• The effect of under ice crude oil spills on sympagic biota of the Arctic: a mesocosm approach

      Dilliplaine, Kyle B.; Gradinger, Rolf; Bluhm, Bodil; Collins, Eric; Eicken, Hajo (2017-05)
      The Arctic marine environment is facing increasing risks of oil spills due to growing maritime activities such as tourism and resource exploration. Encapsulation and migration of spilled oil through the brine channel system in sea ice poses significant risk to ice-associated biological communities. The first objective of this study was to establish mesocosms that allow the growth of artificial sea ice leading to sea ice physical properties similar to young natural sea ice. In addition, the mesocosms should be capable of growing and maintaining a sea ice community. Six sea water tanks with 360 l capacity each were inoculated with biological cultures collected from landfast sea ice near Utqiaġvik AK in April 2014 (year 1) and March 2015 (year 2). The two experiments lasted 24 and 27 days, and final ice thickness reached a mean value of 33 cm. The light conditions under the ice mimicked natural spring irradiances of 15 umol photons m² s⁻¹. Different inoculation approaches for ice biota were used. In year 1 we did not observe any algal growth. In year 2, biological characteristics in the ice prior to oil release (chlorophyll a, Extracellular Polymeric Substance (EPS) concentrations and algal and bacterial abundances) were similar to natural concentrations from early spring first year ice. The second objective was to evaluate the impact of Alaska North Slope crude oil on sea ice biota. Two different oil spill scenarios were tested in the mesocosms: discrete oil lenses and dispersed emulsions. Tanks were sampled prior to oil release and 13 or 10 days post-release in year 1 and year 2, respectively. In year 1, bacterial abundances increased after oil release, while establishment of algal populations was unsuccessful. In year 2, algal growth rates and EPS production increased over time in the control tanks, while they did not change in the oil exposed tanks. Differential response of bacteria and algae between year 1 and 2 not only point to the potential of nutrient competition, but also to the need of measuring several biological properties to detect effects of oil exposure in the event of a spill. Future studies can build upon the developed experimental framework including biological responses to low, sub-lethal oil dosing.
    • Effects of areas closed to bottom trawling on fish and invertebrate species in the eastern Bering Sea

      Frazier, Christine Ann; Norcross, Brenda; Hills, Sue; Norcorss, Brenda; Witherell, David (2003-12)
      The Bering Sea is a productive ecosystem with some of the most important fisheries in the United States. Constant commercial fishing for groundfish has occurred since the 1960s. The implementation of areas closed to bottom trawling to protect critical habitat for fish or crabs resulted in successful management of these fisheries. The efficacy of these closures on non-target species is unknown. This study determined if differences in abundance, biomass, diversity and evenness of dominant fish and invertebrate species occur among areas open and closed to bottom trawling in the eastern Bering Sea between 1996 and 2000. This study represented four areas: two within Bristol Bay closed areas and two within comparable fished areas. Total abundance and biomass were not significantly different among fished and closed areas or between pre-closure (1990-1994) and post-closure (1996-2000) years. Diversity and evenness were greater in fished areas than closed areas. The biomass of some functional feeding groups (i.e. piscivores, detritivores) of species decreased when compared among areas and in pre-closure versus post-closure years while others increased. These results support the need for continued research and monitoring of eastern Bering Sea closed areas to determine recovery time and the efficacy of closures as a management tool.
    • Effects of disturbance by clipping on two distinct forms of Zostera marina L.

      Roth, Joanna E. (1986-05)
      Biweekly clipping of leaves was used as a type of disturbance to compare the responses of eelgrass (Zostera marina) in shallow and deep water to those predicted from a terrestrial ecosystem succession model. All clipped plants had lower leaf growth rates than controls. Clipped plants decreased root-rhizome biomass in shallow water, but not in deep-water stands during 1981. During 1982 (better weather), shallow-water plants increased leaf carbon concentrations; deep-water plants decreased root-rhizome biomass. Root-rhizome to leaf ratios (high in shallow water and low in deep water) and weather conditions appeared important in determining the response to clipping. All plants had similar nitrogen content. These responses were typical of those reported for the tropical turtle grass, but were contrary to differences in plant growth strategies and nutrient use predicted from some terrestrial ecosystem studies of other higher vascular plants.
    • Effects of environmental characteristics on the fish assemblages of high latitude kelp forests in South-central Alaska

      Efird, Terril P.; Konar, Brenda; Seitz, Andrew; Stekoll, Michael (2013-12)
      Alaskan kelp forests are patchy habitats, varying greatly in size, physical complexity, and biotic and abiotic characteristics, and are important to fish communities. Patchy habitats often support different communities on patch edges versus interiors, while patch size and physical complexity are typically correlated to the resident community structure. This study quantified the biological and physical heterogeneity within different sized kelp forests and identified which factors are important in structuring the associated fish communities. Fish and habitat surveys were conducted at ten kelp forests of varying sizes. Significantly different fish communities were found at edge compared to interior locations. The relative abundance of seven species explained 91.4% of the variability in the fish community. Fish community structure was not correlated with kelp forest size or the species composition of canopy forming kelps. Instead, it related to the abundances of two understory kelps, bottom rugosity, and water depth. Together these benthic attributes correlated with 53.6% of the fish community variability. These findings suggest that within patchy systems that are spatially and structurally non-uniform, associated fish species composition and abundance may be more directly linked to location within the patch and year-round habitat complexity rather than habitat patch size or foundational species composition.
    • Effects Of Glacial Discharge On Kelp Bed Organisms In An Alaskan Subarctic Estuary

      Sparkland, Tania Marie; Iken, Katrin; Braddock, Joan; Gradinger, Rolf; Himelbloom, Brian; Konar, Brenda; Whitledge, Terry (2011)
      Global climate warming is having large-scale, pronounced effects on the physical environment of Arctic and subarctic nearshore marine ecosystems, such as the widespread melting of glaciers. The purpose of this study was to determine how changing environmental conditions due to glacial melting affect subarctic kelp bed community structure and organism fitness. This study compared kelp bed community structure under disparate environmental conditions on a glacially-influenced and an oceanic shore in the same subarctic Alaskan estuary. Laboratory tests assessed the effects of varying salinity and irradiance on growth and physiological competence (as maximum quantum yield ( Fv/Fm)) of the dominant kelp, Saccharina latissima. Reciprocal in situ shore transplant studies examined seasonal growth, Fv/Fm, morphology and storage product levels (mannitol) in S. latissima. This study showed that kelp communities were distinctly different in these two nearshore regions within the same subarctic estuary. In addition, the kelp S. latissima from these two environments, exhibited phenotypic plasticity in terms of growth to varying levels of salinity and light availability, while both populations maintained high physiological competence year-round. However, this phenotypic plasticity was constrained within different seasonal growth patterns in the populations from the two shores, which likely are genetically fixed. This is the first time that phenotypic plasticity within a genetically fixed seasonal growth cycle has been described for macroalgae and especially for two populations in such close proximity. However, the ability to elicit plastic responses and seasonal adaptations in S. latissima may be limited and concerns remain about the long-term persistence of this and other important foundation species and nearshore habitats with continued climate change.
    • Effects of ocean acidification on development of Alaskan crab larvae

      Descôteaux, Raphaëlle; Hardy, Sarah; Iken, Katrin; Mathis, Jeremy (2014-05)
      The oceans absorb a large proportion of the carbon dioxide gas (CO₂) emitted into the atmosphere. This CO₂ changes the chemistry of seawater to make it more acidic, a phenomenon termed ocean acidification. Ocean acidification can have negative impacts on marine fauna, especially during early life stages, presenting a risk to ecosystems and fisheries. This research tested the effects of ocean acidification on the larval development of three crab species in Alaska: Tanner crab (Chionoecetes bairdi), rock crab (Glebocarcinus oregonensis), and Dungeness crab (Metacarcinus magister). Experiments were undertaken to assess the effects of exposure to low-pH conditions (decrease of up to 0.6 pH units from current levels, range of pH ~8.1 to 7.5) on survival, growth (morphometrics and mass), and carapace mineral composition of larval Tanner, rock, and Dungeness crabs. Results showed a decrease in survival as well as a small but nonsignificant decrease in size of Tanner crabs. There was a small and complex effect of pH on survival of Dungeness crabs. Rock crabs raised in low-pH conditions (pH 7.5) had higher individual biomass than those raised in ambient conditions (pH 8.1). There was no significant impact of pH on mineralization of any species. Therefore, low pH had a negative effect on development of Tanner crabs, a small effect on Dungeness larval survival and no discernible negative effect on rock crab larvae. Differences in response to ocean acidification may be related to pre-adaptation to variable pH conditions through lifestyle such that species that live in deeper, more stable waters (e.g., Tanner crab) are more vulnerable than species living in shallower, more variable waters (e.g., rock and Dungeness crabs). These observations suggest that ocean acidification will have negative impacts on Tanner and Dungeness crab larval survival with potential implications for recruitment to the adult population and consequently, for their fisheries.
    • Effects of rising sea surface temperature and decreasing salinity on kelps and associated macroalgal communities

      Lind, Alyssa; Konar, Brenda; Danielson, Seth; Edwards, Matthew (2016-05)
      Kelp forests provide a multitude of vital ecosystems services, such as habitat for commercially and recreationally important species, support of complex food webs, and reduction of coastal erosion. The diversity and resilience of kelp forest communities are threatened as the severity of climate change and other anthropogenic stressors continues to mount. Particularly in the North Pacific, sea surface temperature (SST) is warming and glacier melt is discharging into coastal waters, causing decreases in salinity. This study assesses possible impacts of increasing SST and decreasing salinity on kelp forests by examining the response of key kelp species and their associated macroalgal community to these parameters in a North Pacific estuary, using Kachemak Bay as a model system. This two-part study combines both 1) a retrospective analysis of effects of environmental variables on existing kelp populations (Agarum clathratum, Laminaria yezoensis, and Saccharina latissima) and their associated macroalgal communities at three discreet water depths (5, 10 and 15 m), and 2) a factorial laboratory experiment investigating the effects of rising SST and decreasing salinity on kelp spore settlement and initial gametophyte growth in Eualaria fistulosa, Nereocystis luetkeana, and S. latissima. No strong correlations were observed between adult kelp biomass of any individual species with past SST and salinity changes, with the exception of a negative correlation between SST and L. yezoensis biomass at 10 m. In addition, SST and salinity were insignificant factors in shaping the associated macroalgal community biomass. In contrast to the retrospective analyses, the experimental results indicated that the early life-history stages of all kelp study species experienced decreased settlement and growth at elevated temperatures and decreased salinities. Eualaria fistulosa spores and gametophytes were the most negatively impacted, compared to the more widely distributed N. luetkeana and S. latissima. These results suggest that N. luetkeana and S. latissima are more likely to outperform E. fistulosa under projected conditions. By exploring how both early and late life-history stages of several key kelp species are impacted by dual stressors, this research enhances our understanding of how these species and their associated macroalgal communities will respond to projected changes in SST and salinity.
    • Effects of variable maternal diet conditions on the reproductive success and development of the California sea cucumber (Parastichopus californicus)

      Regula-Whitefield, Charlotte Marie; Hardy, Sarah Mincks; Oliveira, Alexandra; Iken, Katrin; Gradinger, Rolf; Hervey, H. Rodger (2016-12)
      Anthropogenic and natural climate change is altering the biology and ecology of marine organisms, which can be reflected in the supply of primary production that provides food for consumers. Primary producers differ in their biochemical composition, and marine food webs are thus based on specific combinations of producers that provide key nutrients such as dietary fatty acids (FA). Some FA cannot be synthesized by marine invertebrates, and must be acquired directly from diets. Reproductive processes in marine invertebrates are often timed to correspond with seasonal patterns in primary production, such that dietary FA and other nutrients can be partitioned to eggs to provide energy for cell division and biomolecules needed for membrane development. My dissertation investigates the consequences of changing patterns in primary production by examining the effects of maternal diet on reproductive fitness of a deposit feeder, and provides information to support the management and continued captive culturing of the commercially harvested Parastichopus californicus (California sea cucumbers). In chapter 1, I describe a novel live-spawning method and quantify basic reproductive parameters for P. californicus. Peak spawning in the Southeast AK population was about two months earlier and three times smaller than previously observed in British Columbia, Canada. Live-spawned captive females produced more viable eggs and strip-spawned females produced higher fecundity rates. These findings are relevant for the management of commercially harvested populations of P. californicus because they more accurately define spawning seasons, and provide a reliable method to spawn captive animals for further aquaculture development. In chapter 2, I present the results of feeding experiments that explore the effects of two mono-specific algal feeds with different FA profiles on female reproductive output and pre-feeding larval fitness. Females fed with the green alga Tetraselmis sp. had higher fecundity, but there was reduced larval survival relative to females that were fed the diatom Thalassiosira sp. Similar rates of larval development were recorded in both feed treatments. Significant differences were observed in the abundance of FA 20:5ɷ3 (EPA), 22:3ɷ6 (DHA), 12:0, 16:0, and 18:0 FAs in eggs and female gonads between the two feed treatments. In chapter 3, I used field collections in Southeast AK to assess temporal patterns feeding behavior and diet, and examined tissue-specific patterns in total lipid and FA storage and utilization, in in situ populations of P. californicus. All tissue ratios (percent of each tissue relative to the total body mass) varied significantly among collection dates. Tissue and gut content total lipid content also varied significantly among collection dates, except for muscle tissue. Shell debris and terrestrial debris were abundant in all guts regardless of collection date. FA composition differed significantly among females with different gonad maturation periods in skin, viscera, and gonads, suggesting the use of lipids stored in skin and viscera for gonad development. These results further the understanding of dietary factors affecting reproductive fitness in deposit feeders by demonstrating the importance of diet and lipid storage to gonad development.
    • The effects of water temperature on the seasonal distribution and growth of walleye pollock, Theragra chalcogramma (Pallas), in the southeast Bering Sea

      Chen, Lih-Feng (1983-05)
      The distribution and growth of walleye pollock, Theragva ohalaogvamna (Pallas), were studied in relation to bottom water temperatures, in an area between latitude 54°30'N and 57°30'N and longitude 160°W and 170°W, from the data collected from 1976 to 1980. The annual variations of bottom temperature distribution, including mean temperature, are described. It is found that temperature boundaries regulate spawning aggregation areas and feeding distribution of adult pollock. Young pollock were distributed in a wider temperature range and revealed a clearer feeding migration pattern than the adults. The weight growth for walleye pollock aged 2 to 4 was determined. The growth rate varied with age, sex and year. The relative growth rate was related to the initial weight of the fish and the mean temperature. Additional seasonal variations in the length-weight relationship and condition factor were observed.
    • Endocrine And Immune Profiles Of Immature Pinnipeds

      Keogh, Mandy Jean; Atkinson, Shannon; Castellini, Michael; Hellman, Tuula; Ortiz, Rudy; Runstadler, Jonathan (2011)
      There is increasing interest in assessing the health of individuals and populations of pinnipeds found in the North Pacific, primarily due to population declines leading to conservation concerns. This study assessed the "health" of animals by quantifying hormones associated with fat mass (leptin), lipid and water metabolism (cortisol and aldosterone), and growth and metabolism (thyroxine and triiodothyronine) as well as circulating total and differential leukocyte counts and in vitro proliferation of peripheral blood mononuclear cells (PBMC). Body mass and condition are influenced by an individual's disease and nutritional state. Glucocorticoids are known to affect the immune system and may be stimulated by a multitude of factors. I hypothesized that age or body mass would influence leukocyte counts, PBMC proliferation, and hormone concentrations in Steller sea lion (Eumetopias jubatus) pups and that the response of cortisol to an acute stressor would impact immune parameters in juvenile harbor seals (Phoca vitulina ). Further, given the inherent requirements of disturbance and animal handling necessary for sampling pinnipeds, the impact of these activities on endocrine and immune profiles was assessed. Total white blood cell (WBC) counts, neutrophil counts and T cell proliferation decreased with increasing age in Steller sea lion pups. However, no relationship between body condition index and circulating concentration of hormones quantified was detected. Circulating concentrations of cortisol, thyroxine, and triiodothyronine were influenced by the rookery disturbance. However, the variation attributed to the disturbance was low and did not alter total or differential WBC counts or in vitro proliferation of PBMC. In harbor seals, cortisol and aldosterone concentrations increased following an acute stressor which resulted in a stress leukogram. Total WBC decreased driven primarily by the decrease in neutrophil counts with simultaneous increase in lymphocytes leading to an overall decrease in neutrophil to lymphocyte ratio. These findings highlight the endocrine system's influence on the immune system in immature pinnipeds.
    • Energetics of arctic Alaskan fishes: carbon isotope evidence

      Ziemann, Paul J. (1986-12)
      The natural abundance of carbon isotopes were used to investigate the energy requirements of arctic aquatic consumer organisms. A mathematical model was developed that describes the relationship between the rate of consumer isotope turnover rates of growth and metabolism, and the utility of the model for calculating energy requirements from seasonal changes in consumer isotopic composition was demonstrated in laboratory experiments and with field data. The energy requirements of anadromous fishes, which were the major consumers studied, could not be determined using the isotopic data. Instead, the requirements were calculated using biochemical data and rates of growth and oxygen consumption, and were about 2.6-6.0 kcal day⁻¹ in the summer and 0.4-1.2 kcal day⁻¹ in the winter. Seasonal changes in lipid and protein contents indicate that anadromous fishes cannot find enough food during the winter to supply their energy requirements, and that about 50% of the energy needed comes from the metabolism of tissues accumulated during the summer. The relative importances of marine and freshwater food webs in supplying the energy requirements were determined by comparing the seasonal isotopic components of anadromous fishes to the isotopic compositions of fish that are permanent residents in each environment. It appears that anadromous fishes that overwinter in the Coleville River (the largest river on the Alaska North Slope) depend almost entirely on the marine environment for their energy, whereas those that overwinter in Canada's Mackenzie River rely on both marine and freshwater habitats.
    • Environmental controls of fish growth in the southeast Bering Sea

      Palmer, Michael Collins (2003-08)
      Environmental controls of fish growth in the Bering Sea were investigated by examining growth increments and length-at-age. A sea ice-initiated conceptual model of growth that differentiates between food and water temperature controls was proposed. The timing of ice retreat in the region was hypothesized to control food availability by influencing the fate of primary production and inversely affecting prey availability in pelagic and benthic environments. The extent and persistence of ice coverage was hypothesized to influence shelf water temperatures through' cold pool' development. Utility of the conceptual model was assessed through regression and correlation analyses of the growth of two representative pelagic feeding species, walleye pollock and Pacific herring, and two benthic feeders, yellowfin sole and rock sole. The usefulness of herring and rock sole as indicator species of their respective feeding guilds is lessened due to feeding location and diet breadth, respectively. Food availability was shown to be the primary control of fish growth as evidenced by the growth model results of pollock and yellowfin sole and inverse size-at-age time series of these two species. The ecosystem implications of differential fish growth were assessed through investigation of the relationship of growth to condition factor and recruitment.
    • Estimates of primary production sources to Arctic bivalves using amino acid stable carbon isotope fingerprinting

      Rowe, Audrey G.; Wooller, Matthew; Iken, Katrin; O'Brien, Diane (2018-12)
      Benthic invertebrates are a crucial trophic link in Arctic marine food webs. However, estimates of the contribution of primary production sources sustaining these organisms are not well characterized. Potential sources could include sinking particulate organic matter from sea ice algae and phytoplankton, terrestrial organic matter eroded from the coastal environment, macroalgal material, or microbial organic matter. Proportions of these sources could also be significantly altered in the future as a result of environmental change. We measured the stable carbon isotope values of essential amino acids in muscle tissue from two common bivalve genera (Macoma spp. and Astarte spp.) collected in Hanna Shoal in the northeastern Chukchi Sea, considered an Arctic benthic hotspot. We used stable isotope mixing models in R (simmr) to compare the stable carbon isotope amino acid fingerprints of the bivalves to a suite of amino acid source endmembers, including marine phytoplankton, brown and red macroalgae, bacteria, and terrestrial plants, to estimate the proportional contributions of primary production sources to the bivalve species from Hanna Shoal. The models revealed relatively high contributions of essential amino acids from phytoplankton and bacteria averaged across both species in the region as a whole. We also examined whether stable carbon isotope fingerprints could be measured from essential amino acids preserved in bivalve shells, which could then allow proportional contributions of food sources to be estimated from ancient bivalve shells, allowing source estimates to be extended back in time. To investigate this, we measured the stable carbon isotope values of essential amino acids in a suite of paired modern bivalve shells and muscle from Macoma calcarea from the Chukchi Sea. These analyses revealed a correspondence between the fingerprints and mixing model estimates of the dominant primary production source of essential amino acids derived from analyses of these two tissue types. Our findings indicate that stable carbon isotope amino acid fingerprinting of marine bivalves can be used to examine dominant organic matter sources in the Arctic marine benthos in recent years as well as in deeper time.
    • Estimating ¹³C and ¹⁵N turnover rates in the Arctic amphipod Onisimus litoralis: implications for analysing the transfer of sea ice production to under-ice fauna

      Nielson, Mette R. (2006-12)
      The Arctic amphipod Onisimus litoralis migrates from the seafloor to the sea ice to graze on ice algae, a rich food source during the Arctic spring, resulting in complex trophic dynamics. I assessed the effect of temperature and season on the rate of change in stable isotopic composition of amphipods by simulating a diet switch in the laboratory using amphipods collected near Barrow, Alaska in spring and autumn 2004. Additionally, the proportional contributions of food sources to the amphipods' diet in the field were estimated. Isotopic change occurred faster in spring with half-lives of 13.9 (1°C) and 18.7 (4°C) days for carbon and 22.4 days for nitrogen compared to autumn rates of 77 (carbon) and 115 days (nitrogen). Temperature did not have a significant effect on turnover. Change occurred primarily through metabolic turnover (versus growth-related dilution) and was responsible for 84-89% of the change in carbon and 67-77% of the change in nitrogen in both seasons. A two-source mixing model estimated that ice-derived biota contributed 59 (±17)% to the amphipods' diet in May. These data show that the rate of isotopic change can vary temporally for a single species, highlighting the importance of experimental work for interpreting stable isotope field-data.
    • Evaluation of prey composition and nutritional value of diets of free-ranging harbor seals (Phoca vitulina) from Tugidak Island

      Geiger, Gretchen L.; Atkinson, Shannon; Carpenter, James; Horstmann-Dehn, Larissa; Wynne, Kate (2012-12)
      Changes in climate can cause shifts in ecosystem structure that can affect quantity or quality of prey available to predator populations. Due to sex or age-specific behaviors of predators, certain classes within a population may be more severely impacted by changes in their diet. This study evaluated prey composition and nutritional value of summer diets of harbor seals (Phoca vitulina richardii) from Tugidak Island, Alaska from 2001-2009. The MIXIT-WIN program was used to estimate the nutritional value of average harbor seal diets. Changes in relative abundance of certain prey species were correlated to sea surface temperature anomalies. Despite changes in prey composition, the nutritional value of the average harbor seal diet did not change. Fecal corticosteroid metabolite profiles were analyzed to identify age and sex of individual harbor seals from scats. Profiles obtained from a known adult male harbor seal could be differentiated from those of known adult female and juvenile male seals. Similar profiles were observed in unknown age and sex samples. Even though diet diversity differed between these groups, the nutritional quality of consumed diets was not significantly different. Tugidak Island harbor seals have flexible diets allowing them to capitalize on available prey to maintain their nutritional intake.
    • An examination of hydrography and sea level variability in the Gulf of Alaska

      Kelly, James Bruce; Weingartner, Thomas; Simmons, Harper; Kowalik, Zygmunt (2015-05)
      This thesis summarizes a detailed analysis of Seward sea level (SSL) in the Gulf of Alaska (GOA) and hydrography at oceanographic station GAK1 along the oceanographic monitoring line outside of Resurrection Bay, Alaska. SSL variability was examined with respect to forcing by tides, sea level pressure (SLP), wind, the steric contribution due to water column variations in temperature and salinity, and several climatic indices. In addition, multi-decadal trends in sea level and hydrography were also examined. The period of analysis spans 1970 -2010. Tidal motion (periods < 1day), account for ~97% of the total sea level (SL) variance while SLP variations, induced by the inverted barometer effect, account for ~2% of the total variance. After removing these influences, along-shore wind stress and sea level are highly coherent for the 2 - 60 day subtidal period range and account for ~40 - 50% of the SSL variance over these timescales. The steric contribution, based on the geopotential height referenced to 200 m (GH200), is also coherent with SSL, but it only accounts for ~10% of the SSL variance at these timescales. The along-shore wind stress-SSL coherence varies seasonally and is greatest in winter when winds are strongest and smaller in summer when wind variability is reduced. The annual cycle in SSL is coherent and in-phase with GH200. The latter is primarily controlled by the annual cycle in GOA coastal freshwater discharge and its effect on coastal salinities. SSL variations are also significantly correlated with the Pacific Decadal Oscillation (PDO) and the Southern Oscillation Index (SOI). Over the 40-year record examined here SSL shows a decreasing trend due to continental rebound. There are also statistically significant linear long-term trends in temperature and salinity as measured at GAK1. These trends indicate that the upper 100 m is warming at ~0.20 oC decade-1 and at 0.15 oC decade-1 between 100 - 200 m. Surface salinities are decreasing at 0.15 decade-1, while salinities between 100 and 200 m are increasing by 0.025 decade-1. The surface salinity trends are consistent with an increase in coastal freshwater discharge due to increased glacial ablation and increased precipitation. In aggregate, these trends indicate that the GOA shelf has become more stratified over the past 40 years.
    • Factors affecting estuarine populations of Nereocystis luetkeana in Kachemak Bay, Alaska

      Chenelot, Héloïse Anne Claude (2003-12)
      Nereocystis luetkeana forms extensive kelp beds in Kachemak Bay, Alaska. Salinity and turbidity gradients apparently regulate kelp bed distribution throughout this estuary. The beds are large at the entrance of the bay, only solitary stands occur in the inner bay, and no kelp is found at the head of the bay. The role of salinity and turbidity on Nereocystis sporophyte growth was investigated by performing reciprocal transplants among three beds along the bay axis and regularly measuring stipe growth. The effects of salinity and light on spores were studied in the laboratory by recording sinking tendency, settlement success, germination success, and germ tube length under different salinity and light levels. Grazing effects of Lacuna vincta impacted the survival of Nereocystis transplants in-situ and on plants of different age classes in the laboratory. Overall, this study suggests a possible negative estuarine effect on sporophytes transplanted from the outer to the inner bay and on certain aspects of spore development. Herbivory pressure had significant localized effects on Nereocystis survival and was most pronounced on juvenile plants. The dynamics of Nereocystis kelp beds in Kachemak Bay results from large-scale environmental factors and local-scale biological processes.
    • Factors influencing zooplankton populations in Alaskan sockeye salmon (Oncorhynchus nerka) nursery lakes: insights from limnological and paleolimnological analyses

      Sweetman, Jon N.; Finney, Bruce; Barry, Ronald; Hughes, Nicholas (2001-08)
      The relative importance of sockeye salmon, invertebrate predators, and other environmental factors in structuring the size and abundance of zooplankton populations was examined in a series of 23 lakes from southern Alaska. Zooplankton abundance was strongly related to sockeye density, along with nutrient availability and alkalinity. The mean size of Bosmina longirostris, the dominant herbivorous cladoceran, was positively correlated with the abundance of the predatory copepod, Cyclops columbianus. Changes in the size and abundance of Bosmina remains over the past 300-500 years were then determined for sediments from two lakes on Kodiak Island, Alaska. The zooplankton communities showed varying responses to past changes in salmon populations, resulting from relative changes in the magnitude of adult salmon-derived nutrient loading and in predation pressure from juvenile sockeye and cyclopoid copepods. Knowledge of how various factors impact zooplankton can have important implications for the effective management of sockeye within these lake systems.
    • Fatty acid profiles of Alaskan Arctic forage fishes: evidence of regional and temporal variation

      Dissen, Julia; Hardy, Sarah; Horstmann-Dehn, Lara; Oliveira, Alexandra (2015-08)
      Fatty acids, the main components of lipids, are crucial for energy storage and other physiological functions in animals and plants. Dietary fatty acids are incorporated and conserved in consumer tissues in predictable patterns and can be analyzed in animal tissues to determine the composition of an individual's diet. This study measured the variation in fatty acid profiles of three abundant Arctic forage fish species, Arctic Cod (Boreogadus saida), Canadian Eelpout (Lycodes polaris), and Longear Eelpout (Lycodes seminudus) across multiple years (2010-2013) and geographic locations (Beaufort and Chukchi seas). These fishes are important prey items of marine mammals, sea birds, and predatory fishes, and as such they serve as a critical trophic step connecting lower trophic-level production to higher level predators. Analyzing forage fish fatty acid profiles across multiple years and geographic locations can provide insight into system-level trends in lipid transfer through the Arctic ecosystem. Fatty acid profiles differed among species, with Arctic Cod having higher concentrations of pelagic zooplankton indicator fatty acids, and Eelpout species containing higher concentrations of indicators for benthic prey. While the two Eelpout species displayed major overlap in fatty acid profiles, differences in individual fatty acids may represent niche separation between Canadian and Longear Eelpout in the Beaufort Sea. In addition to variation between species, fatty acid profiles also differed in Arctic Cod between the Beaufort and Chukchi seas, and among collection years. High lipid content and energy-rich fatty acid classes observed in Chukchi Sea Arctic Cod relative to the Beaufort Sea Arctic Cod may indicate favorable feeding conditions in this region over the years sampled, and high energy density of Arctic Cod as prey. Despite the within-species variation observed, the results of this study suggest that Alaskan Arctic forage fish with different foraging ecology can be distinguished based on fatty acid profile, which could be useful in studies that use fatty acid data to characterize diets of top predators.