• Habitat characteristics of black oystercatcher breeding territories

      McFarland, Brooke A.; Konar, Brenda; Goldstein, Michael I.; Rosenberger, Amanda (2010-05)
      Habitat use in birds is often related to forage resources and predation avoidance. The large, long-lived black oystercatcher is a shorebird that defends a composite breeding territory for foraging in the intertidal zone and nesting in the immediate upland. Predation on young is a major source of mortality for many bird species, including black oystercatcher. As these are long-lived birds with many reproductive opportunities, adult survival, associated with forage resources, is expected to be more important in habitat use than less-predictable breeding success. To identify which factors most influence black oystercatcher breeding territory use, logistic regression models were developed and tested in south-central Alaska and tested in southeast Alaska. Intertidal community composition was sampled at a subset of sites. All known breeding sites in Kenai Fjords National Park and western Prince William Sound, plus sites in southeast Alaska, were matched with available breeding sites based on substrate and exposure classifications. Two factors available breeding related to predation avoidance, greater distance to vegetation and isolation from the mainland, were the most important variables in habitat models. Intertidal community composition did not vary between known breeding and available breeding sites. This suggests black oystercatchers choose breeding territories that reduce predation risk, contrary to expectations.
    • Habitat use of Pacific herring (Clupea pallasii) in Prince William Sound, Alaska

      Kelly, Seanbob R. (2007-12)
      To determine the spawning area contributions of Pacific herring (Clupea pallashii) larvae to nursery bays, otolith chemical analysis was conducted on juvenile fish collected from 1995 to 1997 in Prince William Sound, Alaska. The otolith edge, representing the chemical signature of the known capture location, and the otolith core, representing the unknown spawning ground chemistry, were compared with discriminant function analysis to infer spawning area origin. Chemical signatures of ⁸⁷Sr/⁸⁶Sr, ⁸⁸Sr/⁴⁸Ca, ²⁴Mg/⁴⁸Ca, and ¹³⁸Ba/⁴⁸Ca were used to identify broad spawning regions from inner and outer PWS that persisted for the three years sampling period despite significant interannual variability in otolith edge chemistry within nursery bays. Age of juvenile Pacific herring, age-0, 1, 2, did not significantly affect the otolith edge signatures; thus, this study is able to conclude from the otolith core chemistry that spawning areas do not contribute equally to nursery bays. This is the first demonstration that otolith chemical signatures can be used to identify the important spawning areas of this commercially important species in the Gulf of Alaska coastal areas.
    • Harmothoe imbricata: species complex or complex species?

      Gastaldi, Angela; Lopez, J. Andres; Hardy, Sarah; Kelley, Amanda; Sikes, Derek (2019-05)
      Accurate estimates of species diversity are constrained by cryptic species complexes, in which multiple closely related species are grouped under a single species name due to the absence of clear morphological differences. Cryptic diversity is known to be prevalent in polychaete worms, a mostly marine group commonly known as bristle worms. A recent survey of polychaete diversity discovered that the widespread scale-worm Harmothoe imbricata comprises multiple distinct mitochondrial lineages based on analysis of the Cytochrome c oxidase I (COI) gene, which is often referred to as the 'barcoding' gene. Analyses based solely on DNA sequences from COI may overestimate the number of lineages comprising a cryptic species complex, so it has been recommended that cryptic species investigations incorporate nuclear gene sequences. The goal of this study was to determine whether the incorporation of DNA sequences from the nuclear genome corroborates the designation of H. imbricata as a cryptic species complex. I sequenced segments of COI and five nuclear genes: ITS1, ITS2, H3, and portions of the 18S and 28S genes of H. imbricata and analyzed them using distance measures, maximum likelihood, and Bayesian inference. I compared phylogenetic trees produced from mitochondrial and nuclear DNA sequences, as well as from a combined mitochondrial/nuclear dataset. Harmothoe imbricata was found to include five mitochondrial lineages, whereas the nuclear sequences only supported four well-defined lineages. These results corroborate previous reports showing COIbased cryptic species investigations find more lineages than nuclear DNA based investigations. These results provide additional lines of evidence that H. imbricata is a cryptic species complex. These divergent lineages likely arose after being separated during the last glacial maximum but they are now found in sympatry. A thorough morphological study of H. imbricata populations may reveal phenotypic differences correlated with the genetic lineages identified here.
    • Heat And Freshwater Controlling Processes On The Northern Gulf Of Alaska Shelf

      Janout, Markus A.; Weingartner, Thomas; Coyle, Kenneth; Hedstroem, Ketherine; Johnson, Mark; Okkonen, Stephen (2009)
      We examined conditions and processes that control the distribution of heat and freshwater on the northern Gulf of Alaska (GOA) shelf. Cross-shelf heat gradients are weak throughout the year, while salinity gradients are substantial due to the impact of coastal freshwater runoff. Outer shelf water properties are influenced by large anticyclonic eddies, while the inner and middle shelves may be regulated by wind and freshwater runoff dynamics around the Alaska Coastal Current (ACC). On the outer shelf, anticyclonic eddies propagate from the eastern GOA southwestward along the continental slope, where they favor on-shelf (off-shelf) transport of saline and nutrient-rich (fresh and iron-rich) waters Certain along-shelf locations are identified where low-salinity coastal waters are found near the shelfbreak within reach of eddies and may be regions of enhanced cross-shelf freshwater transport. The eddies have lifetimes of ~5 years and increase in size and sea level anomaly west of the Seward Line, which implies more vigorous eddy cross-shelf exchange in the northwestern GOA. By comparison, on the inner shelf the heat and freshwater distribution is dominated by large coastal river runoff, which forces the ACC and controls the vertical distribution of temperatures through stratification. In May 2007, the coastal GOA revealed some of the lowest ocean temperatures since the early 1970s, initiated by strong atmospheric cooling and reduced coastal runoff in November 2006. Stepwise regression shows that 81% of the variability of deep temperatures is explained by salinity stratification and air-sea heat fluxes. Weak baroclinic flow in May 2007 likely aided the cooling through reduced along-shore heat transport. A more detailed examination of heat transport indicated that along-shore heat flux convergence in the ACC may re-supply 10-35% of the heat removed by air-sea fluxes throughout the coastal GOA cooling season, while the annual mean cross-shore heat flux convergence is insignificant. Spatial gradients show increasing heat fluxes from off- to on-shore and from east to west. The cross-shore gradients result from wind speed gradients due to ageostrophic near-shore wind jets near coastal mountains, while the along-shore gradients result from larger-scale pressure systems. While the ACC advects coastal freshwater around the GOA shelf its waters are subjected to disproportional heat loss west of the Seward Line.
    • Heavy metals in the sediments of an arctic lagoon, northern Alaska

      Sweeney, Michael Devlin (1984-12)
      The total abundances of V, Cr, Mn, Fe, Co, Ni, Cu, and Zn in oxic, nearshore sediments of north arctic Alaska, are similar to those of corresponding pristine or pre-industrial-age sediments of many tropical-temperate regions, and thus do not reflect the unique weathering and depositional processes of the Arctic. Laboratory experiments on metal partitioning suggest that about 50% of the metal contents (<20% for V, Cr), which are bound predominantly in Fe oxides, may be mobilized into solution following the onset of reducing conditions at the sediment surface. A three-part extraction design would be effective in discriminating the three major associations of heavy metals in the sediments: easily leachable, Fe hydroxides, and refractory particles, and is recommended for use in monitoring the nearshore Beaufort Sea for future contamination by heavy metals.
    • Hemocyte and tissue changes by crude oil in the blue mussel Mytilus edulis

      McCormick-Ray, M. Geraldine (1983)
      This study examines the effects of Prudhoe Bay crude oil on the number and types of circulating hemocytes, on the phagocytic response, on spawning progression, and on internal structural changes. The number of hemocytes was reduced with 4-5 week exposure to 1000 nL/L of oil; a significant number of individuals showed a higher than average cell count with longer exposure. An increase in agranulocytes in the 8-9 week control population does not occur in populations exposed to 1000 nL/L and 500 nL/L of oil for 8-9 weeks, but, the phagocytic response was significantly depressed. The Chi-square test showed that oil interferes significantly with progression of spawning. Analysis of internal tissue structure indicates that oil can affect adipogranular storage cells, vesicular tissue, and digestive tubule cells. The changes occurring in circulating hemocytes are not necessarily consistent with changes in internal morphology.
    • Humpback whale (Megaptera novaeangliae) entanglement in fishing gear in northern southeastern Alaska

      Neilson, Janet L. (2006-05)
      The prevalence of non-lethal entanglements of humpback whales (Megaptera novaeangliae) in fishing gear in northern southeastern Alaska (SEAK) was quantified using a scar-based method. The percentage of whales assessed to have been entangled ranged from 52% (minimal estimate) to 71% (conditional estimate) to 78% (maximal estimate). The conditional estimate is recommended because it is based solely on unambiguous scars. Eight percent of the whales in Glacier Bay/Icy Strait acquired new entanglement scars between years, although the sample size was small. Calves were less likely to have entanglement scars than older whales and males may be at higher risk than females. The temporal and spatial distribution of commercial fisheries is complex and difficult to correlate with these results. The percentage of whales with entanglement scarring is comparable to the Gulf of Maine where entanglement is a substantial management concern. Consequently, SEAK humpback whale-fisheries interactions may warrant a similar level of scrutiny.
    • Humpback whale habitat use patterns and interactions with vessels at Point Adolphus, Southeastern Alaska

      Koehler, Nicole (2006-12)
      Humpback whales at Point Adolphus, in southeastern Alaska, are faced with the challenge of maximizing their energy gain from feeding and minimizing energy losses that can occur due to disturbance by vessel traffic. Point Adolphus is unique because of abundant prey resources that attract high concentrations of humpback whales during the summer and high levels of vessel activity. Using scan sampling and focal behavior observation sessions data were collected from an elevated shore station on the northern coast of Chichagof Island in 2001. Humpback whale numbers peaked during early ebb tide. Whales were distributed west during ebbing tides and east during flooding tides. During flood tides, humpback whales exhibited non-directional movement. Differences in humpback whale numbers, distribution and movement patterns in relation to tide appeared related to small-scale fronts and headland wake effects associated with Point Adolphus. Overall, humpback whale swimming speeds were faster when the number of vessels present was greater and distance to the nearest vessel was smaller. However, responses of individual whales differed. Humpback whales at Point Adolphus appear to have developed strategies to exploit predictable times to feed which are tidally-induced and practice short-term avoidance strategies that may reduce the effects of vessel traffic.
    • Humpback whales and humans: a multi-disciplinary approach to exploring the whale-watching industry in Juneau, Alaska

      Teerlink, Suzanne F.; Horstmann, Larissa; Witteveen, Briana; Mueter, Franz; DeMaster, Doug; Beaudreau, Anne (2017-05)
      A booming whale-watching industry in Juneau, Alaska is leading to complicated resource management challenges. Juneau's growing commercial whale-watching industry includes over 60 vessels and generates more than $25 million in annual revenue. As this industry has increased, so too have concerns for the welfare of humpback whales (Megaptera novaeangliae) exposed to this vessel traffic. However, we lack a fundamental understanding of long-term impacts, if any, that vessel disturbance has on humpback whales. Further, we have insufficient data on local abundance and seasonal attendance of humpback whales that are necessary to detect potential future changes. The aim of this project is to investigate Juneau area humpback whales and their interactions with whale-watching tourism to set a foundation for sustainable management of this resource and industry. To reach this objective, three studies were employed. 1) Methods for monitoring humpback whale population parameters through a citizen science program were developed and tested. Photo-identification data were collected on whale-watching platforms and compared to data from dedicated surveys to objectively evaluate the citizen science data collection methods and identify biases. 2) Physiological markers were evaluated for signs of a chronic stress response in blubber of Juneau-area humpback whales compared with humpback whales from other areas in Alaska with far less vessel traffic. The concentrations of several steroid hormones, including cortisol, were measured from biopsy samples and used to infer a relative cumulative stress response in whales exposed to Juneau's tourism fleet. 3) Community perceptions toward Juneau's whale-watching industry and humpback whale management were collated to consider stakeholder concerns and suggestions for local humpback whale management. Participants were given the opportunity to share their perspectives on humpback whale welfare, community considerations and concerns, and recent and proposed management changes that affect the whale-watching industry. I found that citizen science data can produce reliable estimates of abundance, especially with sufficient effort. I did not find evidence for increased stress response in Juneau-area humpback whales and argue that this indicates habituation in these animals. Respondents in our survey generally supported Juneau's whale-watching industry, but expressed concerns for the vessel crowding and the welfare of humpback whales in this area. This project combines multiple scientific disciplines to tackle the initial steps necessary in understanding the complex interaction between humans and humpback whales near Juneau, and in making management decisions that ensure a sustainable future for Juneau's humpback whales and the whale-watching industry that relies on them.
    • Idealized Modeling Of Circulation Under Landfast Ice

      Kasper, Jeremy Lucas; Weingartner, Thomas; Gradinger, Rolf; Hedstrom, Katherine; Johnson, Mark; Kowalik, Zygmunt (2010)
      Idealized analytical and numerical models are used to elucidate the effects of a spatially variable landfast ice cover on under-ice circulation. Three separate forcing mechanisms are investigated; lateral inflow onto an ice-covered shelf (an elevated sea level at the western boundary), a spatially uniform upwelling wind blowing along the seaward landfast ice edge and a buoyant inflow under the ice cover that enters the domain through the southern coastal wall. The idealized models are configured to resemble the shallow Alaskan Beaufort Sea shelf. Models show that the inclusion of landfast ice means shelf response is substantially different from an ice-free shelf. In the case of a lateral inflow, landfast ice spreads the inflow offshore (in a manner similar to bottom friction) but the change in surface stress across the ice edge (from ice-covered to ice-free) limits the offshore spreading. In the case of an upwelling wind along the ice edge, the low sea level at the ice edge (due to ice edge upwelling) leads to a cross-shore sea level slope between the coast (high sea level) and the ice edge (low sea level), which drives a geostrophically balanced flow upwind. In the absence of along-shore changes in wind or ice the circulation does not vary along the shelf and currents near the coast are O(10 -3) m s-1. Along- and cross-shore variations in the ice-ocean friction coefficient introduce differences in the response time of the under-ice flow and can lead to along-shore sea level slopes, which drive along-shore flows near the coast (< 0.06 m s-1). In the case of a time dependent buoyant inflow, the landfast ice spreads the buoyant inflow much farther offshore (~ 9 times the local baroclinic Rossby radius, ~ 45 km) than in the ice-free case (< 30 km). When the ice width is finite, the change in surface across the ice edge acts to restrict offshore flow (in the anti-cyclonic bulge) and inhibits onshore flow farther downstream.
    • Idealized Modeling Of Seasonal Variation In The Alaska Coastal Current

      Williams, William James; Weingartner, Thomas (2003)
      Analytical and idealized-numerical models were used to understand the physical processes that govern the seasonal variation and fate of the freshwater in the Alaska Coastal Current (ACC). The ACC is forced by freshwater inflow and by mean easterly winds that cause downwelling over the shelf. Two-dimensional modeling using a line-source buoyant inflow gives the coastal current depth <math> <f> H=<fr><nu>3<sup>2/3</sup></nu><de>2</de></fr><fen lp="par"><fr><nu> f<sup>2</sup>Q<sup>2</sup></nu><de>g<sup>'</sup></de></fr> <rp post="par"></fen>t<sup>2/3</sup></f> </math> and coastal current width <math> <f> Y<inf>2D</inf>=3<sup>1/3</sup><fen lp="par"><fr><nu>g<sup>' </sup>Q</nu><de>f<sup>2</sup></de></fr><rp post="par"></fen><sup> 1/3</sup>t<sup>1/3</sup></f> </math>, where f is the Coriolis frequency, g ' is reduced gravity, Q is inflow rate and t is time since inflow began. Addition of downwelling wind-stress causes a steep coastal current front that intersects the bottom and is either convecting, stable and steady, or stable and oscillatory depending on <math> <f> <fr><nu>D</nu><de><g>d</g><inf>*</inf></de></fr></f> </math> and <math> <f> <fr><nu>b<inf>y</inf></nu><de>f<sup>2</sup></de></fr></f> </math>, where D is bottom depth, delta* is an Ekman depth and by is the cross-shelf buoyancy gradient. Three-dimensional modeling of a half-line source initially develops two-dimensionally but becomes three-dimensional from a balance between coastal influx of buoyancy and its downstream transport. This balance results in a coastal current depth limit <math> <f> H<inf><rf>max</rf></inf>=<fen lp="par"><fr><nu>2Qf</nu><de>g<sup> '</sup></de></fr><rp post="par"></fen><sup>1/2</sup>x<sup> 1/2</sup></f> </math>, where x is along-shelf distance. This limit is unchanged under downwelling wind-stress and is reached on time scales of less than 1 month for the ACC. The half-line source coastal current width develops as <math> <f> Y<inf>2D</inf></f> </math> away from the beginning of the line source. Imposition of a downwelling wind-stress tau results in an approximate balance among wind-stress and along- and cross-shelf momentum advection so that the current width is reduced to <math> <f> Y<inf>wind</inf>&ap;L<inf>D</inf><fen lp="par"><fr><nu>Qf</nu> <de><g>t</g>/<g>r</g><inf>0</inf></de></fr><rp post="par"></fen><sup> 1/2</sup></f> </math>, where LD is the Rossby radius of deformation. Waves and eddying motions eventually grow in the half-line source coastal current with wavelengths proportional to the coastal current width and with a downstream phase speed slower than the maximum current speed. These features cause an offshore flux of buoyant water, a broader coastal current and accumulation of buoyancy on the shelf. Increasing downwelling wind stress reduces the effects of the instabilities. Although buoyancy accumulates on the shelf during most model runs, there is little accumulation under maximum winter downwelling wind-stress. This suggests that freshwater accumulates on the shelf from spring through fall, but is then transported downstream during winter.
    • Influence of physical and biological oceanography on the structure of the seabird community in the northeastern Chukchi Sea

      Gall, Adrian E.; Blanchard, Amy L.; Weingartner, Thomas J.; Mathis, Jeremy T.; Hopcroft, Russell R.; Day, Robert H. (2015-12)
      The Chukchi Sea is losing seasonal ice cover as global temperatures rise, facilitating human access to the region for activities such as oil and gas exploration, shipping, and tourism. Processes and responses to environmental change by marine ecosystems are often challenging to quantify because they are hidden under water. Seabirds, however, offer visible evidence of the health and status of marine ecosystems. I studied the community structure, variability in abundance and distribution, and habitat associations of seabirds in the eastern Chukchi Sea. My results provide insights into the influence of climate change on seabirds and a benchmark against which to evaluate possible impacts of anthropogenic activity. Repeated sampling of systematic transects in the northeastern Chukchi Sea during the ice-free seasons of 2008-2012 showed that the community consisted of ~40 species and was dominated numerically by planktivorous seabirds, particularly Crested Auklets (Aethia cristatella) and Short-tailed Shearwaters (Puffinus tenuirostris). In contrast, benthic-feeding birds were rare. The abundance of seabirds in the offshore northeastern Chukchi Sea varied by up to two orders of magnitude among years and birds generally were more abundant in September than August. Despite these seasonal and interannual variations in abundance, the species composition was similar among years, with anomalies occurring only in years of persistent ice cover. I compared data from this recent period (2008-2012) with data from historical surveys (1975-1981) to evaluate decadal trends in seabird abundance and composition and related those changes to reductions in seasonal ice cover. The seabird community shifted from one consisting primarily of piscivorous seabirds to one consisting primarily of planktivorous seabirds. This shift suggests that zooplankton prey are more accessible now to avian predators as seasonal ice cover has declined. I explored the relationships between seabirds, hydrography, and zooplankton abundance with spatially explicit generalized additive models. The associations of seabirds with habitat characteristics varied with foraging method and preferred prey. Species that fed primarily by pursuit diving were more abundant in warm, weakly stratified water, whereas surface-feeding species were more abundant in cold, strongly stratified water. Planktivorous seabirds (auklets, shearwaters, and phalaropes) were more abundant within 20 km of thermal surface fronts and in contrast, omnivores (gulls and murres) were more abundant far from thermal fronts. For 5 of the 8 seabird species, information about prey biomass improved predictions of seabird abundance, although the relationships were not as clear as they were for the physical habitat characteristics indicative of processes that aggregate prey. Advective processes that transport oceanic species of zooplankton from the Bering Sea to the Chukchi Sea, together with the local influence of sea ice on physical and biological processes, strongly influence the distribution of seabirds, particularly the planktivorous species. Scientists and decision-makers can use the results of this multi-species and multi-disciplinary study as a benchmark to assess the ecological consequences of anthropogenic activity against the backdrop of climate change that is affecting the Chukchi Sea.
    • The influence of rookery terrain on population structure, territorial behavior, and breeding success of Steller sea lions in the Gulf of Alaska

      Smith, Louise N. (1988-05)
      The effect of rookery terrain on population structure, territorial behavior and breeding success of Steller sea lions was assessed at two rookeries, in the northern Gulf of Alaska. The sea lions using Sugar loaf and Marmot Islands differed in age structure, juveniles being absent from Sugar loaf but present on Marmot during the breeding season. Territory boundaries of breeding bulls on Sugarloaf were stable, and were unaffected by tides. Territory boundaries on Marmot were unstable, shifting with the tide. Territorial bulls occupied two types of territories on Sugarloaf Island (landlocked and water-access) and three types on Marmot (landlocked, tidal and semiaquatic). The behavior of territorial bulls on Marmot was influenced by tides and presence of juvenile animals. These factors were not important on Sugarloaf. The breeding success of territorial bulls was unaffected by location of territory on Sugarloaf. Territory location was important in the breeding success of Marmot Island bulls.
    • The Influence of terrestrial matter in marine food webs of the Beaufort Sea shelf and slope

      Bell, Lauren; Iken, Katrin; Okkonen, Steve; Wooller, Matthew; Bluhm, Bodil (2015-05)
      Terrestrial organic matter (OMterr) can function as a food source for Arctic marine consumers, though the relative contribution of OMterr to the structure and efficiency of marine food webs compared to marine production is unclear. Forecasted increases in OMterr inputs to the Arctic Beaufort Sea necessitate a better understanding of the proportional contribution of this organic matter source to the trophic structure of marine communities. This study investigated the relative ecological importance of OMterr across the Beaufort Sea shelf and slope by examining differences in community trophic structure concurrent with variation in terrestrial versus marine organic matter influence. Hydrogen stable isotope ratios (δD) of surface water, surface sediment particulate organic matter (sPOM), and selected benthic consumers were used as an exploratory assessment of freshwater and OMterr distribution in the Beaufort Sea. δD values of surface water confirmed the widespread influence of Canada's Mackenzie River plume across the Beaufort Sea; however, δD values of terrestrial and marine production were not sufficiently distinguishable to differentiate organic matter sources in consumers. Carbon stable isotope ratios (δ¹³C values) of pelagic particulate organic matter (pPOM) and marine consumers confirmed a significant decrease in OMterr presence and utilization by consumers with increasing distance from the Mackenzie River outflow. Food web length, based on the nitrogen stable isotope ratios (δ¹⁵N values) of marine consumers, was longer closer to the Mackenzie River outflow both in shelf and slope locations due to relatively higher δ¹⁵N values of pelagic and benthic primary consumers. The absence of macrofaunal consumers at the lowest trophic levels of OMterr-influenced food webs was interpreted to result from the prior metabolic turnover of OMterr by the microbial loop, which was not sampled in this study. The inferred presence of strong microbial processing of OMterr in the eastern regions of the Beaufort Sea resulted in a higher proportion of relative epifaunal biomass occupying higher trophic levels, suggesting that OMterr as a basal food source can provide substantial energetic support for higher marine trophic levels. These findings challenge the current conception of low terrestrial matter contributions to the Arctic marine food web, and compel a more specific understanding of energy transfer through the OMterr-associated microbial loop.
    • Insight into the diet history of ice seals using isotopic signatures of muscle tissue and claws

      Carroll, Sara Shanae; Norcross, Brenda; Horstmann-Dehn, Larissa; Quakenbush, Lori; Wooller, Matthew (2012-05)
      Climate change and sea ice reduction in the Arctic may impact foraging of ice-associated predators. The goal of my thesis work was to examine interannual differences in the diet of ringed, bearded, spotted, and ribbon seals as described by stable nitrogen and carbon isotope ratios of muscle tissue and claws to assess foraging plasticity. Isotopic mixing models from muscle data were used to describe the proportional contribution of prey groups during 2003, 2008-2010. Results showed a higher proportional contribution of smelt (Osmeridae) and benthic prey to ringed and bearded seal diets in 2003 compared to 2008-2010. Seasonal keratin layers deposited in claws can document trophic history up to about 10 years. During 2007 (record ice minimum), proportionally more ringed seals fed at a lower trophic level, while spotted seal adults and young-of-the-year fed at a lower trophic level during 2006. Bearded seals may have been foraging more pelagically from 2008 to 2010. Ice seals may be taking advantage of more abundant pelagic crustaceans as the Arctic ecosystem changes to a pelagic-dominated food web. Interannual variations and high variability among species and individual diets illustrate the opportunistic nature and flexibility of ice seals to changes in prey composition.
    • Interannual variability of epibenthic communities in the Chukchi Sea, Alaska

      Powell, Kimberly Keeler; Konar, Brenda; Coyle, Ken; Winsor, Peter (2015-08)
      Epibenthic communities contain a wide range of organisms and serve an important role in marine ecosystems. They are involved in carbon remineralization, benthic production, and are important prey items for higher trophic levels. Arctic epibenthic communities may be experiencing significant changes in species composition, abundance, and biomass at both short and long term time scales. While epibenthic communities may be responding to long term shifts in the environment, differentiating long term trends from short term interannual variation can be problematic. The present study examined interannual differences of epibenthic communities and potential environmental drivers of their variability in the Chukchi Sea. For this, a plumb-staff beam trawl was used to sample epibenthic species composition, abundance, and biomass of the dominant invertebrate taxa at 71 stations around the Chukchi Sea during the ice free seasons of 2009, 2010, 2012, and 2013. Over the entire study area and within a smaller area with the most temporal coverage, the largest separation was between 2009 and 2013, with more difference between 2009 to 2010 than between 2012 and 2013. Crustaceans were the most significant contributors to community composition, based on abundance, and biomass. The important environmental drivers that varied along with the epibenthic community in some but not all years included bottom water temperature, salinity, dissolved oxygen, mean sediment chlorophyll a, and sediment organic matter. In contrast, sediment grain size was important in all years and, therefore, was the least likely to contribute to the biological variability among years. While these data provide a benchmark on interannual variability of epibenthic communities in the Chukchi Sea, more monitoring is essential to determine long term trends.
    • Interannual variations in the carbon to chlorophyll a ratios during the spring bloom in Prince William Sound, Alaska

      Tamburello, Kathereen Rachel (2005-05)
      The carbon to chlorophyll a ratio of phytoplankton during the spring bloom in Prince William Sound, Alaska was investigated for 3 seasons and related to major physical and chemical variables. Carbon to chlorophyll a ratios (C:Chl) were determined by two methods, based on particulate organic carbon to chlorophyll (POC:Chl) and phytoplankton cell carbon to chlorophyll (PCC:Chl). These ratios were compared to a more commonly used estimate, a fixed ratio of C:Chl, taken from literature, for the spring phytoplankton community. The hypothesis that the C:Chl ratios were significantly different between years was proven false. This research indicates that the C:Chl ratio is primarily determined by species composition of the phytoplankton community rather than external factors such as nutrients, temperature or salinity. In addition, this research indicates that the identification and enumeration method, although rarely used because it is the most time and labor intensive method, provides the best estimate of phytoplankton carbon. The mean PCC:Chl ratio for all three years was 18, and is the best fixed ratio to estimate spring phytoplankton carbon in Prince William Sound when an EI Niño is not present.
    • Interrelationship among temperature, metabolism, swimming performance and recovery in Pacific cod (Gadus macrocephalus): implications of a changing climate

      Hanna, Shannon K. (2006-12)
      Physiological constraints are suggested to contribute to the observed changes in relative abundance of Pacific cod (Gadus macrocephalus) seen in association with interdecadal changes in sea surface temperatures. To examine this concept, two experiments were conducted to determine critical swimming speed (Ucrit), rates of oxygen consumption and recovery post-exhaustion of adult cod acclimated to different temperatures. In addition, hematocrit and plasma concentrations of cortisol, metabolites and ions from resting and exhausted fish were measured to assess the impact of swim trials on fish condition. In experiment one, fish acclimated to 4°C had similar mean Ucrit (1.07 BL/s) and resting metabolic rates (35.34 mg O₂/kg⁰⁸/hr) compared to fish acclimated to 11°C fish (1.07 BL/s; 49.43 mg O₂/kg⁰⁸/hr). Similarly, concentrations of blood constituents differed little between temperature treatments; each exhibited increases in plasma cortisol and metabolites from pre- to post-swim. Experiment two illustrated few differences in rates of recovery between temperature groups (2 and 7°C). After four hours of recovery there was no evidence of plasma cortisol or metabolites returning to pre-swim concentrations in either temperature group. It seems unlikely that physiological constraints on the metabolic performance of adult Pacific cod contribute to changes in their relative abundance.
    • Intertidal community development along a distance/age gradient in a tidewater glacial fjord

      Sharman, Lewis Crook (1987-12)
      Glacier Bay has recently undergone rapid deglaciation, exposing new substrates to colonization and biological development. There is a clearly defined increase in marine intertidal community development with substrate age (0-200 y) and distance (0-90 km) from present-day locations of tidewater glacier termini. The objectives of this research were (1) to describe length-of-fjord patterns of intertidal community composition and corresponding gradients of the near-surface marine physical environment and (2) to use this approach to evaluate the relative contributions of substrate age and physical factors to determining the degree of community development. Distance and age were almost perfectly correlated. Intertidal species richness increased linearly with distance/age. Environmental factors can be grouped into those that also varied linearly along this gradient, and those that varied exponentially. Distance from the glaciers and the other linearly correlated marine environmental factors of water temperature, salinity, and suspended particulate nitrogen factors are probably the most important determinants of intertidal community development.