Showing papers in "Polar Biology in 2020"

The importance of Calanus glacialis for the feeding success of young polar cod: a circumpolar synthesis

Abstract: Understanding the feeding ecology of polar cod (Boreogadus saida) during its first year of life is crucial to forecasting its response to the ongoing borealization of Arctic seas. We investigated the relationships between diet composition and feeding success in 1797 polar cod larvae and juveniles 4.5–55.6 mm standard length (SL) collected in five Arctic seas from 1993 to 2009. Prey were identified to species and developmental stages when possible, measured, and their carbon content was estimated using taxon-specific allometric equations. Feeding success was defined as the ratio of ingested carbon to fish weight. Carbon uptake in polar cod larvae 25 mm and the only copepodite positively selected for. Pseudocalanus spp. copepodites became important replacement prey when C. glacialis left the epipelagic layer at the end of summer. Calanus glacialis was the preferred prey of polar cod, contributing from 23 to 84% of carbon uptake at any stage in the early development. Feeding success was determined by the number of prey captured in larvae 30 mm. As Arctic seas warm, the progressive displacement of C. glacialis by the smaller Calanus finmarchicus could accelerate the replacement of polar cod, the dominant Arctic forage fish, by boreal species.

Impacts of combined temperature and salinity stress on the endemic Arctic brown seaweed Laminaria solidungula J. Agardh

Abstract: Macroalgae such as kelp are important ecosystem engineers in the Polar Regions and potentially affected by freshening and ocean warming. The endemic Arctic kelp Laminaria solidungula might be particularly imperiled and become locally extinct from Arctic fjord systems in the future, since temperature increase is most pronounced in the Polar Regions. Additionally, increased temperatures cause glacier and sea ice melting and enhancing terrestrial run-off from snowfields, which eventually can result in hyposaline conditions in fjord systems. We conducted a multiple-stressor experiment at four temperatures (0, 5, 10, 15 °C) and two salinities (SA 25, 35) to investigate the combined effects of increasing temperature and decreasing salinities on the physiological and biochemical status of young L. solidungula sporophytes. Both drivers had significant and interacting impacts, either in an additive or antagonistic way, dependent on the respective response variable. The maximum quantum yield of photosystem II (Fv/Fm) significantly declined with temperature increase and low salinity. Even though the absolute pigment content was not affected, the deepoxydation state of the xanthophyll cycle increased with intensified stress. Higher temperatures affected the C:N ratio significantly, mainly due to reduced nitrogen uptake, while SA 25 supported the nitrogen uptake, resulting in an attenuation of the effect. The concentration of mannitol decreased at SA 25. At control SA 35 mannitol level remained steady between 0 and 10 °C but significantly decreased at 15 °C. Conclusively, our results show that L. solidungula is very susceptible to both drivers of climate change, especially when they are combined. Implications to species ecology are discussed.

Influences of temperature, predators, and competitors on polar cod ( Boreogadus saida ) at the southern margin of their distribution

Abstract: Polar cod (Boreogadus saida) is the most abundant and ubiquitous fish species throughout the Arctic Ocean. As such, they serve an important ecosystem role linking upper and lower trophic levels and transferring energy between the benthic and pelagic realms. Our objective is to explore what limits the southern distribution of polar cod in Pacific and Atlantic sectors by examining time series of survey and oceanographic data. We quantify the variability in the southern extent of the polar cod distribution in the Bering and Labrador Seas, and determine mechanisms (bottom temperature and potential predators: Pacific cod Gadus macrocephalus, Atlantic cod Gadus morhua, and Greenland halibut Reinhardtius hippoglossoides and competitors: capelin Mallotus villosus and walleye pollock Gadus chalcogrammus) driving the variability. When temperatures were lower, polar cod occupied larger areas and had higher abundances in both regions, suggesting that as temperatures increase with climate warming the range of polar cod is likely to contract. Temperature had a much larger impact on polar cod abundance than competitor abundance and predator abundance, especially in the eastern Bering Sea. However, when we included data from northern and eastern Bering Sea in 2010 and 2017, polar cod were less likely to occur in warmer waters when either Pacific cod or walleye pollock were present. Northward range expansions of subarctic Pacific cod and walleye pollock may further restrict polar cod distributions.

Population trends of penguins in the French Southern Territories

Abstract: Penguins are important top consumers in marine food webs and are one of the most threatened bird families, especially by climate change and food web alterations by marine fisheries. Yet, long-term population trends are lacking or are uncertain for many populations. Seven species of penguins breeding at the French Southern Territories in the southern Indian Ocean on the Crozet, Kerguelen, Saint-Paul–Amsterdam archipelagos and in Terre Adelie/Adelie Land, Antarctica are monitored regularly. This monitoring started in the early 1950s and most populations have been surveyed during the past four years, allowing assessments of population trends. King penguins increased at nearly all breeding sites within the Crozet and Kerguelen archipelagos. Emperor penguins have decreased at Terre Adelie/Adelie Land, with a partial recovery of the colony during the 2010s. Gentoo penguin populations at Crozet and Kerguelen are highly variable but stable. Adelie penguins have been increasing in Terre Adelie/Adelie Land. The trends in eastern rockhopper penguins vary between colonies and archipelagos. Northern rockhopper penguins have continuously decreased in numbers at Amsterdam Island, but appear to have increased at the nearby Saint-Paul Island. Macaroni penguins have first increased and then stabilized since the 2000s at Kerguelen and are stable at the Crozet Islands. Overall, most penguin populations breeding in the French Southern Territories increased or were stable over the past 30–60 years, with the exception of the northern rockhopper penguin, king and gentoo penguins on Crozet and the emperor penguin. The ecological reasons for these trends are poorly understood and require further investigation.

Opportunistic fungi found in fairy rings are present on different moss species in the Antarctic Peninsula

Abstract: We surveyed the distribution and diversity of fungi present in moss fairy rings from the South Shetland Islands. In the different islands accessed, the mosses Bartramia patens, Brachythecium austrosalebrosum, Bryum pseudotriquetrum, Pohlia nutans, Polytrichastrum alpinum, Sanionia uncinata, Syntrichia magellanica, and Syntrichia saxicola were infected with fairy rings. Among them, B. patens, B. pseudotriquetrum, P. nutans, P. alpinum, S. magellanica, and S. saxicola were reported for the first time as species susceptible to infection with fairy rings. From five different fairy ring moss species sampled, we isolated 40 fungal taxa identified as belonging to the genera Alpinaria, Cadophora, Cladosporium, Chalara, Cosmospora, Drechmera, Glarea, Gyoerffyella, Hymenoscyphus, Juncaceicola, Melanodiplodia, Mortierella, Mycosysmbioses, Pseudogymnoascus, Phoma, and Velucrispora. A high level of fungal richness was associated with the infected mosses, and Mortierella was the dominant genus. However, most of the fungi were present as minor components of the fungal assemblages. Among the mosses studied, S. uncinata harboured the greatest fungal diversity. Some fungal taxa present have previously been reported as opportunistic plant pathogens, including Cladosporium sp. and Phoma herbarum. We hypothesize that some of the fungi recovered from fairy ring mosses might represent secondary opportunistic pathogens and contribute to the reduced natural defences of the infected mosses, thus accelerating the dissemination of the pathogenic fairy rings in the Antarctic Peninsula. In addition, the presence of fairy rings on previously unreported moss species suggests that the disease may be becoming more widespread in Antarctica.

Estimates of density of mesopelagic fish in the Southern Ocean derived from bulk acoustic data collected by ships of opportunity

Abstract: The demand for information on mid-trophic level (MTL) organisms in open-ocean marine ecosystems has led to initiatives to collect acoustic data opportunistically in different regions around the world. Although, bulk acoustic data can provide information on the distribution patterns and dynamics of MTL organisms, it is necessary to convert acoustic-derived indices into biologically relevant quantities for parameterising and validating ecosystem and trophic models. A 7-year time series of acoustic data collected by ships of opportunity (SOOP) in the New Zealand sector of the Southern Ocean, information on species’ distribution derived from trawl samples collected in research voyages, and target strength (TS) estimates obtained using a resonance-scattering model and literature TS–length relationships, were used to obtain the first estimates of density of mesopelagic fish in this region. Estimates of mesopelagic fish density decreased from north to south reflecting changes in species composition and scattering properties across three latitudinal regions (Northern, Central and Southern). Density estimates ranged from 16.4–40.1 in the north to 4.4–13.4 g m−2 in the south. Catches revealed that the Northern region was dominated by Lampanyctodes hectoris and Protomyctophum sp. (Myctophidae) and Maurolicus australis (Sternoptychidae); the Central and Southern regions were dominated by the myctophids Electrona antarctica and Protomyctophum sp. and the Antarctic krill, Euphausia superba. Information on species composition was the main source of uncertainty in the density estimates, highlighting the need for more biological sampling. This study demonstrates that it is possible to integrate acoustic data collected opportunistically with auxiliary information from research voyages and literature to provide estimates of mesopelagic fish biomass in remote areas.

The coastal Arctic marine soundscape near Ulukhaktok, Northwest Territories, Canada

Abstract: The soundscape is an important habitat feature for marine animals, and climate change may cause large changes to the Arctic marine soundscape through sea ice loss and increased anthropogenic activity. We examined the marine soundscape over eight months near Ulukhaktok, Northwest Territories, Canada, and assessed the relative contribution of the geophony (wind and wave sounds), biophony (marine mammal and fish sounds), and anthrophony (noise from vessel traffic). Sound pressure levels (SPL) were significantly higher during the summer than during the autumn and winter, and these differences were caused by increased wind/waves and vessel traffic in the summer. Increased wind speed drove increased SPL, while increased ice concentration resulted in decreased SPL. When vessel traffic was closer, SPL was higher. Marine mammal and fish vocalizations did not influence SPL; however, timing of vocalizations of both whales and seals matched seasonal patterns shown in other studies within the region. Overall, the marine soundscape near Ulukhaktok varied greatly through time and may be prone to large changes in the future as the ice-free season continues to lengthen and more vessels travel through the region.

Ontogenetic patterns in lipid and fatty acid biomarkers of juvenile polar cod (Boreogadus saida) and saffron cod (Eleginus gracilis) from across the Alaska Arctic

Abstract: 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.

Update on the global abundance and distribution of breeding Gentoo Penguins ( Pygoscelis papua)

Abstract: Though climate change is widely known to negatively affect the distribution and abundance of many species, few studies have focused on species that may benefit. Gentoo Penguin (Pygoscelis papua) populations have grown along the Western Antarctic Peninsula (WAP), a region accounting for ~ 30% of their global population. These trends of population growth in Gentoo Penguins are in stark contrast to those of Adelie and Chinstrap Penguins, which have experienced considerable population declines along the WAP attributed to environmental changes. The recent discovery of previously unknown Gentoo Penguin colonies along the WAP and evidence for southern range expansion since the last global assessment in 2013 motivates this review of the abundance and distribution of this species. We compiled and collated all available recent data for every known Gentoo Penguin colony in the world and report on previously unknown Gentoo Penguin colonies along the Northwestern section of the WAP. We estimate the global population of Gentoo Penguins to be 432,144 (95th CI 338,059 – 534,114) breeding pairs, with approximately 364,359 (95th CI 324,052 – 405,132) breeding pairs (85% of the population) living in the Atlantic sector. Our estimates suggest that the global population has increased by approximately 11% since 2013, with even greater increases (23%) along the WAP. The Falkland Islands population, which comprises 30% of the global population, has remained stable, though only a subset of colonies have been surveyed since the last comprehensive survey in 2010. Our assessment identifies South Georgia and sub-Antarctic islands in the Indian Ocean as being the most critical data gaps for this species.

The buoyancy-based biotope axis of the evolutionary radiation of Antarctic cryonotothenioid fishes

Abstract: In the absence of any prior comprehensive analysis, I evaluate divergence along the biotope axis in the habitat stage of the evolutionary radiation of Antarctic cryonotothenioids. I utilize the available percentage buoyancy (%B) measurements as habitat proxies for recognition of the pelagic, semipelagic, demersal, and benthic biotopes that include, respectively, 5%, 10%, 73%, and 12% of the 59 species and 1749 specimens in the study. The majority of species retain the ancestral demersal biotope of Eleginops maclovinus, and this probably enhances ecological plasticity. Divergence into the pelagic biotope is the most distinctive organismal feature of the radiation and, although only 5% of species are pelagic, this biotope is not depauperate in global comparisons. Pelagic or potentially pelagic species are Dissostichus mawsoni, D. eleginoides, Pleuragramma antarctica, Aethotaxis mitopteryx, and Gvozdarus svetovidovi. Small ontogenetic changes in %B with growth are typical; however, this is extensive in D. mawsoni, a species with the potential to transition through benthic to pelagic biotopes over ontogeny. Occupation of the pelagic biotope by large D. mawsoni may be impermanent as it is lipid-dependent, a contingency reliant on the availability of P. antarctica as prey. In unusual conditions, the specialized sacs of P. antarctica can also yield their lipid for metabolism with possible loss of buoyancy. Pelagic species are inordinately important in the food web. In the southwestern Ross Sea a guild of large mammalian and avian predators, which includes D. mawsoni, is reliant on lipid-rich, energy-dense cryonotothenioid prey. This includes asymmetrical intraguild predation on D. mawsoni, with P. antarctica as a basal resource for the guild.

Pelagic production and the recruitment of juvenile polar cod Boreogadus saida in Canadian Arctic seas

Abstract: 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.

Bowhead whale ( Balaena mysticetus ) and killer whale ( Orcinus orca ) co-occurrence in the U.S. Pacific Arctic, 2009–2018: evidence from bowhead whale carcasses

Abstract: Imagery and sighting data on bowhead whale (Balaena mysticetus) carcasses documented from 2009 to 2018 during aerial surveys in the eastern Chukchi and western Beaufort seas have provided evidence for killer whale (Orcinus orca) predation on bowhead whales of the Bering–Chukchi–Beaufort Seas stock. The Aerial Surveys of Arctic Marine Mammals (ASAMM) project provides information on distribution, behavior, and relative density of marine mammals. ASAMM surveys large areas of bowhead whale and killer whale summer and autumn habitat and offers consistent information on bowhead whale carcasses. Thirty-three bowhead whale carcasses were documented in July–October, from 2009 to 2018. Carcasses were distributed across the eastern Chukchi and western Beaufort seas from 141.6° W to 168.1° W and 68.9° N to 72.0° N. Carcass sighting rates (carcasses/1000 km) varied by month, year, and region. Statistical results suggest an alternating series of high and low annual carcass sighting rates. Eighteen bowhead whale carcasses having injuries consistent with probable killer whale predation were photo-documented: four each in 2016 and 2018, three each in 2013 and 2015, two in 2012, and one each in 2010 and 2017. Four carcasses, two in 2015 and one each in 2013 and 2018, were likely whales struck and lost during aboriginal subsistence hunting. Cause of death could not be determined for 11 carcasses. This study is the first systematic inquiry into non-harvest related mortality of bowhead whales in the U.S. Pacific Arctic and provides multi-year evidence for killer whale predation on bowhead whales in this portion of their range.

Key processes regulating the early life history of Barents Sea polar cod

Abstract: The polar cod (Boreogadus saida) in the Barents Sea is one of the main stocks of this species in the Arctic, reaching a total biomass of almost 2 million tonnes in some years. It has been fluctuating considerably in abundance, and in recent years, it has been at a low level. Only small catches have been taken from the stock over the last four decades, and consequently, the observed variation in abundance must be caused by natural (environmental and/or biological) changes in the ecosystem. Sea temperatures have been rising in the Barents Sea in recent years, possibly causing changes to the living conditions of this true Arctic stock. Consequently, there is a need for investigating how the observed changes might affect polar cod in this area. One important aspect of the environmental impact on the stock is possible effect on the recruitment, which has been varying considerably from year to year. In this modelling study, we thus recreate and analyse the environmental and developmental histories of the observed 0-group individuals in the Barents Sea (young of the year), with emphasis on the importance of ice cover, ice breakup time, maximum temperature, and spawning stock biomass. Our simulations indicate that the environmental conditions experienced by individuals successfully “recruited” to the 0-group are characterized by high ice concentration well into summer, and low temperatures throughout the pelagic juvenile phase, and any perturbations from the Arctic ocean climate typically found in the northern and eastern Barents Sea appears to be detrimental to stock recruitment. In light of the projected warming of the Barents Sea in the next decades and the potential reduction in ice cover, this will entail, the mechanisms investigated herein might lead to future marginalization of polar cod in the Barents Sea.

Unmanned aerial vehicle (UAV) survey of the Antarctic shag ( Leucocarbo bransfieldensis ) breeding colony at Harmony Point, Nelson Island, South Shetland Islands

Abstract: Monitored seabird populations—useful sentinels of marine ecosystem health—have been declining worldwide at a rapid pace. Yet, lack of reliable long-term monitoring data constrains assessment of the conservation status of many seabird populations. Unmanned aerial vehicles (UAVs) have the potential to increase survey efficiency and count precision of seabird populations, especially where time constraints or inaccessible terrain, such as sea stacks, limit meaningful ground-based surveys. Furthermore, tremendous potential exists to combine fine-scale spatially integrated habitat mapping obtained from UAV images with occupancy to unravel how abiotic factors such as topography affect animal populations. In late December 2018, we used an UAV to create a georeferenced orthomosaic image and digital elevation model (DEM) from which we determined the size of the Antarctic shag (Leucocarbo bransfieldensis) breeding colony at Harmony Point, Nelson Island, South Shetland Islands. Our population estimate of 69 breeding pairs is approximately double that reported for the early 2000s and the highest count since the late 1980s. Most nests were located 10 to 20 m above sea level, on relatively shallow gradients that predominantly faced southeast. While it is difficult to compare historical ground-based counts with the UAV-derived estimates presented here, our new data provide robust baseline information for future monitoring of the colony population size using comparable survey methods. Our basic mapping of the topography of the breeding colony also highlights how UAV-derived habitat information can facilitate our understanding of the influence of landscape structure on animal population dynamics.

Polar cod egg and larval drift patterns in the Svalbard archipelago

Abstract: Spawning of polar cod (Boreogadus saida) in the vicinity of the Svalbard archipelago has not been directly observed. From the distribution pattern of polar cod 0-group observed during annual monitoring of the Barents Sea, it has, however, been inferred that spawning occurs in Svalbard waters most years. We wanted to investigate the possibility of back-tracking the larvae from these observed distribution areas to the spawning areas from which they originated and applied a coupled ocean–sea ice and particle tracking model to simulate the drift of particles released at suggested spawning sites. The model was run for 1 year (December 2006–September 2007), and the results were compared to observations of polar cod larvae in the autumns of 2007 and 2004–2010. The particles released in the western fjords were mostly retained in the fjords. For the rest of the suggested spawning grounds, the released particles drifted mostly clockwise around the archipelago. Model runs mainly indicated a drift pattern with end points that qualitatively match the main features of the August–September distribution of the polar cod 0-group observed. We conclude that the suggested spawning sites on the southern, northern and eastern sides of Svalbard could have caused a distribution of 0-group polar cod similar to that observed during August–September 2007. From the environmental factors experienced during drift of eggs and larvae and assumptions about habitat suitability for survival and growth, we conclude that spawning in the Svalbard area probably occurs on the southern and eastern sides and later than the area in the southeastern Barents Sea.

Circumpolar genetic population structure of polar cod, Boreogadus saida

Abstract: Polar cod, Boreogadus saida, is an important part of Arctic and boreal marine ecosystems. Knowledge of polar cod population genetic structuring can provide insight into how the species may respond to environmental change, and allow for establishment of meaningful management units. To examine population genetic structure of B. saida, we analysed nine microsatellite DNA loci in 2269 fish collected at 19 locations across the species’ range. Genetic differentiation was detected (FST = 0.01, p < 0.01), which had concordance with geography. A Canada East group consisted of fish collected from Resolute Bay to the Gulf of St. Lawrence. Three additional groups were observed. These consisted of a Canada West group containing specimens from the Canadian Beaufort Sea and Amundsen Gulf, a Europe group containing specimens from the Greenland Sea, Iceland and the Laptev Sea, and a US group consisting of specimens collected in the North Bering, Chukchi and Western Beaufort seas. Very little genetic differentiation was detected within the identified groups. Physical distance, geophysical structure and oceanography all appeared to have the potential to influence levels of genetic divergence. The population genetic structure detected is likely to be important for the response of B. saida to environmental change, and should be considered in management of human activities that may impact this foundational species.

Ringed seal ( Pusa hispida ) diet on the west coast of Spitsbergen, Svalbard, Norway: during a time of ecosystem change

Abstract: Global warming is causing Atlantification of water masses and concomitant changes in food webs in the Barents Sea region. To determine whether changes that have been documented at lower trophic levels are impacting the diet of ringed seals (Pusa hispida) gastrointestinal tracts (GITs) from 99 coastal-feeding ringed seals, collected in western Spitsbergen, Svalbard, were analysed via identification of hard-parts. The study animals were shot in spring (n = 30; April–July) or autumn (n = 69; August–October) during four consecutive years (2014–2017). Thirty different prey types were identified, but most seals (55.6%) had consumed between 2 and 4 different types of prey. Polar cod (Boreogadus saida) dominated the diet of the ringed seals in terms of relative biomass (Bi = 60.0%) and frequency of occurrence (FOi = 86.9%), followed by pricklebacks (Stichaeidae; Bi = 23.4%; FOi = 79.8%). Redundancy analysis (RDA) revealed that year was the only significant predictor explaining variance in autumn diet composition (RDA, F3 = 4.96, AIC = − 76.49, p ≤ 0.0050; blubber content and maturity/sex group were not significant). Blue whiting (Micromesistius poutassou) occurred in the diet in small quantities; this Atlantic fish species has not previously been documented in the ringed seals’ diet. Atlantic cod (Gadus morhua) had the highest Bi (9.2%) among Atlantic prey types. However, despite major changes in the last decade in the fish and zooplankton community in western Svalbard, and consumption of a few Atlantic prey types, the ringed seals’ diet in Svalbard continues to be dominated by Arctic prey, especially polar cod.

Recent change in benthic macrofaunal community composition in relation to physical forcing in the Pacific Arctic

Abstract: There is growing evidence that increased Pacific water transport into the Arctic affects the marine ecosystem. One of the theoretical predictions for a future Arctic characterized by such environmental change is that subarctic taxa will expand northward and invade the native Arctic ecosystem. This study focuses on variation in macrofaunal community composition and the influence of changing physical drivers at known benthic hotspots in the Pacific Arctic. The average number of macrofaunal family-level taxa has increased significantly south of St. Lawrence Island and in the Chirikov Basin, whereas the number of macrofaunal taxa in the southeastern Chukchi Sea showed no significant trend over the 2000–2013 time period. However, the Shannon–Weaver diversity index, based on abundance, did not mirror these regional changes in the number of macrofaunal taxa, indicating that the abundance of newly present taxa was negligible compared to the entire abundance already present. We also investigated temporal variations in meridional sea level gradient and local winds, which contribute 2/3 and 1/3 of the variation in northward volume transport at Bering Strait, respectively. There were significant increasing trends in the meridional sea level gradient and local winds, suggesting the increased northward seawater volume transports over the benthic hotspots could contribute to the expansion of subarctic taxa into these northern Arctic regions. Our data suggest an increase in macrofaunal taxa type with increasing current transport northward into the Pacific Arctic region that could have a strong influence in restructuring the benthic ecosystem in this region in the future.

Environmental and biological influences on the distribution and population dynamics of polar cod ( Boreogadus saida ) in the US Chukchi Sea

Abstract: 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.

Variability in primary productivity and bio-optical properties in the Indian sector of the Southern Ocean during an austral summer

Abstract: The Southern Ocean (SO), in spite of its major contribution to global primary productivity (PP), remains underexplored in this aspect. Light being the most limiting parameter affecting primary production, it is crucial to study the ambient light field to understand PP and associated processes. The current study makes a dual effort to present PP estimates as well as understand the bio-optical variability in the Indian sector of the Southern Ocean (ISSO). Results suggest that PP was highest at Sub-Tropical Front (STF) and lowest at Polar Front-2 (PF2). Most PP profiles were characterized by subsurface maxima, indicating probable photoinhibition or micronutrient limitation at surface layer. Strong correlation between measured and satellite-based integrated PP (R2 = 0.94, RMSE = 77.48, p < 0.01) indicated the efficacy of global models in their original formulation in bio-optically complex SO waters. The maximum photochemical efficiency of phytoplankton (Fv/Fm) measured by fast repetition rate fluorometry varied from 0.1–0.4, implying reduced phytoplankton photosynthetic efficiency in ISSO. The ratio between remote sensing reflectance (Rrs)-derived phytoplankton absorption (aph) at blue-red band (B/R ratio) indicated dominance of smaller phytoplankton in surface and larger phytoplankton at subsurface. Higher Chl-a specific phytoplankton absorption (aph* ) than phytoplankton absorption (aph) suggested an adaptation of dominant phytoplankton species to low light, yet a better light harvest efficiency. However, low contribution of aph suggested a strong influence of non-phytoplankton materials to the total absorption budget. We therefore infer that, the surrounding physical environment in terms of nutrients and bio-optical variability modulated phytoplankton size class and thereby productivity more critically in the surface than in the deeper layers of ISSO.

Spatial patterns, environmental correlates, and potential seasonal migration triangle of polar cod ( Boreogadus saida ) distribution in the Chukchi and Beaufort seas

Abstract: Polar cod (Boreogadus saida) is a key forage fish in the Arctic marine ecosystem and provides an energetic link between lower and upper trophic levels. Despite its ecological importance, spatially explicit studies synthesizing polar cod distributions across research efforts have not previously been conducted in its Pacific range. We used spatial generalized additive models to map the distribution of polar cod by size class and relative to environmental variables. We compiled demersal trawl data from 21 cruises conducted during 2004–2017 in the Chukchi and Beaufort seas, and investigated size-specific patterns in distribution to infer movement ecology of polar cod as it develops from juvenile to adult life stages. High abundances of juvenile polar cod (≤ 70 mm) in the northeastern Chukchi Sea and western Beaufort Sea were separated from another region of high abundance in the eastern Beaufort Sea, near the US and Canadian border, suggesting possible population structure in the Pacific Arctic. Relating environmental correlates to polar cod abundance demonstrated that temperature and salinity were related to juvenile distribution patterns, while depth was the primary correlate of adult distribution. A comparison of seasonal 2017 abundances of polar cod in the southern Chukchi Sea found low demersal abundance in the spring when compared to the summer. Seasonal differences in polar cod abundance suggest that polar cod migration may follow a classical ‘migration triangle’ route between nursery grounds as juveniles, feeding grounds as subadults, and spawning grounds as adults, in relation to ice cover and seasonal production in the Chukchi Sea.

Detection of lamprey in Southernmost South America by environmental DNA (eDNA) and molecular evidence for a new species

Abstract: Lampreys are jawless fishes belonging to the order Petromyzontiformes. Geotria australis is the sole representative lamprey species of the Geotriidae family and is widely distributed around South America, Australia, New Zealand, and sub-Antarctic Islands. In South America, the presence and distribution of G. australis are well characterized in Western Patagonia, in rivers flowing into the Pacific Ocean. In contrast, there is scarce information about the presence of this species in Eastern Patagonia, in rivers flowing into the Atlantic Ocean. Here, we provide the first report on the distribution of lamprey at the extreme south of Patagonia and suggest the occurrence of a new lamprey species. We developed an environmental DNA (eDNA) method to detect G. australis from water samples and obtained positive results in five basins flowing into the Atlantic Ocean and one river basin flowing into the Beagle Channel. Lampreys were captured from two eDNA-positive basins and used for genetic analysis. An 875 bp-sequence of the cytochrome b mitochondrial gene was obtained, and a phylogenetic analysis was carried out with this sequence and those available in GenBank, revealing Argentinean lamprey reported here, as a sister species of G. australis from Chile, Australia, and New Zealand. Also, the genetic distance values between lamprey reported here and G. australis were consistent with the genetic distances between species of different genera. Our results suggest that the Argentinean lamprey corresponds to a new specific taxon that could represent a new monotypic genus in Geotriidae.

Ontogenetic changes in the buoyancy and salinity tolerance of eggs and larvae of polar cod (Boreogadus saida) and other gadids

Abstract: Climate change in Arctic and sub-Arctic seas is leading to rapid changes in the dispersal potential of marine organisms. In Alaskan waters, loss of sea ice and salinity changes associated with warming may have a strong effect on the distribution and survival of eggs and larvae of key fish species at the Pacific–Arctic interface, such as polar cod (Boreogadus saida) in the Chukchi Sea and walleye pollock (Gadus chalcogrammus) in the northern Bering Sea. We conducted laboratory experiments to investigate how changes in ontogeny and salinity influenced the buoyancy and survival of eggs and larvae of these and two other gadids (Pacific cod, Gadus macrocephalus and saffron cod, Eleginus gracilis). Polar cod egg density varied among family groups, but eggs were more buoyant than those of walleye pollock overall. Eggs of both species followed a typical pattern of increasing density early in development. After hatching, polar cod and walleye pollock larvae were similar in density, and were notably more buoyant than the larvae of species with demersal eggs (Pacific cod and saffron cod). Larvae of the two Arctic species (polar cod and saffron cod) were less sensitive to salinity challenges than the sub-Arctic gadids, but polar cod became more sensitive at 6 weeks post-hatch. These results highlight possible adaptations of polar cod to ensure that their eggs are positioned under or near ice after spawning so that larvae hatch in productive surface waters during ice break-up. A comparison of modeled seawater densities to egg densities during the post-spawning period suggests that walleye pollock eggs would only be in contact with seasonal sea ice on the northern edge of their distribution at latitudes above ~ 63 °N. The synergic effects of environmental variables on vertical distribution of eggs and their survival potential will be important biogeographic mechanisms to consider with climatic warming and continued loss of sea ice.

Cultivable fungi associated with bryosphere of bipolar mosses Polytrichastrum alpinum and Polytrichum juniperinum in King George Island, South Shetland Islands, Maritime Antarctica

Abstract: We characterized the diversity of cultivable fungal assemblages associated with the bryospheres of the bipolar mosses Polytrichastrum alpinum and Polytrichastrum juniperinum resident in King George Island, South Shetland Islands, Maritime Antarctica. From different parts of the mosses, 160 fungal isolates were obtained and identified using molecular biology methods as 43 taxa of 28 distinct genera. Antarctomyces psychrotrophicus, Mrakia gelida, Pseudogymnoascus sp., Melanodiplodia sp., and Vishniacozyma victoriae were the dominant taxa and displayed the highest values of frequency. Ecological diversity indices showed that the fungal assemblages were high but ranged among the mosses. Fungi of the bryospheres of both mosses showed different colonization patterns. Only A. psychrotrophicus, M. gelida, Pseudogymnoascus sp., and Leotiomycetidae sp. occurred as endophytes, epiphytes, and in the rhizoidosphere of P. alpinum. In contrast, the bryosphere of P. juniperinum did not show a single common fungus across its different portions. Our results show that the bryosphere of the bipolar Antarctic mosses seem to represent an interesting hostspot of fungal diversity dominated by cosmopolitan cold-adapted and endemic species recognized as symbionts and decomposer species. The high fungal diversity detected suggests that the Antarctic mosses may offer a protected microhabitat (bryosphere) favorable for the survival, dispersal, and colonization of symbionts and decomposer fungi in the different extreme environments of Antarctica.

Dietary plasticity and the importance of salmon to brown bear ( Ursus arctos ) body size and condition in a low Arctic ecosystem

Abstract: Ecological flexibility within animal populations can allow for variation in resource use and foraging decisions. We estimated brown bear (Ursus arctos) diet composition in Gates of the Arctic National Park and Preserve, Alaska from 2013 to 2015 to evaluate how variation in foraging behavior influences body condition and size. We used stable carbon (δ13C) and nitrogen (δ15N) isotope analyses of sectioned brown bear hair samples to evaluate assimilated diet. We then developed a set of a priori linear models to evaluate differences in the diet composition of brown bears (n = 80) in relation to body fat (%) and mass. The proportion of meat (salmon [Oncorhynchus keta] and terrestrial meat combined) in the diet from July through late September varied between male and female bears, with males ( $$\stackrel{-}{x}$$ = 62%, SD = 30) assimilating significantly more meat than females ( $$\stackrel{-}{x}$$ = 40%, SD = 29). Most of the meat consumed came from marine-derived resources for males (53% of the total diet or 86% of the meat) and females (31% of the total diet or 77% of the meat). As we found the range of observed diets was unrelated to physiological outcomes (i.e., percentage body fat), we suggest that ecological flexibility within populations may provide an adaptive advantage by allowing individuals to reduce competition with conspecifics by foraging on alternate food resources. Identifying variable foraging behaviors within a population can allow for a better understanding of complex behaviors and, ultimately, lead to more informed management decisions related to habitat use, development, and harvest.

Arctic gadids in a rapidly changing environment

Abstract: This special issue originated from an international workshop on the Biology and Ecology of Arctic Cods convened in Fairbanks, Alaska, in June 2018 as part of the Ecosystem Studies of the Subarctic and Arctic Seas (ESSAS) Annual Science Meeting. This followed an earlier ESSAS workshop on Arctic gadids held in Copenhagen, Denmark, in April 2014 (Mueter et al. 2016). The aim of both workshops was to synthesize recent advances in our understanding of the biology, ecology, and dynamics of Arctic gadids around the circumpolar North in the context of a rapidly changing Arctic marine environment. Changes in the structure of Arctic marine ecosystems with direct effects on humans have been particularly pronounced on the major Arctic inflow shelves (Fig. 1), including the Northern Bering Sea and Chukchi Sea (Huntington et al. 2020) and the Barents Sea (SkernMauritzen et al. 2018; Haug et al. 2020), where the majority of the contributed papers are focused. The growing interest in the Arctic, combined with increased accessibility of formerly ice-covered regions within these major gateways to the Arctic, has led to a proliferation of research in Arctic seas over recent decades, including research on Arctic gadids (Fig. 2). The strong focus on the polar cod (Boreogadus saida) throughout these papers reflects the central role of this species in Arctic marine ecosystems (Bradstreet et al. 1986; Hop and Gjøsæter 2013), as well as its circumpolar distribution (Mecklenburg et al. 2011). The importance of polar cod as prey for seabirds and marine mammals is consistent with estimates of very high natural mortality rates in the Chukchi Sea (Marsh et al. 2020). In addition to a number of regional studies of polar cod, contributions include circumpolar studies on diets (Bouchard and Fortier 2020) and genetics (Nelson et al. 2020) of polar cod and laboratory studies comparing aspects of polar cod with other Subarctic and Arctic gadids (Copeman et al. 2020; Leo et al. 2020; Spencer et al. 2020). Only two studies primarily focus on other species, namely the navaga (Eleginus nawaga) (Maznikova and Orlov 2020) and the saffron cod (Eleginus gracilis) (Smé et al. 2020). These congeners are limited to relatively nearshore waters in the White, Barents, and Kara seas, and in the Pacific Arctic, respectively. Few studies on navaga are available outside the Russian literature, and the synthesis of their biology and distribution in the White Sea by Maznikova and Orlov (2020) makes much of what is known about this true Arctic gadid more widely available. The first main theme in this special issue is the population structure of polar cod and other Arctic gadids. Population genetic structure is evident in polar cod collections from around the Arctic, suggesting the existence of at least four major groups in the Alaskan Arctic (northern Bering Sea to western Beaufort Sea), western Canadian waters (Beaufort Sea and Amundsen Gulf), eastern Canadian waters (Resolute Bay to Gulf of St. Lawrence), and European waters including the Greenland, Iceland and the Laptev Sea (Nelson et al. 2020). The differentiation between the Alaskan and western Canadian groups is consistent with an earlier regional study that found small-scale geographic partitioning in the transition zone between these groups (Wilson et al. 2019). However, the mitochondrial genome suggests little populationlevel structure but high levels of genetic diversity in polar cod from the northern Bering Sea to the Canadian Beaufort Sea, suggesting the potential for local differentiation (Wilson et al. 2020). Population differentiation in the Pacific Arctic is supported by a distinct gap in the distribution of juvenile polar cod between the western Beaufort Sea, which is contiguous with the Chukchi Sea, and the eastern Alaskan * Franz Mueter fmueter@alaska.edu

Regional gold mining activities and recent climate warming alter diatom assemblages in deep sub-Arctic lakes

Abstract: Previous paleolimnological investigations have examined the effects of gold mining operations, local land-use changes, and regional climate warming on the aquatic biota from shallow lakes in Yellowknife, Northwest Territories, Canada. However, the long-term impacts of these multiple environmental stressors on the biota of deeper lakes that support large-bodied fish species have not been investigated. In this study, we examined multiple sedimentary proxies from two deep lakes around Yellowknife to assess the long-term effects of metalloid contamination, development of the city, and recent warming over the past ~ 200 years. The sedimentary metalloid profiles tracked the influence of mining operations and local land-use changes in the Yellowknife area and there were some similarities in the diatom responses to multiple stressors across the two lakes. However, the increases in sedimentary metalloid concentrations, eutrophic diatom taxa, and whole-lake primary production were more pronounced at Grace Lake relative to Alexie, likely because Grace is located nearer to the gold mines, as well as local city development. The overall lake primary production and the relative abundance of the planktonic diatom Discostella stelligera increased at both sites suggesting that some of the biological changes may be influenced by changes in thermal stratification, as has been documented in a wide spectrum of lakes across the Northern Hemisphere. Furthermore, the diatom assemblage changes in these deep lakes differed from those observed from shallow lakes in the region, suggesting that site-specific limnological characteristics will influence the biological responses to multiple environmental stressors through time.

Estimating microbial mat biomass in the McMurdo Dry Valleys, Antarctica using satellite imagery and ground surveys

Abstract: Cyanobacterial mat communities are the main drivers of primary productivity in the McMurdo Dry Valleys, Antarctica. These microbial communities form laminar mats on desert pavement surfaces adjacent to glacial meltwater streams, ponds, and lakes. The low-density nature of these communities and their patchy distribution make assessments of distribution, biomass, and productivity challenging. We used satellite imagery coupled with in situ surveying, imaging, and sampling to systematically estimate microbial mat biomass in selected wetland regions in Taylor Valley, Antarctica. On January 19th, 2018, the WorldView-2 multispectral satellite acquired an image of our study areas, where we surveyed and sampled seven 100 m2 plots of microbial mats for percent ground cover, ash-free dry mass (AFDM), and pigment content (chlorophyll-a, carotenoids, and scytonemin). Multispectral analyses revealed spectral signatures consistent with photosynthetic activity (relatively strong reflection at near-infrared wavelengths and relatively strong absorption at visible wavelengths), with average normalized difference vegetation index (NDVI) values of 0.09 to 0.28. Strong correlations of microbial mat ground cover (R2 = 0.84), biomass (R2 = 0.74), chlorophyll-a content (R2 = 0.65), and scytonemin content (R2 = 0.98) with logit transformed NDVI values demonstrate that satellite imagery can detect both the presence of microbial mats and their key biological properties. Using the NDVI—biomass correlation we developed, we estimate carbon (C) stocks of 21,715 kg (14.7 g C m−2) in the Canada Glacier Antarctic Specially Protected Area, with an upper and lower limit of 74,871 and 6312 kg of C, respectively.

Broad feeding niches of capelin and sand lance may overlap those of polar cod and other native fish in the eastern Canadian Arctic

Abstract: As ocean temperatures rise, sub-Arctic capelin (Mallotus villosus) and sand lance (Ammodytes spp.) have become increasingly abundant in regions of the eastern Canadian Arctic. These fish have a similar trophic role to the keystone polar cod (Boreogadus saida), potentially competing for food resources when co-occurring. To evaluate this, we calculated feeding niche breadth and overlap based on fatty acids and δ15N- and δ13C-derived trophic position and carbon source, among sub-Arctic fish and 10 Arctic fish and invertebrates within low, mid, and high latitudes of the Canadian Arctic. Diverse feeding strategies including benthic Myoxocephalus sp., anadromous and pelagic fish, led to limited feeding niche overlap among species (13% average, range 0–96%). Feeding niche overlap between capelin and sand lance from the low Arctic was generally high (36–93%); while fatty acid niches of these fish overlapped 0–21% with polar cod in the mid and high Arctic, and their isotopic niches overlapped up to 96%. Capelin and sand lance showed 3–8 times broader feeding niches than polar cod. Regarding regional variation, polar cod had similar niche breadth between regions and highly overlapping fatty acid niches. Niche variation for Myoxocephalus sp. and Gammarus spp. between low and high Arctic was likely associated with more diverse sources of primary production in the shallower, more brackish low Arctic. Although regional variation in food availability play an important role defining feeding niches, broader niches and isotopic niche overlap with polar cod indicated a potential ecological advantage for capelin and sand lance over polar cod under climate change.

The diet of the Patagonian toothfish Dissostichus eleginoides, a deep-sea top predator off Southwest Atlantic Ocean

Abstract: The present study is a valuable contribution to the knowledge of feeding habits of Patagonian toothfish Dissostichus eleginoides in Southwestern Atlantic (53–55°S, 351 to 1073 m depth) near Burdwood Bank/Namuncura marine-protected area, where diet has not been previously investigated. Based on stomach content analyses of 441 specimens ranging from 38 to 190 cm total length (TL), our study tested the hypotheses that diet was influenced by TL, sex, maturity stage, depth, and region, using generalized linear models and information theory selection criteria. The Patagonian toothfish fed primarily on fish (morid cod Notophycis marginata, myctophids, rattails Macrourus holotrachys and Coelorinchus fasciatus, notothenids Patagonotothen ramsayi, and hoki Macruronus magellanicus), followed by cephalopods (Onykia ingens, Doryteuthis gahi) and shrimps (Acanthephyra pelagica). One case of cannibalism was recorded. The trophic level was 4.57 (4.22 juveniles, 4.78 adults). The pelagic fish and bathypelagic shrimp were more consumed in the east region, whereas demersal fish and cephalopods were more consumed in the west one. Ontogenetic dietary changes associated with TL and maturity stage were reported: pelagic fish and shrimp A. pelagica had the main importance in the diet of intermediate-sized toothfish, reinforcing the hypothesis that juveniles exhibited a bento-pelagic behavior. Demersal fish were more heavily consumed by juvenile specimens, and the size of demersal fish predated by Patagonian toothfish increased according to the predator TL. Cephalopods were more consumed by adults. The preference of sexually mature specimens for cephalopods could have a positive effect on spawning and egg quality.