Recent Submissions

  • Benthic carbon demand and community structure across the Pacific Arctic continental shelves

    Charrier, Brittany Robinson; Mincks, Sarah; Danielson, Seth; Ingels, Jeroen; Kelly, Amanda; Thurber, Andrew (2022-04)
    High 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.
  • Environmental influence on size frequency distributions of the Pacific blue mussel (Mytilus trossulus) in two glacially inlfuenced estuaries

    Dowling, Amy; Konar, Brenda; Iken, Katrin; Horstmann, Lara (2021-12)
    The 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.
  • Characterization of reproductive cyclicity of sex steroids by fecal analysis in Steller sea lions (Eumetopias jubatus)

    Litz, Beate (2008-08)
    "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
  • The impact of sea kayak tourism and recreation on harbor seal behavior in Kenai Fjords National Park: integrating research with outreach, education, and tourism

    Jezierski, Caroline M.; Norcross, Brenda; Hoover-Miller, Anne; Wynne, Kate M.; Polasek, Lori (2009-12)
    "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
  • Total serum immunoglobulin Y in Steller's eiders and a surrogate species as a marker of humoral immune status and viral response

    Bozza, Maryann; Hollmen, Tuula; Hofmeister, Erik; Polasek, Lori (2009-12)
    "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
  • Recent paleoenvironmental changes recorded in three non-anadromous lakes in Southwest Alaska: effects of climatic and vegetation dynamics on lake productivity

    Cohn, Brian R.; Heiser, Patricia; Finney, Bruce; Whitledge, Terry; Wooller, Matthew (2009-05)
    "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
  • Quantifying diet to tissue isotopic (δ¹³C and δ¹⁵N) fractionation factors in captive spectacled eiders (Somateria fischeri): implications for nutrient allocation and foraging studies

    Federer, Rebekka; Hollmén, Tuula; Esler, Daniel; Wooller, Matthew (2009-08)
    "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
  • Humpback whale (Megaptera novaeangliae) numbers and distribution on their summer feeding grounds of the Eastern Aleutian Islands

    Riley, Heather; Hills, Sue; Straley, Jan; Matkin, Craig; Stockwell, Dean (2010-08)
    "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
  • Larval transport of brachyuran crab in Kachemak Bay, Alaska

    Murphy, Megan M.; Iken, Katrin; Eckert, Ginny; Pegau, Scott (2010-08)
    "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
  • Growth rates of juvenile Scolelepis squamata (Polychaeta: spionidae) from the Chukchi Sea fast ice

    McConnell, Brenna; Gradinger, Rolf; Iken, Katrin; Bluhm, Bodil (2010-08)
    "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
  • Hydrographic controls and seasonal variability on the carbonate system in the northern Gulf of Alaska

    Shake, Kristen L.; Mathis, Jeremy T.; VanLaningham, Sam; Weingartner, Thomas J. (2011-12)
    The 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.
  • Influence of environmental attributes on intertidal community structure in glacial estuaries

    McCabe, Mary K.; Konar, Brenda; Iken, Katrin; Kelley, Amanda (2021-05)
    High-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.
  • Sources and effects of strontium in waterfowl eggs

    Latty, Christopher J.; Hollmén, Tuula E.; Matz, Angela C.; Powell, Abby N.; Hobson, Keith A.; Adkison, Milo D. (2021-05)
    Strontium (Sr) may be a contaminant of concern for wild birds. Because of chemical similarities to calcium (Ca), Sr is readily incorporated into calcified tissues, such as eggshells. My objectives were to determine the potential drivers of both total and radio-Sr in the eggshells of waterfowl, and to assess the relationship between eggshell Sr and thickness. I collected eggs from sympatrically nesting waterfowl species in interior Alaska from 2011-2013. I measured total and radio-Sr in eggshells, environmental chemistry, and eggshell thickness. Local water chemistry explained much of the variation in eggshell Sr for canvasback (Aythya valisineria) and northern shoveler (Spatula clypeata), but not lesser scaup (Aythya affinis). Most of the remaining variation was associated with heterogeneity among eggs in the same nest (intra-clutch variance). General trends in eggshell Sr/Ca among species aligned with what would be expected had diet and/or endogenous reserve use affected eggshell chemistry. Results were similar for radio-Sr, with local water chemistry accounting for far less ⁹⁰Sr in the eggshells of lesser scaup, compared to the other species studied. At the site where water chemistry was stable, canvasback and northern shoveler eggshell thickness was not related to eggshell Sr, but lesser scaup eggshells with more Sr were thicker. At the site where water chemistry was variable, canvasback and northern shoveler eggshells with more Sr were thicker at low to intermediate concentrations, but this effect was moderated when the source of eggshell Sr appeared to be explained by the local environment. In contrast, lesser scaup eggshells with more Sr were consistently thicker, but only at higher concentrations. The different relationships between eggshell Sr and thickness across species, and interactions with apparent Sr sources, suggest the relationship between eggshell thickness and Sr is not a simple dose-dependence. My results show that for some species like lesser scaup, factors associated with the laying hen (e.g., diet or physiology) may have a larger impact on both eggshell total and radio-Sr, as well as how Sr interacts with eggshell quality, than the local environment.
  • Tracing carbon sources of southern Beaufort Sea and Chukchi Sea polar bears using stable isotope analyses

    Smith, Malia E.K.; Horstmann, Lara; Wooller, Matthew; Rode, Karyn (2020-12)
    The Southern Beaufort Sea (SBS) polar bear (Ursus maritimus) subpopulation has declined in response to sea ice loss, while the Chukchi Sea (CS) subpopulation appears stable. The substantial population decline in the SBS subpopulation in recent years is concurrent with increases in the proportion of polar bears coming on shore, and the duration they spend there. Both of these changes have been associated with the loss of access to their primary sea ice habitat, which is mainly used as a platform to hunt seals. The first objective of this study was to determine if the SBS and CS polar bear subpopulations could be distinguished based on stable isotope signatures (delta¹³C and delta¹⁵N values) of bone collagen. The second objective was to examine patterns in SBS polar bear trophic level and terrestrial carbon sources over a 65-year time period, as polar bears have increasingly used coastal environments. We analyzed 112 SBS and CS polar bear bones (predominantly mandibles) from 1954-2019 that had been archived at the University of Alaska Museum of the North, as well as bones from subsistence-harvested polar bears. In addition to delta¹³C and delta¹⁵N, samples from the SBS bears were analyzed for compound-specific stable carbon isotopes of amino acids (delta¹³CAA values). Another 50 bone collagen samples from terrestrial mammals and pinnipeds from northern Alaska were analyzed for delta¹³CAA values to provide a regional comparative dataset. Our study showed a significant difference in bulk delta¹³C (p<0.001) values, but not delta¹⁵N (p=0.654) values between the CS (-13.0‰±0.3‰ and 22.0‰±0.9‰, respectively) and the SBS bears (-14.7‰±1.3‰ and 22.2‰±1.0‰, respectively). We performed a logistic regression analysis (LR) using bulk delta¹³C and delta¹⁵N values of the polar bears to predict their placement into these two subpopulations. Using Icy Cape, AK as the geographical boundary, LR correctly placed polar bears in their respective subpopulations 82% of the time. Overall accuracy of placement changed to 84% when using the current geographical boundary at Utqiaġvik, AK. Bone collagen has a slow turnover rate, providing long-term, potentially life-long stable isotope signatures. Our findings could be used to determine the association of harvested polar bears to Alaska subpopulations, thus aiding in harvest quota management. The LR predicted samples collected from the Wainwright, AK region to be 58% CS and 42% SBS polar bears. This indicates that the area between Wainwright and Icy Cape is a polar bear mixing zone that includes bears from both subpopulations. Over the 65-year study period, two distinct groups of SBS polar bears were identified based on their delta¹³C values of the amino acid proline: a high delta¹³CPro group (1.8‰±2.3‰, n=45) and a low delta¹³CPro group (-15.7‰±1.9‰, n=26). The high proline polar bear group had delta¹³CPro values similar to those of Arctic brown bears (Ursus arctos; 0.4‰±1.6‰), while the low group had delta¹³CPro values similar to ice seals (-15.3‰±1.2‰). Among the available samples, there were more high proline/pelagic bears (n=17) after the 2007 sea ice minimum than high proline/coastal bears (n=12), which is opposite of what we expected. This study provides evidence that two distinct ecotypes in Southern Beaufort Sea polar bears, pelagic and coastal, have existed since at least the 1950's. Overall, our results represent a detailed isotopic view of the Alaskan polar bear subpopulations, demonstrating the possibility of distinguishing and categorizing individuals as either SBS or CS, while also highlighting the existence of two ecotypes in the SBS subpopulation.
  • Sea urchin ecology: effects of food-web modification, climate change, and community structure

    Weitzman, Benjamin P.; Esler, Daniel; Konar, Brenda H.; Hardy, Sarah M.; Johnson, Mark A.; Tinker, Martin T. (2020-08)
    Ecosystem structure and function of temperate rocky reef habitats are subject to change as a result of food-web modification, climate change, and changes in biological community interactions. Sea urchins are a global driver of change in nearshore marine habitats though their ability to heavily graze marine vegetation and force rocky reef ecosystems from kelp forest to sea urchin barren ground states. The Aleutian Archipelago in southwest Alaska provided an ideal natural laboratory to study sea urchin (Strongylocentrotus spp.) ecology following the functional loss of the keystone predator, the sea otter (Enhydra lutris) during the 1990s. The objectives of this dissertation were to 1) determine the important drivers of sea urchin demographics following the functional loss of their keystone predator; 2) determine how projected ocean warming and acidification may affect sea urchin physical condition; and 3) identify biological drivers of sea urchin recruitment in both kelp forest and barren ground habitats. To determine demographic drivers, I used a time series of benthic habitat, sea urchin demographic, and environmental data, dating back almost forty years. In the absence of sea otters, environmental conditions, specifically ocean temperatures, became more important to sea urchin demographics, but recruitment was the primary process affecting the resultant abundance and size class structure over time. To understand how predicted ocean warming and acidification could impact S. polyacanthus survival, growth, calcification, gonad development, and energy content, a 108-day laboratory experiment was conducted. This experiment determined that temperature caused a greater reduction in survival than acidification, and that projected changes in temperature and acidification will result in investment trade-offs between reproduction and maintenance or growth of somatic and calcified tissues. To determine how recruitment varied between kelp forest and sea urchin habitats, fine-scale surveys of benthic community structure found that specific taxa, and not overall community structure, correlated with sea urchin recruitment. Results from this dissertation will allow managers to make predictions about how sea urchin demography will change as a result of keystone predator loss and climate change and how that will affect nearshore community structure and function. Overall, my dissertation establishes likely pathways by which coastal habitats may change over time, in a system no longer under strong top-down control.
  • Trophic structure of rocky intertidal communities in contrasting high-latitude environments

    Siegert, Danielle; Iken, Katrin; Konar, Brenda; Lindeberg, Mandy (2020-08)
    Coastal ecosystems in high latitudes are increasingly impacted by glacial melt and river discharge due to climate change. One way to understand ecosystem responses to these stressors is assessing trophic relationships. The goal of this study was to better understand how hydrographic conditions influence trophic structure in high-latitude rocky intertidal systems. I compared the trophic structure of rocky intertidal assemblages in two regions in the northern Gulf of Alaska that comprise the same regional species pool but are hydrographically distinct, one glacially influenced and one primarily marine influenced. Common macroalgal and invertebrate taxa, as well as particulate organic matter (POM) were sampled at three rocky intertidal communities in each region in 2017 and 2018. Food web structure was compared using trophic metrics based on the distribution of shared taxa in isotopically-derived (delta¹³C and delta¹⁵N) trophic niche space. I found that trophic niche space in the glacially-influenced rocky intertidal system was larger, driven by larger ranges in both carbon and nitrogen stable isotope values. In particular, the lower delta¹³C values in Kamishak Bay suggest that an additional food source, most likely terrestrial organic material from glacial discharge, was incorporated into the food web. This supported the hypothesis that patterns in food web structure differed based on hydrographic influences to maintain overall stability. Isotopic evenness, i.e., the distribution of the shared taxa within trophic space, did not differ between the two regions. Macroalgae were overall a more important food source than POM in both regions, and even more so in the glacially-influenced region, where macroalgae may be an energetically beneficial food source compared to silt-laden glacial inputs. This study showed that common intertidal taxa have high tropic flexibility enabling them to respond to variable food sources under a variety of environmental conditions. As hypothesized, taxa in food webs occupying a larger trophic niche space engaged in more heterogeneous trophic pathways and used diverse resources depending on local environmental conditions, making these systems more stable to perturbations affecting a single resource. The common taxa of high-latitude rocky intertidal systems studied here are responding to current levels of glacial input with more diverse resource use, but it remains to be seen how well those systems are suited to maintain trophic stability with an expected increase in glacial stress from climate warming.
  • Defining genetic population structure and historical connectivity of snow crab (Chionoecetes opilio)

    Albrecht, Gregory T.; Hardy, Sarah M.; Lopez, J. Andres; Hundertmark, Kris J. (2011-08)
    The snow crab (Chionoecetes opilio) is a valuable commercial resource within the Bering Sea, as well as other areas in the North Pacific and Atlantic Oceans. Large populations are known to exist within the Chukchi and Beaufort Seas, including recently discovered commercial sized individuals (Beaufort). However, genetic connectivity throughout these regions has not been examined until now. Based on seven polymorphic microsatellite loci, relatively low population genetic structuring occurs throughout the Alaskan region (Gst = 0.001). This homogeneity is likely due to long-distance larval dispersal, adult migrations, and a possible recent population expansion following the last glacial maximum. Furthermore, meta-population analysis was conducted for Alaskan and Northwest Atlantic stocks. Although significant genetic divergence characterizes the West Greenland stock in relation to all other populations, low divergence (Gst = 0.005) was found between Atlantic Canada crabs and those from the Alaska region. Larval dispersal between regions is highly unlikely due to the transit distance. Therefore, low divergence is likely the result of a recent population expansion into the Northwest Atlantic <5000 years ago.
  • Kelp forests and barren grounds: phlorotannin production and holdfast community structure in the Aleutian dragon kelp, Eualaria fistulosa

    Schuster, Martin D.; Konar, Brenda; Iken, Katrin; Coyle, Kenneth (2012-12)
    The canopy forming kelp Eualaria fistulosa inhabits two organizational states throughout the Aleutian archipelago, kelp forests and barren grounds. Urchin abundance and behavior determines which state dominates in any given area. Sporophyll phlorotannin content and holdfast epibiont fauna were investigated at multiple islands along the Aleutian archipelago to determine how the organizational state affects the production of secondary metabolites and the taxon richness, abundance and biomass of holdfast communities. Barren ground sporophylls had higher phlorotannin content than kelp forest sporophylls, although grazing rates on sporophylls from each state did not differ during in situ grazing experiments. The taxon richness, abundance and biomass of holdfast communities were similar between kelp forests and barren grounds at all islands, although these communities varied among islands and were mostly driven by holdfast volume. These results suggest that physical differences such as light and nutrient availability in the kelp forest structure between organizational states may be responsible for differences in phlorotannin content, but that these differences are not reflected in the holdfast community structure. It appears that barren ground holdfast communities are remnants of a once forested area.
  • Organic matter sources on the Chukchi Sea shelf in a changing Arctic

    Zinkann, Ann-Christine; Iken, Katrin; Wooller, Matthew; Danielson, Seth; Leigh, Mary Beth; Gibson, Georgina (2020-05)
    Climate-change induced alterations of the organic matter flow from various primary production sources to the benthic system in the Arctic Chukchi Sea could have major implications on carbon cycling, sequestration, and benthic food web structure sustaining upper trophic levels. In particular, the role and contribution of terrestrial matter and bacterial matter could become more prominent, with increasing erosion and permafrost melt being discharged from land, and warming water temperatures raising bacterial metabolism. In this study, I used essential amino acid (EAA) specific stable isotope analysis to trace the proportional contributions of bacterial, phytoplankton, and terrestrial organic matter in sediments, as well as benthic invertebrates on the Chukchi Sea shelf. Across the upper 5 cm of sediments, most organic matter sources were equally distributed, except for a slight decrease with depth in phytoplankton EAA. Terrestrial sources contributed the majority of EAA (~76 %) in all sediment layers, suggesting a potential accumulation of this material due to slow degradation processes. These results indicate a well-mixed upper sediment horizon, possibly due to bioturbation activity by the abundant benthos. Experimental observations of increases in bacterial production, measured as phospholipid fatty acid (PLFA) production, at water temperatures 5 °C above ambient (0 °C) and under sufficient substrate conditions suggest that bacterial organic matter in sediments could become a greater organic matter source in the sediments of a future, warmer Arctic. EAA source contribution to various benthic invertebrate feeding types (FT) were similar but showed significant differences among genera within the same FT, suggesting that feeding habits are more genus-specific rather than FT-specific. These differences were attributed to variations in other characteristics such as mobility, selectivity, and assimilation efficiency. Terrestrial EAA contributed high amounts to all benthic genera, supporting other recent findings that this source is readily utilized by benthic invertebrate consumers. These results of organic matter source contributions across sediments and benthic invertebrate feeding types were then used to better resolve the detrital pathways in an Ecopath mass-balance model of the Chukchi Sea. The incorporation of terrestrial matter as an organic matter source to Chukchi Sea food webs and updated organic matter use in benthic invertebrate diets balanced energy flow from phytoplankton and bacterial production through the food web. Simulations of potential future reductions of the pelagic production to the benthos negatively impacted benthic feeding taxa, which could be partially compensated by a simulated increase in terrestrial and bacterial organic matter supply.
  • Wasting disease and environmental variables drive sea star assemblages in the northern Gulf of Alaska

    Mitchell, Timothy James; Konar, Brenda; Iken, Katrin; Kelley, Amanda (2019-05)
    Sea stars are ecologically important in rocky intertidal habitats. The recent (starting 2013) sea star die-off attributed to sea star wasting disease throughout the eastern Pacific, presumably triggered by unusually warm waters in recent years, has caused an increased interest in spatial and temporal patterns of sea star assemblages and the environmental drivers that structure these assemblages. This study assessed the role of seven potential static environmental variables (distance to freshwater, tidewater glacial presence, wave exposure, fetch, beach slope, substrate composition, and tidal range) influencing northern Gulf of Alaska sea star assemblages before and after regional sea star declines. For this, intertidal surveys were conducted annually from 2005 to 2018 at five sites in each of four regions that were between 100 and 420 km apart. In the years leading up to the regional mortality events, assemblages were different among regions and were structured mainly by tidewater glacier presence, wave fetch, and tidal range. The assemblages after wasting disease were different from those before the event, and there was a partial change in the environmental variables that correlated with sea star structure. In these recent years, the environmental variables most highly correlated with sea star assemblages were slope, wave fetch, and tidal range, all of which relate to desiccation, attachment, and wave action. This indicates that the change in sea star density and structure by wasting disease left an assemblage that is responding to different environmental variables. Understanding the delicate interplay of some of the environmental variables that influence sea star assemblages could expand knowledge of the habitat preferences and tolerance ranges of important and relatively unstudied species within the northern Gulf of Alaska.

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