Date of Award
Master of Science (MS)
Ocean & Earth Sciences
H. Rodger Harvey
In the eastern Bering Sea, Thysanoessa raschii are the most abundant krill species and a keystone trophic member that serve as both an important grazer and link to upper level consumers. In this system krill experience large annual variation in food resources, especially during ice advance and retreat; multiple lipid classes are used to temper the effects of those fluctuations, as well as to fuel reproduction and growth. Two shipboard feeding experiments that occurred during late spring and early summer of 2010, respectively, monitored the lipid retention in adult T. raschii and examined the fluctuation of specific lipid biomarkers under food-limited conditions. Retention of neutral and polar lipid hydrolysis products (e.g. sterols, hydrocarbons, and fatty acids) and bulk lipid classes were followed over the 19- and 31-day experiments using gas chromatography with various detectors and Iatroscan techniques, respectively. One potential marker for consumption of sediment detritus was also tracked in water column particles, surface sediment, and tissue of other crustaceans in both the Bering and Chukchi Seas. Finally, glycerophospholipids (GPL), as well as di- and triacylglycerols (referred to here as di- and triglycerides; DG and TG), were followed using tandem liquid chromatography mass spectrometry (LC-MSn) to gain detailed information about detailed fatty acid stereochemistry in the lipid subclasses. Polar lipids as phospholipids comprised the dominant lipid class of euphausiids throughout both experiments. Losses were seen in phospholipids, which appear to function in both structural integrity and for energy storage. Major sterols including cholest-5-en-3β-ol (cholesterol), 24-methylcholest-5,22-dien-3β-ol (brassicasterol), and cholest-5,24-dien-3β-ol (desmosterol) comprised 98-99% of total sterol abundances in T. raschii with little variation during the experimental incubations, but small concentrations of the dinoflagellate derived sterol cholesta-5,7,22-trien-3β-ol, and a novel C28:8 fatty acid, generally found in dinoflagellates and prymnesiophytes, indicated predation on smaller algae in summer by T. raschii in those periods when diatom abundances were low. Steroidal hydrocarbons (i.e. sterenes) were detected in sediments and known benthic-dwelling detritivores, but absent from water column particles. Additionally, detection of these detrital products in the neritic krill species T. raschii suggests detrital feeding as a mechanism for their winter survival. Among intact molecules, fatty acids were largely represented by six structures – C14:0, C16:0, C16:1, C18:1, C20:5, C22:6 – with most present as mixed acyl groups within each intact lipid class. Across the combinations of fatty acids within the intact lipids, most contained mixed moieties as fatty acids with differing degrees of unsaturation which has implications for temperature tolerance and buoyancy of animals as they adapt to varied and changing environmental conditions.
Pleuthner, Rachel L..
"Lipid Biomarkers of Bering and Chukchi Sea Euphausiids and Their Application to Diet History"
(2019). Master of Science (MS), Thesis, Ocean/Earth/Atmos Sciences, Old Dominion University, DOI: 10.25777/2pr9-ta33