Now showing items 41-60 of 1509

    • Explorations 1995

      Petersen, Art; Watson, Cecilia (University of Alaska Southeast, 1995)
      Explorations ’95 is published with support from the University of Alaska Southeast School of Education, Liberal Arts, and Science, the Chancellor’s Office, and contributor reader/entry fees. Works do not necessarily reflect the views of the University. Editor: Art Petersen; Asst. Student Editor: Cecilia Watson. Submissions (910) were “blind juried” by Nancy Lord, Art Petersen, Ron Silva, Leslie Williams, and Bob Mayberry—poets, writers, and faculty in literature. Nancy Lord awarded first place prizes of $500 each (and 2nd and 3rd places) for poetry and short fiction. Art Editor Alice Tersteeg and students awarded $175 in prizes for art.
    • Use of hormones in assessing reproductive physiology of humpback whales (Megaptera novaeangliae) from Juneau, Alaska

      Atkinson, S.; Melica, V.; Teerlink, S.; Mashburn, K.; Moran, J.; Pearson, Heidi (Elsevier, 2023)
      Humpback whales (Megaptera novaeangliae) in Southeast Alaska have been studied for over 50 years, and are largely considered a recovery success since the cessation of commercial whaling. Reproductive physiology is an important factor to consider in studying population health and can provide important insights into the drivers contributing to population abundance fluctuations. Validated assays for progesterone and testosterone were used on blubber biopsies from humpback whales (N = 33 whales, 71 samples) near Juneau, Alaska, in 2020 and 2021. Long-term sighting histories were used to confirm detected pregnancies with calf sightings the following year. Blubber samples were divided into two seasonal bins (early and late summer). Pregnant females sampled in both early and late summer of both 2020 and 2021 showed elevated progesterone concentrations compared to other reproductive states (p < 0.05). Progesterone concentrations in adult male whales (0.3 ± 0.2 ng/g) were not significantly different from lactating or resting female whales. Blubber testosterone concentrations in adult male humpback whales ranged from 0.05 to 1.1 ng/g, and mean concentrations were approximately double those of female whales in any reproductive state. Pregnancy was detected in 5 of 11 and 4 of 9 adult females in 2020 and 2021 respectively, yielding summer season pregnancy rates for sexually mature females at 0.45, and 0.44, respectively. Calving rates were 0.36 and 0.22 in 2020 and 2021, respectively, and the annual growth rate for this subpopulation was calculated at 2.6 % per annum. One female had successful pregnancies for four consecutive years. These results demonstrate the synergistic value of combining immunoreactive assays and long-term sighting histories to further knowledge of reproductive physiology in individual humpback whales, which can be expanded to assessing the health of a population or ecosystem.
    • Macronutrient composition of sea otter diet with respect to recolonization, life history, and season in southern Southeast Alaska

      LaRoche, Nicole; King, Sydney; Fergusson, Emily; Eckert, Ginny; Pearson, Heidi (John Wiley & Sons, Inc., 2023-05-02)
      The sea otter (Enhydra lutris) population of Southeast Alaska has been growing at a higher rate than other regions along the Pacific coast. While good for the recovery of this endangered species, rapid population growth of this apex predator can create a human-wildlife conflict, negatively impacting commercial and subsistence fishing. Previous foraging studies throughout the sea otter range have shown they will reduce invertebrate prey biomass when recolonizing an area. The goal of this study was to examine and quantify the energy content of sea otter diets through direct foraging observations and prey collection. Our study area, Prince of Wales Island in southern Southeast Alaska, exhibits a gradient of sea otter recolonization, thus providing a natural experiment to test diet change in regions with different recolonization histories. Sea otter prey items were collected in three seasons (spring, summer, and winter) to measure caloric value and lipid and protein content. We observed 3523 sea otter dives during the spring and summer. A majority of the sea otter diet consisted of clams. Sea otters in newly recolonized areas had lower diet diversity, higher energetic intake rates (EIR, kcal/min), and prey had higher energy content (kcal/g). Females with pups had the highest diet diversity and the lowest EIR. Sea otter EIR were higher in the fall and winter vs. spring and summer. Sea cucumber energy and lipid content appeared to correspond with times when sea otters consumed the highest proportion of sea cucumbers. These caloric variations are an important component of understanding ecosystem-level effects sea otters have in the nearshore environment.
    • A deep learning approach to photo–identification demonstrates high performance on two dozen cetacean species

      Patton, Philip T.; Cheeseman, Ted; Abe, Kenshin; Yamaguchi, Taiki; Reade, Walter; Southerland, Ken; Howard, Addison; Oleson, Erin M.; Allen, Jason B.; Ashe, Erin; et al. (John Wiley & Sons, Inc., 2023-07-13)
      1. Researchers can investigate many aspects of animal ecology through noninvasive photo–identification. Photo–identification is becoming more efficient as matching individuals between photos is increasingly automated. However, the convolutional neural network models that have facilitated this change need many training images to generalize well. As a result, they have often been developed for individual species that meet this threshold. These single-species methods might underperform, as they ignore potential similarities in identifying characteristics and the photo–identification process among species. 2. In this paper, we introduce a multi-species photo–identification model based on a state-of-the-art method in human facial recognition, the ArcFace classification head. Our model uses two such heads to jointly classify species and identities, allowing species to share information and parameters within the network. As a demonstration, we trained this model with 50,796 images from 39 catalogues of 24 cetacean species, evaluating its predictive performance on 21,192 test images from the same catalogues. We further evaluated its predictive performance with two external catalogues entirely composed of identities that the model did not see during training. 3. The model achieved a mean average precision (MAP) of 0.869 on the test set. Of these, 10 catalogues representing seven species achieved a MAP score over 0.95. For some species, there was notable variation in performance among catalogues, largely explained by variation in photo quality. Finally, the model appeared to generalize well, with the two external catalogues scoring similarly to their species' counterparts in the larger test set. 4. From our cetacean application, we provide a list of recommendations for potential users of this model, focusing on those with cetacean photo–identification catalogues. For example, users with high quality images of animals identified by dorsal nicks and notches should expect near optimal performance. Users can expect decreasing performance for catalogues with higher proportions of indistinct individuals or poor quality photos. Finally, we note that this model is currently freely available as code in a GitHub repository and as a graphical user interface, with additional functionality for collaborative data management, via Happywhale.com.
    • High-latitude kelps and future oceans: A review of multiple stressor impacts in a changing world

      Farrugia Drakard, Veronica; Hollarsmith, Jordan; Stekoll, Michael (John Wiley & Sons, Inc., 2023-07-04)
      Kelp forests worldwide are threatened by both climate change and localized anthropogenic impacts. Species with cold-temperate, subpolar, or polar distributions are projected to experience range contractions over the coming decades, which may be exacerbated by climatic events such as marine heatwaves and increased freshwater and sediment input from rapidly contracting glaciers. The northeast Pacific has an extensive history of harvesting and cultivating kelps for subsistence, commercial, and other uses, and, therefore, declines in kelp abundance and distributional shifts will have significant impacts on this region. Gaps in our understanding of how cold-temperate kelp species respond to climate stressors have limited our ability to forecast the status of kelp forests in future oceans, which hampers conservation and management efforts. Here, we conducted a structured literature review to provide a synthesis of the impacts of multiple climate-related stressors on kelp forests in the northeast Pacific, assess existing knowledge gaps, and suggest potential research priorities. We chose to focus on temperature, salinity, sediment load, and light as the stressors most likely to vary and impact kelps as climate change progresses. Our results revealed biases in the existing literature toward studies investigating the impacts of temperature, or temperature in combination with light. Other stressors, particularly salinity and sediment load, have received much less focus despite rapidly changing conditions in high-latitude regions. Furthermore, multiple stressor studies appear to focus on kelp sporophytes, and it is necessary that we improve our understanding of how kelp microstages will be affected by stressor combinations. Finally, studies that investigate the potential of experimental transplantation or selective cultivation of genotypes resilient to environmental changes are lacking and would be useful for the conservation of wild populations and the seaweed aquaculture industry.
    • Pregnancy rate and reproductive hormones in humpback whale blubber: Dominant form of progesterone differs during pregnancy

      Atkinson, S.; Branch, T. A.; Pack, A. A.; Straley, Janice; Moran, J. R.; Gabriele, C.; Mashburn, K. L.; Cates, K.; Yin, S. (Elsevier, 2023-01-01)
      To better understand reproductive physiology of humpback whales Megaptera novaeangliae that reside in Hawai’i and Alaska, enzyme immunoassays were validated for both progesterone and testosterone in free-ranging and stranded animals (n = 185 biopsies). Concentrations were analyzed between different depths of large segments of blubber taken from skin to muscle layers of stranded female (n = 2, 1 pregnant, 1 non-pregnant) and male (n = 1) whales. Additionally, progesterone metabolites were identified between pregnant (n = 1) and non-pregnant (n = 3) females using high pressure liquid chromatography (HPLC). Progesterone concentrations were compared between juvenile (i.e., sexually immature), lactating, and pregnant females, and male whales, and pregnancy rates of sexually mature females were calculated. Based on replicate samples from ship struck animals collected at 7 depth locations, blubber containing the highest concentration of progesterone was located 1 cm below the skin for females, and the highest concentration of testosterone was in the skin layer of one male whale. HPLC of blubber samples of pregnant and non-pregnant females contain different immunoreactive progesterone metabolites, with the non-pregnant female eluate comprised of a more polar, and possibly conjugated, form of progesterone than the pregnant female. In females, concentrations of progesterone were highest in the blubber of pregnant (n = 28, 28.6 ± 6.9 ng/g), followed by lactating (n = 16, 0.9 ± 0.1 ng/g), and female juvenile (n = 5, 1.0 ± 0.2 ng/g) whales. Progesterone concentrations in male (n = 24, 0.6 ng/g ± 0.1 ng/g) tissues were the lowest all groups, and not different from lactating or juvenile females. Estimated summer season pregnancy rate among sexually mature females from the Hawai’i stock of humpback whales was 0.562 (95 % confidence interval 0.528–0.605). For lactating females, the year-round pregnancy rate was 0.243 (0.09–0.59), and varies depending on the threshold of progesterone assumed for pregnancy in the range between 3.1 and 28.5 ng/g. Our results demonstrate the synergistic value added when combining immunoreactive assays, HPLC, and long-term sighting histories to further knowledge of humpback whale reproductive physiology.
    • Engaging northern rural and Indigenous students: Case studies using One Health principles of educational resilience

      Cotter, Paul; Gildehaus, Lori; Chenoweth, Ellen; Straley, Janice; Hueffer, Karsten; Reynolds, Arleigh J. (University of Aberdeen, 2023)
      Indigenous and rural populations are underrepresented in many science-related educational fields, leading to underrepresentation in biomedical, science, and related professions. A contributing factor is the misalignment of Western education and engagement strategies and these cultures; this is especially true for northern subsistence cultures. We review the influence of a combined One Health/Quadripartite Model of Educational Resilience approach in promoting interest in, recruiting for, and retaining students in biomedical research and community health across three education levels. We suggest a One Health context resonates with Indigenous and rural populations and may be more culturally aligned than conventional education approaches. Implementing Quadripartite Model elements promotes educational accessibility and attractiveness to these populations across our programs. We suggest that 1) disciplines that may be perceived as remote and inaccessible to these populations can be culturally contextualized through a One Health lens and; 2) a more equitable sharing of responsibility for educational success may benefit students from underrepresented populations. Applying One Health/Quadripartite Model approaches may help increase representation of Indigenous and rural populations in a wide range of STEM, biomedical, and community health disciplines. We support continued efforts to modify conventional educational structures, institutions, and strategies to further engage these communities.
    • Woosh jín toolshát yeisú, Weʼre still holding each otherʼs hands : Relationships and revitalization in Lingít country

      Burge, Éedaa Heather Dawn (University of British Columbia, 2024)
      This dissertation examines the relationships the Lingít language revitalization movement has to concepts of gender, identity, organizations and academia. The Lingít language and the Lingít people reside within Southeast Alaska in the United States, as well as northern British Columbia and the southern Yukon territory in Canada. Relying on my own lived experience as a Lingít learner and educator, as well as interviews and conversations with Lingít community members, we discuss how relationality supports the larger goal of Lingít language and cultural revitalization. Specifically we talk about the role of women within the language movement, and what approaches can best support current and future female language learners and speakers. Next we discuss the role identity plays within Lingít language revitalization and how varying understandings of Indigeneity both support and add additional pressure to language learning. We also reflect on the various roles multiple institutions play in Lingít language work, and touch on some of the programming organizations have implemented. Last, we discuss the role universities in particular, and academia in general plays within language revitalization, and how that role has evolved over time. The thread throughout is relationality, how personal and collective relationships with individuals, organizations, and identities shape language work, and how that relationality can best support the larger goal of continued Lingít language resurgence.
    • Big avalanches in a changing climate: Using tree-ring Derived avalanche chronologies to examine avalanche frequency across multiple climate types

      Peitzsch, Erich H.; Pederson, Gregory; Martin, Justin; Hood, Eran; Greene, Ethan; Birkeland, Kelly Elder; Wolken, Gabriel; Kichas, Nick; Stahle, Daniel; Harley, John R. (Montana State University Library, 2023-10-08)
      Large-magnitude snow avalanches pose a hazard to humans and infrastructure worldwide. Analyzing the spatiotemporal behavior of avalanches and the contributory climate factors is important for understanding historical variability in climate-avalanche relationships as well as improving avalanche forecasting. This study uses established dendrochronological methods to develop long-term regional avalanche chronologies for three different climate types: high-latitude maritime climate of southeast Alaska, intermountain climate of the northern Rocky Mountains, and continental climate of Colorado. In the maritime study area, we collected 434 cross sections throughout six avalanche paths near Juneau, Alaska. This resulted in 2706 identified avalanche growth disturbances between year 1720 and 2018 Common Era (CE), which allowed us to reconstruct 82 years with large magnitude avalanche activity across three sub-regions. By combining this tree-ring derived avalanche dataset with a suite of climate and atmospheric variables and applying a generalized linear model to fit a binomial regression, we found February and March precipitation and the Oceanic Niño Index (ONI) were significant predictors of large magnitude avalanche activity in the southeast Alaska study area. In the intermountain climate study area, tree-rings from 647 trees exhibited 2134 avalanche-related growth disturbances in the northern Rocky Mountains of northwest Montana from 1867 to 2019. The data show that the amount of snowpack across the northern Rocky Mountain region is directly related to avalanche probability. Coincident with warming and regional snowpack reductions, a decline of ~ 14% (~ 2% per decade) in overall large magnitude avalanche probability is apparent through the period 1950–2017 CE. In the continental climate of Colorado, we sampled 24 avalanche paths throughout the state and collected 1188 total samples with 4135 identified growth disturbances from 1698 to 2019. Preliminary results suggest years with large magnitude avalanche activity across the sub-regions of this study area are generally characterized by stormy winters with above average snowpack development but that early and late winter temperature and precipitation also play an important role in large avalanche activity. Characterizing historical climate-avalanche relationships across different climate types provides a broad baseline for understanding potential future changes in avalanche activity. Overall, this work helps forecasters and planners better understand the influence of climate on large magnitude avalanche frequency, and how potential changes in avalanche character and occurrence will affect their operations in the context of a warming climate.
    • Modeling coho salmon (Oncorhynchus kisutch) population response to streamflow and water temperature extremes

      Bellmore, J. Ryan; Sergeant, Christopher; Bellmore, Rebecca; Falke, Jeffery; Fellman, Jason (Canadian Science Publishing, 2023-01-06)
      Models that assess the vulnerability of freshwater species to shifting environmental conditions do not always account for short-duration extremes, which are increasingly common. Life cycle models for Pacific salmon (Oncorhynchus spp.) generally focus on average conditions that fish experience during each life stage, yet many floods, low flows, and elevated water temperatures only last days to weeks. We developed a process-based life cycle model that links coho salmon (Oncorhynchus kisutch) abundance to daily streamflow and thermal regimes to assess: (1) “How does salmon abundance respond to short-duration floods, low flows, and high temperatures in glacier-, snow-, and rain-fed streams?” and (2) “How does the temporal resolution of flow and temperature data influence these responses?”. Our simulations indicate that short-duration extremes can reduce salmon abundance in some contexts. However, after daily flow and temperature data were aggregated into weekly and monthly averages, the impact of extreme events on populations declined. Our analysis demonstrates that novel modeling frameworks that capture daily variability in flow and temperature are needed to examine impacts of extreme events on Pacific salmon.
    • Effects of landslides on terrestrial carbon stocks with a coupled geomorphic-biologic model: Southeast Alaska, United States

      Booth, A. M.; Buma, B.; Nagorski, Sonia (Wiley, 2023-06-16)
      Landslides influence the global carbon (C) cycle by facilitating transfer of terrestrial C in biomass and soils to offshore depocenters and redistributing C within the landscape, affecting the terrestrial C reservoir itself. How landslides affect terrestrial C stocks is rarely quantified, so we derive a model that couples stochastic landslides with terrestrial C dynamics, calibrated to temperate rainforests in southeast Alaska, United States. Modeled landslides episodically transfer C from scars to deposits and destroy living biomass. After a landslide, total C stocks on the scar recover, while those on the deposit either increase (in the case of living biomass) or decrease while remaining higher than if no landslide had occurred (in the case of dead biomass and soil C). Specifically, modeling landslides in a 29.9 km2 watershed at the observed rate of 0.004 landslides km−2 yr−1 decreases average living biomass C density by 0.9 tC ha−1 (a relative amount of 0.4%), increases dead biomass C by 0.3 tC ha−1 (0.6%), and increases soil C by 3.4 tC ha−1 (0.8%) relative to a base case with no landslides. The net effect is a small increase in total terrestrial C stocks of 2.8 tC ha−1 (0.4%). The size of this boost increases with landslide frequency, reaching 6.5% at a frequency of 0.1 landslides km−2 yr−1. If similar dynamics occur in other landslide-prone regions of the globe, landslides should be a net C sink and a natural buffer against increasing atmospheric CO2 levels, which are forecast to increase landslide-triggering precipitation events.
    • Alaska's new electoral system: Countering polarization or "crooked as hell"?

      Reilly, Benjamin; Lublin, David; Wright, Glenn (eScholarship University of California, 2023)
      In November 2020, Alaska introduced a new electoral system, combining a “top four” all-party primary with ranked choice voting (RCV) general elections. Supporters of this reform claimed it would reduce the partisan polarization and minority victories generated by closed primaries and plurality elections. But critics suggest that it could make polarization worse by weakening political parties—an important check on political extremism. These are high-stakes issues that go well beyond Alaska, given the problem of political polarization and the search for institutional reforms in America today. Placing the Alaskan reforms in this broader national context, this paper presents an initial assessment of Alaska’s new system at the 2022 primary and mid-term elections. We find the reform was both consequential and largely beneficial, promoting greater choice for voters, more accommodative campaigning, and generally more moderate outcomes than likely under the old rules.
    • Conformity and tradition are more important than environmental values in constraining resource overharvest

      Wright, Glenn; Salk, Carl; Magnuszewski, Piotr; Stefanska, Joanna; Anderson, Krister; Benavides, Jean Paul; Chazdon, Robin (PLOS, 2023-02-02)
      We present the results of a hybrid research design that borrows from both experimental techniques—experimental games—and observational techniques—surveys—to examine the relationships between basic human values and exposure to natural ecosystems, on the one hand, and collective action for resource governance, on the other. We initially hypothesize that more frequent exposure to forests, and more pro-environmental values will be associated with more conservation action. However, we find that other values—tradition and conformity—are more important than pro-environmental values or exposure to nature. Our results imply that resource governance is likely to be more successful where resource users hold values that facilitate cooperation, not necessarily strong pro-environmental values.
    • Hydroclimate drives seasonal riverine export across a gradient of glacierized high-latitude coastal catchments

      Jenckes, J.; Munk, L. A.; Ibarra, D. E.; Boutt, D. F.; Fellman, Jason; Hood, Eran (American Geophysical Union, 2023-04-14)
      Glacierized coastal catchments of the Gulf of Alaska (GoA) are undergoing rapid hydrologic fluctuations in response to climate change. These catchments deliver dissolved and suspended inorganic and organic matter to nearshore marine environments, however, these glacierized coastal catchments are relatively understudied and little is known about total solute and particulate fluxes to the ocean. We present hydrologic, physical, and geochemical data collected during April–October 2019–2021 from 10 streams along gradients of glacial fed to non-glacial (i.e., precipitation) fed, in one Southcentral and one Southeast Alaska region. Hydrologic data reveal that glaciers drive the seasonal runoff patterns. The ẟ18O signature and specific conductance show distinctive seasonal variations in stream water sources between the study regions apparently due to the large amounts of rain in Southeast Alaska. Total dissolved solids concentrations and yields were elevated in the Southcentral region, due to lithologic influence on dissolved loads, however, the hydroclimate is the primary driver of the timing of dissolved and suspended yields. We show the yields of dissolved organic carbon is higher and that the δ13CPOC is enriched in the Southeast streams illustrating contrasts in organic carbon export across the GoA. Finally, we illustrate how future yields of solutes and sediments to the GoA may change as watersheds evolve from glacial influenced to precipitation dominated. This integrated analysis provides insights into how watershed characteristics beyond glacier coverage control properties of freshwater inputs to the GoA and the importance of expanding study regions to multiple hydroclimate regimes.
    • Bellwethers of change: population modelling of North Pacific humpback whales from 2002 through 2021 reveals shift from recovery to climate response

      Cheeseman, Ted; Barlow, Jay; Acebes, Jo Marie; Audley, Katherina; Bejder, Lars; Birdsall, Catlin; Bracamontes, O. S.; Bradford, Amanda L.; Byington, Josie; Calambokidis, John; et al. (The Royal Society, 2024-02-28)
      For the 40 years after the end of commercial whaling in 1976, humpback whale populations in the North Pacific Ocean exhibited a prolonged period of recovery. Using mark–recapture methods on the largest individual photo-identification dataset ever assembled for a cetacean, we estimated annual ocean-basin-wide abundance for the species from 2002 through 2021. Trends in annual estimates describe strong post-whaling era population recovery from 16 875 (± 5955) in 2002 to a peak abundance estimate of 33 488 (± 4455) in 2012. An apparent 20% decline from 2012 to 2021, 33 488 (± 4455) to 26 662 (± 4192), suggests the population abruptly reached carrying capacity due to loss of prey resources. This was particularly evident for humpback whales wintering in Hawai‘i, where, by 2021, estimated abundance had declined by 34% from a peak in 2013, down to abundance levels previously seen in 2006, and contrasted to an absence of decline in Mainland Mexico breeding humpbacks. The strongest marine heatwave recorded globally to date during the 2014–2016 period appeared to have altered the course of species recovery, with enduring effects. Extending this time series will allow humpback whales to serve as an indicator species for the ecosystem in the face of a changing climate.
    • Macroalgal input into the coastal food web along a gradient of seasonal sea ice cover along the Western Antarctic Peninsula

      Iken, Katrin; Amsler, Charles D.; Gorman, Kristen B.; Klein, Andrew G.; Galloway, Aaron W. E.; Amsler, Margaret O.; Heiser, Sabrina; Whippo, Ross; Lowe, Alexander T.; Schram, Julie; et al. (Inter-Research, 2023-09-07)
      Coastal food webs that are supported by multiple primary producer sources are considered to be more stable against perturbations. Here, we investigated how declining macroalgal abundance and diversity might influence coastal food web structure along an annual sea ice cover gradient along the Western Antarctic Peninsula (WAP). The most common benthic invertebrate consumers, macroalgae, and surface particulate organic matter were collected at 15 stations along the WAP. Stable carbon and nitrogen isotope values of primary producers changed negligibly in relation to the sea ice cover gradient, while isotope values of most invertebrate feeding groups increased with higher sea ice cover, although at low explanatory power. Food web length became shorter and consumer trophic niche width smaller in regions with higher sea ice cover. Changes in food web structure were mostly associated with shifts in trophic position of lower trophic levels. Food web structure in higher ice-covered regions resembled that of more generalist feeders with a loss of specialist species, concurrent with an increased reliance on a more reworked detrital food source. These results suggest that a number of benthic invertebrates are able to adjust to differences in basal energy sources. Conversely, these food webs dominated by generalist feeders are likely less efficient in energy transfer, which can create less-stable systems with lower adaptive capacity to disturbance. The predicted sea ice loss along the WAP may ultimately lead to a longer food web with higher macroalgal abundance, more specialist species, and wider consumer trophic niches in the currently more ice-covered regions.
    • Juvenile Dungeness crab foraging behavior and lipid composition is altered more by food quantity than seawater pH in a multi-stressor experiment

      Schram, Julie; Hayes, Hannah G.; Street, Erica; Thompson, Natalie; Yoshioka, Reyn M.; Galloway, Aaron W. E. (Elsevier, 2023-06)
      Increases in atmospheric, anthropogenic carbon are driving reductions in seawater pH, a process referred to as ocean acidification. Reduced seawater pH can influence behavior of marine animals, but little is currently known about how juvenile crustaceans will respond. We conducted lab experiments to improve our understanding of the consequences of pH exposure and food quantity on juvenile Dungeness crab (Metacarcinus magister, (Dana, 1852)) behavior and nutritional condition. To understand the foraging and pH sensing behavior of juvenile crab, and how this interacts with their nutritional status, we exposed recently settled second instar juveniles to either ambient pH or reduced pH for 42-d, crossed with either a ‘maintenance’- or low-quantity ‘challenge’ diet treatment. After the experimental exposure period, we introduced crab into foraging and sensing pH behavior experiments. In the foraging experiment, we placed crab in a behavior arena with unidirectional flow, where we measured the food discovery time and time allocation of activities in 300-s trials for all individual crab. Food quantity and pH exposure influenced both the speed with which juvenile crab identified and allocation of activities but there was no interactive effect of experimental factors. For our pH sensing experiment, we used a two-current flume plumbed with both ambient and reduced pH seawater. This flow-through flume provided a choice between the pH treatment waters and allowed us to measure the amount of time individuals spent on either side of the arena in 300-s trials. There was no effect of prior diet or pH exposure on the amount of time juvenile crab spent in either seawater pH condition. In addition to the behavior trials, we evaluated crab nutritional condition by quantifying the total lipid content of whole-body tissues and fatty acid profile composition of juvenile crab fed either the maintenance or low-quantity diet during the experimental pH exposure period. The proportional fatty acid profiles differed for crab based on their diet and pH exposure, with no interactive effects. However, we did not detect differences in the concentrations of key summary categories of fatty acids (e.g., saturated, monounsaturated, or polyunsaturated) based on pH exposure. Our results indicate that reduced food availability has a greater impact on juvenile Dungeness crab foraging behavior and nutritional condition than reduced seawater pH exposure representing the 0.3 pH unit decrease predicted by 2100.
    • Riverine dissolved inorganic carbon export from the Southeast Alaskan Drainage Basin with implications for coastal ocean processes

      Harley, John R.; Biles, Frances E.; Brooks, Mariela K.; Fellman, Jason M.; Hood, Eran; D'Amore, David V. (American Geophysical Union, 2023-10-16)
      Dissolved inorganic carbon (DIC) represents an important but poorly constrained form of lateral carbon flux to the oceans. With high precipitation rates, large glaciers, and dense temperate rainforest, Southeast Alaska plays a critical role in the transport of carbon to the Gulf of Alaska (GOA). Previous estimates of DIC flux across the Southeast Alaska Drainage Basin (SEAKDB) are poorly constrained in space and time. Our goal was to incorporate recent measurements of DIC concentrations with previous measurements from the U.S. Geological Survey in order to model the spatial and temporal patterns of riverine DIC transport from SEAK to the GOA. We aggregated DIC concentration measurements from 1957 to 2020 and associated measurements of mean daily discharge. We then constructed load estimation models to generate concentration predictions across 24 watersheds. By spatially matching measurements of DIC with SEAKDB watersheds, we extrapolated concentration predictions across 2,455 watersheds encompassing approximately 190,000 km2. Models were aggregated according to two factors, the presence of karst and the discharge regime. Finally, monthly flux predictions were generated for each watershed using predicted concentrations and runoff estimates from the Distributed Climate Water Balance Model. Mean annual DIC flux from the SEAKDB was 2.36 Tg C with an average yield of 12.52 g C m−2. Both karst presence and flow regimes modified DIC flux and speciation across coastal marine areas. The high resolution of DIC flux estimates will provide useful inputs for describing seasonal C dynamics, and further refines our understanding of C budgets in the Pacific temperate rainforest and the surrounding marine environment.
    • Persistent overcut regions dominate the terminus morphology of a rapidly melting tidewater glacier

      Abib, Nicole; Sutherland, David A.; Amundson, Jason M.; Duncan, Dan; Eidam, Emily F.; Jackson, Rebecca H.; Kienholz, Christian; Morlighem, Mathieu; Motyka, Roman J.; Nash, Jonathan D.; et al. (Cambridge University Press, 2023-05-29)
      Frontal ablation, the combination of submarine melting and iceberg calving, changes the geometry of a glacier's terminus, influencing glacier dynamics, the fate of upwelling plumes and the distribution of submarine meltwater input into the ocean. Directly observing frontal ablation and terminus morphology below the waterline is difficult, however, limiting our understanding of these coupled ice–ocean processes. To investigate the evolution of a tidewater glacier's submarine terminus, we combine 3-D multibeam point clouds of the subsurface ice face at LeConte Glacier, Alaska, with concurrent observations of environmental conditions during three field campaigns between 2016 and 2018. We observe terminus morphology that was predominately overcut (52% in August 2016, 63% in May 2017 and 74% in September 2018), accompanied by high multibeam sonar-derived melt rates (4.84 m d−1 in 2016, 1.13 m d−1 in 2017 and 1.85 m d−1 in 2018). We find that periods of high subglacial discharge lead to localized undercut discharge outlets, but adjacent to these outlets the terminus maintains significantly overcut geometry, with an ice ramp that protrudes 75 m into the fjord in 2017 and 125 m in 2018. Our data challenge the assumption that tidewater glacier termini are largely undercut during periods of high submarine melting.
    • Impacts of tidewater glacier advance on iceberg habitat

      Kaluzienski, Lynn M.; Amundson, Jason M.; Womble, Jamie M.; Bliss, Andrew K.; Pearson, Linnea E. (Cambridge University Press, 2023-08-17)
      Icebergs in proglacial fjords serve as pupping, resting and molting habitat for some of the largest seasonal aggregations of harbor seals (Phoca vitulina richardii) in Alaska. One of the largest aggregations in Southeast Alaska occurs in Johns Hopkins Inlet, Glacier Bay National Park, where up to 2000 seals use icebergs produced by Johns Hopkins Glacier. Like other advancing tidewater glaciers, the advance of Johns Hopkins Glacier over the past century has been facilitated by the growth and continual redistribution of a submarine end moraine, which has limited mass losses from iceberg calving and submarine melting and enabled glacier thickening by providing flow resistance. A 15-year record of aerial surveys reveals (i) a decline in iceberg concentrations concurrent with moraine growth and (ii) that the iceberg size distributions can be approximated as power law distributions, with relatively little variability and no clear trends in the power law exponent despite large changes in ice fluxes over seasonal and interannual timescales. Together, these observations suggest that sustained tidewater glacier advance should typically be associated with reductions in the number of large, habitable icebergs, which may have implications for harbor seals relying on iceberg habitat for critical life-history events.