RSS 1.0Marine Biology
Includes Marine Science and Limnology
Recent Submissions
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Benthic community composition and ecosystem function in southern Kachemak Bay, AlaskaThe benthic environment in southern Kachemak Bay, Alaska provides critical ecosystem services, processing organic matter from the land and the sea, and returning nutrients to the food web. In Kachemak Bay, concerns have arisen that marine agriculture (mariculture) operations in the form of salmon hatcheries and oyster farms may have negative impacts on the local environment. This thesis investigates the seafloor sediment environment to assess these potential impacts under salmon hatchery net pens in Tutka Bay Lagoon, and under an oyster farm in Jakolof Bay. We found that beneath the net pens, high waste inputs of fish food, feces and dead fish contribute to negative impacts on the local environment. Very few sediment organisms were found, and most are likely excluded from that habitat by lack of oxygen that arises due to inputs of excess organic matter. Furthermore, the hatchery site showed high oxygen and carbon fluxes associated with microbial and physical processes, because macrofaunal organisms were not present. Time series data show how the lagoon frequently experiences conditions that are outside of the regionally expected values and indicate that waste inputs from hatchery operations, together with the isolated nature of the lagoon, contribute to low oxygen conditions persisting in the deeper portion of the lagoon. Overall, the Tutka Bay Lagoon salmon hatchery has an adverse impact on the local environment. However, oyster farms sites did not show any negative impacts on this specific environment, being similar in terms of their community and ecosystem to non mariculture sites, which are good measures of ecosystem status.
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Sea-ice bloom dynamics, putative parasitoids, and crude-oil impacts to microbiota modified by irradianceArctic sea ice serves as a critical habitat for microbial communities, supporting, in part, the Arctic food web and influencing global biogeochemical cycles. However, climate change is rapidly altering this environment leading to a shorter ice-covered period and increased light transmittance. Greater accessibility due to less ice coverage is increasing industrial and commercial activities which raises the risk of crude oil spills that threaten sea-ice microbial communities. This dissertation explores the seasonal dynamics of prokaryotes and unicellular eukaryotes during the spring algal bloom, and the impacts of potential light stress in combination with crude oil exposure on Arctic sea-ice diatoms and microbial communities with time-series data and laboratory-based experiments. Chapter 2 examines microbial community succession during the 2021 vernal ice-algal bloom near Utqiagvik, Alaska. The bloom reached was larger than previously observed in this region. An unprecedented bloom of the oil-degrading bacterium Oleispira suggested potential environmental hydrocarbon contamination. Metabarcoding and co occurrence analyses revealed that diatoms, particularly Nitzschia spp., were primary hosts for parasitoid taxa such as chytrids Cryothecomonas and, highlighting the potential for top-down control of algal populations and the maintenance of diversity. Chapters 3 & 4 investigate the interactive effects of crude oil exposure and irradiance on Arctic sea-ice diatoms. These experimental results show species-specific responses to oil, with Fragilariopsis cylindrus being highly sensitive, while Synedropsis hyperborea exhibited stimulated growth at low oil concentrations. (Meta)transcriptomic analyses in Chapter 4 revealed that oil exposure induced a switch of metabolism in diatoms from autotrophic to catabolic, particularly in pathways related to lipid degradation. The findings suggest that oil spills may favor flagellates over diatoms, shifting microbial community composition with potential consequences to biogeochemical cycles. Together, these studies provide novel insights into the importance of internal lipid reserves, alternative metabolic pathways, and microbial interactions in supporting microalgal resilience within the Arctic sympagic ecosystem.
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Spatial and temporal variability of carbohydrate compositions in cultivated Alaria marginata, Nereocystis luekteana, and Saccharina latissimaCarbohydrates derived from Laminariales (kelp), including polysaccharides and sugar alcohols, present significant market opportunities for nascent mariculture industries. These carbohydrates can enhance crop biomass value through extractive processing, with applications in medicine, manufacturing, health supplements, and bio-plastics. The relative abundance and composition of carbohydrates in kelp can vary depending on species, life history, tissue type, season, and environmental conditions. In Alaska, mariculture of kelp focuses on three species: Alaria marginata, Nereocystis luetkeana, and Saccharina latissima. This study assessed the relative abundance of carbohydrates (glucan, mannitol, alginate, and fucoidan) in these species, as well as the sulfate content of fucoidan and the ratio of mannuronic to guluronic acids in alginate (M:G ratio) as proxies of chemical attributes for these carbohydrates. Samples were collected from commercial farm sites in the Kodiak Archipelago, Prince William Sound, and Southeast Alaska between April and June of 2023. Carbohydrate composition was analyzed using high- performance anion-exchange chromatography with pulsed amperometric detection. Composition varied among species, where on a dry mass basis, A. marginata had the highest average contents of fucoidan and alginate, while S. latissima had the highest average glucan content. Fucoidan was the only measured component to have consistent trends over time across sites for all species. Inconsistency in trends over time across sites for biochemical components was most notable in A. marginata. Seawater temperature was the most consistent environmental predictor across species, having a moderate, negative correlation the M:G ratio in all species and a moderate, positive correlation with fucoidan in A. marginata and S. latissima. Of the species studied, S. latissima harvested in June may have the highest potential for extractive processing in Alaska. This species had a balanced composition of valuable carbohydrates, high consistency across sites, and high potential yield from a relatively large fraction of solids in wet biomass combined with generally high wet mass growth. This study highlights the complex variability of carbohydrate compositions in kelp and provides the first detailed assessment of A. marginata, N. luetkeana, and S. latissima in Alaska.
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Cultivation protocols for the red seaweeds, Devaleraea mollis and Palmaria hecatensis from AlaskaSpecies diversification is crucial for the long-term viability, competitiveness, and sustainability of the seaweed farming industry in the United States. This study investigated the effects of temperature (4, 8 and 12 °C), photoperiod (8L:16D, 12L:12D and 16L:8D), and irradiance (20, 40, 100 ± 10 μmol photons m-2 s-1) on the specific growth rate (SGR) of Devaleraea mollis and Palmaria hecatensis from Alaska. Outputs were used to adjust indoor cultivation protocols for D. mollis and develop the first protocols for Palmaria hecatensis. This study also explored the use of two relatively low-cost commercial nutrient products (F/2 and Jack's Special 25-5-15) as potential alternatives to the recommended nutrient medium, von Stoch Enrichment medium. Assessments focused on determining whether their use resulted in similar SGRs without compromising biomass quality or raising production costs. Quality was assessed as a function of protein and pigment content in the tissue, with higher content considered higher tissue quality. Both species showed significant differences in SGR for all factors tested. Results showed that both species responded differently to each factor, indicating distinct ecological and physiological adaptations. D. mollis exhibited higher growth rates in warmer temperatures and responded to higher irradiance levels with spore release but showed no clear preference between neutral and long-day photoperiods. In contrast, P. hecatensis demonstrated higher growth rates in cooler environments with a long-day photoperiod promoting the most growth without spore release. Nutrient supplementation revealed that growth in D. mollis was affected by nutrient formulation, while P. hecatensis showed no significant growth variation. Outcomes also revealed that protein and pigment content could be increased depending on the formulation used. These findings underscore the importance of species and geographic-specific protocols for seaweed farming. Further research is needed to optimize the potential cultivation protocols provided here. Cultivation protocols would also benefit from exploring the ecological and physiological nuances of both species.
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Sea otter interactions with mariculture oyster farmsSea otters (Enhydra lutris) are considered a keystone species and can be found around mariculture oyster farms. While oyster farms and sea otters have been coexisting in some locations, sustaining these farms, and the growing interest in expanding them, necessitates a comprehensive evaluation of potential interactions. Here, sea otter interactions with oyster farms were assessed through behavioral observations (i.e., activity and foraging dives) in oyster farms, adjacent non-farm areas (controls), and bays with no farming activity (references). Behavioral observations, conducted through scan surveys, captured sea otter activities (e.g., resting, grooming, swimming, and foraging). Targeted foraging observations tracked foraging success and prey (species and count). This study hypothesized that sea otters preferentially use oyster farms for foraging and resting activities compared to non-farm areas. Contrary to our hypothesis, sea otter activities showed no significant difference in these behaviors between oyster farms and controls. Similarly, foraging behavior, including success and prey diversity did not significantly differ among the areas. The dominant prey items in our study included clams (e.g., Saxidomus gigantea), crabs (e.g., Telmessus cheiragonus, Cancer productus), and mussels (e.g., Mytilus trossulus). Notably, there were no observations of farm oysters being consumed by sea otters. There were significant differences in the average number of prey consumed per sea otter per dive between the control and reference areas, with the control area averaging 2.6 prey items per dive (SD = 3.6), and the reference area nearly doubling to 4.8 prey items per dive (SD = 7.3). These differences may be attributed to variations in prey biomass and environmental conditions. Our observations indicate that there are no discernible differences in overall sea otter activity or foraging behavior in the presence of oyster farms.
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Direct and cascading effects of sea star wasting on rocky intertidal communitiesPredation is an important driver of rocky intertidal community structure. Top predators like sea stars often regulate competitive species like barnacles and mussels by preying on them, which maintains ecosystem diversity. Fluctuations of top predators can have cascading effects in terrestrial, freshwater, and marine environments, often resulting in the restructuring of communities and ecosystems into alternative states. Sea star wasting (SSW) was a large-scale disturbance, starting in 2013 in the East Pacific Ocean and ranging from Alaska to Mexico, that removed sea stars from the rocky intertidal. While recovery has been ongoing in many places, community-wide effects may persist in places where sea stars have not recovered, or where predation continues to be reduced. In Alaska, it remains unclear if sea stars have recovered and if SSW had direct effects on intertidal sea star prey, which are often mid-trophic organisms, and if there were cascading effects down the food web. I used a long-term monitoring dataset from Gulf Watch Alaska (2006-2022) from four monitoring regions (Katmai Park and Preserve (KATM), Kachemak Bay (KBAY), Kenai Fjords National Park (KEFJ), and western Prince William Sound (WPWS)) with multiple sites each to investigate motile invertebrate community structure changes in relation to SSW. Permutational multivariate analysis of variance tests were used to test changes in motile invertebrate community structure and were paired with linear mixed effects models and analysis of variance tests to track any cascading changes down the food web. My results suggest that SSW had significant but variable effects on motile invertebrate community structure across different regions in the Gulf of Alaska. Two regions (KATM and KEFJ) significantly changed and then returned to the pre-SSW structure after 2-3 years, one region (KBAY) significantly changed and has not returned to the pre-SSW structure, and one region (WPWS) remained unchanged. Other than motile invertebrates, I found no indication of trophic cascades despite the significant reduction of sea stars across all regions. My analyses also showed the recovery of sea stars in many of the monitoring regions. Results of this study suggest that rocky intertidal ecosystem resilience and stability in the Gulf of Alaska may be dependent on recruitment dynamics and predator redundancy. This resilience and stability may also vary among regions, with some regions being more susceptible to large-scale disturbances than others.
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Effect of macroalgae diet on growth rate and nutrition of the pinto abalone, Haliotis kamtschatkanaDeveloping methods for the cultivation of the pinto abalone, Haliotis kamtschatkana, has seen increased attention, both by groups using restoration aquaculture to reestablish endangered populations in Washington and British Columbia, and in the State of Alaska, where pinto abalone are viewed as a promising new species for commercial mariculture. To enhance the viability of cultivating H. kamtschatkana for commercial and restoration purposes, more information is needed on the optimal macroalgal diet that maximizes abalone growth and nutrition. This study compares the suitability of two commonly cultivated species of macroalgae as feed: Saccharina Iatissima, a kelp with relatively low protein content, and Devaleraea mollis, a rhodophyte with comparatively higher protein content. Fifty H. kamtschatkana specimens, each measuring 50 ± 10 mm, were collected from the wild and fed either S. latissima, D. mollis, or an alternating diet of the two for 28 weeks. Feed consumption was measured weekly, while shell growth and weight change were recorded every two months. Despite consuming significantly more S. latissima than D. mollis (p = 0.000), H. kamtschatkana showed no significant difference in specific growth rate (p = 0.775) or linear growth rate (p = 0.746) among the diets. Feed conversion efficiency was significantly higher for D. mollis than S. latissima (p = 0.000), although there was no significant difference in protein conversion efficiency (p = 0.129). Proximate composition analyses showed no significant difference in protein, lipid, carbohydrate, or caloric content across the diets. Additionally, sexual dimorphism was observed, with females exhibiting significantly higher daily feed consumption (p = 0.001), specific growth rate (0.003), and linear growth rate (p = 0.001) than males. These results indicate that while both macroalgae species are suitable as feeds for H. kamtschatkana cultivation, the benefits of a D. mollis diet are less pronounced compared to other commercially cultivated abalone species. This study provides actionable insights for those interested in cultivating H. kamtschatkana for commercial or restoration purposes and adds to our understanding of an environmentally and culturally important species in the Northeast Pacific Ocean.
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Characterizing ocean change impacts on three marine species vital to recreational, subsistence, and commercial fisheries in AlaskaGlobal climate change, facilitated by increased greenhouse gas production, is driving physical and chemical alterations to the marine environment, including a long-term decrease in oceanic pH, referred to as ocean acidification (OA), and an increase in global marine temperature, referred to as ocean warming (OW). Alterations to the chemistry and temperature of the marine environment may result in bottom-up community restructuring mediated by changes in food web dynamics. In Alaska, there are many species-specific knowledge gaps, thus necessitating an assessment of the potential sensitivity of said species to climate change-related conditions. Pacific razor clams (Siliqua patula), bidarkis (Katharina tunicata), and pink salmon (Oncorhynchus gorbuscha) are prominent species utilized by Alaska’s recreational, subsistence, and commercial fisheries, respectively. This dissertation examines how, and to what extent, anthropogenically forced ocean change impacts these organisms, while simultaneously bridging knowledge gaps regarding their development and biomineralogy. This research 1) characterized the embryonic and early larval development of S. patula, and 2) examined the developmental and biomineralogical responses of S. patula in Alaska to elevated and variable pCO2 conditions. Additionally, I 3) investigated the impact of future OA and OW conditions on bidarki physiology, biomineralogy, and behavior, and 4) assessed the impact of both elevated pCO2 and reduced food availability on juvenile pink salmon. My research yielded several novel discoveries. Firstly, shell development in S. patula involves a unique concretion development process, which could leave this species vulnerable to dissolution in an acidic environment, and the developmental rate of S. patula concretions is accelerated under future OA conditions. Secondly, results suggest that bidarkis are resilient to future conditions of OA and OW. In addition, bidarkis exert a strong level of biomineralogical control under OA conditions, as calcification increased within the pleural shell margin (despite observed de-silicification) and display no evidence of dissolution in the jugal lamina. This robust response could position bidarkis as particularly successful grazers in the rocky intertidal of a future warmer and more acidic ocean. Juvenile pink salmon displayed the most sensitivity to ocean change of the species investigated here, experiencing significant reductions in conditional index and mass, significant increases in cortisol levels and routine metabolic rate, while producing significantly larger otoliths (mass-corrected) under elevated pCO2 conditions. The interaction between elevated pCO2 and reduced food availability also altered caudal fin morphology significantly.
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Eavesdropping on killer whales: distribution, calling rates, and acoustic abundance of fish-eating and mammal-eating killer whales in the Gulf of AlaskaThe 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.
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Environmental and biotic habitat attributes affect rocky intertidal community variability in glacially influenced estuariesClimate 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.
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Effects of commercial otter trawling on essential fish habitat of the southeastern Bering Sea shelfSediment 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.
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Effects of placer gold mining on stream macroinvertebrates of interior AlaskaPlacer 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.
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Photosynthetic response of phytoplankton to changing light intensity in a southcentral Alaskan lakeLittle 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.
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Aquatic ecology of two subarctic lakes: Big and Little Minto Lakes, AlaskaDuring 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).
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The effect of sedimentation on spore settlement and recruitment of the endemic Arctic kelp, Laminaria solidungulaThe 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.
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Variability of total mercury concentrations in Steller sea lion bone locations and bone elementsMercury (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.
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Trophic pathways and their relationship to growth in nearshore consumers across the northern Gulf of AlaskaHighly 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.
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Dietary resource use of nearshore fishes among estuaries that differ in glacial coverGlaciers 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.
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Exploring the North American Arctic benthos: community structure and oil degradation potential of sediment bacteria and archaeaThe Chukchi and Beaufort seas benthic habitats are home to a multitude of ecologically and commercially important organisms that are subject to ongoing environmental changes, including the impacts of climate change and increased exposure to contaminants. Benthic bacteria and archaea can be considered biogeochemical engineers. They play a major role in organic matter (OM) degradation and nutrient cycling and their community structure can reflect changes in environmental conditions such as OM composition and quantity, nutrient availability, redox conditions, and natural/anthropogenic contaminants (e.g. petroleum hydrocarbons). Yet, sediment microbial communities have rarely been examined in these marginal seas of North American Arctic. In this dissertation, I characterized marine sediment microbial communities along environmental gradients in the Beaufort (Chapter 2) and Chukchi seas (Chapter 3) and assess Arctic benthic microbial community response to oil exposure (Chapter 4). I assessed diversity, community structure, and environmental correlates of prokaryotic communities via 16S rRNA amplicon sequencing in surface sediments (upper 1 cm) from the Northern Bering Sea to the Amundsen Gulf in the southern Beaufort Sea. On a broad spatial scale encompassing the whole study area, I observed three distinct microbial assemblages. One assemblage was characteristic of the Northern Bering-Chukchi seas shelf, and two distinguished nearshore and offshore sediments in the Beaufort Sea. Within the Beaufort Sea, four assemblages were identified, reflecting habitat heterogeneity with respect to OM loading, water depth, and nearshore/riverine input, including a major influence of the Mackenzie River. Two assemblages were distinguished within the Bering-Chukchi region, including one representative of suboxic sediments and one suggesting influence of phytodetrital OM input as evidenced by the abundance of diatom/particle-associated microbes. These two assemblages may also reflect differences between local versus advective OM inputs. Incubation experiments exposing Arctic marine sediments to fresh and weathered crude oil under anaerobic and aerobic conditions were performed to assess oil biodegradation potential and identify putative oil-degrading microbes in the benthos. Molecular analyses revealed that significant community shifts occurred in the oiled treatments, with distinct communities emerging following exposure to fresh versus weathered oil, and in oxic versus anoxic conditions. The work presented here constitutes the first large-scale survey of benthic microbes in this region of the North American Arctic, including their response to petroleum contamination, generating valuable baseline data for the changes to come.
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Seaweeds across ecosystem boundaries: from habitat formation to harvest implicationsThis dissertation broadly investigates the response of wild stock seaweeds to harvesting, and their role as biogenic habitat formers when cast ashore. Seaweeds are important primary producers and foundation species that maintain their functional roles across coastal ecosystem boundaries. Climate-driven loss of seaweed biomass, including that of kelp forests, is exacerbated by other human-related activities that directly impact their persistence, such as overharvesting. Attached rockweeds and kelps are commonly harvested for food, while diverse assemblages of beach-cast seaweed wrack are collected for fertilizer. The importance of wrack habitat in Alaska has not been extensively explored, especially in regions where there is a growing interest in harvesting by coastal communities. This research explores precautionary approaches to lessen wild stock seaweed decline in the face of increased harvest interests by: 1) characterizing information on reproductive timing, standing crop, and regrowth potential of attached populations; 2) investigating reproductive viability of seaweed wrack and identifying how landscape variables influence wrack distribution through paired on-the-ground and aerial surveys; and 3) characterizing wrack-associated macrofaunal communities and determining successional states in aging wrack. Regrowth following harvest of attached focal seaweeds (i.e., Fucus distichus, Saccharina latissima, and Nereocystis luetkeana) was generally low after two months, but the amount of biomass after four- and six-months post-harvest was more comparable to non-harvested areas. Depending on the species (e.g., F. distichus), attached individuals that became reproductive at larger sizes were associated with lower density and lower biomass areas with slower recovery. Differences in diversity and composition of wrack were correlated with coastline (substrate type, slope, and exposure) and adjacent watershed characteristics (percent glacial cover and range in seawater salinity). On-the-ground and drone-based surveys of beach-cast wrack both revealed seasonal patterns of patchy (spring) and continuous (summer) distribution. Macroinvertebrate community diversity was positively correlated with seaweed biomass and tidal height of the wrack line. Furthermore, succession experiments revealed that aged wrack harbored diverse and changing macroinvertebrate communities over time, with decomposers being early colonizers, and predators arriving later. Altogether, the findings of this research offer key information to developing sustainable harvest regulations in Alaska, as human use of seaweed increases.
