RSS 1.0Marine Sciences
Recent Submissions
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Exploring the North American Arctic benthos: community structure and oil degradation potential of sediment bacteria and archaeaThe Chukchi and Beaufort seas benthic habitats are home to a multitude of ecologically and commercially important organisms that are subject to ongoing environmental changes, including the impacts of climate change and increased exposure to contaminants. Benthic bacteria and archaea can be considered biogeochemical engineers. They play a major role in organic matter (OM) degradation and nutrient cycling and their community structure can reflect changes in environmental conditions such as OM composition and quantity, nutrient availability, redox conditions, and natural/anthropogenic contaminants (e.g. petroleum hydrocarbons). Yet, sediment microbial communities have rarely been examined in these marginal seas of North American Arctic. In this dissertation, I characterized marine sediment microbial communities along environmental gradients in the Beaufort (Chapter 2) and Chukchi seas (Chapter 3) and assess Arctic benthic microbial community response to oil exposure (Chapter 4). I assessed diversity, community structure, and environmental correlates of prokaryotic communities via 16S rRNA amplicon sequencing in surface sediments (upper 1 cm) from the Northern Bering Sea to the Amundsen Gulf in the southern Beaufort Sea. On a broad spatial scale encompassing the whole study area, I observed three distinct microbial assemblages. One assemblage was characteristic of the Northern Bering-Chukchi seas shelf, and two distinguished nearshore and offshore sediments in the Beaufort Sea. Within the Beaufort Sea, four assemblages were identified, reflecting habitat heterogeneity with respect to OM loading, water depth, and nearshore/riverine input, including a major influence of the Mackenzie River. Two assemblages were distinguished within the Bering-Chukchi region, including one representative of suboxic sediments and one suggesting influence of phytodetrital OM input as evidenced by the abundance of diatom/particle-associated microbes. These two assemblages may also reflect differences between local versus advective OM inputs. Incubation experiments exposing Arctic marine sediments to fresh and weathered crude oil under anaerobic and aerobic conditions were performed to assess oil biodegradation potential and identify putative oil-degrading microbes in the benthos. Molecular analyses revealed that significant community shifts occurred in the oiled treatments, with distinct communities emerging following exposure to fresh versus weathered oil, and in oxic versus anoxic conditions. The work presented here constitutes the first large-scale survey of benthic microbes in this region of the North American Arctic, including their response to petroleum contamination, generating valuable baseline data for the changes to come.
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Seaweeds across ecosystem boundaries: from habitat formation to harvest implicationsThis dissertation broadly investigates the response of wild stock seaweeds to harvesting, and their role as biogenic habitat formers when cast ashore. Seaweeds are important primary producers and foundation species that maintain their functional roles across coastal ecosystem boundaries. Climate-driven loss of seaweed biomass, including that of kelp forests, is exacerbated by other human-related activities that directly impact their persistence, such as overharvesting. Attached rockweeds and kelps are commonly harvested for food, while diverse assemblages of beach-cast seaweed wrack are collected for fertilizer. The importance of wrack habitat in Alaska has not been extensively explored, especially in regions where there is a growing interest in harvesting by coastal communities. This research explores precautionary approaches to lessen wild stock seaweed decline in the face of increased harvest interests by: 1) characterizing information on reproductive timing, standing crop, and regrowth potential of attached populations; 2) investigating reproductive viability of seaweed wrack and identifying how landscape variables influence wrack distribution through paired on-the-ground and aerial surveys; and 3) characterizing wrack-associated macrofaunal communities and determining successional states in aging wrack. Regrowth following harvest of attached focal seaweeds (i.e., Fucus distichus, Saccharina latissima, and Nereocystis luetkeana) was generally low after two months, but the amount of biomass after four- and six-months post-harvest was more comparable to non-harvested areas. Depending on the species (e.g., F. distichus), attached individuals that became reproductive at larger sizes were associated with lower density and lower biomass areas with slower recovery. Differences in diversity and composition of wrack were correlated with coastline (substrate type, slope, and exposure) and adjacent watershed characteristics (percent glacial cover and range in seawater salinity). On-the-ground and drone-based surveys of beach-cast wrack both revealed seasonal patterns of patchy (spring) and continuous (summer) distribution. Macroinvertebrate community diversity was positively correlated with seaweed biomass and tidal height of the wrack line. Furthermore, succession experiments revealed that aged wrack harbored diverse and changing macroinvertebrate communities over time, with decomposers being early colonizers, and predators arriving later. Altogether, the findings of this research offer key information to developing sustainable harvest regulations in Alaska, as human use of seaweed increases.
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Compound-specific stable isotopes of amino acids reveal the influence of trophic level and primary production sources on mercury concentrations in fishes from the Aleutian Islands, AlaskaTotal mercury (THg) concentrations exceed thresholds of concern in some Steller sea lion (Eumetopias jubatus; SSL) tissues from certain portions of the Aleutian Islands, Alaska. Here, compound-specific stable isotope analyses (CSIA) of carbon in essential amino acids ([delta]¹³CEAA values) and nitrogen in AAs ([delta]¹⁵NAA values) in fish muscle tissue was applied to quantify the proportional contributions of primary production sources and trophic positions of eight prey species (n = 474 total) that are part of SSL diets. Previous THg analyses of fish muscle, coupled with additional monomethylmercury (MMHg) analyses of a subset of samples, substantiated previous findings that fishes from the west of Amchitka Pass, a discrete oceanographic boundary of the Aleutian Archipelago, have higher muscle THg concentrations relative to fishes from east of the pass. All fish muscle samples were analyzed separately for, both, CSIA-AA of carbon and nitrogen. The [delta]¹³CEAA values in fish muscle demonstrated that although most fishes obtained their EAAs primarily from algae, some species varied in the extent to which they relied on this primary production source. Certain [delta]¹⁵NAA values of the same fish samples indicated that trophic positions of fishes were higher from the west relative to the east of the pass for some species. Total Hg was positively correlated with bulk [delta]¹⁵N values, [delta]¹⁵N values of glutamic acid ([delta]¹⁵NGlu), and trophic positions. However, only trophic magnification slopes using [delta]¹⁵NGlu values indicated a higher rate of Hg biomagnification to the west of Amchitka Pass. Broad and species-level multiple linear regression models revealed that trophic position was the most important driver of fish muscle THg with a smaller amount of variation explained by other parameters, such as proportional contributions of primary production sources, fish body condition, and catch location. Collectively, results indicate that differences in fish trophic positions were the most consistent determinants of the higher fish THg concentrations to the west of Amchitka Pass. However, a higher rate of THg biomagnification to the west of Amchitka Pass may also play a role in the regional differences in fish muscle THg.
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Drivers of functional ecology of the Alaskan Arctic epibenthosThis dissertation explored multiple facets of functional diversity for epibenthic invertebrate communities of Alaskan Arctic shelves. Functional diversity is the range of organismal traits within a community that determines ecosystem functioning. As a complement to taxonomic diversity, functional diversity reflects what species "do" as opposed to "who" they are, providing information on community-level ecosystem resilience and vulnerability. The Alaskan Arctic marine system is presently changing at an unprecedented rate, which impacts the biomass-rich benthos that is of great importance to upper trophic level fishes, birds, and marine mammals as a food source. In my first chapter, I tested the Biodiversity-Ecosystem-Functioning hypothesis that states ecosystem functioning increases with increasing diversity, using the functional composition of epibenthic communities on the Beaufort and Chukchi Sea shelves as case studies. Functional diversity generally followed taxonomic diversity patterns on both shelves; however, functional composition was more similar between the two shelf systems compared to taxonomic composition. Higher functional diversity on the Beaufort Sea shelf resulted from a more even distribution of functional traits, pointing to stronger resource partitioning and niche complementarity. This, in turn, suggests stronger maintenance of ecosystem function through more efficient nutrient cycling, energy turnover, and recovery from disturbances. In chapter 2, I applied the Community Assembly Theory that assumes species assemble in a non-random way due to a series of biotic and environmental filters using the same Chukchi and Beaufort seas epibenthic communities. Environmental conditions in the Chukchi Sea exerted a stronger environmental filter (i.e., stronger influence of cumulative environmental drivers) on epibenthic functional diversity, especially through gradients in temperature, depth, and mud, compared to weaker depth- and salinity-related filters in the Beaufort Sea. This suggests that the Beaufort Sea community may be less affected by climatic change compared to those in the Chukchi Sea. Strong environmental filtering in the Chukchi Sea can act as a barrier to invading taxa, who must possess a suite of functional traits that allows them to survive in the specific Arctic environment. Continued warming and declining sea ice are assumed to encourage poleward movements of boreal taxa, a process especially likely for taxa migrating from the Bering Sea into the Chukchi Sea. Thus, in the third chapter, I modeled future functional composition of epibenthic communities in the Northern Bering and Chukchi seas, based on past (2009-2019) and predicted environmental conditions under a warmer and fresher, "worst case" scenario for mid- and end of-century timeframes. All regions exhibited functional changes over time associated with specific shifts in trait composition in each region; however, the magnitude of these functional shifts varied among time periods. The rate of functional changes suggests that Northern Bering Sea and Chukchi Sea communities may have already undergone a major transformation during the past decade, with fewer shifts expected by the mid-century. This dissertation employed a new approach of using functional traits to examine Arctic epibenthic community function and stability in relation to environmental conditions. It created a much-needed benchmark to assess regions of ecosystem vulnerability and resilience in the Alaskan Arctic.
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Acute toxicity of copper to three species of pacific salmon in water with low hardness and low dissolved organic carbonDespite a history of investigation, the toxicity of copper (Cu) to fishes remains difficult to predict due to the complex influential effects of water chemistry. Water hardness and dissolved organic carbon (DOC) concentrations can vary significantly within a watershed and also attenuate the toxicity of Cu to fishes. To account for location-specific water chemistry and predict Cu toxicity to aquatic organisms the United States Environmental Protection Agency (USEPA) endorses use of the biotic ligand model (BLM). Though the BLM has proven useful in many instances, it has performed inaccurately for waters low in hardness and DOC; this has raised questions regarding the model's applicability in certain regions. One such region is Alaska's Bristol Bay watershed, where tributaries low in hardness and DOC support an abundance of Pacific salmon (Oncorhynchus spp.) life. The Bristol Bay watershed also contains one of the largest Cu deposits on earth. Here, to determine empirical lethal Cu concentrations for water conditions relevant to the Bristol Bay watershed, and to assess the accuracy of the BLM in such waters, juvenile sockeye salmon (O. nerka), Chinook salmon (O. tshawytscha), and coho salmon (O. kisutch) were exposed to Cu in low-hardness (5.6-13.7 mg/L) and low-DOC (0.4-2.7 mg/L) water during 96 h flow-through bioassays. Juveniles were used to assess toxicity at a known Cu-sensitive life stage. The experimentally determined acute median lethal concentrations (LC50s) were 35.2 µg Cu/L (95% confidence interval [CI]: 32.3, 38.1) for sockeye salmon, 23.9 µg Cu/L (95% CI: 20.3, 27.4) for Chinook salmon, and 6.3 µg Cu/L (95% CI: 5.6, 7.0) for coho salmon. The BLM consistently under-predicted LC50s; predictions were 62.6 µg Cu/L for sockeye salmon, 35.4 µg Cu/L for Chinook salmon, and 15.1 µg Cu/L for coho salmon. These discrepancies demonstrate that the BLM is inaccurate for waters with low hardness and DOC and that currently assessed levels of risk of Cu to salmon are incorrect. These findings reveal a need for further calibration of the BLM for use in areas like the Bristol Bay watershed and provide information necessary to accurately assess Cu toxicity to three important species of Pacific salmon.
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Species distribution modeling of northern sea otters (Enhydra lutris kenyoni) in a data-limited ecosystemSpecies distribution models are used to map and predict geographic distributions of animals based on environmental covariates. However, species distribution models often require high resolution habitat data and time-series data on animal locations. In data-limited regions with little animal survey data or habitat information, modeling is more challenging and often ignores important environmental attributes. For sea otters (Enhydra lutris), a federally protected keystone species with variable population trends across their range, predictive modeling of distributions has been successfully conducted in areas with an abundance of sea otter and habitat data. Here, we used open-access data across a single time step and leveraged a presence-only model, Maximum Entropy (MaxEnt), to investigate subtidal habitat associations (substrate and algal cover, bathymetry, and rugosity) of northern sea otters (E. lutris kenyoni) in a data-limited ecosystem, Kachemak Bay, Alaska. These habitat associations corroborated previous findings regarding the importance of bathymetry and understory kelp as predictors of sea otter presence. Novel associations were detected, as filamentous algae and shell litter were positively and negatively associated with sea otter presence, respectively. This study provides a quantitative framework for conducting species distribution modeling with limited temporal and spatial animal distribution and abundance data and utilized drop camera information as a novel approach to better understand habitat requirements of a stable sea otter population.
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Marine and not terrestrial resources support nearshore food webs across a gradient of glacial watersheds in the northern Gulf of AlaskaEstuaries are among the most productive ecosystems on Earth, yet are especially at risk in high-latitude regions due to climate-driven effects on the connected terrestrial and marine realms. Warming in these regions exceeds the global average and is a major cause of the rapid melting of glaciers. As a result, the timing and magnitude of freshwater discharge into estuaries are subject to increase during the peak in glacial meltwater, ultimately affecting the riverine flux of nutrients and organic matter (OM) from the land to coastal environments. Intertidal communities near the outflow of rivers often rely on supplementing local (marine) food sources with allochthonous (terrestrial) subsidies, despite the fact that terrestrial OM can be problematic for marine consumers to assimilate. We investigated if terrestrial matter subsidizes nearshore food webs in northern Gulf of Alaska watersheds, and if the relative proportion of terrestrial versus marine OM supporting these food webs differed with watershed glaciation characteristics and with seasonal glacial discharge regimes. We employed a Bayesian stable isotope mixing model to determine the contribution of marine (phytoplankton, particulate OM, macroalgae) and terrestrial (vascular plant) sources to the diets of grazing/detritivore and filter/suspension-feeding coastal invertebrates at the outflows of watersheds of varying glacial influence and across various discharge periods. Additionally, we conducted a distance-based redundancy analysis to investigate the effects of watershed-characteristic sourcing and transport of terrestrial OM on nearshore consumer diets. The diets of both feeding groups were predominantly marine (>90%) and varied little among sites or glacial discharge periods. However, consumers were depleted in ¹³C isotopes with increasing glaciation; the significant watershed descriptors suggest that this change was more associated with discharge effects on marine primary production rather than consumption of terrestrial OM by the invertebrates. These results suggest that, while watershed exports may influence the stable isotope composition of OM sources, the diets of these feeding groups are mostly decoupled from terrestrial influence during the time of sampling. It is possible that marine OM availability in the study system is not limiting, and terrestrial OM subsidies in such productive systems are not needed to support nearshore food webs.
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Assessing annual nearshore carbonate chemistry trends in Alaska's marginal seasOne of the consequences of anthropogenic carbon emissions is ocean acidification (OA). As atmospheric concentrations of carbon dioxide (CO₂) continue to rise, oceanic absorption of CO₂ changes the balance of dissolved inorganic carbon species (DIC) in seawater and alters marine carbonate chemistry. OA is predicted to be more pronounced in high-latitude environments, highlighting the importance of characterizing nearshore carbonate chemistry in polar and subpolar habitats, such as Alaska's marginal seas. OA can have significant impacts on calcifying organisms (including pteropods, clams, mussels, and oysters), lowering the saturation of calcium carbonate minerals that are essential for shell formation in seawater. Despite the economic, subsistence, and cultural importance of vulnerable Alaskan marine biota, to date there are limited in situ data tracking the nearshore carbonate chemistry fluctuations of coastal Alaskan waters. To address this knowledge gap, this study's research goal is to compare, in highfrequency resolution, the seasonal carbonate chemistry fluctuations in two representative nearshore Alaskan ecosystems: Kaktovik Lagoon (Arctic Ocean) and Kachemak Bay (Gulf of Alaska). Moored sensors detected pH, temperature, salinity, and O₂ data to characterize which physicochemical variables have the greatest average contributions to site-specific pH variability across one year (September 2018-August 2019) in these two regions. Analyses of the annual time series from both regions revealed interregional disparities, especially related to seasonality, biotic activity, and physicochemical fluctuations in the seawater. The pH dynamics of the Kachemak Bay mooring sites demonstrated a strong connection to a seasonal biotic signal, specifically through the push-pull effect of photosynthesis and respiration on DIC. Kaktovik's pH dynamics suggested an interplay among salinity, biotic activity, and seasonal ice coverage. Both regions demonstrated high pH variability, with pH values shifting a maximum of 0.85 and 0.39 pH units over three hours in the two Kachemak Bay mooring sites, and 0.49 pH units over one hour in Kaktovik Lagoon. Forecast data for these regions project large declines in pH values over the coming century, with potentially deleterious impacts on local biota. Forecasted average monthly values based on 2018/2019 sampling reached pH < 7.5 for at least one month at all sites. Given the ocean change expectations for Alaskan marine environments, it is highly important that we establish seasonal carbonate chemistry baselines for Alaskan nearshore ecosystems.
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Benthic carbon demand and community structure across the Pacific Arctic continental shelvesHigh latitude continental shelves are experiencing rapid environmental change. The Pacific Arctic, which includes the northern Bering and southern Chukchi Sea continental shelves, is undergoing warming temperatures, reductions in sea ice, and changes to the marine ecosystem. Fieldwork was conducted across the northern Bering and southern Chukchi Sea continental shelves in June 2017 and June 2018 on the R/V Sikuliaq. The overall objective of this dissertation was to characterize benthic community structure, function, and carbon demand in the Pacific Arctic to serve as baselines for assessing impacts of environmental change. Spatial patterns of macrofauna and meiofauna were characterized, including abundances, biomass, composition, and vertical distribution within the sediment. Polychaete structure and function were assessed in detail by identifying polychaetes to family level and assigning each a functional guild based on feeding mode, motility, and feeding structures. Nematodes were identified to genus level and characterized by feeding type and life-history strategy. Clusters of polychaete functional guilds and nematode genera assemblages were similar and occupied different general regions within the Pacific Arctic: northern Bering Sea, Bering Strait, offshore Chukchi Sea, and coastal Chukchi Sea. These polychaete and nematode assemblages were associated with different depositional and food environments, characterized by grain size and the amount and quality of sediment organic matter. In addition, metabolic and carbon demand of dominant macrofaunal were estimated based on oxygen consumption rates. Species-specific rates suggest that shifts in macrofaunal community composition in the region will impact benthic carbon demand. Overall, the research presented here provides critical baseline data for benthic community structure, function, and carbon demand in the Pacific Arctic and can be used to evaluate change and constrain region-specific ecosystem models, especially in the context of a rapidly changing environment.
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Environmental influence on size frequency distributions of the Pacific blue mussel (Mytilus trossulus) in two glacially inlfuenced estuariesThe Pacific blue mussel (Mytilus trossulus) is a foundation species in high-latitude intertidal and estuarine systems that can create complex habitats, provide sediment stability, serve as food for top predators, and act as connectors between the water column and the benthos. M. trossulus also makes an ideal model species to assess biological responses to environmental variability, as its size frequency distributions can be influenced by the environment in which it lives. Size frequency distributions can provide valuable information about ecological systems that are experiencing environmental change (e.g., increased global temperatures). M. trossulus populations in high latitude estuaries receive freshwater runoff from snow and glacial-fed rivers or can be under oceanic influence. These hydrographic conditions work together with local static environmental variables, such as substrate, fetch (potential for wave action), beach slope, distance to freshwater, and percent glaciation (glacial discharge) to influence recruitment, growth, and mortality of mussels. In 2019 and 2020, M. trossulus was collected from 15 intertidal sites in two Gulf of Alaska ecoregions with varying hydrographic conditions to determine if and how mussel size frequencies change over spatial and hydrographic scales, and whether any static environmental characteristics correlated with this variability. This study demonstrated that M. trossulus size frequencies were most comparable at sites with similar hydrographic conditions and grouped according to the ecoregion and year of collection. M. trossulus recruits (0-2 mm) were mostly seen at sites with higher fetch, while large mussels (> 20 mm) were mostly seen at more protected sites (low fetch) and in areas with more freshwater influence. Hydrographic conditions explained approximately 43% of the variation in M. trossulus size frequencies for both years, which was three times more than the variation explained by ecoregion and four times more than collection year. Fetch and distance to a freshwater source explained most of the variation in mussel size frequencies for both years, while substrate type was also important in 2019, and percent glaciation in 2020. M. trossulus recruitment was significantly different between 2019 and 2020, possibly resulting in the different static variable correlates between the two years. This study suggests that hydrographic conditions play an important role in structuring M. trossulus size frequencies, and that these differences also depended on environmental conditions.
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Characterization of reproductive cyclicity of sex steroids by fecal analysis in Steller sea lions (Eumetopias jubatus)"Steller sea lions (Eumetopias jubatus) have experienced a drastic population decline in the past several decades. Among hypotheses for the decline and failure of the population to recover is decreased reproductive success. Harsh environmental conditions within the species range and the large body size of the animals can limit sampling efforts to investigate these hypotheses. Three captive Steller sea lions were used as models to validate the use of fecal steroid analysis for this species. Their annual endocrine fluctuations were monitored over four years to gain a better understanding of their reproductive endocrinology and overcome sampling challenges typically associated with hormonal studies of large mammals. Radioimmunoassays (RIA) and enzyme immunoassays (EIA) reliably measured testosterone, total estrogens, and progesterone extracted from Steller sea lion feces. Lack of refrigeration for five days and freezing ( -20°C) for 8 weeks did not alter concentrations of fecal testosterone and total estrogens measured. The stability of fecal progesterone in the absence of cold storage was compromised by 4.5 days; however, it remained stable while frozen ( -20°C) for 8 weeks. Thus, for field research, there are two primary implications. Firstly, samples of freshly voided scat collected from rookeries and haulouts can reliably reflect hormone concentrations for <̲ 4.5 days and secondly, these samples can be stored for later analysis for at least 8 weeks. Long-term serial sampling demonstrated fecal progesterone may be more useful in providing information on reproductive function than fecal estrogens. Annual endocrine profiles suggest the females are seasonally monoestrus, supporting the general assumption for the species, and the male has a strong seasonal cycle in testosterone with maximum concentrations measured just prior to the natural breeding season. These data also suggest fecal testosterone reflects changes in testicular activity despite breeding status and proximity to females. Collectively, these data suggest this non-invasive endocrine monitoring technique has potential to provide a useful alternative method of sample collection"--Leaf iii
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The impact of sea kayak tourism and recreation on harbor seal behavior in Kenai Fjords National Park: integrating research with outreach, education, and tourism"Increasing numbers of sea kayakers in Kenai Fjords National Park, Alaska prompted a study to evaluate human disturbance on harbor seals. Harbor seal behavior recorded during the molt from 2004-2006 via remotely controlled cameras and direct field observations were used to evaluate effects of human activities. Behaviors of the seals observed in the presence and absence of kayakers/walkers were contrasted by method of collection, year, presence of humans, presence of a guide, and guide training. Results demonstrated that harbor seals abandoned the ice and were more alert when kayakers were present than when humans were absent. Harbor seals became progressively sensitive to the presence of walkers. Sea kayak guides were advised to observe seal behavior and minimize contact by avoiding areas with high concentrations of hauled-out seals. Educational training provided to sea kayak guides effectively reduced the impact of human disturbance on harbor seals"--Leaf iii
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Total serum immunoglobulin Y in Steller's eiders and a surrogate species as a marker of humoral immune status and viral response"Steller's eiders (Polysticta stelleri) and other sea duck species have undergone population declines in recent decades, and the causes for the declines remain largely unknown. As part of a study to investigate the role of disease in sea duck population declines, I further characterized Steller's eider humoral immunity by quantifying total serum immunoglobulin Y (IgY). Baseline values of total serum IgY were determined for a captive flock of Steller's eiders housed at the Alaska SeaLife Center using species-specific assays. There were no significant differences in total serum IgY between males and females or between seasons (molt and winter) for captive birds. For free-ranging Steller's eiders, mean total serum IgY was significantly higher during molt and mid-winter compared to captive baseline values, suggesting increased disease exposure. As a further investigation of the humoral immune response, experimental inoculations (low pathogenicity avian influenza and adenovirus) were conducted in mallards (Anas platyrhyncus) as a surrogate species. Quantification of total serum IgY from captive Steller's eiders provides a baseline for comparative studies of total serum IgY from free-ranging Steller's eiders. This study also provided first quantitative information about circulating IgY in free-ranging Steller's eiders"--Leaf iii
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Recent paleoenvironmental changes recorded in three non-anadromous lakes in Southwest Alaska: effects of climatic and vegetation dynamics on lake productivity"Paleolimnological investigations, landscape analyses, and repeat photographs were used to provide a long-term view (~150 yrs. BP to present) of nutrient dynamics and lake ecosystem change in southwest Alaska. Recent major changes in lake ecology and landscape are generally attributed to climate warming since the end of the Little Ice Age and to the recent warm phase of the Pacific Decadal Oscillation. Disturbances driven by climate, glacial retreat, and volcanism also contribute to changes in aquatic-driven processes. Sediment cores reveal a complex yet progressive set of changes that are expressed in the study lakes. Changes in the biogeochemical proxies began in the mid-19th to early-20th century, but major inflections occurred significantly later, most pronounced after 1950. Among these changes are increases in biogenic opal, and indicators of enhanced C and N cycling. These systems act as integrators of climatic, terrestrial, and aquatic processes without additions of marine-derived nutrient subsidies from spawning salmon and thus allow us to isolate and identify factors (e.g. productivity, spawning and rearing success of salmonids, or terrestrial nutrient inputs) important for interpreting sediment records in anadromous systems"--Leaf iii
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Quantifying diet to tissue isotopic (δ¹³C and δ¹⁵N) fractionation factors in captive spectacled eiders (Somateria fischeri): implications for nutrient allocation and foraging studies"The spectacled eider (Somateria fischeri) was listed as threatened under the Endangered Species Act in 1993, and potential threats to population recovery include changes in the marine prey abundance and availability. Therefore, development of diet assessment techniques has been listed as an eider recovery task. Stable isotopes have been used to evaluate foraging ecology and nutrient allocation to reproduction in birds. Application of this technique requires knowledge of how stable isotope signatures of animal tissues differ from their diet, referred to as isotopic fractionation, and these values can be determined experimentally using captive populations. I established stable isotopic fractionation factors for d¹³C and d¹⁵N from diet to egg components, down feathers, contour feathers, cellular blood, blood plasma, and fat of captive spectacled eiders. Sensitivity analyses indicate that choice of isotopic fractionation values from eggs of different species could considerably alter model conclusions. Therefore, I incorporated isotopic fractionation factors from spectacled eider eggs into two published sea duck nutrient allocation models that previously used these values from falcons (Falco spp.) to assess differences in model conclusions. Results from these studies provide further resources to understand foraging and nutrient transfer in eiders and may offer more accurate estimates for sea duck models"--Leaf iii
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Humpback whale (Megaptera novaeangliae) numbers and distribution on their summer feeding grounds of the Eastern Aleutian Islands"In summer, Humpback whales (Megaptera novaeangliae) of the North Pacific stock feed in Alaska's nearshore waters. My research focused on the Bering Sea between Unimak and Samalga Pass with the objectives: 1) Estimate the number of humpback whales using the study area from 2001 through 2006; 2) Determine to what extent humpback whales exhibit site fidelity; 3) Describe the distribution of humpback whales and determine if depth, slope, and chlorophyll-a can predict the humpback whale presence. To investigate the degree to which whales return to the Eastern Aleutian summer feeding ground, 1,985 whale photographs were collected and an identity matrix was created; Humpback whales exhibited a 22 percent return rate with 181 whales out of 802 total whales seen in more than one year during the six year study. Program MARK (Mark and recapture parameter estimation) was used to estimate the number of humpback whales utilizing this area, resulting in an estimate of 500 to 1600 animals. Logistic regression and random forest classification determined that depth and longitude are significant predictors of humpback whale presence. These results support other studies in the Eastern Aleutians and North Pacific and further confirm the importance of oceanographic and biological features in concentrating prey and predicting humpback whale distribution"--Leaf iii
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Larval transport of brachyuran crab in Kachemak Bay, Alaska"This study's primary goal was to understand the oceanographic effects on larval crab transport and distribution between an estuarine inner and more oceanic outer bay in the subarctic estuary of Kachemak Bay, Alaska. Plankton tows and hydrographic measurements (temperature and salinity) were taken along the boundary between the two bay parts from March - October on spring and neap tides. Summer water flow and in Kachemak Bay is predominantly freshwater-driven and density patterns vary inter-annually with the amount of freshwater supplied to the inner bay. Larvae of seven crab species occurred in a seasonal sequence and the crab larval assemblage was closely correlated to temperature in the upper 20 m. The influence of tidal forcing on larval transport was not clear even though most species exhibited peak abundances at spring tides. Larval distribution patterns across the inner/outer boundary indicated that Oregonia gracilis larvae may be transported into inner Kachemak Bay; however, late larval stages of the two commercially relevant species, Chionoecetes bairdi and Cancer magister, were never observed and may be exported from the inner estuary. These observations provide an important baseline for further studies to understand Kachemak Bay's role as a source or sink for larval crab"--Leaf iii
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Growth rates of juvenile Scolelepis squamata (Polychaeta: spionidae) from the Chukchi Sea fast ice"Arctic coastal fast ice supports high densities of sea ice algae, and is thermally stable at the ice-water interface at around the freezing point of sea water, providing a suitable environment for sympagic meiofauna feeding on the sea ice algae during spring months. Changes in water temperature due to seasonality and climate change may affect physiological processes of these organisms. We tested the hypothesis that juvenile growth rates of a common sympagic polychaete, Scolelepis squamata (Polychaeta: Spionidae), would be significantly faster at typical spring sea ice algal concentrations compared to concurrent phytoplankton concentrations and at open water summer versus winter temperatures. Juvenile S. squamata from fast ice off Barrow, Alaska were fed three algal concentrations at 0°C and 5°C, simulating ambient high sea ice algal concentrations, concurrent low phytoplankton concentrations and an intermediate concentration. Growth rates, calculated using a simple linear regression equation, were significantly higher (up to 225 times) at the highest algal concentration compared to the lowest in all experiments, showing sea ice to provide more beneficial food situation compared to the under-ice water column. Additionally, juveniles grew over five times faster at 5°C compared to those feeding at 0°C, forecasting faster juvenile growth as Arctic temperatures warm"--Leaf iii
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Hydrographic controls and seasonal variability on the carbonate system in the northern Gulf of AlaskaThe Northern Gulf of Alaska (GOA) supports a dynamic and economically viable marine ecosystem. One notable potential stressor to this ecosystem is ocean acidification (OA), a byproduct of the increased uptake of anthropogenic carbon dioxide (CO₂) by the ocean. Measurements of dissolved inorganic carbon (DIC) and total alkalinity (TA) were made along the continental shelf of the northern GOA and in Prince William Sound (PWS) and used to calculate seawater pH and the saturation state of aragonite Warp). Observations showed a high degree of seasonal variability in DIC concentrations in surface and bottom waters. TA was depleted relative to DIC due to the influence of glacial run off. Seasonally high rates of primary production lowered DIC concentrations causing an increase in pH and [omega]arg in the mixed layer. However, DIC concentrations increased in the bottom waters due to the remineralization of exported organic matter and the intrusion of high salinity water from offshore waters, which suppressed pH and caused [omega]arg to become undersaturated. Observations of GOA in 2009 showed a general seasonal cycle of the carbon parameters, while a regional downwelling anomaly observed during transects in 2008 captured the effect physical variability has on the carbonate system in this region.
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Influence of environmental attributes on intertidal community structure in glacial estuariesHigh-latitude coastal environments are experiencing dramatic changes due to climate warming. Increased glacier discharge rates modulate downstream environmental conditions in coastal watersheds. These fast-changing environments are predicted to influence the structure of nearshore marine communities. Here, rocky intertidal community structure, recruitment of key organisms, and environmental correlates were examined at nine watersheds in two regions (Kachemak Bay and Lynn Canal) that bookend the Gulf of Alaska, which were separated by approximately 1000km. Each watershed was part of a gradient in each of the regions that spanned 0-60% glacial coverage. Percent cover, biomass surveys, and recruitment of intertidal organisms, along with environmental monitoring of salinity, temperature, dissolved oxygen, river discharge, turbidity, and nutrient loading were completed from April - September 2019 in each watershed. Biological community structure and variance were analyzed by taxa and by ecological group (i.e., primary producer, filter feeder, omnivore, grazer, predator) and then in relation to the local environmental spatiotemporal profiles. In general, larger watersheds with more glacial coverage and river discharge resulted in higher cover of primary producers and less cover of filter feeders. This pattern was more apparent in the region with more oceanic influence as compared to the other region located within an inlet. In relation to specific environmental drivers, salinity was negatively correlated with primary producer cover (r = -0.52), but positively associated with barnacle cover (r = 0.40). Additionally, turbidity was positively correlated with primary producer biomass (r = 0.50), but negatively correlated with mussel cover (r = -0.30). In contrast, there was a positive relationship among mussel recruitment and discharge and turbidity. There was variability in within-ecological group response between regions that could be a response to local circulation and oceanic influences. Barnacles were the main filter feeder species driving patterns in the more saline region located close to the open ocean, while mussels drove patterns in the other less oceanic region. As glaciers recede, environmental conditions, such as salinity, will increase and turbidity will decrease, which may alter future intertidal community assemblages dominated by filter feeders.
