• Regulation of ecdysteroid and vitellogenin levels during the molt and reproductive cycles of female dungeness crab, Cancer magister

      Thomton, Jamie David (2005-12)
      The reproductive cycle of Dungeness crabs is complicated by the requirement for molting prior to mating. The temporal requirements for molting and ovarian maturation may prohibit an annual reproductive cycle in a proportion of crabs. The goal of this study was to quantify temporal concentrations of circulating ecdysteroids and vitellogenins in female crabs during an annual cycle. Hemolymph in laboratory maintained crabs was sampled to assess physiological state (molting or reproduction). In laboratory crabs, ecdysteroid concentrations were low during intermolt (20.3 ng/ml), increased to maximal levels 15 days before ecdysis (1,886.5 ng/ml), and declined to low concentrations (<90 ng/ml) 5 days before ecdysis. Premolt duration was 150 days, with peak molting in November. Vitellogenin concentrations increased 6-fold during induced (via eyestalk ablation) ovarian maturation over a 90 ± 7.4 day vitellogenic period, and 4-fold for natural ovarian maturation over a 75 to 100 day period. The capability to predict ecdysis 150 days before molt and spawning 100 days before egg extrusion through hemolymph analysis is useful in molt and reproductive assessment of Dungeness crab populations. Additionally, in a preliminary study, reproductive failure and shell-disease were induced by physiological stress due to captive environmental conditions
    • The relationship between the depth to the 0°C isotherm of the Arctic Ocean and atmospheric forcing

      Moon, Sookmi (2004-05)
      Empirical Orthogonal Function (EOF) analyses of the depth to the 0°C isotherm of the Arctic Ocean were performed to determine the variability of the depth to the 0°C isotherm in the Arctic Ocean. The data are from the 'Environmental Working Group - Joint US. Russian Atlas of the Arctic Ocean.' The first three modes explain 99% of the total variance with each mode explaining 51 %, 26%, and 23%, respectively. Mode 1 shows the pattern of the outflow through Fram Strait and the Lincoln Sea. Mode 2 shows the variability of the inflow from the Barents Sea and the variability of the outflow through the Canadian Archipelago as well as the variability of the Transpolar Drift. Mode 2 has a close relationship with atmospheric conditions (Arctic Oscillation or North Atlantic Oscillation index). Mode 3 is significantly correlated with the annual mean vorticity index, when the vorticity index leads by 1 year. Composite analyses of the data using the AO, NAO, and vorticity index confirm that the EOF analyses of this study are valid. This study shows that the variability of the 0°C isotherm of the Arctic Ocean is significantly correlated with atmospheric conditions.
    • Reproductive and larval biology of northern shrimp, Pandalus borealis Kroyer, in relation to temperature

      Nunes, Pepsi (1984-05)
      The northern shrimp, Pandalus borealis Kr^yer, is an important fishery resource in Alaska. However, a drastic decline in the commercial catch since 1978 poses a serious problem for the fishery. This study examined the effects of temperature on reproduction and larval survival of P. borealis. These are factors though to be vital to the determination of year class strength. P. borealis was found to have narrow thermal requirements for egg production with moderate (6°C) to low (3°C) temperatures generally more favorable than high (9°C) temperatures. In contrast with egg production, larval survival was enhanced by higher (6 and 9°C) temperatures. This study provides useful information for management of the fishery by demonstrating that temperature can trigger flucuations in the commercial catch from 5-50% through its effects on rates or reproduction and larval survival, and thereby population size. In warm water areas averaging >6°C, temperature exerts its main influence on reproduction, causing fecundity to vary by as much as 50%. While in colder areas average <3°C, fecundity and larval survival can vary with temperature by as much as 20 and 40%, respectively. Use of the information derived here requires monitoring temperature in the major fishery areas to detect changes in abundance of ovigerous females, egg number and larval mortality. Changes in these parameters are valuable indicators of stock condition when combined with abundance surveys and fishing intensity estimates.
    • Reproductive Potential Of Pacific Cod (Gadus Macrocephalus) In Alaska

      Ormseth, Olav Aleksander; Norcross, Brenda L. (2007)
      The reproductive potential of female fishes, which results from the number of eggs they produce and the quality of individual eggs, is a critical factor in fisheries biology. Reproductive potential is important to individuals because maternal fitness is the product of the number of offspring produced and how many offspring survive. The growth rate of populations and their capacity for supporting commercial fisheries also depend on the number of viable offspring that females produce. I studied the reproductive potential of female Pacific cod (Gadus macrocephalus) in the North Pacific Ocean. Pacific cod is an important ecological and economic resource, yet much of its reproductive biology remains unexplored. I used several different approaches to investigate whether egg number or egg size are more important in determining reproductive potential, and to evaluate factors that influence reproduction. An analysis of life history variation among Pacific cod in Canada and Alaska demonstrated that despite differences in life history strategies, females from different populations had similar lifetime reproductive success (a proxy for individual fitness). I also collected Pacific cod in the Gulf of Alaska, eastern Bering Sea, and western Aleutian Islands from 2002 to 2005. Biochemical analyses of Pacific cod eggs revealed that Pacific cod produce low-energy eggs that are adapted for rapid development on the seafloor. Larger females produce eggs with less arachidonic acid (a fatty acid that has been linked to egg quality) than smaller females, suggesting that they may sacrifice egg quality to maintain fecundity. Determination of fecundity and egg size in 590 females from different areas and years revealed that maternal length and weight are excellent predictors of fecundity, but that variability in egg size is not related to the age or size of females, The greatest difference in reproductive potential among years and areas was reduced egg size in the eastern Bering Sea in 2003, which may have been due to changes in ocean temperature or prey availability that impacted the ability of females to store energy. These results suggest that female Pacific cod maximize their fitness through increased egg production, not egg quality, and that their reproductive success is under strong environmental control.
    • Resource Partitioning Among Sympatric Stellar Sea Lions And Northern Fur Seals On Lovushki Island, Russia

      Waite, Jason N.; Andrews, Russel; Castellini, Michael; Atkinson, Shannon; Rea, Lorrie; Trumble, Stephen (2010)
      The competitive exclusion principle maintains that one of two non-interbreeding species occupying the same ecological niche and geographical territory will be displaced if population growth is not the same between species. Steller sea lions (Eumetopias jubatus; SSL) and northern fur seals (Callorhinus ursinus; NFS) breed sympatrically on four rookeries in the Russian Far East, creating the potential for inter-specific competition for limited prey resources. Approximately 1,000 SSL and 14,000 NFS breed on Lovushki Island in the Kuril Island chain. An additional 13,000--14,000 juvenile NFS are present during the breeding season. The partitioning of forage resources among breeding SSL and both breeding and non-breeding NFS from 2003--2008 was examined through analysis of prey remains recovered from scats and spews, stable isotope (SI) analysis of vibrissae, fatty acid (FA) analysis of blubber, and analysis of foraging behavior through satellite-linked telemetry. Analysis of prey remains indicated a biologically significant overlap in the prey species and size selection of SSL and juvenile NFS and significant differences between the diets of SSL and breeding NFS. SSL fed primarily on Atka mackerel, while breeding NFS fed primarily on cephalopods and northern smoothtongue. SI analysis indicated significant differences in the trophic level and relative foraging location. SSL foraged at a higher trophic level, nearshore, and benthically, while NFS foraged at a lower trophic level, offshore, and pelagically. Analysis of FA signatures also suggested significant differences in the relative diets of breeding NFS and SSL. Foraging behavior analysis also indicated that SSL foraged nearshore and benthically and breeding NFS foraged offshore and pelagically. The combination of these four methodologies suggests breeding NFS and SSL partition their forage resources by prey type and prey size, as well as spatially. This partitioning of resources between breeding animals currently allows both species to coexist within the same geographical region and likely reflected the differences in foraging abilities and provisioning strategies of the adults, as well as the fasting abilities of their pups. However, continued growth of the non-breeding NFS population on Lovushki Island may lead to the competitive exclusion of SSL due to inter-specific competition for food resources.
    • Retrospective Analysis Of Marine Biological Data From Port Valdez, Alaska: A Case Study In Long -Term Monitoring

      Blanchard, Arny L.; Fedev, Howard (2006)
      Efforts to understand anthropogenic effects within the Port Valdez study area provide a simple and adaptive model for developing and refining hypotheses to measure the structure of and detect, change in nearshore and benthic habitats. Drivers of change detected by this study are the 1964 Prince William Sound earthquake and the oil transportation and salmon aquaculture industries within the fjord. The study area is a glacial-outwash fjord characterized by strong seasonal and spatial environmental gradients due to glacial influences including seasonally low salinity, high suspended sediment loads, and subsequent high sedimentation rates. Direct and indirect effects from intolerance to low salinity are important in organizing intertidal communities as is habitat structure. Previously unrecognized subtle effects on subtidal fauna from anthropogenic stressors near the marine oil terminal in Port Valdez are identified. Demonstration of statistical methods (variogram estimation, repeated measures analysis of variance, and geostatistical modeling) for field studies with spatially and temporally correlated data should be useful to others seeking to establish new long-term studies or analyze previously collected, long-term field data. Investigation of the re-adjustment of benthic fauna from a large earthquake and ecosystem-level effects of salmon aquaculture are not readily available and this dissertation provides a reference point for any such future studies. Although re-adjustment from the large earthquake was a key process during the study period, salmon aquaculture appears to have a strong effect on the benthic ecosystem. The model of detecting change is simple and adaptive and provides inputs for larger models and scientific investigations in marine ecosystems. Broad questions are developed through a long-term study of an ecosystem. The hypotheses formulated are then evaluated and refined through retrospective analysis of long-term data and results can be used to refine larger models. This dissertation contributes rigorous, statistically bounded biological time series to regional monitoring programs by providing small-scale, ecological information necessary for larger models. As a result, the information provided in this dissertation should increase the accuracy of ecological models and aid in the management of marine resources.
    • A retrospective assessment of primary productivity on the Bering and Chukchi Sea shelves using stable isotope ratios in seabirds

      Abromaitis, Grace Elizabeth; Schell, Donald; Castellini, Michael; Springer, Alan (2000-12)
      Recent declines of marine mammal seabird populations in the Bering Sea have raised the question of whether the changes are caused by fishing pressure or a decrease in ecosystem carrying capacity. Stable carbon (¹³C⁾ and nitrogen (¹⁵N⁾ isotope ratios in Thick⁻billed Murre muscle and feathers were used as indicators of changing seasonal primary production. ¹³C values in phytoplankton vary directly with growth rates and are passed up the food web to consumers. Muscle and feather ¹³C values decreased over the period 1976-1998 suggesting a decline in Bering/Chukchi continental shelf primary production. Carbon isotope ratios in murres were correlated with bowhead whale baleen isotope ratios and to some climate indices. In contrast, ¹⁵N values in the birds showed no significant change indicating no concurrent shifts in trophic status.
    • The role of stratification in the spring ice edge bloom in the Bering Sea: a numerical model

      Freed, Martin (1984-09)
      Marginal ice edge zones are unique frontal systems with air-ice-sea interfaces. Phytoplankton blooms which occur along the edge of some melting ice packs in the spring, appear to be related to melt water driven density stratification. In this thesis a numerical model of a marginal ice edge zone is constructed. The wind driven circulation and spring phytoplankton bloom at the Bering Sea ice edge are simulated as functions of air-ice-sea-biology interaction. It was found that as long as the ice was allowed to melt, blooms occur regardless of wind direction. However, because of the compactness dependent melt scheme invoked, the faster the ice advects out from the pack, the faster the water column stratifies. The speed and the area of the bloom depend on the rate and extent of stratification. The model data compare favorably with field data.
    • Satellite evidence of physical features and processes in the Bering Sea

      Paluszkiewicz, Theresa (1982-05)
      Satellite infrared imagery is used to study temporal and spatial relationships of physical features and processes in the Bering Sea. A two-year collection of enhanced infrared imagery reveals that the maximum extent of the ice corresponds with the location of the Bering Slope current. Sea surface temperature patterns visually correlate with the 50-m and 70-m bathymetric contours. Processes which establish fronts in these regions are possible explanations for this correlation. Warm surface water extending from the Gulf of Alaska, through the Aleutian passes into the Bering Sea, is found simultaneously with warm surface water and eddies along the shelf break. Spatial and temporal relationships of these patterns imply surface circulation in the Bering Sea basin with inflow of Gulf of Alaska water through the Aleutian passes, cyclonic flow in the basin, and flow along the shelf by the Bering Slope current. Several generating mechanisms for the eddies are proposed.
    • Saxitoxins: role of prokaryotes

      Baker, Tracie Renee (2001-05)
      Saxitoxins, the toxins associated with paralytic shellfish poisoning (PSP), are synthesized by dinoflagellates, cyanobacteria, and possibly bacteria. The specific objectives of this study were to determine growth conditions that promote high and low levels of toxin accumulation in Aphanizomenon flos-aquae (cyanobacterium) and Pseudomonas stutzeri (bacterium). Putative saxitoxins of P. stutzeri identified by HPLC-FLD in this study, and previously by other laboratories, were determined to be 'imposters' based on their chemical and physical properties, suggesting that this bacterium may not synthesize PSP toxins. In the cyanobacterium, toxin production was enhanced under higher light intensities and temperatures. Toxin accumulation reached maximal levels when cellular nitrogen was from either (NO₃-+NH₄)-N or N₂-N, while urea-N drastically reduced toxin levels. These data will be used in future studies aimed at identifying the genes involved in saxitoxin synthesis via molecular technologies that rely upon expression of the 'saxitoxin genes' under different growth conditions.
    • Sea ice near-inertial response to atmospheric storms

      Stoudt, Chase A.; Simmons, Harper; Gradinger, Rolf; Johnson, Mark; Hibler, William (2015-05)
      A moored oceanographic array was deployed on the Beaufort Sea continental slope from August 2008-August 2009 to measure Arctic sea ice near-inertial motion in response to rapidly changing wind stress. Upward looking Acoustic Doppler Current Profilers detected sea ice and measured ice drift using a combination of bottom track and error velocity. An analysis of in-situ mooring data in conjunction with data from National Center for Environmental Prediction (NCEP) reanalysis suggest that many high and low pressure systems cross the Beaufort in winter, but not all of these create a near-inertial ice response. Two unusually strong low pressure systems that passed near the array in December 2008 and February/March 2009 were accompanied by elevated levels of near-inertial kinetic energy in the ice. The analysis suggests pressure systems which have a diameter to ground track velocity ratio close to 3/4 of the local inertial period can excite a large near-inertial response in the sea ice. It is conjectured that this results from the combined effect of resonance arising from similar intrinsic timescales of the storm and the local inertial period and from stresses that are able to overcome the damping of sea ice arising from ice-mechanics and damping in the ice-ocean boundary layer. Those systems whose intrinsic times scales do not approach resonance with the local inertial period did not excite a large near- inertial response in the sea ice. From an analysis of two storms in February 2009, and two in December 2008, it appears that wind stresses associated with previous low pressure systems preconditioned the ice pack, allowing for larger near-inertial response during subsequent events.
    • Seabird Habitat Use And Zooplankton Abundance And Biomass In Relation To Water Mass Properties In The Northern Gulf Of Alaska

      De Sousa, Leandra; Coyle, Kenneth; Weingartner, Thomas; Barry, Ronald; Springer, Alan; Jr., George Hunt (2011)
      Understanding of biological and physical mechanisms that control the Gulf of Alaska (GOA) ecosystem is of major importance to predicting the responses of bird and zooplankton communities to environmental changes in this region. I investigated seasonal (March-October) changes in seabird abundance in relation to changes in zooplankton biomass and water mass properties from 1998 to 2003. Oceanodroma furcata and Fratercula cirrhata were most abundant during the peak of the zooplankton production season (May-August). Overall abundance of seabirds did not follow seasonal changes in zooplankton biomass. Seabird abundance was low in the study area when compared to other regions in the GOA. Furthermore, low bird densities suggest that productivity in this study area is not high enough to sustain a significant seasonal increase in local seabird abundance. I further investigated the distribution and abundance of seabird foraging guilds across the neritic and oceanic domains in relation to water mass properties and zooplankton biomass during March and April. Overall zooplankton biomass increased from the inner shelf to the oceanic domain. Highest density of subsurface-foraging seabirds occurred in the middle shelf and surface-feeding seabirds were most abundant in the middle shelf and oceanic domain. Murre (Uria spp.) abundance was positively correlated with the biomass of Thysanoessa inermis, and Northern Fulmars (Fulmarus glacialis) were associated with cephalopod paralarvae and Eucalanus bungii. Elevated biomass of Thysanoessa inermis in March and April may be an important factor influencing habitat choice of wintering murres in this region. Lastly, I investigated the inter-annual variation in the abundance of sixteen zooplankton taxa in relation to water mass properties during May from 1998 to 2009. Significant variations in temperature, salinity and zooplankton abundance were identified. Thysanoessa inermis and Calanus marshallae had increased abundances in years when there was a strong phytoplankton spring bloom preceded by anomalously cold winters. However, abundances of Pseudocalanus spp., Neocalanus plumchrus/Neocalanus flemingeri, Euphausia pacifica and Oithona spp. were not strongly affected by relatively higher mean water temperatures. The abundance of zooplankton in the northern GOA was highly influenced by advective processes.
    • Seabirds at sea in relation to oceanography

      Day, Robert Hugh (1992)
      This study investigated the macroscale distribution of seabirds in relation to oceanography in a neritic environment characterized by well-defined water masses (the northern Bering Sea) and an oceanic environment characterized by weaker differences between water masses (the northern North Pacific Ocean). In the northern Bering Sea, the total density (birds/km$\sp2)$ of all seabirds combined and densities and/or frequencies of occurrence of seven of nine species of seabirds that exhibited significant differences among water masses showed the strongest attraction to Anadyr Water. In general, attractions were second highest in Bering Shelf Water, third highest in Two-layered Water (Alaska Coastal Water overlying Bering Shelf Water), and lowest in Alaska Coastal Water. This pattern of seabird distributions reflected distributions of zooplankton biomass, which were highest in Anadyr Water and consisted of species that were large enough to be eaten directly by seabirds. Further, whereas copepods in Bering Shelf Water also are large, they are much smaller in Alaska Coastal Water and, thus, must pass through more trophic levels to fishes before the energy is directly accessible to seabirds. Consequently, zooplankton-based food webs dominated in Anadyr and Bering Shelf waters and fish-based food webs dominated in Two-layered and Alaska Coastal waters. In addition, seabirds concentrated near a strong, mesoscale thermal front between Bering Shelf and Alaska Coastal waters. In the northern North Pacific, assemblages of seabirds exhibited three main groupings, a "subarctic assemblage," a "transitional assemblage," and a "'subtropical/tropical assemblage." These assemblages matched those for zooplankton, squids, and fishes in the same vicinity, suggesting that there are geographically- and temporally-stable biological communities in the North Pacific that are associated with well-defined, persistent physical environments. The total density of all seabirds combined and densities and/or frequencies of occurrence of 13 of 16 species of seabirds that exhibited significant two-way ANOVAs exhibited primarily a water mass effect; only one species exhibited primarily a year effect, and two exhibited primarily an interaction (i.e., a change in habitat use between years).
    • Seasonal abundance and diversity of nearshore fishes around Steller sea lion haulouts of Kodiak Island

      Hegwer, Catherine L. (2003-12)
      Nearshore fishes around haulouts are potential prey for Steller sea lions, especially pups, as they learn to forage and supplement their milk diets during weaning. Visual surveys in July and November 2001, and March, May and July 2002 were used to quantify spatial and temporal variation in fish diversity and abundance around two Steller haulouts and two control sites. SCUBA divers sampled depths of 9, 15, 21, 27, and 33 m. Concurrent habitat surveys were used to quantify substrate, macroalga and benthic invertebrate cover. Steller haulout sites had fewer fish than control sites, but similar species richness and species composition at the 9, 15 and 21 m depths during the summer sampling periods. In winter, fish were fewer but more evenly distributed. Habitats were not significantly different between Steller haulouts and control sites. All sites had seasonal cover of canopy forming kelp, and overstory algal cover was heavy down to 21 m. At approximately 27 m the habitat changed abruptly from kelp-covered bedrock to bare gravel and shell hash. While nearshore fish are an important component of Steller diets, results from this study do not indicate that fish assemblages at haulouts are substantially different from other headland sites.
    • Seasonal and interannual patterns of larvaceans and pteropods in the coastal Gulf of Alaska, and their relationship to pink salmon survival

      Doubleday, Ayla; Hopcroft, Russell; Gradinger, Rolf; Coyle, Kenneth (2013-12)
      Larvacean (=appendicularians) and pteropod (Limacina helicina) composition and abundance were studied with physical variables each May and late summer across 11 years (2001 to 2011), along one transect that crosses the continental shelf of the subarctic Gulf of Alaska and five stations within Prince William Sound (PWS). Collection with 53-µm plankton nets allowed the identification of larvaceans to species: five occurred in the study area. Temperature was the driving variable in determining larvacean community composition, yielding pronounced differences between spring and late summer, while individual species were also affected differentially by salinity and chlorophyll-a concentration. During the spring Oikopleura labradoriensis and Fritillaria borealis were most abundant and present at all stations. Late summer had highest abundances of O. dioica at nearshore stations, while F. borealis dominated numerically at outer stations. The 53-µm plankton nets collected higher abundances of Oikopleura spp., Fritillaria spp., and L. helicina than coarser 150 and 505-µm plankton nets. Limacina helicina abundance had a significant interaction effect among years, seasons and station location. Limacina helicina abundance in nearby PWS explained 30% of the variability in pink salmon survival; however, no significant correlations existed with larvacean or L. helicina abundances from the Gulf of Alaska stations.
    • Sensitivity to hydrocarbons and cytochrome P4501A enzyme activity in Arctic marine birds and waterfowl

      Riddle-Berntsen, Ann E.; Hollmén, Tuula; Buck, C. Loren; Aguilar-Islas, Ana (2017-12)
      The Arctic is host to a taxonomically diverse group of birds, including species of conservation and subsistence importance that spend many months of their annual cycle in the region. With prospects for oil and gas resource development and increases in vessel traffic in the Beaufort and Chukchi Seas, arctic birds could be valuable bioindicators to monitor contaminants and specifically hydrocarbons from crude oil. Using liver cytochrome P4501A (CYP1A) activity, I measured levels of hydrocarbon exposure in three bird species of subsistence importance: king eiders (Somateria spectabilis), common eiders (Somateria mollissima), and greater white-fronted geese (Anser albifrons). Over the course of three years, I collected liver samples during spring and fall hunts near Utqiaġvik (formally Barrow) and validated methods for both direct-take and opportunistic liver sampling. Enzyme activity results show significant differences in CYP1A activity levels among species, seasons, and years. Except birds collected during fall 2014, when significantly high enzyme activity was observed in all sampled species, all other collections resulted in median activity levels similar to those reported in other sea duck species in Alaska from un-oiled or non-industrialized habitats. I also used species-specific hepatocyte culture in a broader selection of arctic marine birds and waterfowl candidate bioindicators to assess and compare species CYP1A activity responses as a measure of sensitivity to hydrocarbons. Cytochrome P4501A results from hepatocyte cultures dosed with positive control reference reagents and Alaska North Slope crude oil showed differences in species responses. Based on sensitivity results, I recommend the common eider and common murre (Uria aalge) as bioindicators for use in CYP1A monitoring due to their consistent and measureable responses in our experiments. However, additional species are promising candidates (e.g., tufted puffin; Fratercula cirrhata) but further testing is needed. This is the first study of reference hydrocarbon exposure and comparative laboratory assessment of CYP1A inducing compounds for arctic marine birds and waterfowl and these results form the basis for hydrocarbon monitoring programs and risk assessments.
    • Six Thousand Years Of Change In The Northeast Pacific: An Interdisciplinary View Of Maritime Ecosystems

      Misarti, Nicole; Finney, Bruce (2007)
      The goal of this thesis is to develop long-term records of North Pacific ecosystems and explore relationships between change in marine ecosystems and prehistoric Aleut culture through soil chemistry, isotope analyses of lake cores, and isotope analyses of bone from archaeological middens. Chemical analysis of soils yielded differences in soils of various archaeological features as well as middens of varying composition. Sites that had no middens were chemically distinguishable from sites that did have middens helping to define resource consumption in the local region. An important result of this study is that no single ecosystem (nearshore benthic, coastal pelagic or deep-ocean pelagic) experienced the same changes in delta13C and delta 15N over the past 4,500 years. This suggests that changes in climate affected different ecosystems in unique ways. Only one change spans all species studied, the decrease in modern delta13C in comparison to delta13C of prehistoric specimens. According to these comparisons, the modern Gulf of Alaska may not be in the highly productive state that it was for the past 4,500 years, with the possible exception of the Medieval Warm Period. Lake core sediment analysis suggests an increase in salmon stocks in the Gulf of Alaska beginning &sim;6,000 years ago, with a decrease during the Medieval Warm Period. In fact, salmon stocks in the Gulf of Alaska appear to be healthiest during periods of atmospheric cooler and wetter climate over the past 4,500 years. In comparing my paleoecological records to the archaeological record of the area it appears that humans were affected by changes in their environment but, even in relatively small numbers, humans also influenced local ecosystems for the past 6,000 years. By building on our understanding of long-term climate change and long-term fluctuations in ecosystems and trophic dynamics of species in the North Pacific, and through considering humans in the ecological context, we can better understand present conditions in marine ecosystems.
    • Small-scale variability in benthic food webs in the Northeastern Chukchi Sea

      Tu, Kelley Lannon; Blanchard, Arny; Horstmann-Dehn, Larissa; Iken, Katrin (2013-08)
      Benthic food web structure can differ over large scales across Arctic shelves in relation to hydrographic conditions, but little is known if such differences also may occur on smaller scales in hydrographically complex areas. The length, food sources, trophic composition, and energy distribution of benthic food webs in three study areas in the northeastern Chukchi Sea (i.e., Klondike, Burger, and Statoil, as part of the Chukchi Sea Environmental Studies Program) were compared using stable isotope analysis and bomb calorimetry. Food web length (four trophic levels), food sources, and linear models of food webs were comparable among areas. Marked differences in food web structure were observed when trophic levels were quantified by benthic biomass and abundance. High proportions of biomass and abundance of trophic level 3 taxa at Burger were attributed to high deposition of refractory material. High proportions of trophic level 1 and 2 taxa at Klondike and Statoil reflected availability of fresh material. Burger could potentially present a rich foraging ground for some benthic predators due to especially high benthic prey energy densities. Findings emphasize that marine food webs can vary on small spatial scales in accordance with hydrographic conditions, particularly when quantitative trophic level distribution is considered.
    • Spatial and temporal patterns of epibenthic community and food web structures in the Chukchi sea between 2004-2012

      Serratos, Carlos; Iken, Katrin; Bluhm, Bodil; Danielson, Seth (2015-12)
      The Chukchi Sea shelf, an area undergoing rapid environmental change and concurrently increasing human activity, supports communities of epibenthic organisms and food webs that are sustained by high primary productivity in the overlying water column and are influenced by physical environmental conditions. The goal of this study was to characterize these epibenthic communities (using trawl hauls) and benthic food webs (using carbon and nitrogen stables isotopes) in 2009 and 2012 and to identify persisting or changing patterns between 2004, 2009 and 2012 as part of NOAA's Russian-American long-term Census of the Arctic (RUSALCA) program. Fifteen stations each were sampled in August to September of 2009 and 2012 in the Chukchi Sea, of which eight repeat stations in the southern Chukchi were sampled in 2004, 2009 and 2012 for temporal comparisons. Epibenthic communities differed in structure between the northern and the southern study regions, with somewhat variable subgroupings within each of those larger regions between years. Overall biomass (mean 49680 ± 45510 g wet weight 1000 m⁻²) was dominated by echinoderms in particular at northern stations, followed by crustaceans. Repeat stations retained relatively consistent epibenthic community composition across sampling years, despite the at times drastic temporal variability in abundance and biomass. Point in time measurements of water column environmental variables (e.g., salinity, oxygen, temperature) were less strongly correlated to the epifaunal community structure than comparatively stable environmental measures (e.g., substrate type, depth, latitude). Benthic food web structure in the southern Chukchi Sea varied significantly and consistently between water masses in all study years, while δ¹⁵N and δ¹³C of pelagic particulate organic matter (PPOM) did not. This indicates that benthic consumers integrate the highly variable POM isotopic signatures and reflect long-term conditions. A persistent gap in δ¹⁵N values between PPOM and epibenthic consumers in nutrient-poor Alaska Coastal Water indicated that the majority of consumers in that water mass did not directly consume POM, which may undergo an additional trophic step of microbial processing before entering the benthic food web. In contrast, shorter food webs without this gap in the nutrient-rich Bering Sea Anadyr Water reflected tight pelagicbenthic coupling. The mostly consistent temporal patterns in epibenthic and food web structure compared to variable standing stock stress the importance of selecting multiple metrics for ecosystem monitoring. The data from this study may serve as a benchmark by which to measure a biological response to climate change and human impacts.