Now showing items 169-188 of 199

• #### Temperature and food effects on larval Pacific herring (Clupea pallasi) in Prince William Sound, Alaska

The effects of food availability and water temperature on larval Pacific herring growth rates and survival were studied using a coupled biophysical model for 1993 through 1997. The herring growth model included feeding gains, metabolic costs, mortality losses and vertical migration of the herring larvae. In years when springtime oceanographic processes resulted in a high concentration of zooplankton, food availability did not limit larval herring growth rates; water temperature determined survival. However, in other years, food availability did limit survival, either due to insufficient food concentrations or to inaccessibility of the food. Vertical migration occasionally was restricted by strong water column stratification, which prevented the larvae from reaching food concentrations sufficient for growth. Thus the amount of food, the temperature, and the vertical distribution of the food and the larvae were found to affect growth. The study of vertical properties of factors affecting larval fish must be included in larval fish research.
• #### Temporal and spatial distribution of grazers and kelp phlorotannins in Kachemak Bay, Alaska

The potential influence of grazers on the density and distribution of kelp thalli is substantial and may be mediated by kelp phlorotannins serving in a defensive role. The purpose of this study was to determine how temporal and spatial phlorotannin patterns in four kelp species in Kachemak Bay, Alaska, are influenced by density and distribution of the gastropod grazer Lacuna vincta and environmental variables. Temporal phlorotannin patterns from June 2004 through December 2005 were mainly explained by the life history of particular kelp species as well as strong correlations with light attenuation and nitrate concentration. The Optimal Defense Theory of resource allocation to differentiated tissues was supported by observations of higher proportional allocation to attachment structures and meristematic tissue in all kelp species. Lacuna vincta distribution was not clearly related to phlorotannin content and therefore, grazer habitat and food choices may be influenced by the combination of high phlorotannin content, tissue toughness and/or nutritional content. Strong physical disturbances such as currents and wave action may supersede these factors and drive grazer distribution. An understanding of the biological and physical factors affecting phlorotannin content and distribution in kelp thalli may suggest reasons for temporal and spatial kelp bed variability.
• #### Temporal and spatial variability of sinking particles in the southeast Bering Sea

The factors affecting the timing, quantity and fate of southeastern Bering Sea primary production, including coupling to higher trophic levels, were investigated via sinking particles collected using sediment traps. Stable carbon and nitrogen isotopic composition and lipid composition of zooplankton and sinking particles were measured for middle (M2) and outer (M3) shelf samples collected during 1997-2000. The quantity collected by the M2 sediment trap was high in late summer and fall, as well as during spring blooms, and was much greater than that collected at M3. M2 zooplankton and trap samples were enriched in ¹⁵N and ¹³C over those from M3. This could be explained by greater primary productivity over the middle shelf, associated with consumption of more of the available inorganic nitrogen. M2 sediment trap samples contained more fatty acids typical of diatoms, while M3 samples contained more fatty acids typical of zooplankton. Diatoms were much more numerous in the M2 than the M3 trap. Cholesterol was the dominant sterol, indicating that much of the material in the traps was fecal matter. During two of the years sampled, 1997 and 1999, ice edge blooms occurred from late April to early May. Ice receded earlier in 1998 and 2000, so phytoplankton bloomed in open water in late May. Lipids indicating greater phytoplankton input were high in the M2 trap during the ice-edge bloom years. Conversely, in 1998 and 2000, there was greater coupling between phytoplankton and zooplankton, much of the material collected was fecal pellets rather than intact diatoms and lipids were more characteristic of zooplankton sources. In zooplankton some monounsaturated fatty acids decreased sharply between February and April, reflecting mobilization of lipids for egg production. A polyunsaturated fatty acid characteristic of prymnesiophytes was elevated in winter and spring 1998 zooplankton, resulting from grazing of the 1997 coccolithophorid bloom. Overall, the results indicate that primary productivity is greater at M2 than at M3. Much of the annual primary production occurs outside of the April-May spring bloom period. Grazing of primary production is greater at M3 than M2, and at M2 more primary production is grazed in warm than cold years.
• #### A Temporal comparison of the eelgrass (Zostera marina L.) food web and community structure at Izembek Lagoon, Alaska from the mid-1970's to 2008

This thesis investigates food web and community structure in Izembek Lagoon, Alaska, an ecologically important sub-arctic seagrass system. Unprecedented environmental changes in high latitudes, such as increased sea-surface temperatures and a shorter duration of shore-fast sea ice, may now favor seagrass over phytoplankton production as compared to forty years ago. Any resulting shifts in food web and community dynamics could have substantial consequences given the importance of seagrass habitat for Alaskan fisheries, global migratory bird populations and benthic energy transformation. Recent (2008) stable isotope (C and N) values and benthic community metrics were gathered and compared to results from a similar study from the mid-1970’s to gauge temporal food web and community structure differences. An increase in reliance on seagrass carbon was detected in organisms involved in detrital and sediment processing. An increase in abundance of certain benthic organisms and a decrease in overall community evenness were also seen. These findings suggest an escalation in delivery of seagrass carbon to the food web, possibly induced by changing seagrass morphology or bed density at this location.
• #### Temporal variation and habitat use of nearshore crab populations in Kachemak Bay, Alaska

Larval, juvenile, and adult crab distribution was surveyed in three different habitats in Kachemak Bay, Alaska from June 2005 to September 2006 to determine temporal and spatial variability. Crab distribution varied temporally and spatially in all life stages. Nine sites of varying habitat complexity were surveyed monthly using scuba, light traps, and shrimp pots to measure habitat variables, quantify larval, juvenile, and adult crabs, and survey potential crab predators. No single bay-wide variable determined the appearance of all crab larvae. Spatial differences in larval abundance probably resulted from large scale physical transport mechanisms. Overall juvenile and adult crab abundance increased with habitat complexity; however species richness was not positively correlated with complexity. This study suggested that the canopy structure provided by Nereocystis luetkeana had minimal effects on spatial crab distribution in all life stages. Canopy structure may not influence the spatial distribution of larval crabs and is thought to have little importance for juvenile and adult crabs. Understory kelp density may more directly affect juvenile and adult crabs by providing more microhabitats for refuge. Habitat use and the importance of structural complexity vary by life history stage and species depending on survival strategy.
• #### The carbon cycle in an anoxic marine sediment: Concentrations, rates, isotope ratios, and diagenetic models

The carbon cycle in the anoxic sediments of Skan Bay, Alaska, was investigated in order to better understand the processes that control biogeochemical transformations in an organic-rich sediment environment. Depth distributions of concentration and $\delta\sp{13}$C were determined for five major carbon reservoirs: methane (CH$\sb4$), dissolved inorganic carbon (DIC), dissolved organic carbon (DOC), particulate inorganic carbon (PIC), and particulate organic carbon (POC). In addition, methane oxidation and sulfate reduction rates were measured under quasi-in situ conditions using radio-tracer techniques. Diagenetic models were applied to concentration, reaction rate, and isotope ratio depth distributions and the results were integrated into a comprehensive, depth-dependent model of the Skan Bay carbon cycle that considered advective, diffusive, and biological and chemical reactive fluxes for the five major carbon reservoirs. The Skan Bay carbon cycle is fuelled by POC, which is deposited at the sediment surface at a rate of 2290 $\pm$ 480 umol $\cdot$ cm$\sp{-2}$ $\cdot$ yr$\sp{-1}$. Isotope mass-balance calculations indicate that about 60% of this material is derived from kelp while the remainder originates as phytoplankton. About 60% of the organic matter is consumed in the upper 40 cm of the sediment column. The $\delta\sp{13}$C-POC and $\delta\sp{13}$C-DOC depth distributions suggest that the material derived from kelp is more labile, accounting for greater than 60% of the total POC consumption. The products of anaerobic metabolism of POC accumulate in the DOC reservoir creating a large DOC concentration gradient at the sediment-water interface. Flux and stable carbon isotope mass-balance calculations suggest that a sizable portion (30 to 80%) of the DOC produced by degradation of POC diffuses from the sediment prior to oxidation to dissolved inorganic carbon. Methane production appears to occur primarily at depths greater than 40 cm. The CH$\sb4$ diffuses upward and is almost quantitatively oxidized to DIC in a narrow subsurface zone. Methane oxidation accounts for only 20% of the DIC production, but exerts a profound influence on the $\delta\sp{13}$C-DIC profile, contributing to the distinct mid-depth minimum. Pore waters are supersaturated with respect to calcite at depths greater than 10 cm, but isotope mass-balance considerations indicate that carbonate mineral formation is not occurring in these sediments.
• #### The Concept Of Microbial Affinity For Limiting Nutrients In Steady State And Rhythmic Systems

To evaluate the role of biological rhythms in competition for survival, rhythms in cell division and limiting nutrient transport ability induced by light/dark (LD) cycles were investigated for three species of pelagic, freshwater algae growing in phosphoruslimited continuous and serially diluted batch (SDB) cultures. Nutrient transport ability of nutrient-starved microbial populations was measured as the initial slope (affinity) of a plot of limiting nutrient transport rate (V) versus extracellular limiting nutrient concentration (S). A method was devised for the determination of the affinity in continuous culture (a(,T)) by monitoring S with time. Cell division was asynchronous for the green alga, Selenastrum capricornutum, grown in LD continuous cultures and a rhythm in a(,T) for soluble reactive phosphate (Pi) was greatly affected by choice of biomass parameter. Division was strongly phased in LD SDB culture and weakly phased in continuous light (LL) SDB culture, indicating that nutrient perturbations have a greater effect on phasing of division than LD cycles for S. capricornutum. A rhythm in Pi transport rate in LD SDB culture was similar to the rhythm in continuous culture a(,T) when expressed per cell volume or cell dry weight but not when expressed per cell number. Cell division was phased for the green alga, Scenedesmus quadricauda, grown in LD continuous culture. A rhythm in a(,T) for Pi was not greatly affected by choice of biomass parameter. Cell division was also rhythmic in LD for the blue-green alga, Synechococcus Nageli. Synechococcus was an extremely efficient Pi transporter at low Pi concentrations in LD continuous culture, indicating that it should be widespread in oligotrophic systems and has probably been overlooked in past floristic studies.
• #### The ecology of a high-latitude rocky intertidal community: Processes driving population dynamics in Kachemak Bay, Alaska

The population dynamics and interactions of selected key species relative to community structure were investigated in the rocky intertidal of Kachemak Bay, southcentral Alaska (59$\sp\circ$35$\sp\prime$N, 151$\sp\circ$30$\sp\prime$W). The roles of recruitment processes and predation in regulating intertidal populations were emphasized in this investigation. Species cover was distinctly seasonal. Total cover typically exceeded 80% during the summer, especially in lower intertidal. Winter cover averaged 40-60%, with macroalgal cover varying up to six-fold between summer and winter. Barnacle recruitment varied both inter-annually and with respect to species. From 1991-1993, mean recruitment densities varied from 0.85-8.71 cm$\sp{-2}$ (range = 0-71 cm$\sp{-2}).$ In the upper intertidal, time-integrated summer recruit density of Semibalanus balanoides and Balanus glandula was 0.13 cm$\sp{-2}.$ Recruit density of S. cariosus in the low intertidal was 4.32 cm$\sp{-2}.$ In the low intertidal, recruits often saturated the surface, resulting in density-dependent mortality in two out of three years, a phenomenon which did not occur in the upper intertidal where space was never limiting. Predation was a significant source of mortality for barnacle recruits only in 1991, a poor recruitment year. However, predation by Nucella lima limited mussel (Mytilus trossulus) populations at some sites. Where N. lima density exceeded 100 m$\sp{-2},$ mussel cover was less than half that where Nucella was rare (31% vs. 72%). High densities of N. lima were estimated to remove 60-90% of mussels per season. Recruitment of the macroalga Fucus gardneri was almost 50 times greater in the presence of live barnacles than on bare rock surfaces or barnacle shells killed by heating. Recruitment in quadrats with tests of mechanically killed barnacles was intermediate. The results indicate that F. gardneri propagules are stimulated to attach by a chemical cue, probably a polypeptide, produced by barnacles. Based on population dynamics and species interactions investigated in Kachemak Bay, the mid- to low intertidal community appears to function similarly to the classical paradigm of regulation by competition and predation. The major exception is high inter-annual variability in predation relative to recruitment and competition.
• #### The effects of ocean acidification on walleye pollock (Theragra chalcogramma) early life history stages

Since the Industrial Revolution of the late 1700's, atmospheric and marine carbon dioxide levels have drastically increased. Ocean acidification is the result of the shift in the marine carbon cycle caused by the increase in marine and atmospheric carbon dioxide. Changing environmental conditions caused by ocean acidification have been shown to have adverse effects on different marine species as well as life history stages. As a result, ecologically and economically important teleost fish species such as walleye Pollock (Theragra chalcogramma) could be adversely affected by ocean acidification conditions. This study explores the responses of walleye pollock eggs and larvae incubated under different projected levels of ocean acidification, looking at hatch timing and growth parameters to examine potential adverse responses to more acidic conditions. Older walleye pollock juveniles (age 1+) were used to uncover potential physiological responses to ocean acidification pertaining specifically to stress, overall body condition indices, and blood chemistry. I found that while the two early life history stages of walleye pollock could survive under ambient, high, medium, and low pH conditions (pH 8.1, 7.9, 7.6, and 7.2, respectively), there were some physiological responses to projected levels of ocean acidification. Hatch timing was not delayed in the lowest pH treatment as expected. In addition, size at hatch, yolk area, and eye diameter did not differ among pH treatments. Walleye pollock juveniles reared under projected levels of ocean acidification demonstrated shifts in blood gas levels and blood pH. However, exposure to a lower pH environment of pH 7.9, 7.6, or 7.2 did not induce a response for either the stress indicators or body condition indices that were measured. To uncover the mechanism for their resilience, more testing is needed to gain further insight into underlying compensatory mechanisms of various life history stages and populations.
• #### The Geochemistry Of Manganese, Iron And Phosphorus In An Arctic Lake

Sediment redox processes were investigated in an oligotrophic, arctic lake containing metal oxide crusts in oxidizing surficial sediments (up to 22% Mn and 26% Fe). Toolik Lake, Alaska, a 12,000 year old kettle lake, has the lowest Pb-210 derived sedimentation rates reported for any lake (27 g m('-2) yr('-1)). Three independent methods for estimation of Mn, Fe and P retention within the lake (stream budgets, sediment traps and sediment burial rates) provide similar rates. Of the amounts entering the lake, 28% of P, 50% of Mn and 55% of Fe are retained. Common water column removal mechanisms for these elements and organic C are suggested by sediment trap data. A steady state diagenetic model with terms for diffusion, reduction and oxidation shows that Mn and Fe crusts migrate within surficial sediments. Metal oxide burial rates are equivalent to oxide dissolution rates (reduction), rates of upward diffusion of soluble divalent metals and metal precipitation rates (oxidation). High inputs of labile Mn and Fe from streams, plus low sedimentation and organic matter oxidation rates are important for crust formation. Approximately 12% of Mn and 2% of acid reducible Fe retained by the lake since its formation exist as diagenetic oxides; the rest is buried within reducing sediment. Sediment inorganic P migrates with Fe to form P enriched sediment zones with pore water PO(,4) concentrations beneath these zones regulated by vivianite (Fe(,3)(PO(,4))(,2) 8H(,2)O) formation. The migration of Mn and Fe within sediments results in the enrichment of Ba, Co, Ca, Ni, Ra-226 and carbonate in metal oxide enriched sediments. Barium is enriched in Mn crusts because of diagenetic migration.
• #### The Influence Of Habitat Complexity, Prey Quality, And Predator Avoidance On Sea Otter Resource Selection In Alaska

The differential selection of habitat by animals is one of the fundamental relationships that enable species to coexist. Habitat selection may be among various discrete categories (e.g., mudflat, boulder field, or meadow) or among a continuous array of characteristics such as vegetation percent cover, benthic substrate size, substrate rugosity, distance to prey resources, or distance to suitable escape terrain from predation. Sea otters are particularly suitable for resource selection studies because they are capable of selecting a wide variety habitat types in response to prey availability, competition, and predation. In Alaska, sea otters associate with a range of habitats types including continuous bedrock reefs in the western Aleutians to heterogeneous fjord systems in Kackemak Bay, Lower Cook Inlet. Sea otters inhabiting the western Aleutians exhibit highly restricted habitat selection patterns characteristic of declining populations. In contrast, sea otters inhabiting Kachemak Bay exhibit selective use of a broad range of habitat types. Many factors contribute to the selective use of habitats by animals, including habitat suitability, prey quality, and predation risk. This thesis was designed to test factors contributing to sea otter resource selection in an area undergoing population increase versus an area experiencing high predation pressure. The contribution of prey size, abundance, biomass, potential energy density are considered in addition to physical habitat characteristics such as grain size, rugosity, depth, structural habitat complexity, and exposure to prevailing weather. Findings suggest that foraging sea otters differentially select habitat and prey resources based on prey accessibility and not on prey abundance or potential prey energy density. Findings further suggest that sea otter foraging site selection is based on habitat complexity in areas with increasing populations, but in areas with high predation pressure, proximity to suitable escape terrain appears to be more important than prey quality or benthic habitat complexity.
• #### Thyroid hormone binding to brain nuclear extracts during smoltification in coho salmon

Salmon complete a metamorphosis called smoltification prior to entering salt water. Increased thyroid activity, olfactory imprinting, and chemical and structural changes in the brain are known to occur at this time. This study was undertaken to determine if triiodothyronine (T$\sb3$) binding to brain nuclear extracts changes during smoltification. During this investigation serum thyroxine (T$\sb4$) concentrations increased three fold during smoltification coincident with changes in coloration and morphology and surged again during downstream migration to six times presmolt concentrations. Using ultrafiltration assays, homologous displacement experiments of KCl extracts of recovered brain cell nuclei indicated that maximal binding capacity increased during smoltification and down-stream migration. The increase in receptor concentration lagged the increase in serum thyroxine by one week. Dissociation constants increased during smolt transformation but declined abruptly during down-stream migration. However, dissociation constants did not change during smoltification if nuclear extracts had been previously incubated at room temperature to remove endogenous ligand. Dissociation rate increased significantly, coincident with the increase in receptor concentration measured by homologous displacement. The maximal probable percent occupancy of available receptors increased from 60% before to greater than 95% during the smolt transformation climax. These results provide evidence that thyroid hormone receptors participate in brain development and olfactory imprinting in smolting salmon.
• #### To pup or not to pup? Using physiology and dive behavior to answer the Weddell Seal's overwinter question

Female Weddell seals (Leptonychotes weddellii) haul-out on the fast-ice surrounding the Antarctic continent in October and November each year to give birth to and nurse their pups. Breeding follows directly after weaning (December) and the annual molt begins in January-February. Animals reduce foraging efforts during the lactation and molting periods, but very little is known regarding the influence of this reduced activity on physiological condition. After a period of embryonic diapause, the annual molt coincides with embryo attachment and the start of active gestation. Consequently, female physiological condition at this time may influence reproductive success the following year. Overall female health and the ability to forage successfully throughout the gestation period (austral winter) may impact the likelihood that a pregnancy is brought to term. Therefore, this study tested whether overwinter changes in Weddell seal physiology and foraging efforts are reflected in reproductive outcomes the following year (i.e., to answer the over winter question of "to pup or not to pup?"). From 2010-2012, 100 (January-February: n = 53; October-November: n = 47) adult female Weddell seals were captured in Erebus Bay, Antarctica to assess overwinter changes in physiological condition and/or dive behavior that may be associated with reproductive success. Morphometric measurements and isotopic dilution procedures revealed that female Weddell seals gain ~10-15% of their body mass across the winter period, primarily in the form of blubber and lipid mass. The proportion of mass and lipid gain was similar regardless of whether females returned the following year and successfully gave birth, or did not produce a pup. Further, the amount of mass and energy acquired across gestation in the Weddell seal was markedly less than previously reported for other phocid species. Despite changes in activity patterns and body composition, Weddell seals maintained blood hemoglobin and muscle myoglobin concentrations across the winter. Therefore, Weddell seal total body oxygen stores and calculated aerobic dive limit (cADL) were conserved. This ensures that females have the physiological capabilities to effectively forage directly following the annual molt when they are at their leanest and must regain body mass and lipid stores. Although aerobic capacities did not change, dive effort varied considerably throughout the austral winter. Proxies of dive effort (duration, depth, %dives > cADL) were highest just after the molt (January-February) and just prior to the subsequent pupping season (August-September). Additionally, the proportion of each day spent diving increased mid-winter. Females that were observed the following year with a pup significantly increased all indices of foraging effort during the austral winter as compared to females that returned without a pup. This study is the first to identify and measure differences in dive efforts due to reproductive status, and indicates that successful reproduction is associated with greater foraging effort.
• #### Toxins And Toxicity Of Protogonyaulax From The Northeast Pacific

Dinoflagellates of the genus Protogonyaulax contain a group of substances that can be lethal to many creatures, including man, and may accumulate at many points in the food web. The substances are most familiar as paralytic shellfish poison (PSP), which occurs sporadically in bivalves. The present study was undertaken because previous work left in doubt both the origin and chemical nature of the toxins along the Alaskan coast. To investigate the problem, dinoflagellates were isolated from locations along the Pacific coast ranging from San Francisco to Dutch Harbor. Most isolates were obtained by incubating subtidal sediments to germinate resting cysts. Toxic isolates were obtained from most locations sampled. On the basis of morphology, all toxic isolates fell within the genus Protogonyaulax. The growth and toxicity of one clone (PI07) was studied under a variety of culture conditions. Toxicity was greatly suppressed under the conditions traditionally employed for culturing Protogonyaulax, suggesting that the toxicity of cells in nature may in general be higher than has been recognized. Chemical studies of the toxins extracted from Protogonyaulax revealed that the six toxins previously known (saxitoxin, its N-1-hydroxyl and 11-hydroxysulfate derivatives) are generally accompanied by somewhat larger amounts of their 21-sulfo derivatives. These have likely not been recognized in past studies due to their greatly reduced toxicity, facile hydrolysis, and altered chromatographic properties. The toxin composition of several isolates was determined and indicates that toxin composition is a conservative property of each clone and that there are regional populations of Protogonyaulax with uniform toxin composition, but that toxin composition differs substantially among regions. This pattern of variation, coupled with the great differences in the properties of the toxins, indicates that the nature of PSP will similarly vary from one region to another but will be uniform within each.
• #### Tracing sea ice algae into various benthic feeding types on the Chukchi Sea shelf

Climate change in the Arctic is expected to have drastic effects on marine primary production sources by shifting ice-associated primary production to an overall greater contribution from pelagic primary production. This shift could influence the timing, amount, and quality of algal material reaching the benthos. We determined the contribution of sea ice particulate organic matter (iPOM) to benthic-feeding invertebrates by examining concentrations and stable carbon isotope values (expressed as δ¹³C values) of three FAs prominent in diatoms: 16:4(n-1), 16:1(n-7) and 20:5(n-3). Our underlying assumption was that diatoms make up the majority in sea ice algal communities compared with phytoplankton communities. According to the FA concentrations, subsurface deposit feeders consumed the most iPOM and suspension feeders the least. Conversely, there were little differences in δ¹³C values of FAs between deposit and suspension feeders, but the higher δ¹³C values of 16:1(n-7) in omnivores indicated greater consumption of iPOM. We suggest that omnivores accumulate the ice algal FA biomarker from their benthic prey, which in turn may feed on ice algae from a deposited sediment pool. The dissimilar results between FA concentrations and isotope values suggest that the FAs used here may not be sufficiently source-specific and that other unaccounted for production sources, such as bacteria, may also contribute to the FA pool. We propose that FA isotope values are a more indicative biomarker than FA concentrations, but there is a further need for more specific ice algal biomarkers to resolve the question of ice algal contributions to the Arctic benthic food web.
• #### Tracking carbon sources through an Arctic marine food web: insights from fatty acids and their carbon stable isotopes

Marine production across the Bering-Chukchi continental shelf is influenced by seasonal sea ice dynamics and climatic conditions. Of particular importance is variability in the magnitude and timing of annual phytoplankton production in the water column and in sea ice, and effects of such variability on food web composition and productivity. Of primary concern is the long-term effect of the projected loss of Arctic sea ice on ecosystem productivity and stability, and the fate of upper trophic level species. I examined a portion of the Bering-Chukchi Sea food web by analyzing the fatty acid composition and stable carbon isotope ratios of individual fatty acids in particulate organic matter from sea ice and the water column. These techniques were used to make inferences about diets of three species of zooplankton (Themisto libellula, Calanus marshallae/glacialis, Thysanoessa raschii) sampled during a recent climatically cold, relatively heavy sea ice period in the Bering Sea. I also analyzed fatty acids of four species of ice-associated seals--ringed (Pusa/Phoca hispida), bearded (Erignathus barbatus), spotted (Phoca largha), and ribbon seals (Histriophoca fasciata)--sampled during the same relatively cold period (2007-2010) as well as a preceding warm (2002-2005), relatively low sea ice period in the Bering Sea. Particulate organic matter from sea ice and the water column had different fatty acid characteristics, most likely stemming from differences in algal composition. My results also showed that in the Bering Sea cold period, the amphipod T. libellula was predominately carnivorous, and the copepod C. marshallae/glacialis and euphausiid T. raschii were primarily herbivorous, but displayed some degree of omnivory. Across all years (2002-2010), fatty acid composition of ice seals showed clear evidence of resource partitioning among them, and little niche separation between spotted and ribbon seals, which is consistent with previous studies. The fatty acid composition of primarily pelagic feeding adult ringed seals and predominantly benthic feeding adult bearded seals did not differ between the recent warm (2002-2005) and cold (2007-2010) periods in the Bering Sea, suggesting that their diets and possibly food web structures were not affected by these large multiyear environmental fluctuations. Notably however, the stable carbon isotope ratios of individual fatty acids of bearded seals from the Bering Sea cold period were higher than those from the warm period, which suggests that their prey base in the Bering Sea was receiving more input from particulate organic matter from sea ice than the water column during those years. By using the stable carbon isotope ratios of individual fatty acids of particulate organic matter from sea ice and the water column in a series of stable isotope mixing models, I estimated the proportional contribution of fatty acids from sea ice particulate organic matter in T. libellula, C. marshallae/glacialis, and T. raschii collected in 2009 and 2010 as 36-72%, 27-63%, and 39-71%, respectively. Using a similar set of mixing models, I estimated that adult bearded seals had the highest level of fatty acids from sea ice particulate organic matter (62-80%), followed by spotted seals (51-62%), and then ringed seals (21-60%) in 2009 and 2010. Although estimates could not be made for ribbon seals due to lack of samples in 2009 and 2010, their stable carbon isotope ratios of individual fatty acids from 2003 were very similar to those of spotted seals suggesting that the proportional contribution of fatty acids from sea ice particulate organic matter to ribbons seals was similar to that of spotted seals. Assuming that seals sourced their sympagic fatty acids from the Bering Sea, these results suggest that sympagic production is currently an important contributor to food webs supporting both benthic and pelagic upper trophic level species in years with heavy ice cover in the Bering Sea. Thus, the question is raised--with the projected continuing loss of seasonal sea ice in the Arctic, will organic matter input from sympagic production also decline, and will it be compensated for by pelagic production to balance both pelagic and benthic carbon and energy budgets?
• #### Trophic dynamics and stock characteristics of snow crabs, Chionoecetes opilio, in the Alaskan Arctic

Arctic waters off the coast of Alaska have become increasingly open to human activities via dramatic climatic changes, such as reduced sea ice thickness and extent, warming ocean temperatures, and increased freshwater input. This research advances knowledge of snow crab trophic dynamics and stock characteristics in Arctic waters off the Alaska coast. Here, I provided baseline information regarding snow crab position in Beaufort Sea benthic food webs, its specific dietary habits in the Chukchi and Beaufort seas, and expanded upon previously limited life-history and population dynamic data in the Chukchi and Beaufort seas. I first detailed benthic food webs on the Alaskan Beaufort Sea shelf and snow crab trophic positions within these food webs using stable δ¹³C and δ¹⁵N isotope analysis. Water column and sediment particulate organic matter (POM) were used as primary food web end members. Isotopic niche space (δ¹³C – δ¹⁵N) occupied by benthic taxa provided measures of community-wide trophic redundancy and separation. Water column and sediment POM δ¹³C values generally reflected terrestrial POM inputs in the eastern and central shallow (14-90 m) Beaufort regions, but were indicative of persistent marine influence in the western and central deep (100-220 m) regions. Food web structure, as reflected by consumer trophic levels (TLs), trophic redundancy, and trophic niche space, supported the POM findings. In the eastern and central shallow regions, consumers occupied mainly lower TL (TL= 1-3), whereas consumers in the western regions occupied intermediate and higher TL (TL= 3-4). Overall trophic redundancy and niche space occupied by food webs in these four regions, however, was similar. The central deep Beaufort food web was unique in all metrics evaluated, and the comparatively largest isotopic niche space, with high trophic niche separation but low trophic redundancy, suggests that this region may be most vulnerable to perturbations. Snow crabs occupied food webs in the central deep and western shallow and deep Beaufort regions, where they maintained a consistent TL of 4.0 across regions. I then investigated snow crab dietary habits across the Chukchi, and the Alaskan and Canadian Beaufort seas in the size range of 40 to 130 mm CW using stomach contents and stable isotope analyses. Snow crabs consumed four main prey taxa: polychaetes, decapod crustaceans (crabs, amphipods), echinoderms (mainly ophiuroids), and mollusks (bivalves, gastropods). Crab diets in the southern and northern Chukchi Sea regions were similar to those in the western Beaufort Sea in that bivalve, amphipod, and crustacean consumption was highest. The Canadian Beaufort region was most unique in prey composition and in stable isotope values. Cannibalism on snow crabs was higher in the Chukchi Sea regions relative to the Beaufort Sea regions, suggesting that cannibalism may have an impact on recruitment in the Chukchi Sea via reduction of cohort strength after settlement to the benthos, as known from the Canadian Atlantic. Based on a comparison with southern Chukchi Sea macrofauna data, these results document the non-selective, omnivorous role of snow crabs across the entire Pacific Arctic, as well as providing first evidence for cannibalism in the Chukchi Sea. Finally, I generated new estimates of stock biomass, abundance, and maximum sustainable yield, length-weight relationships, size-at-maturity, and fecundity of snow crab in the Alaskan Arctic. Although snow crabs were more abundant in the Chukchi Sea, no crabs larger than the minimum marketable size (> 100 mm carapace width, based on Bering Sea metric) occurred in this region. Harvestable biomass of snow crabs only occurred in the Beaufort Sea, but was considerably lower than previous estimates in the Arctic FMP. Length-weight relationships were generally similar for male and female snow crabs between the Chukchi and Beaufort seas. Size-at-maturity and female fecundity in the Chukchi Sea were similar to snow crabs occurring in other geographic regions; low sample sizes in the Beaufort prevented size-at-maturity and fecundity analysis. Together these results contribute new understanding of Arctic snow crab population dynamics by utilizing a rich dataset obtained recently from the Chukchi and Beaufort regions.
• #### Trophic dynamics of pinniped populations in Alaska using stable carbon and nitrogen isotope ratios

Trophic changes in populations of Stellar sea lions (Eumetorias jubatus), northern fur seals (Callorhinus ursinus) and harbor seals (Phoca vitulina) in the eastern Bering Sea and Gulf of Alaska were studied using stable isotope analysis. Declining populations of all three species of pinnipeds prompted this study to determine if changes in diet, likely resulting from food limitation, contributed to the declines. Stable carbon and nitrogen isotope ratios were analyzed in the vibrissae (whiskers) and body tissues of pinnipeds from 1993-1998 and compared with muscle tissue from prey species during the same time period to determine pinniped trophic dynamics. Vibrissae growth rate studies revealed harbor seal vibrissae are only retained for one year and then replaced, while Steller sea lions maintain their vibrissae for several years. Isotopic data from all three species are consistent with diets composed of walleye pollock (Theragra chalcogramma) at various times and locations throughout the year. Steller sea lion and northern fur seal vibrissae revealed regular oscillations along their lengths in both carbon and nitrogen isotope ratios that likely corresponded to regional isotopic differences. As these animals moved or migrated from one region to another during the year, they metabolically incorporated the different regional isotope ratios through their prey. Because these animals return to their rookery to pup, breed and molt each year, the isotope ratios in the vibrissae showed a regular pattern of enrichment and deplection. Harbor seals, which tend to stay in one geographic location, have relatively static isotope ratios in their vibrissae, while seals that moved into offshore waters had fluctuating isotope ratios that corresponded to regional difference. No trophic shifts, as evidenced by major changes in nitrogen isotope ratios, were present in any tissues from the three species over the period 1975-1998. Stable isotope ratios of bone collagen for all three species from 1950-1997 indicated no change in trophic level but did reveal that the seasonal primary production in the North Pacific Ocean has declined and may have contributed to a decreased carrying capacity impacting these top trophic organisms
• #### Underwater bioacoustic analysis of bearded seal behavior off Barrow, Alaska

Bearded seal vocalizations were collected incidentally during the 1993 bowhead whale census. Analysis of seal locations, calculated by triangulation of the vocalizations, provided information on seal swim velocity, distribution, and movement. Swim speeds fell within previously documented values. Seal positions, when correlated with satellite images, suggested that seal distribution was directly associated with ice topography. Individually tracked seals exhibited different types of movements including: maintenance of position, rapid increase in speed and slower, prolonged directional travel. Swim speeds, distributions, and movements suggest distinct behaviors which may include foraging, territorial or female defense, or display. Movement and behaviors may alter as ice conditions change throughout the breeding season. Bioacoustics, when coupled with other research methods, is a useful tool in the study of the behavior of less accessible animals.