Browsing Marine Biology by Subject "food"
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Biogeochemical tracers of change in Pacific walruses past and presentReduced 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.
Dietary effects on protein turnover in three pinniped species, Eumetopias jubatus, Phoca vitulina, and Leptonychotes weddelliiThe 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.
Tracing sea ice algae into various benthic feeding types on the Chukchi Sea shelfClimate 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.