Algal biomarkers and their metabolites in the lower food web of the Great Lakes, analyzed by HPLC-PCA/FL, LC-MS and GC-MS

At the base of the trophic ladder of aquatic food webs, phytoplankton synthesize various organic compounds that are (i) useful environmental biomarkers and (ii) essential toward growth and development processes of primary consumers and higher organisms. These essential organic compounds include carotenoids, chlorophylls and fatty acids, which are transferred from primary producers (phytoplankton) to higher trophic levels, where they are reprocessed, bioaccumulated and/or metabolized to other bioactive compounds (i.e., vitamin A).;In this thesis, I investigated the distribution and metabolic bioconversion of this pool of lipophilic pigments and fatty-acids in tissues of primary consumers (the dreissenid bivalves and various benthic and zooplanktonic crustaceans) and higher trophic levels (several fish) of the Laurentian Great Lakes. All these organisms constitute essential components of the food-web of these lakes, between primary producers and higher trophic levels.;Biomarkers of diatoms and chlorophytes were detected in tissues of dreissenids from Lake Erie. Fucoxanthinol and mactraxanthin were the most abundant xanthophylls extracted from their tissues, as revealed by liquid chromatography/photodiode array/atmospheric pressure chemical ionization ion trap mass spectrometry (LC-PDA/APCI-MS). Besides, these biomarkers were conjugated to a wide variety of saturated and unsaturated fatty acids. Full chromatographic and spectrometric characterization of the carotenol fatty acid ester conjugates bioaccumulated in tissues of dreissenids was also conducted using enzymatic hydrolysis, solid phase extraction (SPE) combined with LC-APCI-MS and GCMS analysis of fatty acids. The study revealed that palmitic (C16:0), palmitoleic (C16:1o7), eicosapentaenoic (C20:5o3, "EPA") and docoxahexaenoic (C22:6o3, "DHA") acids were the most abundant fatty acids esterified to the carotenoids.;Crustaceans, such as the zooplankter Mysis relicta, the amphipod Diporeia sp. or the invasive species Gammarus fasciatus and Echinogammarus ischnus also constitute an important source of energy and antioxidants for higher trophic level organisms. In this work, we report on the comparative analysis of dietary pigments, vitamins (A and E) and fatty acids in these four freshwater crustaceans originating from Lake Superior and Lake Ontario. Also, a high resolution study of astaxanthin fatty acid monoesters and diesters, extracted from Mysis relicta is reported. This powerful anti-oxidant was found to be highly conjugated to the two polyunstaturated, o-3 EPA and DHA.;Also, various tissues of several fish species were analyzed to study if any of these biomarkers could be traced at higher levels in the food web, and bioaccumulation of algal pigments were calculated.;Finally, a new sensitive and selective method was developed, based on LC/PDA/APCI-MS for the analysis of 16 algal biomarkers (12 carotenoids, 2 chlorophylls and 2 pheopigments) of chemotaxonomic importance that are typically detected in natural environmental samples.