to differentiate between births/newborns (offspring ≤ 14 days old) and pups (> 14 days but < 6 months old). We compiled 19 birth/newborn and 141 pup records and examined their occurrence by month, region, substrate, birth-specific attributes (i.e. birth observations, fresh umbilicus or placental), standard length, weight, presence of mother, presence of lanugo, sex, status (e.g. born alive) and fate. These records indicate that leopard seal births occur between September and December, with peak records from September to November, whilst pup records peaked between August and December. The regions with the most birth/newborn records were the sub-Antarctic Islands (31.6%) and Chile (31.6%), followed by Antarctica (15.8%), New Zealand (15.8%) and the Falkland Islands (5.3%). Pups were recorded predominantly in the sub-Antarctic Islands (54.6%), followed by the Antarctic (42.6%), Chile (2.1%) and Australia (0.7%). Whilst leopard seal birth records were predominantly on ice, they were also found on terra firma. The northernmost published leopard seal birth records occurred in New Zealand whilst the northernmost published leopard seal pup records occurred in Australia. This study contradicts the long-standing hypothesis that leopard seals only give birth on Antarctic pack ice, and instead, here we indicate that 84.2% and 57.4% of collated leopard seal birth and pup records, respectively, occur outside of Antarctica. Our records illustrate the importance of northern regions as part of the leopard seal’s range. We emphasise the need to conduct research focused on the reproductive biology of this keystone species throughout its range and that future management of leopard seal populations should also consider their northern range.

In the Arctic, nest predation risk is higher at lower latitudes, and some shorebirds (Charadriidae) nesting at the southernmost limits of their ranges near Churchill, Manitoba tend to experience lower nest success than those at other Arctic sites. This study investigates whether proximity to human settlement affects predator abundance, predation risk, and shorebird daily nest survival near Churchill by measuring these variables at varying distances from town during two nesting seasons. Active fox dens decreased in number close to town; however, there was no clear trend in avian predator abundance in relation to town. Predation risk on artificial nests decreased as distances from active fox dens and Parasitic Jaeger (Stercorarius parasiticus) nests increased, decreased with proximity to town, and decreased with a camera present. Shorebird daily nest survival tended to be lower near jaeger nests and there was some support for a positive effect of camera presence and proximity to town. Overall, these results suggest that shorebird nest survival in the sub-Arctic can be heavily impacted by proximity to nests of avian predators, but that shorebirds may benefit from proximity to town likely due to reduced fox denning activity.

Marine animals such as the southern elephant seal (Mirounga leonina) rely on a productive marine environment and are vulnerable to oceanic changes that can affect their reproduction and survival rates. Davis Base, Antarctica, acts as a moulting site for southern elephant seals that forage in Prydz Bay, but the mitochondrial haplotype diversity and natal source populations of these seals have not been characterized. In this study, we combined genetic and animal tracking data on these moulting seals to identify levels of mitochondrial haplotype diversity, natal source population, and movement behaviours during foraging and haul-out periods. Using partial sequences of the mitochondrial control region, we identified two major breeding mitochondrial lineages of seals at Davis Base. We found that the majority of the seals originated from breeding stocks within the South Atlantic Ocean and South Indian Ocean. One seal was grouped with the Macquarie Island breeding stock (South Pacific Ocean). The Macquarie Island population, unlike the other two stocks, is decreasing in size. Tracking data revealed long-distance foraging activity of the Macquarie Island seal around Crozet Islands. We speculate that changes to the Antarctic marine environment can result in a shift in foraging and movement strategies, which subsequently affects seal population growth rates.

The vocal repertoire of walruses has been widely described in the bioacoustic literature. These marine mammals produce several distinct types of vocalizations for intraspecific communication during the breeding season. In this study, we provide the first evidence of walrus-generated sounds during foraging dives when they feed on bivalves. We recorded two types of sounds that we associated to different feeding mechanisms. The first sound type was brief and low in frequency that we relate to the suction of soft parts from the bivalves’ shells through the use of walrus powerful tongues, which is the common feeding behavior reported in the walrus literature. We also recorded a second sound type composed of multiple broadband pulse trains. We hypothesize the latter were associated with bivalve shell cracking by walruses, which would represent a new feeding mechanism in the walrus literature. This new feeding mechanism is either related to bivalves’ ecology or to walruses removing the sediment when searching for food. During this study, we observed bivalves lying on the seafloor instead of being buried in the sediment in walrus feeding areas while scuba diving. As a result, walruses cannot use suction to feed on soft body part of bivalves and have to use another strategy, mastication. Our findings provide a first step towards using passive acoustics to quantify walrus behavior and feeding ecology.

Copepods of the genera Calanus and Pseudocalanus are important components of Arctic marine ecosystems. Despite the key roles of these zooplankters, little is known about the organisms they interact with most intimately, their parasites and symbionts. We applied metabarcode sequencing to uncover eukaryotic parasites present within these two copepod genera from three areas around the high Arctic archipelago of Svalbard. Ten distinct parasite groups were observed: four different Apostome ciliates, four different dinoflagellates (Chytriodinium sp., Ellobiopsis sp., Thalassomyces sp., and Hematodinium sp.), a Paradinium sp., and a trematode. Apostome ciliates closely related to Pseudocollinia spp. were the most commonly observed parasite, with overall infection rates of 21.5% in Calanus and 12.5% in Pseudocalanus. Infection by these ciliates varied seasonally, with no infections observed in early winter, but infection rates exceeding 75% in spring. Host specificity varied between parasites, with significant differences in infection rate between the two host copepod genera for four parasites (two ciliates, Chytriodinium, and a trematode). The diverse assemblage of parasites observed in these copepods, and the frequency of infection, with over one in five copepod individuals infected, suggest parasites may be playing a greater role in Arctic plankton communities than generally acknowledged.

Studying the trophic ecology of marine fishes in their natural habitat provides insights into their behavior, their role in community dynamics, and in energy flow through ecosystems. The long tail hake Macruronus magellanicus Lönnberg, 1907, is distributed from 35°S in the Atlantic Ocean and 33°S in the Pacific Ocean and supports important fisheries around the southern tip of South America. The trophic ecology of this species was evaluated in the Southwestern Atlantic (52°–56°S, 106 to 932 m depth) for the first time. This is the main fishing area in the southern region of its distribution. Stomach contents and C and N stable isotope analysis were used to assess ontogenetic and spatial variability in long tail hake diet. The main prey items identified in the stomach contents varied spatially, differentiating three feeding grounds with euphausiids, Fuegian sprats (Sprattus fuegensis), and squat lobsters (Munida gregaria) as the main prey in each. However, these differences were not reflected in the stable isotope signals of their muscles. Our results suggest that long tail hake move between feeding grounds in a shorter time period than the isotopic turnover rate of muscle (~ 2–5 months). Independent of the feeding grounds, both methodologies showed ontogenetic variability in diet. Our evidence suggests in the southern tip of South America, long tail hake move among grounds to take advantage of the availability of different resources. These results provide valuable information on the trophic ecology of long tail hake to consider in management and conservation policies.

Three species of Southern Ocean skates, Bathyrajaeatonii,Bathyrajairrasa and Bathyrajamurrayi, are commonly caught as incidental by-catch in fisheries around Heard Island and McDonald Islands of the Kerguelen Plateau. We used length-at-age data to present the species’ life history information (age, growth and maturity for the first-time). Length- and age-at-maturity analyses revealed that B.irrasa matured at > 6 years old and > 1000 mm total length (TL), which was older and larger than B.murrayi (> 5 years old and > 400 mm TL) but similar to B.eatonii (> 5 years old and > 900 mm). We fitted growth models using a multi-model Bayesian framework. Our findings support the assumption that B.irrasa is slow growing and late maturing compared to B.eatonii and B.murrayi, consequently putting it at greater risk to fishery-induced increases in mortality compared to other species (e.g., B.murrayi). This is the first-time age and growth has been estimated for these species, however sample sizes for B.murrayi and B.eatonii were small and hence growth models should be interpreted with caution. Our results represent vital information for population projection models and can therefore assist in the development and/or revision of current by-catch limits to inform ongoing management strategies and conservation efforts.

Studying life-history traits is critical to understanding the intraspecific variation among fish populations. In this research, we investigated the age, growth, and sexual maturity of Galaxias maculatus population from Laguna Negra (LN), the southernmost landlocked population of the species, and compared the results obtained with those obtained before for the diadromous population from Arroyo Negro (AN), 1.8 km away from LN. We read otolith growth bands to estimate age structure and calculated the gonadosomatic index to estimate sexual maturity. We found five age classes (0 + to 4 +) in LN; the maximum age was 4.5 years, the maximum documented age for the species, exceeding in 1 year the maximum age found previously for the AN population. Age class 2 + was the most represented throughout the year, and the greater age and length-at-age ratio observed in this landlocked population suggest a slower growth rate than that of AN. We hypothesize that landlocked individuals reach their first sexual maturity 1 year later than their diadromous counterparts. The protracted reproductive season detected in this landlocked population (9 months) may be related to the high size variability within age classes, where some individuals might maximize growth while others might maximize first sexual maturity. Our results suggest higher energetic costs for these basic biological activities in landlocked than diadromous populations from Tierra del Fuego, Argentina. Further studies are necessary to understand the trade-off between growth and sexual maturation in sub-Antarctic G. maculatus populations.

Antarctic krill (Euphausia superba) are a circumpolar species with an omnivorous diet. Knowledge of krill diet within different regions will help predict how environmental change may impact local krill populations. Krill from the Atlantic, Indian, and Pacific sectors of the Southern Ocean were compared. The total lipid, lipid class, neutral lipid fraction fatty acid and sterol content and composition of whole krill, their digestive glands, and stomachs during the late-summer were examined. Indian sector krill had a distinctly different dietary lipid pattern to Atlantic and Pacific sector krill based on their fatty acid profiles (p < 0.001). Indian sector whole krill had higher phospholipids (55.0 ± 8.9%, % total lipids) compared to Pacific (45.9 ± 3.6%) and Atlantic sector whole krill (43.7 ± 8.2%) but showed lower phospholipid levels in their digestive glands (29.4 ± 8.5%, 52.5 ± 5.7%, 52.5 ± 5.9%, respectively). Indian sector krill had a more copepod and diatomaceous diet (higher levels of 16:1n-7c, 14:0 and 20:1 and 22:1 isomers), with less flagellate input (lower 18:4n−3, 21:5n−3 and 18:3n−6) than other regions. Krill from one site in the Indian sector had particularly high 22:6n-3 levels. Indian sector krill had lower cholesterol levels in their stomachs (52.5 ± 14.1%, as % total sterols) than Pacific and Atlantic sector krill stomachs (62.8 ± 1.9% and 60.9 ± 4.9%, respectively). This study details the regional differences in late-summer krill diet by assessing the lipid, neutral lipid fraction fatty acid and sterol content and composition of different tissue types.

Planktonic ciliates are important components of microzooplankton in marine pelagic ecosystems. However, the study of planktonic ciliate distribution in different water masses of the Southern Ocean was scarce. We investigated planktonic ciliate distribution in different water masses of the Cosmonaut and Cooperation Seas during December 6, 2019 to January 6, 2020. Tintinnids contributed 5.97% and 3.65% to total planktonic ciliate abundance and biomass, respectively. Both total planktonic ciliate and aloricate ciliate abundances were highest in the Winter Water (WW), while tintinnid abundance was highest in the Summer Surface Water (SSW). The biomasses of total planktonic ciliates and aloricate ciliates were highest in SSW, while that of tintinnids was highest in WW. The lowest values were all observed in the Circumpolar Deep Water (CDW). Fourteen tintinnid species were grouped into three types based on their distribution characteristics: Type I (Amphorellopsis quinquealata, Codonellopsis gaussi, Cymatocylis antarctica, Cymatocylis cf. calyciformis, Cymatocylis cf. convallaria, Salpingella faurei, and Salpingella sp.) species distributed in all the water masses; Type II species (Cymatocylis cf. cristallina, Cymatocylis cf. drygalskii, and Laackmanniella naviculaefera) were found in SSW and WW; and Type III species (Amphorides laackmanni, S. costata, S. laackmanni, and one undefined species) were restricted to WW and CDW. Our results characterize the distribution patterns and influencing factors of planktonic ciliates in different water masses in the Cosmonaut and Cooperation Seas, which will be helpful to understand the pelagic assemblage variation and constitute a baseline for studying the marine food web variation in the Antarctic Zone of the Southern Ocean.

Dimethylsulfoniopropionate (DMSP) and dimethyl sulfide (DMS) are critical molecules in the global sulfur cycle and in climate regulation. Bacterial DMSP-dependent DMS production is an important natural source of DMS. The aim of the present work was to use RNA-seq technology to investigate the changes in gene expression profiles of Antarctic Rhodococcus sp. NJ-530 in response to DMSP, and the possible mechanism of DMSP metabolism. In this study, Rhodococcus sp. NJ-530 cells were exposed to 0 (control) and 1 mM DMSP for 9 h. The results showed that DMSP induces transcriptional changes to Rhodococcus sp. NJ-530. DMSP caused upregulation of several genes that may play a potential role in DMSP metabolization. Additionally, transcriptome analysis of DMSP metabolism determinized a total of 1159 differentially expressed genes (DEGs) between two treatment strategies. qRT-PCR was performed to further confirm the changes in these results. GO and KEGG enrichment analyses showed that DMS production is the result of the coordinated action of a multitude of DMSP lysis-associated genes along a pathway, including absorption mechanism, secondary metabolisms, and cellular signaling. In conclusion, our data indicated that DMSP exposure induced DMSP cleavage pathway activity, and the effects on the gene expression profile of strain NJ-530 were analyzed at the transcriptional level during the degradation of DMSP. This work provided insight into the transcriptional characterization of Rhodococcus sp. NJ-530 in response to DMSP and contributed to clarifying the biodegradation and underlying mechanism of DMSP in Rhodococcus sp. NJ-530.

The relationships between birds and invertebrates are very diverse and often extend beyond the host-parasite interaction. Birds can be vectors of some arthropod species and their nests are a specific microhabitat inhabited by mites and springtails. However, the phenomenon is not well described in Antarctica. The aim of this article is to compare the arthropod communities inhabiting the nests of three species of birds and relate observed differences to the biology and ecology of the nest building bird species (i.e., living in colonies or in pairs) as well as the nature of the nest (i.e., nest lining or lack there off). Outcomes include determining the scale of the threat to birds from parasites, as well as to information concerning the ecology (microhabitat preferences) of the arthropod species. The study was conducted in the vicinity of the Arctowski Polish Antarctic Station by comparing the arthropod concentrations in nests of three bird species: Southern Giant Petrel (Macronectes giganteus), Adelie Penguin (Pygoscelis adeliae) and South Polar Skua (Stercorarius maccormicki). Four mite (Acari) species and five springtail (Collembola) species were found in the collected material. None of these species are parasites. The most numerous were Hydrogamasellus racovitzai (Acari, Mesostigmata), Alaskozetes antarcticus (Acari, Oribatida) and Cryptopygus antarcticus antarcticus (Collembola). The results indicate (e.g. the Shannon index, evenness, non-metric multidimensional scaling method, one-way multivariate permutation analysis of variances, Kruskal–Wallis test) significant variability in community composition and individual abundance in the nests dependent on the bird species. Furthermore, that this variability depends on the biology and ecology of the bird species.

Migratory species may shift phenology with climate change so understanding the energetic consequences of behavioural plasticity may provide insight into how migrants respond to warming. We examined the autumn migration of 151 adult female polar bears (Ursus maritimus) in Hudson Bay, Canada from 1991 to 2020 using satellite telemetry. We examined trends in sea ice freeze-up experienced by bears as adults and dependent juveniles to assess if maternal behaviour influenced migrating adults. To quantify vulnerability to increasing fasting, we examined the condition and starvation threshold of 136 females with offspring. There were no temporal trends in departure date or sea ice, but bears departed onto sea ice further north over time by approximately 7 km/year (SE 12 km). Freeze-up date was delayed 0.4 (SE 0.8) days/year for the time when juveniles were dependent on their mothers. Departure date varied across individuals each year by a mean difference of 14 (SE 1.5) days. Inter-annual variation in the on-ice departure date was explained by freeze-up date, delaying in years with later freeze-up, and individual age, with younger bears departing earlier. Condition of females with first-year cubs declined over time, and we estimate that 67% of females with offspring have ceased lactation by on-ice departure or risk starvation while 20% still risk starvation having ceased lactation. Delayed freeze-up over the juvenile period may explain the population’s northward shift in migration suggesting learned behaviour. Declining energetic stores available to females with cubs during this critical stage in their life history is a developing conservation issue.

In zooplankton-feeding baleen whales, site fidelity on the feeding grounds is usually expressed at a relatively large scale: although the whales remain in the general area, they move broadly within it, covering tens of kilometers per day. The gray whale, Eschrichtius robustus, is the only dedicated bottom feeder among baleen whales and its largely infaunal and epibenthic invertebrate prey are more sedentary and therefore have a more predictable distribution than zooplankton. We analyzed movements of individually identified gray whales and humpback whales (Megaptera novaeangliae) in an Arctic feeding area to see if specialization on stationary benthic prey would result in finer-scale site fidelity than specializing in more mobile zooplankton prey in the same area. Compared to humpback whales, the number of feeding gray whales in Senyavin Strait, Eastern Chukotka over three study years was higher; however, the resighting rate between years was lower than for humpback whales in the same area over the same period. All humpback whales moved broadly within their feeding range, while individual gray whales tended to remain at specific locations, returning to these locations in subsequent years. Thus, the fine-scale site fidelity was higher for gray whales and this should be a consideration when estimating anthropogenic impacts—for example, the effects of shipping traffic, fishing, and aboriginal whaling. Gaining an understanding of whale movement patterns, including site fidelity, is crucial for the conservation and sustainable management of whales and their habitats, especially in light of increasing anthropogenic pressures in the warming Arctic.

Penguins are one of the key components of the Antarctic ecosystem. Changes in penguin population size can indicate Antarctic ecosystem change. The two species of pygoscelid penguins, Adélie (Pygoscelis adeliae) and Gentoo (Pygoscelis papua) penguins, breed sympatrically on Ardley Island, King George Island, Antarctica. However, there has been an increase in the Gentoo penguin breeding population and a decline in the Adélie penguin breeding population on the island. Whether the difference in population fluctuations between the two penguin groups is connected to their diet remains uncertain. Herein, the 18S ribosomal ribonucleic acid (18S rRNA) and mitochondrial cytochrome c oxidase subunit I (COI) genes were sequenced from penguin feces using the Illumina MiSeq platform to investigate the fecal eukaryote composition of the two pygoscelid penguin groups to obtain insight into their diets. Significant differences in the abundance of Tardigrada and Rotifera sequences in the fecal eukaryote composition were observed between the Adélie and Gentoo groups. A range of food groups, including Actinopteri, Bivalvia, Coscinodiscophyceae, Florideophyceae, Haptophyceae, Hydrozoa, Malacostraca, and Phaeophyceae, were discovered in the penguin diets. Euphausia was the most important component of the diets of both Pygoscelis penguins. Compared with Adélie penguins, which showed a higher abundance of Actinopteri, Gentoo penguins presented a higher percentage of Euphausiidae in their diet. The COI gene is a more suitable taxonomic marker than the 18S rRNA gene for the dietary analysis of penguins. The results allowed the dietary components of Adélie and Gentoo penguins on Ardley Island to be characterized.

Southern elephant seals (Mirounga leonina) are apex predators that spend several months at sea feeding over vast areas. Their population trends are related to food availability during winter, which in turn is influenced by environmental conditions; thus, fluctuations in their populations reflect changes in the ecosystems. Although population trends for this species are available for large populations, there are still small colonies for which information is scarce, as is the case for the colony located at Peninsula Potter, South Shetland Islands. At this colony, field censuses of the number of breeding females conducted from 1995 to 2018 revealed an overall decline of 11.9% at an annual rate of 0.6%. However, contrasting trends before and after 2008 were observed. A decrease of 46.5% at an annual rate of 4.6% was registered before 2008, while for the subsequent period (2008–2018) the number of females increased by 64.5% at an annual rate of 5%. A positive association was observed between the extent of sea ice in winter foraging areas and population numbers between 1995 and 2008. The females of this colony feed on the edge of the sea ice, so in years of low sea ice extension the effort required to reach these areas is greater. This could lead individuals to choose to breed in areas closer to their feeding grounds in order to avoid the energetic expenditure of body reserves acquired during winter that would sustain the return trip to their natal colony.

A photographic seabed survey conducted off the Antarctic Peninsula region provided the opportunity to study spatial patterns, abundance and behaviour of the notothenioid benthic fish fauna. Overall, a total of 12,715 images taken with the Ocean Floor Observation System (OFOS) along 26 transects in three ecoregions (Joinville Island, Bransfield Strait and Drake Passage) were analysed. The fish fauna consisted of at least 34 species belonging to four families of both low-Antarctic and high-Antarctic origin. Nototheniids showed the highest relative abundance and species richness, followed by channichthyids, bathydraconids and artedidraconids. Direct in-situ observations in OFOS seabed images allowed descriptions of fish behaviour, such as aggregation of individuals (Notothenia coriiceps), specific body postures (Cygnodraco mawsoni and Cryodraco antarcticus) and parental care (Chaenodraco wilsoni, Chionodraco rastrospinosus, Pagetopsis macropterus and Trematomus hansoni). Fish density and species richness was primarily correlated with the occurrence of bryozoans, ascidians, and large cup-shaped sponges, providing a three-dimensional habitat suitable for fish settling, foraging, breeding and refuge from predators. Fish diversity was higher (a) off Joinville Island and in Bransfield Strait than in Drake Passage, where almost exclusively low-Antarctic species were recorded, and (b) between 100 and 600 m than at greater depths. Overall, the benthic fish fauna off the northern Antarctic Peninsula is zoogeographically composite and widespread, with well-structured spatial partitioning.

Light-induced bird strikes on vessels occur frequently in association with areas of high seabird density, often resulting in bird mortalities. These incidents are poorly understood and likely under-reported by vessels. Here we present the details of four separate bird strike events (899, 206, 50 and 47 birds), which took place whilst vessels (two fishing trawlers and one tourist expedition ship) were navigating along the south coast of South Georgia, and discuss possible contributing factors. All species encountered in these events were burrowing petrel species in the family Procellariidae, with diving-petrel species ( Pelecanoides spp.) being most commonly reported. All four events took place during the night in similar meteorological conditions, with poor visibility due to fog, light precipitation and low wind speeds. We identify the waters off the south coast, between King Haakon Bay and Drygalski Fjord, which have remained rat free and are of exceptional importance to breeding seabirds, as high risk for collisions and propose other high-risk areas. The different mortality rates recorded during these events are likely attributed to the varying actions taken by ship crew and persons on board. We propose actions that will help reduce the occurrence of events and mitigate the impact of bird strikes, including the avoidance of high-risk areas in certain night-time conditions. We give recommendations on what to do when birds land on board and stress the importance of reporting of events. Given the expected increase of both fishing and tourist ship activity in South Georgia waters, there is an increasing need to understand and mitigate this threat to seabirds.

Unusual records of marine organisms beyond their known distribution range aid the identification of dispersal capabilities, health issues, changing oceanographic patterns and/or anomalies, and may drive attention to underlying shifts in the polar marine environment. Here we report on an adult male sub-Antarctic fur seal, Arctocephalus tropicalis, sighted at Saint Peter and Saint Paul archipelago, also known as Arquipélago de São Pedro e São Paulo (ASPSP) (00° 56′ N; 29° 22′ W), Brazil, on January 18–21, 2022. The animal appeared healthy and stayed in the rocky islands of the archipelago making frequent incursions to sea. We have compiled information from wandering individuals A. tropicalis and found that this is the first indisputable record for the species in the ASPSP, crossing the ecuador to the Northern Hemisphere. We suggest that it comes from Gough or Tristan da Cunha islands which are the closest breeding locations of this species. Therefore, this male traveled at least ~ 5500 km from the natal area and was 1931 km north from the second northernmost sighting of this species in Ascension Island. We speculate that this species may be using currents and/or shallower mid-ocean ridges to guide dispersal routes from subpolar regions to the North.

Seaweeds contain a wide range of secondary metabolites which serve multiple functions, including chemical and ecological mediation with microorganisms. Moreover, owing to their diverse bioactivity, including their antibiotic properties, they show potential for human use. Nonetheless, the chemical ecology of seaweeds is not equally understood across different regions; for example, Antarctic seaweeds are among the lesser studied groups. With the aim of improving our current understanding of the chemical ecology and potential bioactivity of Antarctic seaweeds, we performed a screening of antibiotic activity using crude extracts from 22 Antarctic macroalgae species. Extractions were performed separating lipophilic and hydrophilic fractions at natural concentrations. Antimicrobial activity assays were performed using the disk diffusion method against seven Antarctic bacteria and seven human pathogenic surrogates. Our results showed that red seaweeds (especially Delisea pulchra) inhibited a larger number of microorganisms compared with brown seaweeds, and that lipophilic fractions were more active than hydrophilic ones. Both types of bacteria tested (Gram negative and Gram positive) were inhibited, especially by butanolic fractions, suggesting a trend of non-specific chemical defence. However, Gram-negative bacteria and one pathogenic fungus showed greater resistance. Our study contributes to the evidence of antimicrobial chemical interactions between Antarctic seaweeds and sympatric microorganisms, as well as the potential of seaweed extracts for pharmacological applications.

The Arctic tundra is characterised by harsh conditions and environmental gradients are especially pronounced. Variation in functional traits along such gradients provide insights into the drivers of species abundance and distribution and are particularly valuable in this region currently experiencing strong climate warming. Over three consecutive years, we analysed the interacting effect of two environmental factors, habitat and elevation, on the abundance, body size, and clutch size in two common Low-Arctic invertebrate predators (Lycosidae, Araneae), Pardosa furcifera (Thorell 1875) and Pardosa hyperbo-rea (Thorell 1872). Using generalised linear models, we firstly showed a habitat partitioning between P. furcifera, which dominated wet habitats, like fens, and P. hyperborea, which was more associated with drier habitats, like shrubs. Secondly, we found smaller body sizes at high elevation in P. hyperborea, a species that has a southern distribution in Greenland, and we identified season length as a major driver of the development in this species. In P. furcifera, a species likely more cold adapted, we found no body size difference between elevations, suggesting that local conditions (e.g. prey availability or snowmelt timing) are more important in explaining body size variations. Finally, body size and clutch size were strongly correlated in both species, but clutch size was not affected by habitat or elevation. We argue that fecundity is likely influenced by trade-offs and that considering additional complementary trait measurements would allow for a better understanding of the mechanisms underlying patterns in species life-history traits along environmental gradients.

Arctic Terns (Sterna paradisaea) share a few routes to undertake the longest annual migrations of any organism. To understand how the wide spatial range of their breeding colonies may affect their migration strategies (e.g., departure date), we tracked 53 terns from five North American colonies distributed across 30° of latitude and 90° of longitude. While birds from all colonies arrived in Antarctic waters at a similar time, terns nesting in the Arctic colonies migrated back north more slowly and arrived to their breeding grounds later than those nesting in the colony farther south. Arrival dates in Antarctic waters coincided with the start of favorable foraging conditions (i.e., increased ocean productivity), and similarly arrival dates at breeding colonies coincided with the start of local favorable breeding conditions (i.e., disappearance of snow and ice). Larger birds followed a more direct southbound migration route than smaller birds. On both southbound and northbound migrations, daily distances traveled declined as time spent in contact with the ocean increased, suggesting a trade-off between resting/foraging and traveling. There was more unexplained variation in behavior among individuals than among colonies, and one individual had a distinctive stop around Brazil. Terns nesting in the Arctic have a narrow time window for breeding that will likely increase with continuing declines in sea ice and snow. Departing Arctic Terns likely have few clues about the environmental conditions they will encounter on arrival, and their response to environmental changes at both poles may be assisted by large individual variation in migration strategy.

Marine Porifera (sponges) are known to produce several bioactive metabolites having a biotechnological potential, mostly derived from their bacterial symbionts; however, current knowledge on the production of metabolites such as enzymes and antibacterial molecules in sponges living in Antarctic environments is not fully exhaustive and needs further deepened investigation. The interest in discovering the broad spectrum of natural products potentially derived from species adapted to colonize extreme environments stimulates the research toward Antarctic sponge bioprospection. In this study, whole homogenates of Antarctic Demospongiae, belonging to five different species [Haliclona (Rhizoniera) sp., Haliclona (Rhizoniera) dancoi, Microxina sarai, Dendrilla antarctica, and Mycale acerata] were collected from Terra Nova Bay (Ross Sea) and examined for presence and activity of enzymes, including lysozyme, and antibacterial substances. Enzyme activities (leucine aminopeptidase, beta-glucosidase, and alkaline phosphatase) were measured using fluorogenic substrates; lysozyme content was determined on plates containing lyophilized Micrococcus lysodeikticus cell walls as a substrate. Homogenates were screened in microtiter plates for their antibacterial activity against Antarctic bacterial isolates, and the absorbance reduction was measured with a microplate reader. All homogenates exhibited proteolytic, glycolytic, and phosphatasic activities, lysozyme and antibacterial activities at near “in situ” temperature (5 °C), with some differences among the examined species. Results confirmed that Antarctic sponge homogenates are interesting sources of different bioactive substances, likely produced from associated bacterial symbionts, and that could have great potential to be used in medicine or industrial applications.

Diatoms constitute an important and diverse component of terrestrial protist communities but remain poorly studied, especially in the Antarctic realm. Here, we investigated the diversity and community structure of the terrestrial diatom flora from the Ulu Peninsula, James Ross Island (Maritime Antarctic Region) using a morphology-based dataset and physico-chemical measurements. A total of 97 taxa belonging to 27 genera was identified in 59 samples from terrestrial environments, including soils and rock walls. The flora was dominated by the genera Hantzschia, Luticola, and Humidophila. Eight distinct diatom assemblages could be distinguished and were mainly structured by differences in environmental characteristics such as vegetation coverage, moisture, conductivity, pH, and nutrient concentrations. In general, James Ross Island harboured a unique diatom flora as evidenced by very low similarity values with other (sub-)Antarctic localities. Only 16% of the taxa have a typical cosmopolitan distribution, whereas 70% showed a restricted Antarctic distribution, supporting previous indications of high species-level endemism in environments characterized by harsh abiotic conditions. In addition, several of the cosmopolitan species uncovered in this study might harbour substantial levels of hidden diversity, including endemic taxa, as previously revealed for the Pinnularia borealis species complex on James Ross Island. Taken together, the present study improves our knowledge and understanding of the diversity, ecology, and community structure of the terrestrial diatom flora of Ulu Peninsula and highlights that soils and wet rock walls represent important terrestrial habitats in this transitional zone between Maritime and Continental Antarctica.

This study was performed to aid the management of the fishery for Antarctic krill Euphausia superba. Krill are an important component of the Antarctic marine ecosystem, providing a key food source for many marine predators. Additionally, krill are the target of the largest commercial fishery in the Southern Ocean, for which annual catches have been increasing and concentrating in recent years. The krill fishery is managed by the Commission for the Conservation of Antarctic Marine Living Resources (CCAMLR), which has endorsed a new management framework that requires information about the spatial distribution and biomass of krill. Here, we use krill density estimates from acoustic surveys and a GAMM framework to model habitat properties associated with high krill biomass during summer and winter in the northern Antarctic Peninsula region, an area important to the commercial fishery. Our models show elevated krill density associated with the shelf break, increased sea surface temperature, moderate chlorophyll-a concentration and increased salinity. During winter, our models show associations with shallow waters (< 1500 m) with low sea-ice concentration, medium sea-level anomaly and medium current speed. Our models predict temporal averages of the distribution and density of krill, which can be used to aid CCAMLR's revised ecosystem approach to fisheries management. Our models have the potential to help in the spatial and temporal design of future acoustic surveys that would preclude the need for modelled extrapolations. We highlight that the ecosystem approach to fisheries management of krill critically depends upon such field observations at relevant spatial and temporal scales. Supplementary information: The online version contains supplementary material available at 10.1007/s00300-022-03039-y.

In the last three decades, several interdisciplinary studies investigated the marine ecosystems off the West Antarctic Peninsula (WAP), one of the most impacted areas of the Southern Ocean by the global warming. Although the extent of near-shore habitats along the WAP is wider than elsewhere in Antarctica, the coastal fish communities have been rarely studied. Complementing these previous studies, we provide new data on the species composition, population structure and relative abundance of the inshore fish community living off the Argentine Islands (Bellingshausen Sea). Fish samples were caught all the year round during four different periods spread over ten years (from 2006 to 2017). The fish fauna consisted of fourteen high-Antarctic and low-Antarctic species of notothenioids, most of them belonging to the Nototheniidae. Notothenia coriiceps was by far the most abundant species, followed in decreasing abundance by Chaenocephalus aceratus , Notothenia rossii , Trematomus newnesi and Trematomus bernacchii . Our findings provide context for future ecological studies as this area represents either a spawning and nursery area for multiple species in this study. More generally, the inshore waters off the Argentine Islands represent the southern limit of distribution for several low-Antarctic species, and our results provide critical baseline data for assessing possible disruptions in population dynamics driven by the ongoing climate change.

Antarctic hairgrass, Deschampsia antarctica Desv. (Poaceae), is one of the two flowering plants that have an established presence in Maritime Antarctica. It has adapted to varying edaphic and climatic conditions. D. antarctica's associations with soil-dwelling bacteria have long been suspected to add to its remarkable resilience. In this study, three compartments within D. antarctica root system and soil have been investigated as microbial habitats: the rhizosphere (root-adjacent soil particles), rhizoplane (root surface) and endosphere (root interior). For this purpose, a modification of existing methods of bacterial extraction from cryophilic plant rhizocompartments was devised with the temperature sensitivity of the source material in mind. Next-generation targeted 16S rRNA gene amplicon sequencing and a culture-based approach were employed to explore the bacterial community residing within those three rhizocompartments. Results showed that each of the compartments housed a distinct bacterial community not only in terms of phylogenetic diversity but also concerning plant-beneficial and-adaptive traits. Although most cultivable bacteria displayed plant-growth promoting abilities such as rock-phosphate solubilisation and phytohormone production (Arthrobacter spp.), some could be potential pathogens (Clavibacter sp.). This study highlights the need for amending the still scarce information on the microbiome of Antarctic flora but also gives tools and insight to explore it further.

The 27 species of the genus Pogonophryne are a distinctive component of the radiation of cryonotothenioid fishes and commonly encountered during benthic trawling and commercial longlining for toothfish. They are difficult to identify because they are morphologically and ecologically similar and sympatric in their distributions. The genus has recently been the subject of a taxonomic consolidation that, on the basis of nuclear gene sequence data and morphometrics, has synonymized the 27 species to the five known species groups and detected an unnamed sixth clade, decreasing the diversity of Pogonophryne by ≈ 78% and that of the radiation of cryonotothenioids by ≈ 16%. We clarify this situation by assigning each of the 27 species to a species group. We also provide an uncomplicated illustrated guide that requires no counting or measuring of characters and facilitates the placement of each of the species into one of three categories, five species groups, and three subgroups within the genus. These are the essential steps in identifying a species of Pogonophryne whether following the traditional or reduced view of diversity. With the exception of the details concerning the undescribed species, this is the heretofore elusive synopsis of the genus that should remain stable into the future.

Across the Drake Passage, planktonic ostracods are a significant component of mesozooplankton communities. Thus, the aim of this study was to investigate their composition structure and distribution within the upper 300-m layer in summer 2010. Our study revealed a complex pattern in their assemblages along the south–north transect, which strongly coincides with three distinct hydrographic regimes the transect crossed: the Antarctic Zone (AZ), the Polar Frontal Zone (PFZ), and the Subantarctic Zone (SAZ). Superimposed on this hydrographic zonation was a northward gradient in increasing ostracod abundance. The overall species number was low—just 12 species—but the composition of ostracod assemblages reflected the origin of the water masses well, since the numerically dominant species in the three hydrographic zones were: Alacia hettacra, in the AZ; Discoconchoecia elegans, in the PFZ; and Pseudoconchoecia serrulata, in the SAZ. Although the Passage acts as a physical bottleneck, diverting typically Antarctic waters further north than in other sectors of the Southern Ocean (SO), the distributional ranges of Conchoecia magna, Obtusoecia antarctica, and P. serrulata were observed further south than had previously been reported. A possible explanation for this shift is that the Polar Front position is located further south than in the other Atlantic part of the SO. It is also likely that, in such a narrow passage containing pelagic fauna of various hydrographical zones, even subtle shifts in distribution, including changes in climate, will be observed at first; therefore, our data might constitute important reference material for tracking further zooplankton biogeography in Antarctic waters.

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.

Small molluscs are known to be particularly abundant towards the poles. Although recent studies on sub-Antarctic waters of the southernmost tip of South America have begun to show a highly diversified small-sized fauna, micromolluscs have not yet received sufficient attention. Recently, samplings targeting the smallest molluscan benthic fauna have been conducted in the sub-Antarctic waters of South America, providing material of three new minute species occurring in The End of the World (Tierra del Fuego, Isla de los Estados and Burdwood Bank). The present study describes Pachykellya fuegiensis n.sp. (Neoleptonidae), Benthocardiella ituartei n.sp. and Benthocardiella finisterra n.sp. (Condylocardiidae). These are not only the smallest bivalves currently known from the area, but are also smaller than any other species thus far known from the adjacent Antarctic waters, and are included among the smallest species of their respective genera. To confirm generic placement, the type species of Pachykellya (P. edwardsi F.B. Bernard 1897) and Benthocardiella (B. pusilla Powell 1930) are studied for the first time with scanning electron microscopy. This study allows to amend the previous descriptions of hinge teeth number, morphology and arrangement for these genera. Based on these new findings, Pachykellya and Benthocardiella are here reported for the first time in South America.

The range of the golden jackal (Canis aureus Linnaeus, 1758) in Eurasia has undergone significant changes over the past decades, revealed in species expansion and range extensions. The article summarizes literature characterizing the dynamics of the species’ range in Russia, and presents data on appearances of animals far outside established ranges. Here we present the first record of the golden jackal in the northern taiga subzone of Russia in an agriculturally undeveloped region, far beyond the species’ range and its presumed ecological preferences. Species identification was confirmed by morphological and craniometrical examinations, and genetic analysis. This jackal mitochondrial DNA haplotype is associated with populations from Europe and Caucasus. The article suggests the possible routes for the jackal’s travel to this geographical location (64°40′20″ N, 43°22′56″ E) and discusses the possibility of the species inhabiting subarctic areas with severe climatic conditions. Moreover, the authors speculate on the phenomenon of range expansion of the golden jackal.

Several studies have attempted to identify the selective pressures leading to reversed size dimorphism (RSD), a characteristic of skuas and of a wide range of bird species with a raptorial lifestyle. One of the prevailing hypotheses posits that females in species of aggressive and well-armed males should select males that are smaller than themselves, to avoid injuries during pair formation and mating. This hypothesis predicts assortative mating by size in such species, and in previous research, this was confirmed to occur in two skua species. This study presents, for the first time, biometric data for Falkland Skuas Stercorarius antarcticus antarcticus based on large sample sizes. Despite the clear RSD, we found no assortative mating by size, which could be related to the low divorce rates and few opportunities for mate selection in this population. Our results highlight the need for further work to find an explanatory hypothesis for the evolution and maintenance of reversed size dimorphism in skuas.

The ice-associated copepods Stephos longipes, Paralabidocera antarctica, and Drescheriella glacialis are the dominant species inhabiting Antarctic sea ice. They influence the pelagic ecosystem after being released into the water column when the ice melts from spring to summer in the marginal ice zone (MIZ), although less is known about those in the off-shelf region. We investigated the occurrence of copepods in drifting sea-ice floes and the adjacent water column off Vincennes Bay in the Indian sector of the Southern Ocean in mid-summer (January) of 2014 and 2016–2018. Sea-ice samples from the ice-growth season (February–March) collected off Australia’s Mawson Station (2016, n = 1) and Cape Darnley (2018, n = 2) provide some comparison with the ice-melt season. In the ice floes off Vincennes Bay, S. longipes and harpacticoid nauplii were abundant, but also highly variable (2016: 2.2 ± 3.5 [× 10⁴ ind. m⁻³], n = 8; 2017: 1.1 ± 5.4, n = 11; 2018: 0.94 ± 1.81, n = 10). Copepod nauplii were very abundant at 0–5 m depths (maximum of 8.1 × 10² ind. m⁻³), but absent at depths below 35 m; this implies that copepods disappear rapidly from the surface layer after being released, mainly due to predation/non-predation death or development from the nauplius to the copepodite stages. Overall, the results indicate that sea ice forming in shelf regions transports some of the ice-associated copepods further north, which supplies food to pelagic predators, although S. longipes is also a primary consumer in the MIZ.

Examining Eastern North Pacific gray whale (Eschrichtius robustus) carcasses and tracking mortality and morbidity are essential for assessing the health of this stock. In the eastern Chukchi Sea, the expansive coastline relative to few coastal communities makes monitoring for and physical examination of gray whale carcasses difficult. The Aerial Surveys of Arctic Marine Mammals (ASAMM) project offers an unparalleled dataset of gray whale carcasses, documented and photographed from July to October 2009–2019, providing a unique opportunity to investigate imaged gray whale carcasses for possible cause of death. Surveys covered expanses of gray whale and killer whale (Orcinus orca) summer and autumn habitat. ASAMM documented a total of 59 gray whale carcasses, distributed across the eastern Chukchi Sea (67.5° N–72.0° N, 155.5° W–169.0° W). Carcass sighting rates ([CPUE] carcasses per 1000-km of effort) varied by month and year. The highest numbers of carcasses were observed in 2012 (13) and 2019 (8). August had the highest number of gray whale carcass sightings (22) and the highest carcass sighting rate (0.231 CPUE). Images were obtained for 56 gray whale carcasses. The majority (41) of imaged gray whale carcasses had injuries consistent with probable killer whale predation, and were photo-documented every year except 2010 (when no carcasses were seen) and 2011. Eight carcasses were suspect killer whale predation, and cause of death could not be determined for seven carcasses. These results will be valuable for evaluating mortality, concurrent with rapid oceanographic changes, and increases in anthropogenic activities.

In the Antarctic seas, where hard substrates are scarce, the presence of secondary bio-substrates formed by calcareous organisms is an essential condition to increase the epibiosis and therefore the diversity of sessile benthic fauna. The aggregations of stylasterid hydrozoa, with their branched carbonate structures, are an example of a secondary habitat defined as a ‘deep marine animal forest’. The three-dimensional habitat made by these corals supports a high biodiversity of associated organisms, usually invertebrates. Recently, deep remotely operated vehicle (ROV) exploration of the Iselin Bank and the Hallett Ridge (Ross Sea, Antarctica) documented wide areas characterised by large thanatocoenosis of stylasterid skeletons lying on flat muddy substrates, with scattered living colonies generally made of few short branches. In our study, sponges associated with 54 dead colonies of two stylasterid species recorded in these areas were investigated. The analysis led to the discovery of a remarkable number of specimens (127) ascribed to 38 sponge species (31 encrusting and 7 massive). Two of these sponges, Asbestopluma (Asbetopluma) sinuosa and Lissodendoryx (Ectyodoryx) inferiolabiatae, are new. In light of the present data, we can assume that, in Antarctica, stylasterid skeletal remains, due to their three-dimensional structure, play an important role in maintaining sponge biodiversity. This is also due to the ability of sponge specie to produce miniaturised specimens able to colonise these peculiar substrata.

Cold-adapted bacterial strains are potentially valuable for biotechnological applications involving the production of cold-active enzymes and bioproducts important to various industries. A psychrotolerant, aerobic, Gram-positive, endospore-forming, bioemulsifier-producing strain, named Val9, was isolated from Vale Ulman soil samples, King George Island, Antarctica and identified as a member of the genus Psychrobacillus. To better characterize this novel strain, its whole genome was sequenced revealing a size of 3,986,526 bp with a G + C content of 36.6%, and 4042 predicted coding DNA sequences (CDSs). Digital DNA–DNA hybridization (dDDH) and average nucleotide identity (ANI) analyses between strain Val9 and the type strains of the seven Psychrobacillus species revealed that the highest values were observed with Psychrobacillus psychrodurans DSM11713T but below the conventional thresholds of 70% dDDH and 95% ANI for bacterial species assignment, suggesting that strain Val9 could represent a distinct species. As potential low-temperature adaptation strategies, genes encoding cold shock proteins, transporters for glycine-betaine, carnitine and choline, and enzymes acting against oxidative stress were found in Val9 genome. DEAD-box RNA helicases, important for cold and oxidative tolerance, and a two-component signal transduction system related to plasmatic membrane fluidity as well as biotechnologically important CDSs, related to levan production, were detected. The sacB gene encoding the enzyme levansucrase was exclusive for Val9 and it was not found in the other Psychrobacillus type strains. Altogether, the comparative genomic analyses presented here highlight important metabolic pathways and the biotechnological potential of this novel strain.

The traditional view is that the Arctic polar night is a quiescent period for marine life, but recent reports of high levels of feeding and reproduction in both pelagic and benthic taxa have challenged this. We examined the zooplankton community present in Svalbard fjords, coastal waters, and the shelf break north of Svalbard, during the polar night. We focused on the population structure of abundant copepods (Calanus finmarchicus, Calanus glacialis, Metridia longa, Oithona similis, Pseudocalanus spp., Microcalanus spp., and Microsetella norvegica) sampled using 64-µm mesh nets. Numerically, copepod nauplii (≥ 50%) and the young developmental stages of small copepods (< 2 mm prosome length as adult) dominated the samples. Three main patterns were identified: (1) large Calanus spp. were predominantly older copepodids CIV–CV, while (2) the small harpacticoid M. norvegica were adults. (3) For other species, all copepodid stages were present. Older copepodids and adults dominated populations of O. similis, Pseudocalanus spp. and M. longa. In Microcalanus spp., high proportion of young copepodids CI–CIII indicated active winter recruitment. We discuss the notion of winter as a developing and reproductive period for small copepods in light of observed age structures, presence of nauplii, and previous knowledge about the species. Lower predation risks during winter may, in part, explain why this season could be beneficial as a period for development. Winter may be a key season for development of small, omnivorous copepods in the Arctic, whereas large copepods such as Calanus spp. seems to be reliant on spring and summer for reproduction and development.

Chen et al. (Polar Biology, 43(11):1769–1781) recently reported lagged, region-specific responses of Adélie penguin (Pygoscelis adeliae) abundance to environmental variability in the Ross Sea, Antarctica. Their study suggests that lags are important toward understanding Adélie penguin population change. Though we agree with many of their findings, there are several issues with these authors’ hypotheses and consequent interpretation of their results. Generally, the selected environmental variables and the scales analyzed need proper justification, as their reasoning of the causality on penguin abundance at the Ross Sea is not in agreement with previous natural history studies of both the penguins and their prey carried out in this region. Here we provide critically constructive comments on their paper and present alternative initial hypothesis to explain their results. We suggest that the variables analyzed and their scale, should be re-considered in order to reach conclusions that help explain the recent changes in Adélie penguin colonies in the Ross Sea, ‘home’ to about one-third of the global population.