• Back to the future: Pacific walrus stress response and reproductive status in a changing Arctic

      Charapata, Patrick Maron; Horstmann, Larissa; Misarti, Nicole; Wooller, Matthew (2016-08)
      The Pacific walrus (Odobenus rosmarus divergens) is an iconic Arctic marine mammal that Alaska Natives rely on as a subsistence, economic, and cultural resource. A decrease in critical sea ice habitat and uncertain population numbers have led to walruses being listed as a candidate for the Endangered Species Act. However, there is no clear understanding of how walruses might be affected by climate change. The first objective of this study was to describe how bone steroid hormone concentrations relate to commonly used blubber and serum steroid hormone concentrations (i.e., cortisol, estradiol, progesterone and testosterone), because steroid hormones have not been extracted from marine mammal bone until now. Bone, blubber, and serum were collected from individual adult walruses (n = 34) harvested by Native Alaskan subsistence hunters during 2014 and 2015. Complete turnover of cortical bone in a walrus skeleton was estimated as ~33 years, approximately the lifetime of a walrus. Results showed bone and blubber steroid hormone concentrations were similar (P = 0.96, 0.51, 0.27 for cortisol, estradiol, and progesterone (males only), respectively), but not testosterone (males and females, P = 0.003) nor progesterone in blubber of female walruses (P = 0.007). Progesterone concentrations in males were significantly correlated between bone and blubber (R² = 0.51, P < 0.001). Estradiol measured in bone had high interannual variability (P < 0.001), indicating a shorter reservoir time in cortical bone compared with other hormones in this study, possibly due to local production of estradiol in walrus bone. Overall, bone serves as a long-term reservoir of steroid hormone concentrations compared with circulating serum concentrations. Progesterone measured in blubber can be compared with bone progesterone, but local production of estradiol in bone should be taken into account when interpreting these concentrations in cortical bone. The second objective of this study was to understand the physiological resiliency of walruses to the current warming in the Arctic. Steroid hormone concentrations were measured in walrus bone collected from archaeological (n = 38, > 200 calendar years before present (BP)), historical (n =135, 200 – 20 BP), and modern (n = 47, 2014 – 2015) time periods, but were also analyzed at a finer decadal (1830s – 2010s) scale. Walrus bone cortisol concentrations measured in modern-day walruses were similar to other time periods (P = 0.38, 0.07, for archaeological and historical time periods, respectively) indicating no increase in the stress response of walruses as a result of current sea ice conditions in the Arctic. Estradiol (females only), progesterone, and testosterone were significantly negatively correlated with walrus population estimates (P = 0.008, 0.003, <0.001, respectively). A negative correlation indicates that walrus population numbers are low when reproductive hormone concentrations are high, and population numbers are high, possibly at carrying capacity, when hormone concentrations are low. Data from the current decade (2014–2015) show that the current walrus population has lower reproductive hormone concentrations compared to times of rapid population increase. These data indicate the present-day walrus population may not be increasing, but is either experiencing low calf production and / or is near its carrying capacity. Overall, these data provide walrus management with insights into the physiological resiliency of walruses in response to arctic warming, and validate bone as a valuable tissue for monitoring long-term physiological changes in the walrus population.
    • Bacteria associated with paralytic shellfish toxin-producing strains of Anabaena circinalis

      Raudonis, Renee Alaine (2007-12)
      Paralytic shellfish toxins (PSTs) are produced by dinoflagellates and cyanobacteria. There is growing evidence that bacteria associated with dinoflagellates play a role in the production of PSTs, however, no studies have examined the type of bacteria associated with toxic cyanobacteria or the role these bacteria could play in PST-production or metabolism. Further, there are no known axenic cultures of PST-producing cyanobacteria, suggesting that cyanobacteria are dependent on one or more bacteria for growth/survival. The research reported here examined the bacterial community associated with six Australian freshwater cyanobacterial strains of Anabaena circinalis obtained from the CSIRO, three toxic and three non-toxic. The goal was to identify bacteria that could be essential for cyanobacterial growth/survival and/or PST production/metabolism. Confirmation of cyanobacterial species identification was confirmed by molecular techniques; one species was found to be more closely related to Anabaena flos-aquae. PST-production by the three toxic strains was confirmed using HPLC. Bacterial communities associated with the cyanobacteria were dominated by the [alpha]-Proteobacteria, of which the Rhizobiales group was dominant. Two bacterial ribotypes were associated with only the toxic cyanobacteria, and could be important in PST-remineralization.
    • Barents Sea hydrographic variability (1975-1991)

      Zimmermann, Sarah Lukens (2003-12)
      Barents Sea temperature and salinity anomalies and their connection to the Arctic Oscillation (AO) are analyzed using a 16-year time-series of hydrographic data (1975-1991). Seasonal and inter-annual variations are investigated along two sections spanning the meridional and zonal length of the Barents Sea over two depth layers, 0 to 50m and 50 to 200m. Depending on location, mean seasonal differences in the deeper layer are as large as 3°C in temperature and 0.2 in salinity, whereas the upper layer differences are 6°C and 1.4. Inter-annual anomalies are 0.6°C and 0.07 in the deeper layer and 0.8⁰C and 1.2 in the upper layer. Temperature and salinity anomalies' leading EOFs explain 49% and 34% of the total variance, and are in-phase from 1975-1985 but out-of-phase for 1985-1991. Examination of the surface heat-flux suggests the temperature anomaly is advective before 1985 and locally formed after 1985. This is supported by the temperature anomaly's changing propagation pattern through the Barents Sea after 1985. The salinity anomaly's source appears to be advective throughout the period. The AO correlates with the temperature EOF suggesting the AO's influence on the temperature anomaly is stronger over the Norwegian Sea before 1985 and stronger over the Barents Sea after 1985.
    • Bathymetry of Alaskan arctic lakes: a key to resource inventory with remote-sensing methods

      Mellor, Jack C. (1982-05)
      Water depth is a major factor in predicting resources associated with tens-of-thousands of uninventoried Alaskan arctic lakes. Lakes were studied for physical, chemical, and biological resources related to water depth in 3 specific areas along a north/south transect extending from Pt. Barrow on the Arctic Ocean to the foothills of the Brooks Range. Side-Looking Airborne Radar (SLAR) imagery was acquired over the same study transect to investigate its application for determining lake depth. Ice thicknesses, necessary for the interpretation of depth contours from SLAR imagery, were measured along with other parameters in the study lakes throughout the winter 1978-79. This ice-thickness data and sequential SLAR images are used to illustrate a method of contouring water depths in arctic lakes. This is based on changes in intensity of SLAR signal return which define the zone at which ice cover contacts the bottom. This intensity is a function of physical and dielectric properties of the snow, ice, water, bottom substrates, and ice inclusions within these lakes. A computer program was developed to manipulate Landsat satellite digital data and compile a master file of lakes and their computer-calculated surface features (i.e. area, perimeter, crenulation, and centroid). The master file uniquely identifies each computer catalogued lake by latitude and longitude and stores the calculated features in a data base that can be retrieved for a specified geographic ABSTRACT area. Each lake record also provides storage space for resource data collected outside the computer generated data. The application of these remote-sensing tools and the knowledge of aquatic resources associated with bathymetry add to our ability for regional inventory, classification, and management of arctic lake resources.
    • Benthic community development in Boca de Quadra, Alaska

      Winiecki, Carol Irene (1986-05)
      The purpose of this experiment was to find ways of evaluating the community development in Boca de Quadra, a fjord in southeast Alaska, after a severe physical disturbance. Containers of defaunated sediment were used near the head of the fjord to simulate the benthic habitat after such a disturbance. Important features of community development were described, potential indicator taxa were selected, and the extent of community development was examined. Seasonal variations tended to mask the developmental trends. However, samples collected during the same season, but representing various lengths of colonization, allowed developmental trends to be observed in faunal composition, numbers of taxa, density, biomass, and diversity. Maldanidae, Nematoda, Lumbrineris luti. Leitoscoloplos pugettensis, Pholoe minuta. and Spionidae are potential indicators of community maturity.
    • Biogeochemical tracers of change in Pacific walruses past and present

      Clark, Casey; Horstmann, Lara; Misarti, Nicole; Konar, Brenda; Severin, Ken; Lemons, Patrick (2019-05)
      Reduced sea ice and projected food web shifts associated with warming of the Arctic have raised concerns about the future of Arctic species. Pacific walruses (Odobenus rosmarus divergens) use sea ice as a platform for molting, giving birth, and resting between foraging bouts. Exactly how sea ice loss will affect walruses is difficult to predict, due to a lack of information about regional ecosystems and their responses to climate change. The objectives of the research in this dissertation were to 1) examine how walrus diet changed in response to shifting sea ice conditions over the last 4,000 years, with the goal of generating predictions about how current and future ice loss may affect the walrus population; 2) make it easier to directly compare the results of retrospective and contemporary stable isotope studies of walruses; and 3) generate new tools to assist wildlife managers in monitoring the walrus population in an uncertain future. Stable carbon and nitrogen isotope ratios of walrus bone collagen indicated that diet was similar during previous intervals of high and low sea ice; however, diet variability among individual walruses was greater when sea ice cover was low, suggesting decreased abundance of preferred mollusk prey. Modern walrus diet was different from both previous high and low ice intervals, meaning that food webs in the Arctic are still in a state of flux, or that recent changes are novel within the last 4,000 years. Tissue-specific stable isotope discrimination factors were generated for walrus muscle, liver, skin, and bone collagen to improve comparisons between retrospective and contemporary studies of walrus diet. Additionally, lipid normalization models were parameterized for walrus skin and muscle, thereby making future walrus stable isotope research more feasible by reducing analytical costs and allowing the use of non-lethal sample collection. Finally, a novel technique for estimating the age at onset of reproductive maturity using concentrations of zinc and lead in the teeth of female walruses was established. This new approach has the potential to become a powerful tool for monitoring the walrus population and may be applicable to other species. Use of this technique on archived specimens may make it possible to examine changes in wildlife population dynamics across thousands of years.
    • Biogeochemistry of a glaciated fjord ecosystem: Glacier Bay National Park, Alaska

      Reisdorph, Stacey; Weingartner, Thomas; Mathis, Jeremy; Hood, Eran; Danielson, Seth; Aguilar-Islas, Ana (2015-05)
      The burning of fossil fuels, coupled with land use and deforestation practices, has resulted in CO₂ being emitted into the atmosphere. As much as one third of the anthropogenic, or man-made, CO₂ that ends up in the atmosphere is absorbed by the oceans and has led to increases in marine dissolved inorganic carbon (DIC) concentrations and a decrease in ocean pH, a process referred to as ocean acidification (OA). Increased concentrations of DIC can reduce saturation states (Ω) with respect to biologically important calcium carbonate minerals, such as aragonite. However, CO₂ may not be the only factor in seasonal changes to calcium carbonate saturation states. With this project I was interested in understanding how glacial runoff impacts the seasonal changes to the marine biogeochemistry in a glaciated fjord. In addition to CO₂, glacial meltwater is low in alkalinity (TA) and may impact the seasonal biogeochemistry of the marine system, as well as how it influences the duration, extent, and severity of OA events in an Alaskan glacial fjord, Glacier Bay National Park (GLBA). Through this study, I found that glacial runoff heavily impacts aragonite saturation states, with the main drivers of Ω (DIC and TA) varying seasonally. In GLBA low Ω values were well correlated with the timing of maximum glacial discharge events and most prominent within the two regions where glacial discharge was highest. The influence of glaciers is not limited to just TA as runoff is also low in macronutrients due to a lack of leaching from the soil and rocky streambeds. This has the potential to greatly impact the efficiency and structure of the marine food web within GLBA, the lowest level of which can be estimated using net community production (NCP). Changes within the lowest level of the food web, as a result of seasonal OA events, may lead to bottom-up effects throughout the food web, though this project focused only on production and respiration signals within the lowest level. We estimated regional NCP values for each sampling season and found the highest NCP rates (~54 to ~81 mmoles C m⁻² d⁻¹) between the summer and fall of 2011, with the most marine influenced lower part of the bay experiencing the greatest production. As the climate continues to warm, further glacial volume loss will likely lead to additional modifications in the carbon biogeochemistry of GLBA. Understanding the dynamics that drive seasonal changes in Ω, NCP, and the associated air-sea CO₂ fluxes within glacially influenced Alaskan fjords can provide insights into how deglaciation may affect carbon budgets and production in similar fjords worldwide.
    • Blubber and beyond: the role of lipids in thermoregulation and energy reserves of phocid seals

      Pearson, Linnea E.; Burns, Jennifer M.; Horstmann-Dehn, Larissa-A.; Pfeiffer, David C.; Mellish, JoAnn E.; Buck, C. Loren (2015-08)
      Phocid seals rely on lipids in the form of a blubber layer as insulation and lipids as energy sources in blubber and muscle. The amount and lipid composition of blubber and other lipid stores vary throughout life within and among species of phocid seals. I hypothesized that this variation in regulation, allocation, and interactions among lipid stores is influenced by species, ontogeny, and tissue-specific thermal regimes in polar phocids: harp (Pagophilus groenlandicus), hooded (Cystophora cristata), and Weddell (Leptonychotes weddellii) seals. I investigated the thermoregulatory strategy of neonatal harp, hooded, and Weddell seals, and throughout the transition to an aquatic environment in harp seals. All three species had similar thermal resistance, though it was achieved differently using either lanugo or blubber. While there was variation in the main thermoregulatory strategy among species, no species possessed all thermal adaptations of adults. Harp and Weddell seals had higher surface area to volume ratios (SA:V), thus higher potential heat loss, though compensatory mechanisms for heat production were different between species. Harp seals were the only species with the potential for nonshivering thermogenesis (NST) in brown adipose tissue (BAT), whereas Weddell seals had the highest potential for shivering thermogenesis (ST) in their skeletal muscle. Hooded seals relied on blubber, and had a significantly lower SA:V than the other two species. As harp seal pups develop, their potential for NST declines and they shift to a reliance on blubber for insulation. By late weaning, harp seal pups have similar insulative capabilities as adults, and can likely meet the thermoregulatory challenges associated with living in water. In neonatal and young seals that have little blubber, other lipid stores such as BAT and skeletal muscle lipids provide heat-generating mechanisms (NST or ST) to offset potentially high rates of heat loss. The potential for NST declines with age, as the blubber layer develops in harp seals, and weaned pups look to have similar insulative capabilities as adults. While phocid adults rely on blubber for insulation and maintain a thermal gradient across the tissue, otariids (fur seals and sea lions) instead maintain an external gradient across a thick fur layer. This has implications for the underlying lipid composition of blubber, as the fatty acids (FA) that make up this lipid respond differently to temperature. In phocid blubber, latitude (a proxy for environmental temperature) had a positive correlation with the proportion of polyunsaturated fatty acids, but a negative correlation with saturated fatty acids. In otariids, these trends were reversed. This suggests interactions between blubber and the ambient environment play a role in the overall relative proportions of FA classes in blubber. Unlike in blubber, the FA class composition of harp, hooded, and Weddell seal skeletal muscle was similar among species. In adult female Weddell seals, the relative proportions of individual FA in blubber and muscle were significantly different between tissues; these differences persisted across seasons, and were independent of female reproductive state. It appears that the FA in blubber and muscle reflect the tissues' roles within the body. Blubber contained a greater proportion of monounsaturated FA, which remain fluid at lower temperatures, while the muscle contains a larger proportion of SFA, which produce the greatest amounts of ATP per mole oxidized to support metabolism. In adult phocids, the FA composition of the blubber layer appears to be influenced by environmental interactions with latitude (temperature), in accordance with the location of and steepness of the thermal gradient through the blubber layer. Finally, environment looks to have little influence on the FA stores in skeletal muscle, and seasonally persistent tissue differences between blubber and muscle highlight how lipid is dynamically modulated within the body of phocid seals. How and what lipids are allocated to blubber is a mixture of abiotic and biotic cues throughout life, linked to thermodynamics, ambient environment, and energy dynamics.
    • Body composition (carbon, nitrogen and calories) and energetics of immature walleye pollock, Theragra chalcogramma (Pallas), in the southeast Bering Sea

      Harris, Robert K. (1985-05)
      The body composition (carbon, nitrogen and calories) of Bering Sea and Resurrection Bay (Alaska) immature walleye pollock (9-360 g wet weight) were related to dry weight and Fulton's condition factor index by regression models. The condition factor was a better predictor of body composition than dry weight. As condition improved from a minimum starvation level of 0.42 to a maximum of 1.16, body caloric, percent carbon, and the carbon-nitrogen ratio increased, while percent nitrogen and percent ash decreased. The body composition measurements allowed energy budget terms (assimilation coefficient, growth, and metabolism) to be expressed in common units. The assimilation coefficient and growth terms were estimated from literature sources. Oxygen consumption measurements at 3-10°C yielded the metabolic term. The daily food requirement for 0-3 year old walleye pollock, at their annual average Bering Sea habitat temperature of 3.8°C, was 1.0 - 1.5% of the body weight.
    • Breeding performance of kittiwakes and murres in relation to oceanographic and meteorologic conditions across the shelf of the southeastern Bering Sea

      Lloyd, Denby S. (1985-12)
      Contrary to expected results, black-legged and red-legged kittiwakes on St. George Island exhibited more variability in annual breeding performance than black-legged kittiwakes at Cape Peirce. Thick-billed and common murres at St. George also showed more annual variability than common murres at Cape Peirce. Kittiwakes at St. George exhibited improved breeding performance during years with colder water temperatures and lower summer wind speeds. Correlations between breeding performance in kittiwakes and murres and environmental conditions at Cape Peirce were inconclusive. A general decline in the annual breeding success of kittiwakes and murres at St. George between 1976 and 1984 coincided with reduced abundance of juvenile walleye pollock. Consistently low breeding success of kittiwakes and murres at Cape Peirce varied little among six years observed between 1970 and 1984. These results challenge previous considerations of pelagic food webs on the outer shelf as being more stable than those in the coastal domain.
    • CARBON AND NITROGEN ASSIMILATION IN THE CLAMS NUCULANA RADIATA AND MACOMA MOESTA FROM THE BERING SEA

      Weems, Jared; Iken, Katrin; Gradinger, Rolf; Wooller, Matthew (University of Alaska Fairbanks, 2011-08)
      The predicted climate-induced reduction in sea ice presence in the Bering Sea could impact benthic trophic interactions; however, species-specific consumer dependence on ice algal production is largely unknown. My objective was to track feeding in the benthic clams, Nuculana radiata and Macoma moesta, using stable carbon and nitrogen isotopes. Nuculana radiata had slow isotopic assimilation rates, with lipids taking up isotope markers fastest and muscle tissue the slowest. Lipids may thus be particularly suitable to track the immediate ingestion of sea ice algal export in benthic consumers. When isotopically enriched food was added to natural sediment cores, N. radiata assimilated 60% less of the isotope markers than when feeding on algal food in isolation. Possibly, this difference is related to the ingestion of other, naturally present food sources in the sediment. Macoma moesta showed 30% higher isotopic assimilation compared to N. radiata in sediment cores. I suggest that differing feeding behaviors between the species provide differential access to the sedimented algal food. Based on these results, N. radiata is likely better able to utilize food sources buried in the sediment and may be more competitive over M. moesta under conditions of reduced ice algal production in the northern Bering Sea.
    • Carbon biogeochemistry of the eastern Bering Sea shelf

      Cross, Jessica; Mathis, Jeremy; Feely, Richard; Stockwell, Dean; Weingartner, Thomas; Whitledge, Terry (2013-12)
      The uptake of anthropogenic carbon dioxide (CO₂) has caused perturbations to marine biogeochemistry in recent years, including decreasing ocean pH and carbonate mineral saturation states (Ω). Collectively termed ocean acidification (OA), these conditions hinder the growth of calcium carbonate shells and effectively reduce habitat for some marine calcifiers. Given that the Bering Sea is one of the world's most productive marine ecosystems and supports both commercial fishing industries and subsistence communities, it is integral to understand its susceptibility to OA. Here, new observations of the organic and inorganic carbon systems are used to identify mechanisms leading to CO₂ accumulation and sub-regional enhancement of vulnerability to OA processes. Chapter 1 describes the state of knowledge of OA in this area, highlighting two regions where low Ω conditions are consistently observed: near the coast, and over the northern shelf. Chapter 2 describes net heterotrophic processes near the coast, in conjunction with low bottom water Ω. Chapter 3 examines this heterotrophy in more detail, showing that focused deposition of organic matter and its subsequent respiration. Chapters 4 and 5 focus on very low Ω values observed over the northern shelf. In combination with natural respiration processes, anthropogenic CO₂ was shown to cause low Ω and seasonal dissolution of carbonate minerals in Chapter 4. Chapter 5 illustrates how sea ice cover inhibits the flux of CO₂ from the surface ocean to the atmosphere, which raises the inventory of CO₂ in the water column. These results are synthesized in Chapter 6. Low-Ω conditions and areas of carbonate mineral dissolution will continue to expand as anthropogenic CO₂ accumulates in shelf waters in the coming decades, further reducing viable habitat for key calcifiers. Model projections of future surface water conditions indicate that average Ω over the Bering Sea shelf will drop below the observed natural variability by 2100, with average conditions favoring carbonate mineral dissolution in surface waters by 2150. Presently, episodic events will cause regions of the Bering Sea to be undersaturated in Ω, which could have significant and cascading impacts throughout the Pacific-Arctic region.
    • Carbon isotopic composition of polycyclic aromatic hydrocarbons and their weathering in Kachemak Bay sediment

      Borland, Tara Ann (2004-05)
      Identification of sources of polycyclic aromatic hydrocarbons (PAH) in sediments is an important step in reducing anthropogenic contamination. Identifications based solely on the composition of PAH can be confounded by compositional changes during weathering and biodegradation. Stable isotopic composition of individual PAH offer a source marker that may be less susceptible to alteration. The [alpha]¹³C values of PAH in major potential sources to the Kachemak Bay area were analyzed. To determine the stability of the [alpha]¹³C values of PAH in crude and diesel oil, microbial degradation experiments using sediment from the Kachemak Bay, Alaska, area were conducted over a one-year period. The impact of weathering on the isotopic composition of North Slope crude oil and diesel oil was also examined over a five-week period in aquaria with Macoma balthica, an intertidal bivalve. For both degradation experiments, PAH concentrations decreased and their composition changed, but the [alpha]¹³C values of individual PAHs remained stable. Hence, [alpha]¹³C values of individual PAHs have excellent potential as a relatively stable indicator of their sources. Based on isotopic and compositional data, the PAH in Kachemak Bay sediments appear to have several sources.
    • Carbon sources and trophic connectivity in seafloor food webs in the Alaska Arctic and sub-Arctic

      Oxtoby, Laura Elizabeth; Wooller, Matthew; O'Brien, Diane; Iken, Katrin; Horstmann, Larissa; Budge, Suzanne (2016-05)
      Stable isotope analysis offers critical insight into organic matter pathways that sustain and link consumers in a food web. Indirect examination of organic matter sources and consumer diets using stable isotope analysis is especially valuable in the Alaska Arctic and sub-Arctic marine realm, where organisms of interest are difficult to observe given their remote habitat and elusive behavior. The research objective of this body of work was to use novel applications of stable isotope analysis to extend our understanding of organic matter sources, trophic pathways, and resource competition among benthic consumers. Microphytobenthos, a community of photosynthesizing unicellular microscopic algal cells on the seafloor sediment, has not been included in stable isotope food web models in the Alaska Arctic and sub-Arctic due to challenges associated with sample collection and analysis. I constrained the isotopic composition of this potential algal source by integrating field measurements, physiological relationships previously established by laboratory studies, and a range of algal growth rates specific to high latitude primary production. Relative to other sources of primary production in the Arctic, sub-Arctic, and lower latitude ecosystems, estimates for stable carbon isotope values of total organic carbon from microphytobenthos in the Beaufort and Chukchi seas were higher than those for Arctic riverine organic matter, but lower than ice algal sources and microphytobenthos measurements from lower latitudes. To further elucidate trophic pathways and resource partitioning among benthic invertebrate consumers, I combined compound-specific stable isotope analysis, a relatively new analytical tool, with fatty acid analysis to estimate proportional contributions of algal sources from ice, open ocean, and surface sediments to common polychaete and bivalve consumers in the Bering Sea. Benthic invertebrates were collected in 2009-2010 and represented a diverse range of feeding strategies, including the suspension/surface deposit-feeding bivalves Macoma calcarea and Ennucula tenuis, the subsurface deposit-feeding bivalve, Nuculana radiata, the head down deposit-feeding polychaete Leitoscoloplos pugettensis, and the predator/scavenger Nephtys spp. Differences in dominant algal sources to these invertebrate consumers corresponded, for the most part, to feeding strategy. Bivalves primarily obtained fatty acids from surface sediments, whereas L. pugettensis obtained fatty acids from a microbially altered phytodetrital fatty acid pool, and Nephtys spp. from ice algal fatty acids acquired indirectly through predation. This multi-proxy compound-specific stable isotope approach was then applied to examine dietary overlap between Pacific walruses (Odobenus rosmarus divergens) and bearded seals (Erignathus barbatus) in 2009-2011 who feed primarily on benthic invertebrate prey. Differences in the relative proportions of fatty acids produced exclusively by benthic prey (non-methylene interrupted fatty acids) indicated that walruses and bearded seals had divergent diets. Proportional contributions of algal sources from ice, open ocean, and surface sediments to the prey consumed by walruses and bearded seals also varied. Walruses consumed prey that relied primarily on benthic and pelagic carbon sources (i.e., suspension/surface and subsurface deposit-feeding bivalves). In contrast, bearded seals consumed prey that relied on benthic and ice algal carbon sources (i.e., omnivorous and predatory benthic invertebrates). In conclusion, this research revealed that, in the recent study years, benthic food webs in the Alaska Arctic and sub-Arctic contained several trophic pathways linking consumers to distinct organic matter sources. Consequently, projected changes in algal production with future climate warming may elicit species-specific responses among benthic organisms.
    • Changes in the spring sea ice concentration in the Bering Sea from 1972-2000 in relation to spotted seal (Phoca largha) pregnancy rates

      Picco, Candace M. (2005-08)
      Spotted seals are most dependent on the seasonal sea ice in the Bering Sea during the spring pupping and mating season. Changes in sea ice characteristics, as related to recent documented changes in climate, may have an effect on spotted seal reproduction. This study investigates the relation between changes in the spatial and temporal patterns of the spring sea ice concentration in the Bering Sea from 1972-2000 to changes in the pregnancy rates of the spotted seal (Phoca largha). Multinomial time-series regressions were used to determine the influence of different climatic variables on the sea ice concentration. Different statistical methods were used to compare the ice conditions of defined regions in the Bering Sea and spotted seal pregnancy rates among 20 years from 1964- 2003. The results showed no definitive patterns relating the monthly climatic variables and sea ice concentration averages; however, noticeable trends in sea ice were found. The variability of the seal pregnancy rates coincided with changes in the Bering Sea ecosystem and ice concentration. This study demonstrated that seal pregnancy rates and sea ice concentration varied temporally and spatially, the direct causality of these variations was uncertain.
    • Characterizing glucocorticoid levels in five species of sea ducks occurring in Alaska

      Nilsson, Peter B. (2004-12)
      Stress hormone analysis, used in conjunction with other physiological parameters, may help identify factors affecting sea duck populations in their natural environment. Corticosterone, the primary 'stress hormone' in birds, is secreted in response to a stressor and enhances an individual's chance of survival by inducing physiological and behavioral changes. Establishing a valid method for evaluating stress hormone levels in sea ducks and gaining basic information on baseline concentrations and stress response in these birds are important first steps to identify factors that may negatively affect sea duck populations. This study validated a radioimmunoassay (RIA) procedure to measure corticosterone concentrations in harlequin duck serum and feces and in Steller's, spectacled, common, and king eider serum. Other objectives included characterization of baseline corticosterone concentrations, investigation of stress response, and the relationship between corticosterone and other variables in captive and wild sea ducks. The results indicate that fecal samples can be used to non-invasively measure corticosterone in harlequin ducks. Captive birds exhibited overall lower baseline levels of corticosterone than wild birds. The stress response observed in harlequin ducks was similar to other avian species. Rapid post-capture blood sampling is critical for evaluation of baseline corticosterone levels.
    • Chemosensory responses and foraging behavior of Pycnopodia helianthoides: predator or scavenger?

      Brewer, Reid; Norcross, Brenda; Highsmith, Raymond; Iken, Katrin (2003-08)
      Chemical cues released by damaged or dead organisms can affect how and where benthic scavengers feed, whether damage or mortality is natural or fishery-related. These cues may also cause predators to act as facultative scavengers. Experiments were performed to determine the role that the seastar Pycnopodia helianthoides plays in the presence of scavengable prey. The results of these experiments suggest that P. helianthoides preferentially scavenge in lieu of its normal predatory role. When given a choice, P. helianthoides choose damaged or decaying food over live prey even when live prey is encountered en route to the damaged animal. The densities and activities of P. helianthoides were compared between areas where food was continually introduced and areas where food was not introduced. Adding scavengable food to areas with P. helianthoides caused a spatial redistribution of the seastar population, a change in the foraging dynamics of the seastars, and in some cases, a change in the densities of the prey that P. helianthoides normally consume. The effects of introducing food appeared to result in a change in the role that P. helianthoides plays in the benthic community. This change in modes could have significant effects on the equilibrium of the benthic community.
    • Comparing the nutritional quality of Steller sea lion (Eumetopias jubatus) diets

      Bando, Monica Kaho Herkules (2002-12)
      Though the primary cause(s) of the Steller sea lion decline remains unknown, one hypothesis is nutritional stress, possibly the result of climatic regime shifts reducing prey availability and/or quality. Researchers at the Alaska SeaLife Center formulated three feeding regimes representative of Steller sea lion diets: prior to and during their population decline and from a stable population. The purpose of this project was to compare the nutritional quality of these diets using proximate composition and bomb calorimetry. The pre-decline and stable diets are composed of more high-fat prey, like herring, with resulting energy densities being significantly higher than the decline diet, comprising more low-fat prey, like octopus. Assumining the feeding regimes analyzed represent Steller sea lion diets prior to and during their population decline and in stable populations, results from this study are consistent with the possibility that nutritional stress is a cause of the Steller sea lion decline.
    • A comparison of sockeye salmon (Oncorhynchus nerka) in two climate regimes in the north Pacific Ocean using stable carbon and nitrogren isotope ratios

      Satterfield, Franklin Robert (2000-12)
      This study explores how the climate shift in the late 1970's impacted sockeye salmon feeding. Stable isotope ratios (¹³C and ¹⁵N) of recent muscle and scale tissues from five mature salmon species are highly correlated (R²=0.96 and 0.91, respectively), validating the use of archived scales for retrospective analysis. These data suggest a trophic separation by species with chinook occupying the highest level, followed by coho with some degree of overlap among sockeye, pink and chum at the lowest level. Archived scales from four different sockeye stocks from Kodiak Island and Southeast region were analyzed over the last 34 years to investigate changes relative to the 1976-1977 Climate Regime Shift. Most stocks show no statistical differences before and after the regime shift in either isotope. Despite recorded differences in sockeye abundance and size between these two regimes, these data suggest only minor changes in prey items.