Includes Marine Science and Limnology

Recent Submissions

  • Eavesdropping on killer whales: distribution, calling rates, and acoustic abundance of fish-eating and mammal-eating killer whales in the Gulf of Alaska

    Myers, Hannah J.; Konar, Brenda; Horstmann, Lara; Matkin, Craig; Mueter, Franz; Guazzo, Regina; Ford, John (2023-12)
    The widespread loss of apex consumers in marine, terrestrial, and freshwater ecosystems throughout the world has precipitated profound trophic cascades and switches to different ecological states. However, conserving top predators can deliver broad biodiversity benefits and improve ecosystem resiliency. Effective conservation and management policy is predicated on a species' distribution and abundance in a given area and time. In this dissertation, I provide new insight into killer whale (Orcinus orca) distribution, vocal behavior, and abundance in the Gulf of Alaska using passive acoustic monitoring and advance long-term monitoring capacity for this species. First, I describe the year-round spatiotemporal distribution and daily acoustic residency patterns of southern Alaska resident (fish-eating) and two populations of transient (mammal-eating) killer whales. I found distinct seasonal patterns across locations for each genetically distinct population and discovered that both resident and transient killer whales used the coastal monitoring areas more extensively than previously known--including in winter. Second, I estimated resident and transient killer whale calling rates, a prerequisite to acoustic abundance estimation. I found that the mean calling rate for southern Alaska resident (fish-eating) killer whales was consistent across space, time, ambient noise level, which pod was calling, and the presence of other pods. Gulf of Alaska transient (mammal-eating) killer whale calling rates were higher than resident's and differed across locations. AT1 transients (mammal-eating) produced fewer calls more rapidly than Gulf of Alaska transients, and their mean rate was stable across spatiotemporal factors. Although transients call less often than residents, I found that once vocalizing, they do so at a higher rate. Finally, I estimated and modeled the year-round daily acoustic abundance of resident and transient killer whales across distinct areas in the Gulf of Alaska and developed Bayesian time series models to describe seasonal patterns and predict future abundance. Acoustic abundance estimates for the southern Alaska resident and Gulf of Alaska transient killer whales matched expectations from visual studies. I established distinct seasonal abundance patterns across areas, and acoustic monitoring enabled killer whale abundance estimation across a greater spatiotemporal extent than other methods. This work is critical for an accurate understanding of killer whales' top-down forcing effects in the marine ecosystem, as well as to inform conservation and management policy for this federally protected species.
  • Environmental and biotic habitat attributes affect rocky intertidal community variability in glacially influenced estuaries

    McArthur, Madeleine G.; Konar, Brenda; Schram, Julie; Umanzor, Schery (2023-12)
    Climate change is increasing the rate of glacial recession in high latitude coastal environments. The associated increase in cold, sediment-laden freshwater into the nearshore may alter a wide array of water attributes, which will likely have ecosystem-wide impacts. One of these potential impacts is a change in typical levels of ecological community variability, which can be an indicator of stress in response to an environmental impact. Fluctuation in community composition over time is natural and can be affected by environmental conditions, as well as by the presence of habitat forming, spatially dominant organisms. The goal of this study was to determine how variation in environmental attributes and spatially dominant species contributes to the variability of rocky intertidal community assemblages in glacially influenced estuaries. The environmental attributes of interest were both dynamic in nature (water temperature, salinity, dissolved oxygen, turbidity, and pCO₂), and static (substrate type, wave exposure, beach slope, and distance to freshwater). Variation in the proportions of three spatially dominant organisms, Mytilus trossulus (mussels), Balanus spp. (barnacles), and Fucus spp. (rockweed) were examined as biotic habitat attributes. The average attachment strength of mussels was also surveyed. It was hypothesized that 1) dynamic environmental attributes would be more strongly correlated to community variability patterns than static attributes, 2) higher proportions of spatially dominant species would correspond to lower levels of community variability, and 3) community variability would be lower when mussels had higher attachment strength. To document community variability, as well as proportions of spatially dominant species, percent cover and biomass data were collected along with environmental data from 2019 to 2022. Barnacle cover, rockweed cover, and substrate characteristics (cover of gravel and total cover of bare rock) were significantly correlated to community variability levels based on percent cover data. Community variability levels based on biomass data were significantly correlated to mussel cover, rockweed biomass, substrate aspects (cover of gravel and mud), distance to a freshwater source, and variation in dissolved oxygen levels. All relationships between community variability and each of these attributes were negative, except distance to freshwater and dissolved oxygen variation. These results highlight significant drivers of community variability in glacially influenced estuaries, providing insights into how these communities may be affected by the progression of climate change.
  • Effects of commercial otter trawling on essential fish habitat of the southeastern Bering Sea shelf

    Brown, Eloise (2003-05)
    Sediment properties and benthic community composition in areas subject to commercial bottom trawling were compared to control areas in a shallow sandy habitat of the southeastern Bering Sea. The top 3 cm sediments in the fished area were slightly better sorted, less variable, and contained fewer finer grains than those of the closed area. Infaunal species assemblages were distinct. The fished area was characterized by reduced infauna richness and biomass, but abundance and diversity were similar to the closed area. No shift in means of any sediment parameter were detected after experimental trawling, but significant increases in variability were observed for several grain size and organic matter parameters. Reduced richness, elimination of rare taxa, and patchy changes in infauna assemblage biomass were found, but there were no differences in abundance, diversity or total biomass relative to controls. A turbulent wake generated by the trawl was on the same order of magnitude as a winter storm wave, but of different seasonal timing and duration. Turbulence combined with friction from contact with fishing gear has the potential to erode sediments from deeper within the seabed than naturally occurring bottom currents. Trawling apparently removed finer grains from the upper sediment layers and altered infauna communities.
  • Effects of placer gold mining on stream macroinvertebrates of interior Alaska

    Wagener, Stephen Mitchell (1984-12)
    Placer gold mining is an economically and politically important industry in Alaska which can have major impacts on the water quality of streams. To determine the effect of placer mining on benthic macroinvertebrates we determined water quality characteristics and sampled benthic invertebrates in nine hydrologicalIy similar and proximally located streams. Sampled streams ranged from unmined control streams to heavily mined streams. Placer mining caused increases in turbidity, settleable solids, percent substrate embeddedness, nonfilterable residue, and total recoverable arsenic, lead, zinc, and copper. Placer mining decreased invertebrate density and biomass. Substrate embeddedness and turbidity were the best predictive descriptors of reduced invertebrate density and biomass. Invertebrate communities in mined streams usually contained higher proportions of collector-gatherers, and lower proportions of crawlers, shredders, filter-feeders, predators, and oligochaetes compared to unmined streams.
  • Photosynthetic response of phytoplankton to changing light intensity in a southcentral Alaskan lake

    Vaught, Kyle Douglas (1989-12)
    Little fresh-water work has been done (compared with published ma­rine studies) using photosynthesis-irradiance (P-I) curves to determine photosynthetic response of natural assemblages of phytoplankton to light above and below thermal stratification structures. Limnological data including physical, chemical, and algal taxonomy and biomass were collected through the summers of 1985 and 1986 at Wasilla Lake, Alaska (approximately 61oN., 148oW.). Algal photosynthesis­irradiance relationships were also determined through the summer of 1986 by means of P-I curves. P-I curve light-limited initial slope (a) was ≈2.5 times higher in phytoplankton populations at 6 m than those in the wind-mixed zone when populations were separated by thermal stratification. Wasilla Lake’s trophic status was estimated to fall between mesotrophic and eutrophic classifications. Phytoplankton in Wasilla Lake were found to require approximately 4-5 days to best adapt to a changing light environment.
  • Aquatic ecology of two subarctic lakes: Big and Little Minto Lakes, Alaska

    Jacobs, Laura Lee (1992-05)
    During 1988, three sampling trips were made to Big and Little Minto Lakes to study their limnological features. Physical and chemical measurements were made of both lakes, while the invertebrate community and habitat characteristics were investigated along Big Minto Lake's shoreline (5-35cm water depth) . Both lakes are shallow and eutrophic, with high dissolved oxygen and pH, and moderate alkalinity. Invertebrate abundance averaged 7,352/m2 (±SE = 406, n = 60) , and was dominated by Diptera (38%) . Gastropoda comprised the largest portion (41%) of total biovolume (11.28 mL/m2, ±SE = 1.28, n = 60). Diptera and Coleoptera contained the majority of invertebrate families. Scrapers (41%) and collectors (23%) dominated the food web in biovolume. Overall, invertebrate abundance was significantly correlated with low detritus biomass; however, Trichoptera abundance was significantly correlated with low vegetation biomass, shallow water, and the August sample period; and both diversity indices, were significantly correlated with aquatic plant biomass (AFDW).
  • The effect of sedimentation on spore settlement and recruitment of the endemic Arctic kelp, Laminaria solidungula

    Phelps, Jaide; Iken, Katrin; Konar, Brenda; Umanzor, Schery (2023-08)
    The Arctic is experiencing rapid rates of environmental change due to ramifications of a warming climate and human development. Environmental changes can enhance the impact of abiotic stressors, such as sedimentation from enhanced river discharge, permafrost melt, coastal erosion, or construction activities on Arctic nearshore ecosystems. Diverse habitat types, such as kelp beds that populate nearshore systems, are especially vulnerable to these environmental impacts. High sedimentation rates can be detrimental to kelp abundance and distribution, possibly due to increased mortality at the spore dispersal and settlement stages. This study aimed to examine sedimentation effects on spore settlement and viability of the endemic Arctic kelp, Laminaria solidungula, through a series of lab-based experiments. We hypothesized that spore settlement, gametophyte development, and spore viability would decrease under increasing sediment loads. Reproductive L. solidungula individuals were collected from the Stefansson Sound Boulder Patch in the Alaskan Beaufort Sea and cultured until the induction of spore release. Spores were exposed to increasing sediment loads in three experimental designs simulating different sedimentation scenarios: depositing sediments on top of settled spores, settling spores on top of sediment-covered substrate, and spores and sediments suspended simultaneously before settlement. Spores were enumerated at the end of the experiment as total and germinated spores. A duplicate set of slides from these treatments was exposed to light after sediments were removed to allow for spore development into gametophytes, and gametophytes were counted after the growing period. In all three types of sediment exposure, increased sediment load led to decreased spore settlement and gametophyte development. However, increasing amounts of sediment had no significant effect on spore viability in any of the three experiments, indicating that the spores that did settle under treatment conditions were viable. These results suggest that increased sedimentation due to rapid advances of climate change and human activities will affect L. solidungula recruitment, and, thus, may affect the long-term persistence of a diverse and productive benthic habitat.
  • Variability of total mercury concentrations in Steller sea lion bone locations and bone elements

    Keenan, Mary P.; Hostmann, Lara; Avery, Julie; Misarti, Nicole; Iken, Katrin (2023-08)
    Mercury (Hg) is a contaminant of global concern with impacts on the health and resilience of marine wildlife. Some forms of ingested Hg are bioaccumulated and biomagnified with greatest concentrations observed in long-lived top predators. High concentrations of Hg in mammals impair immune function, neurochemistry, and reproduction. Steller sea lions (Eumetopias jubatus, SSL) are a long-lived top predator, and some populations have total mercury concentrations ([THg]) in fur that are above the threshold values of concern for toxic effects. While this information is available for present-day populations of SSLs, [THg] in historic and ancient populations of SSLs are unknown. Bone is a biologically resilient material that is well preserved over millennial time scales and can be used to study Hg concentrations in these historic and ancient populations; however, little is known about the variability and distribution of Hg in bone. This study examined [THg] within individual bones and across bone elements in skeletons of SSLs to understand the distribution and variability of Hg in bone. Bones were acquired from necropsies or museum collections from fetuses (stillborn), pups (newborn to 3 months), juveniles (4 months to 5 years), and adults (> 5 years). Bones were analyzed for [THg] with a Nippon MA-3000 (Nippon Instruments Corporation, Tokyo) direct mercury analyzer. To determine differences and variability of [THg] within bones, [THg] were quantified in compact and spongy bone of pups (n = 5) and non-pups (n = 5) at seven locations from the proximal to distal end of long bones. Spongy bone [THg] near the epiphyseal plates were greater compared with mid-diaphysis locations in pups (p = 0.01). Spongy and compact bone [THg] near the epiphyseal plates were greater and more variable compared with mid-diaphysis locations in non-pups (p < 0.01). To determine differences and variability of [THg] among bone elements, [THg] were quantified in compact and spongy bone of three bone elements for pups (rib, long bone, phalange) and non-pups (occipital, mandible, nasal turbinate). Among pup bone elements, there were no differences in [THg] of compact bone (p = 0.17); however, spongy bone in ribs had greater [THg] than long bones (p = 0.03) and phalanges (p = 0.01). Among non-pup bone elements, there were no significant differences in [THg] in spongy bone; however, compact bone in nasal turbinates had greater [THg] compared with mandibles and occipitals (p < 0.01). Differences in bone composition, growth, and turnover rate likely affect Hg distribution and concentration within long bones and among bone elements. This study provides insight into a highly variable tissue that may allow for retrospective analysis of contaminants, such as Hg.
  • Trophic pathways and their relationship to growth in nearshore consumers across the northern Gulf of Alaska

    Corliss, Katherine M.; Iken, Katrin; von Biela, Vanessa; Coletti, Heather; Mincks, Sarah (2023-08)
    Highly productive nearshore ecosystems in cold-temperate regions, such as the Northern Gulf of Alaska (NGOA), are supported by macroalgae and phytoplankton at the base of their food webs. Biomass of these primary producers varies seasonally, suggesting that longer-term environmental change could also shift biomass and/or range of basal producers. Our goal was to determine how proportional contributions of organic matter from macroalgae and phytoplankton to the diet of nearshore consumer species in the NGOA vary in space and time, and if these differences affect consumer growth. We used carbon and nitrogen stable isotope analysis to investigate diet sourcing of filter-feeding mussels (Mytilus trossulus), pelagic-feeding Black Rockfish (Sebastes melanops), and benthic-feeding Kelp Greenling (Hexagrammos decagrammus) in four different NGOA regions: Katmai National Park and Preserve, Kachemak Bay, Kenai Fjords National Park, and Western Prince William Sound. All three focal species used a mix of phytoplankton- and macroalgal-based pathways in each region; however, macroalgae were the major source of organic matter in the diet of all three species. We used recent (last annual) growth recorded by shells or otoliths in each of these consumers as a measure of performance across the four regions to better understand the effect of variation in primary production sources on secondary production. The relationships between organic matter source and growth were neutral to positive for all three focal species, and only significantly positive for mussels, and for Black Rockfish in a single region. As the values for macroalgal contribution were almost always greater than 50 %, the total range of macroalgal contribution in comparison to growth was small and showed that, across this range, one source did not consistently support higher growth. The Pacific Marine Heatwave (PMH) with heat spikes in 2014-2016 and 2019 provided a natural experiment to test the effects of strong climate variation on source contributions to mussels and their growth. Mussels had high variation in macroalgal contribution to their diet, with the lowest contributions during the PMH heat spikes and highest after. This could reflect lower macroalgal primary production during PMH, but a subsequent large pulse of macroalgal detritus from a documented macroalgal die-off late in the PMH may have supplied ample food for mussels after the PMH. Mussels also grew slowest during the PMH compared to the years before and after. While macroalgal contributions were also low at this time, mussel growth rate was more strongly related to macroalgal contributions during the PMH than before or after. Therefore, macroalgal production could be an especially important pathway to support coastal consumers during specific climate regimes. With the high reliance on the macroalgal trophic pathway in all three nearshore consumers, coupled with the significant effect of the PMH on both macroalgal contribution and growth in mussels, we should expect changes in nearshore food-web pathway use and consumer growth in relation to future climate variations. Results here suggest that some of these effects could be muted in the nearshore system based on flexibility in consumers to rely on different primary producer pathways but clarifying relationships among climate, trophic pathways, and growth is important, as such changes in nearshore species could have cascading impacts on many higher trophic level predators.
  • Dietary resource use of nearshore fishes among estuaries that differ in glacial cover

    Stadler, Lindsey R.; Iken, Katrin; Gorman, Kristen; Seitz, Andrew; von Biela, Vanessa (2023-05)
    Glaciers have a major impact on the way climate change manifests in aquatic ecosystems. When glaciers are present, rising air temperatures associated with climate change can decrease water temperatures and increase freshwater flux due to glacier melt compared to the opposite pattern in neighboring watersheds and estuaries without glaciers. This study considers whether differences in glacier cover of watersheds upstream of nearshore estuaries affect fish food web dynamics, because fish are important integrators of energy flow and ecosystem processes within estuaries. Dietary resources of common nearshore fish species were compared among estuaries with a gradient of upstream glacial cover (0 - 60% watershed cover) and across discharge periods (pre-peak, peak, post-peak) in the Northern Gulf of Alaska (Kachemak Bay) using stomach content and stable carbon and nitrogen isotopes. Comparison among estuaries and all three discharge periods focused on crescent gunnels (Pholis laeta), because they are unlikely to move among estuaries and, therefore, are likely represent local conditions. Discharge period had greater influence on the diet composition and trophic niche breadth of crescent gunnels than glacial coverage. Resource use of more mobile staghorn sculpin (Leptocottus armatus) and starry flounder (Platichthys stellatus) were also considered as additional indicator species within the post-peak discharge period. Staghorn sculpin and starry flounder exploited a larger prey base compared to crescent gunnels, as expected for more mobile fishes. Although fishes differed in their dietary resource use among estuaries, there was no obvious pattern associated with the glacial coverage in any fish species examined. Diet seasonality was apparent with a larger niche breadth in crescent gunnel stomach contents during the post-peak discharge period compared to pre-peak and peak periods. Increasing discharge appears to be associated with a shift in prey composition compared to pre-peak and peak discharge periods. Higher degrees of freshwater input during periods with higher discharge volume may change the organic matter pathways that support lower trophic level prey, resulting in lower trophic position of nearshore fishes over the course of the summer. The results presented here suggest that glacier cover alone is not a major driver of estuarine food webs. It appears that environmental conditions associated with glacial cover during our study period (2020-2021) were within a range that allow nearshore fishes to have similar energy pathways and prey bases across these estuaries. The influence of glaciers on estuarine food webs may become more apparent in years of extreme warmth or drought.
  • Exploring the North American Arctic benthos: community structure and oil degradation potential of sediment bacteria and archaea

    Walker, Alexis M.; Mincks, Sarah L.; Leigh, Mary Beth; Islas, Ana Aguilar; Lopez, Andres; Collins, Eric R. (2022-12)
    The 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.
  • Seaweeds across ecosystem boundaries: from habitat formation to harvest implications

    Ulaski, Brian P.; Konar, Brenda; Iken, Katrin; Otis, Edward O.; Gorman, Kristen B.; Sikes, Derek S. (2022-12)
    This 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.
  • 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, Alaska

    Barst, Benjamin; Wooller, Matthew; Horstmann, Lara (2022-12)
    Total 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.
  • Drivers of functional ecology of the Alaskan Arctic epibenthos

    Sutton, Lauren; Iken, Katrin; Bluhm, Bodil; Hauri, Claudine; Konar, Brenda; Mueter, Franz (2022-12)
    This 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.
  • Acute toxicity of copper to three species of pacific salmon in water with low hardness and low dissolved organic carbon

    Porter, Drew E.; Barst, Benjamin; Wooller, Matthew; Westley, Peter; Gorman, Kristen (2022-12)
    Despite 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.
  • Species distribution modeling of northern sea otters (Enhydra lutris kenyoni) in a data-limited ecosystem

    Hasan, Elizabeth L.; Konar, Brenda; Gorman, Kristen; Coletti, Heather (2022-12)
    Species 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.
  • Marine and not terrestrial resources support nearshore food webs across a gradient of glacial watersheds in the northern Gulf of Alaska

    Schloemer, James W.; Iken, Katrin; Konar, Brenda; Munk, LeeAnn (2022-08)
    Estuaries 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.
  • Assessing annual nearshore carbonate chemistry trends in Alaska's marginal seas

    Currie, James; Kelley, Amanda; Miller, Cale; Mincks, Sarah (2022-08)
    One 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.
  • 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.

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