Recent Submissions

  • Defining genetic population structure and historical connectivity of snow crab (Chionoecetes opilio)

    Albrecht, Gregory T.; Hardy, Sarah M.; Lopez, J. Andres; Hundertmark, Kris J. (2011-08)
    The snow crab (Chionoecetes opilio) is a valuable commercial resource within the Bering Sea, as well as other areas in the North Pacific and Atlantic Oceans. Large populations are known to exist within the Chukchi and Beaufort Seas, including recently discovered commercial sized individuals (Beaufort). However, genetic connectivity throughout these regions has not been examined until now. Based on seven polymorphic microsatellite loci, relatively low population genetic structuring occurs throughout the Alaskan region (Gst = 0.001). This homogeneity is likely due to long-distance larval dispersal, adult migrations, and a possible recent population expansion following the last glacial maximum. Furthermore, meta-population analysis was conducted for Alaskan and Northwest Atlantic stocks. Although significant genetic divergence characterizes the West Greenland stock in relation to all other populations, low divergence (Gst = 0.005) was found between Atlantic Canada crabs and those from the Alaska region. Larval dispersal between regions is highly unlikely due to the transit distance. Therefore, low divergence is likely the result of a recent population expansion into the Northwest Atlantic <5000 years ago.
  • Kelp forests and barren grounds: phlorotannin production and holdfast community structure in the Aleutian dragon kelp, Eualaria fistulosa

    Schuster, Martin D.; Konar, Brenda; Iken, Katrin; Coyle, Kenneth (2012-12)
    The canopy forming kelp Eualaria fistulosa inhabits two organizational states throughout the Aleutian archipelago, kelp forests and barren grounds. Urchin abundance and behavior determines which state dominates in any given area. Sporophyll phlorotannin content and holdfast epibiont fauna were investigated at multiple islands along the Aleutian archipelago to determine how the organizational state affects the production of secondary metabolites and the taxon richness, abundance and biomass of holdfast communities. Barren ground sporophylls had higher phlorotannin content than kelp forest sporophylls, although grazing rates on sporophylls from each state did not differ during in situ grazing experiments. The taxon richness, abundance and biomass of holdfast communities were similar between kelp forests and barren grounds at all islands, although these communities varied among islands and were mostly driven by holdfast volume. These results suggest that physical differences such as light and nutrient availability in the kelp forest structure between organizational states may be responsible for differences in phlorotannin content, but that these differences are not reflected in the holdfast community structure. It appears that barren ground holdfast communities are remnants of a once forested area.
  • Evaluation of prey composition and nutritional value of diets of free-ranging harbor seals (Phoca vitulina) from Tugidak Island

    Geiger, Gretchen L.; Atkinson, Shannon; Carpenter, James; Horstmann-Dehn, Larissa; Wynne, Kate (2012-12)
    Changes in climate can cause shifts in ecosystem structure that can affect quantity or quality of prey available to predator populations. Due to sex or age-specific behaviors of predators, certain classes within a population may be more severely impacted by changes in their diet. This study evaluated prey composition and nutritional value of summer diets of harbor seals (Phoca vitulina richardii) from Tugidak Island, Alaska from 2001-2009. The MIXIT-WIN program was used to estimate the nutritional value of average harbor seal diets. Changes in relative abundance of certain prey species were correlated to sea surface temperature anomalies. Despite changes in prey composition, the nutritional value of the average harbor seal diet did not change. Fecal corticosteroid metabolite profiles were analyzed to identify age and sex of individual harbor seals from scats. Profiles obtained from a known adult male harbor seal could be differentiated from those of known adult female and juvenile male seals. Similar profiles were observed in unknown age and sex samples. Even though diet diversity differed between these groups, the nutritional quality of consumed diets was not significantly different. Tugidak Island harbor seals have flexible diets allowing them to capitalize on available prey to maintain their nutritional intake.
  • Wasting disease and environmental variables drive sea star assemblages in the northern Gulf of Alaska

    Mitchell, Timothy James; Konar, Brenda; Iken, Katrin; Kelley, Amanda (2019-05)
    Sea stars are ecologically important in rocky intertidal habitats. The recent (starting 2013) sea star die-off attributed to sea star wasting disease throughout the eastern Pacific, presumably triggered by unusually warm waters in recent years, has caused an increased interest in spatial and temporal patterns of sea star assemblages and the environmental drivers that structure these assemblages. This study assessed the role of seven potential static environmental variables (distance to freshwater, tidewater glacial presence, wave exposure, fetch, beach slope, substrate composition, and tidal range) influencing northern Gulf of Alaska sea star assemblages before and after regional sea star declines. For this, intertidal surveys were conducted annually from 2005 to 2018 at five sites in each of four regions that were between 100 and 420 km apart. In the years leading up to the regional mortality events, assemblages were different among regions and were structured mainly by tidewater glacier presence, wave fetch, and tidal range. The assemblages after wasting disease were different from those before the event, and there was a partial change in the environmental variables that correlated with sea star structure. In these recent years, the environmental variables most highly correlated with sea star assemblages were slope, wave fetch, and tidal range, all of which relate to desiccation, attachment, and wave action. This indicates that the change in sea star density and structure by wasting disease left an assemblage that is responding to different environmental variables. Understanding the delicate interplay of some of the environmental variables that influence sea star assemblages could expand knowledge of the habitat preferences and tolerance ranges of important and relatively unstudied species within the northern Gulf of Alaska.
  • Dietary effects on protein turnover in three pinniped species, Eumetopias jubatus, Phoca vitulina, and Leptonychotes weddellii

    Inglis, Susan D.; Castellini, Michael; Atkinson, Shannon; Barboza, Perry; Carpenter, James; Rea, Lorrie (2019-05)
    The role of dietary protein in pinniped (seal and sea lion) nutrition is poorly understood. Although these marine mammals derive the majority of their daily energetic needs from lipid, lipids cannot supply essential amino acids which have to come from protein fractions of the diet. Protein regulation is vital for cellular maintenance, molt, fasting metabolism, exercise and development. Proteins are composed of linked amino acids (AA), and net protein turnover is the balance between protein synthesis from component AA, and degradation back to AA. Protein regulation is influenced by dietary intake and quality, as well as physiological and metabolic requirements. In this work, pinniped diet quality was assessed through comparisons of amino acid profiles between maternal milk, blood serum, and seasonal prey of wild juvenile Steller sea lions (Eumetopias jubatus) in Southcentral Alaska. Both Pacific herring (Clupei pallasi) and walleye pollock (Gadus chalcogramma) showed similar patterns to milk in essential and branched chain amino acid content. Serum amino acid profiles suggest the juvenile sea lions were not in protein deficit at the time of capture. Protein metabolism in the blood and urine was assessed through turnover studies using amino acid tracers. The turnover kinetics of ¹⁵N-labelled glycine in the blood amino acid and protein pool, red blood cells, and urine urea were measured in wild adult female Weddell seals (Leptonychotes weddellii) in the Antarctic. Labelled glycine moved quickly into serum protein and red blood cells (1-2 hours) and urinary urea (2-4 hours). The turnover rates in the blood amino acid and urine urea pools demonstrated a reduced turnover rate associated with molting. Lastly, whole body protein turnover experiments using a single bolus ¹⁵N-labelled glycine tracer method with endproduct collection of blood, feces and urine were conducted on 2 Cohort groups of captive Alaskan harbor seals over 2 years. Season was found to have the greatest effect on whole body protein turnover, which increased during the winter and decreased in the summer molt. Conversely, protein intake decreased during the winter and increased in the summer molt. This pattern corresponded with an increase in mass and protein synthesis in the winter, while mass decreased and protein degradation rates increased in molting seals. Weaning also influenced the patterns with reduced protein turnover in newly weaned animals that had recently transitioned from milk to a fish diet. This project presents results on whole body protein turnover rates in nonfasting pinnipeds and reveals that protein turnover is strongly regulated by developmental and seasonal physiological and metabolic demands.
  • 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.
  • Biogeochemical tracers of change in Pacific walruses past and present

    Clark, Casey; Horstmann, Lara; Misarti, Nicole; Konar, Brenda; Severin, Ken; Lemons, Patrick (2019-05)
    Reduced sea ice and projected food web shifts associated with warming of the Arctic have raised concerns about the future of Arctic species. Pacific walruses (Odobenus rosmarus divergens) use sea ice as a platform for molting, giving birth, and resting between foraging bouts. Exactly how sea ice loss will affect walruses is difficult to predict, due to a lack of information about regional ecosystems and their responses to climate change. The objectives of the research in this dissertation were to 1) examine how walrus diet changed in response to shifting sea ice conditions over the last 4,000 years, with the goal of generating predictions about how current and future ice loss may affect the walrus population; 2) make it easier to directly compare the results of retrospective and contemporary stable isotope studies of walruses; and 3) generate new tools to assist wildlife managers in monitoring the walrus population in an uncertain future. Stable carbon and nitrogen isotope ratios of walrus bone collagen indicated that diet was similar during previous intervals of high and low sea ice; however, diet variability among individual walruses was greater when sea ice cover was low, suggesting decreased abundance of preferred mollusk prey. Modern walrus diet was different from both previous high and low ice intervals, meaning that food webs in the Arctic are still in a state of flux, or that recent changes are novel within the last 4,000 years. Tissue-specific stable isotope discrimination factors were generated for walrus muscle, liver, skin, and bone collagen to improve comparisons between retrospective and contemporary studies of walrus diet. Additionally, lipid normalization models were parameterized for walrus skin and muscle, thereby making future walrus stable isotope research more feasible by reducing analytical costs and allowing the use of non-lethal sample collection. Finally, a novel technique for estimating the age at onset of reproductive maturity using concentrations of zinc and lead in the teeth of female walruses was established. This new approach has the potential to become a powerful tool for monitoring the walrus population and may be applicable to other species. Use of this technique on archived specimens may make it possible to examine changes in wildlife population dynamics across thousands of years.
  • Tracing sea ice algae into various benthic feeding types on the Chukchi Sea shelf

    Schollmeier, Tanja; Iken, Katrin; Wooller, Matthew; Hardy, Sarah (2018-12)
    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.
  • Estimates of primary production sources to Arctic bivalves using amino acid stable carbon isotope fingerprinting

    Rowe, Audrey G.; Wooller, Matthew; Iken, Katrin; O'Brien, Diane (2018-12)
    Benthic invertebrates are a crucial trophic link in Arctic marine food webs. However, estimates of the contribution of primary production sources sustaining these organisms are not well characterized. Potential sources could include sinking particulate organic matter from sea ice algae and phytoplankton, terrestrial organic matter eroded from the coastal environment, macroalgal material, or microbial organic matter. Proportions of these sources could also be significantly altered in the future as a result of environmental change. We measured the stable carbon isotope values of essential amino acids in muscle tissue from two common bivalve genera (Macoma spp. and Astarte spp.) collected in Hanna Shoal in the northeastern Chukchi Sea, considered an Arctic benthic hotspot. We used stable isotope mixing models in R (simmr) to compare the stable carbon isotope amino acid fingerprints of the bivalves to a suite of amino acid source endmembers, including marine phytoplankton, brown and red macroalgae, bacteria, and terrestrial plants, to estimate the proportional contributions of primary production sources to the bivalve species from Hanna Shoal. The models revealed relatively high contributions of essential amino acids from phytoplankton and bacteria averaged across both species in the region as a whole. We also examined whether stable carbon isotope fingerprints could be measured from essential amino acids preserved in bivalve shells, which could then allow proportional contributions of food sources to be estimated from ancient bivalve shells, allowing source estimates to be extended back in time. To investigate this, we measured the stable carbon isotope values of essential amino acids in a suite of paired modern bivalve shells and muscle from Macoma calcarea from the Chukchi Sea. These analyses revealed a correspondence between the fingerprints and mixing model estimates of the dominant primary production source of essential amino acids derived from analyses of these two tissue types. Our findings indicate that stable carbon isotope amino acid fingerprinting of marine bivalves can be used to examine dominant organic matter sources in the Arctic marine benthos in recent years as well as in deeper time.
  • Spatial trends and environmental drivers of epibenthic shelf community structure across the Aleutian Islands

    Bland, Aaron; Konar, Brenda; Iken, Katrin; Johnson, Mark; Zimmermann, Mark (2018-12)
    The continental shelf around the Aleutian Islands supports important commercial and subsistence fisheries as well as multiple seabird and marine mammal populations. To sustainably manage these populations, more information is needed on the distribution of the benthic communities that support some of the top level consumers. Given the vast size and highly variable physical environment of the Aleutian Islands, it is likely that epibenthic community structure on the continental shelf will vary by geographic area and physical and oceanographic conditions. This project examined spatial patterns in Aleutian epibenthic shelf communities among oceanographic regions (island groups separated by major oceanographic passes) and islands within these regions and identified environmental drivers responsible for important community divisions. Benthic trawls were conducted at 12 Aleutian islands across four oceanographic regions to characterize epibenthic shelf community structure along the island chain. It was tested whether the spatial variability in shelf community structure among regions and islands was correlated to multiple environmental variables including bottom water temperature, water depth, distance from shore, exposure, bottom rugosity, sediment grain size, sediment chlorophyll content, and drift algal food subsidies. Overall, communities differed both among regions and among islands within regions. Communities in the Far Western region (Near Strait to Buldir Strait) differed from communities in other regions, largely due to a high density of sand dollars in the Far West. However, none of the measured environmental characteristics explained this difference. Additionally, there was no evidence for a break in epibenthic shelf community structure across Samalga Pass between the East and the Central regions, even though Samalga represents a biogeographic break for many other Aleutian community types, including zooplankton, fish, and kelp forest communities. Within the Central region, a characteristic soft-sediment community (including the flatfish Atheresthes spp. and the crabs Labidochirus splendescens and Chionoecetes bairdi) distinguished Adak Island from other Central islands. Compared with groundfish trawl surveys conducted by the Alaska Fisheries Science Center (AFSC), this study captured less fish but more invertebrates by biomass, which is likely related to different gear selectivity used by the two studies. These findings provide information on the distribution of Aleutian shelf communities that complement existing information from AFSC surveys. In particular, it is shown that there is potentially an important division in epibenthic shelf communities across Buldir Strait, in agreement with the literature identifying this pass as an important biogeographic break. Furthermore, it is suggested that future assessments of Aleutian epibenthic communities should employ a combination of sampling gear types to better represent various epibenthic taxa.
  • Assessing a macroalgal foundation species: community variation with shifting algal assemblages

    Metzger, Jacob Ryan; Konar, Brenda; Edwards, Matthew; Beaudreau, Anne (2018-08)
    Foundation species provide critical food and habitat to their associated communities. Consequently, they are disproportionately important in shaping community structure, promoting greater biodiversity and increased species abundance. In the Aleutian archipelago, once extensive kelp forests are now relatively rare and highly fragmented. This is due to unregulated urchin grazing shifting the majority of nearshore rocky-reefs from kelp forests to either urchin barrens or "transition forests" - kelp forests devoid of understory algae. The algal communities within kelp forests, transition forests, and urchin barrens represent a stepwise loss in fleshy algal guilds, a regression from a full algal community, to having only canopy kelp, to areas largely denuded of all fleshy algae. This stepwise loss of algal guilds was used to test the designation of the resident canopy-forming kelp, Eualaria fistulosa, as a foundation species--a species that has strong, positive effects on communities where it occurs. Therefore, I assessed the impact that E. fistulosa's occurrence had on faunal community structure (in terms of species diversity, abundance and biomass, and percent bottom cover)and invertebrate size-structure. This study found that the presence of E. fistulosa does not correspond to strong differences in invertebrate size-structure or faunal community structure. However, in kelp forests where E. fistulosa exists in tandem with a variety of subcanopy macroalgae, faunal communities are more species rich, have significantly different community structures with notably higher abundance, biomass, and percent cover of filter feeding taxa, and support sea urchin populations containing significantly higher proportions of larger individuals. Consequently, this study stresses the context dependent role of foundation species and suggests their strong, positive effects on associated communities may change with perturbations to ecosystems. To that end, this study suggests that we may need to reconsider the designation of E. fistulosa as a foundation species following the extensive fragmentation and range restriction that has occurred throughout much of the Aleutian Archipelago.
  • Organic matter accumulation and preservation in Alaskan continental margin sediments

    Ding, Xiaoling; Henrichs, Susan M. (1998)
    Continental margin sediments provide a historical record of the sources and fate of organic matter (OM) originating both from the continents and from primary productivity in the overlying water column. However, since this record can be altered by microbial decomposition within the sediment, the history cannot be interpreted without understanding how decomposition can affect OM composition. Also, the margins accumulate much of the OM buried in ocean sediments; hence, knowledge of processes influencing preservation of OM in these sediments is essential to understanding the global carbon cycle. OM preservation was examined using two approaches. First, I studied sediments in the northeastern Gulf of Alaska to determine sources of OM and temporal changes in carbon accumulation. A large amount of OM, 45--70 x 104 tons/yr, accumulated in this region, about 50% from terrestrial sources. Most of the sediment cores showed little evidence of change in TOC, TN, or C and N stable isotope compositions due to decomposition within the sediment. Second, I investigated the processes that control OM preservation, focusing on the role of the OM adsorption to mineral surfaces. Because proteins are major constituents of sedimentary OM, I examined factors controlling their adsorption, decomposition, and preservation. Three hydrophilic proteins were strongly adsorbed by two clay minerals, an iron oxide, sub-oxic sediments from Resurrection Bay (RB), Alaska, and anoxic sediments from Skan Bay (SB), Alaska. The partition coefficients were large enough to lead to their preservation provided that the proteins did not decompose while adsorbed. Generally, adsorption of proteins to solid phases decreased decomposition rates, suggesting that adsorption is important in protecting these compounds from microbial attack. Greater protein decomposition rates were found in SB than in RB sediments, indicating that anoxia did not inhibit protein biodegradation. Naturally-occurring adsorbed proteins were extracted from SB and RB sediments using a detergent solution. Most of these adsorbed proteins were small (<12 kDa), indicating that only the proteins adsorbed within the micropores of particle surfaces are preserved long-term.
  • Decomposition and adsorption of peptides in Alaskan coastal marine sediments

    Luo, Honghong (1994)
    In organic-rich coastal sediments, hydrolyzable amino acids make up a substantial fraction of the sedimentary content of organic nitrogen. How this organic nitrogen resists decomposition and is preserved in sediments is poorly understood. In order to investigate the factors controlling mineralization and preservation of hydrolyzable amino acids, decomposition and adsorption of peptides were studied in suboxic and anoxic pore water and sediments from Resurrection Bay (RB) and Skan Bay (SB), Alaska. Five tritium-labeled peptides, basic di-lysine, acidic di-glutamic acid, and neutral di-alanine, tri-alanine and hexa-alanine, were used as tracers. In filtered pore water, the hydrolysis rates were usually low. The exception was that the initial enzymatic hydrolysis of di-alanine and di-glutamic acid was rapid in SB pore water. The hydrolysis rates of both peptides increased with concentration. In sediments, hydrolysis was found to be the rate-limiting step of peptide decomposition. Alanyl and glutamyl peptides were hydrolyzed faster than lysyl peptide, and the hydrolysis rates among alanyl peptides decreased with increasing molecular weight. Peptide hydrolysis was affected more by molecular structure than by oxic or anoxic conditions. Adsorption of lysyl peptide to sediments was greater than that of other peptides. Basicity enhanced peptide adsorption more than increased molecular weight. Sedimentary organic matter was mainly responsible for peptide adsorption. The different patterns of peptide adsorption in RB and SB sediments were related to the greater total organic carbon concentration in SB sediment. Some of the peptide adsorption was irreversible. Adsorbed peptides were more resistant to biological decomposition than dissolved peptides. Adsorption may be an important step in the process of peptide preservation in sediments, and thus the preservation of sediment organic matter during early diagenesis.
  • Natural abundance of nitrogen(15) in a subarctic lake and biogeochemical implications to nitrogen cycling

    Gu, Binhe (1993)
    Stable isotope ratios of nitrogen ($\delta\sp{15}$N) were employed to track the origin and fate of nitrogen in a subarctic lake, Alaska. The annual planktonic nitrogen cycle was dominated by N$\sb2$ fixation in spring and NH$\sb4\sp+$ assimilation in summer. In winter, microbial nitrification was the major sink for NH$\sb4\sp+$ and denitrification was accounted for most of the loss of NO$\sb3\sp-.$ The small isotope fractionation in nitrification is proposed as a result of substrate (NH$\sb4\sp+)$ limitation. The temporal and spatial homogeneity of the $\delta\sp{15}$N of dissolved organic nitrogen may be related to its large pool size and refractory nature. A stable isotope mass balance suggests that the winter phytoplankton was only composed of 10 to 20% of the suspended organic matter in water column due to low primary productivity during the ice cover period. A close correlation between $\delta\sp{15}$N of phytoplankton and $\delta\sp{15}$N of dissolved pools indicates that NH$\sb4\sp+$ was the predominant nitrogen source for non-N$\sb2$-fixing algae. The similarity of $\delta\sp{15}$N between a spring blue-green bloom and N$\sb2$ suggests an atmospheric origin for nitrogen. A mixing model estimated that the blue-green algal bloom derived approximately 70% of its nitrogen from molecular nitrogen. This fixed nitrogen was further transferred to higher trophic levels via the food chain and to other primary producers following mineralization. The $\delta\sp{15}$N of aquatic macrophytes indicates that non-rooted species obtained their nitrogen from the water column while rooted species obtained their nitrogen largely from the sediment. Evidence from dual isotope tracers ($\delta\sp{15}$N and $\delta\sp{13}$C) suggests that the zooplankton were supported by phytoplankton throughout the growing season despite an apparent abundance of detritus in the water column. Benthic fauna relied on either phytoplankton detritus or other organic matter in the sediment. The $\delta\sp{15}$N data exhibit only two to three trophic levels in both planktonic and the benthic communities in Smith Lake.
  • The ecology of a high-latitude rocky intertidal community: Processes driving population dynamics in Kachemak Bay, Alaska

    Carroll, Michael Leslie (1994)
    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.
  • 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).
  • Thyroid hormone binding to brain nuclear extracts during smoltification in coho salmon

    Cheek, L. Michael (1991)
    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.
  • The carbon cycle in an anoxic marine sediment: Concentrations, rates, isotope ratios, and diagenetic models

    Alperin, Marc Jon; Reeburgh, W. S. (1988)
    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

    Molot, Lewis Arnold; Brown, E. J. (1981)
    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.
  • Processes Controlling Radon-222 And Radium-226 On The Southeastern Bering Sea Shelf (Chemical Oceanography, Two-Dimensional Model, Continental, Gas-Exchange, Sediment Flux)

    Glover, David Mark (1985)
    An investigation was made into the use of ('222)Rn and ('226)Ra as tracers of air-sea gas exchange, water column mixing and sediment-water exchange on the southeastern Bering Sea shelf. Furthermore, a two-dimensional model was developed to unify these three processes into a coherent picture of ('222)Rn flux out of the sediments, through the water column and into the atmosphere. The best time period to average wind speeds when regressing them against gas transfer coefficients was found to be 3.3 days by a linear regression optimization, approximately the synoptic time scale of storms in the southeastern Bering Sea. A statistically significant relationship between averaged wind speed and transfer coefficients was found at the 80% confidence level. Gas transfer coefficients were found to be obscured in shallow waters by radon flux from the sediments. Two-dimensional mixing in these continental shelf waters rendered the traditional one-dimensional vertical mixing model of excess ('222)Rn unable to obtain reliable vertical eddy diffusivities. Exchange across the sediment-water interface was calculated from the deficiency of ('222)Rn measured in sediment cores, the standing crop of excess ('222)Rn in the overlying water column and the ('222)Rn production rate of sediment surface grab samples. The flux of radon out of the sediments was found to increase in the onshore direction. Biological irrigation appears to be the primary exchange mechanism between the sediment and water columns on this shelf. Distributions in the water column show finestructure reported previously as well as biological removal of ('226)Ra. A (chi)('2) hypersurface search found the optimal horizontal and vertical eddy diffusivities that explained the two-dimensional distribution of ('222)Rn provided from a kriging estimation exercise on the data measured in this study. This model was essentially a hybrid of a least squares surface fit and a numerical integration of the governing differential equation of ('222)Rn. When considered as a two-dimensional system in the cross-shelf direction, the rates of gas exchange, water column mixing and sediment-water exchange agree with each other to an acceptable degree.

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