Application Of Fatty Acids Biomarker In Marine Food Web Research

In this thesis,previous marine food web studies,including gut content analysis,carbon and nitrogen stable isotope analysis,fatty acid components analysis,were reviewed in detail.A new method detecting carbon stable isotope of individual fatty acid was constructed and evaluated.Habitual organisms in north of East China Sea and alongshore estuarine water areas were measured by different methods mentioned above in order to understand the role of diverse aquatic species composing specific food webs and their control on the flow of matter and energy along the food chain.Trophic member phytoplankton,zooplankton,primary fish species and bottom-dwelling species were analyzed.Carbon and nitrogen was analyzed by Elemental Analyzer (Vario ELâ…¢),carbon and nitrogen stable isotope ratios were determined on isotope ratio mass spectrum(IRMS,Thermo Finnigan Delta plus XP),fatty acids were measured by use of Gas Chromatography instrument(GC,Varian CP3800),and carbon stable isotopes of individual fatty acids were tested by combination of Thermo Finngan GC and Thermo Finngan Delt plus XP IRMS.Organic carbon content of fish dorsal muscle varied from 42.11%to 55.8% and nitrogen contnent from 9.19%to 15.52%.The negative linear correlation between organic carbon and nitrogen(R²=0.602)indicated that there existed a relative balance of the ration of lipid and protein in the muscle.The fatty acids pattern or specific biomarker fatty acids of consumers were proved to be effective to identify food sources.Nevertheless,the specific marker eicosapentaenoic acid(EPA,20:5n3)and docosahexaenoic acid(DHA, 22:6n3)for marine algae food source structure fluctuated from 1%to 30%of all fatty acids among species and individuals.Also,DHA has a higher adsorption and assimilation efficiency than that of EPA,thus playing a crucial role for the survival and growth of fish.Seven highly unsaturated fatty acids(PUFA),i.e., 18:2n6,18:3n3,20:4n6,20:5n3,22:5n6,22:5n3,and 22:6n3,change a lot among species in different communities in the north of East Cina Sea.In fish musucle,with trophic level increase,fatty acid 16:1n7 for phytoplankton decreased,while fatty acid 18:1n7 for zooplankton increased.Gender and life stage are critical factors influencing the fatty acid composition of fish species.Total length 11cm is a turning point for Larimichthyspolyactis,whose food habits transformed from crustacean and fish to fish dominant.For Trichiurusjaponicus species with total length increasing,organic carbon of fatty acids increased in male individuals while decreased in female.Spawn had a large amount of organic carbon of fatty acids relatively,wherein unsaturated fatty acid contributed the most.Combined fatty acid content analysis with Cluster and ADS analyses,fish species were separated into two groups.Fish feed on plankton were most pelagic species and larva with specific prey preference,respectively.Benthos feeders were bottom-dwelling or demersal species.Thrissakarnrnalensis was the basal pelagic phytoplankton feeder,while Trachurus japouicu was commonly feed in seagrass circumstance.GC/C-IRMS analysis was applied to fish,zooplankton and demersal species. The results showed thatδ¹³C varied from -19.8 to -32.2‰,of which the minimum one was 22:6n3 for phytoplankton and the maximum 22:1n11 for Trachurus japouicus.Generally,¹³C/¹²C ratio was less negative in saturated fatty acids.With desaturation increases,δ¹³C-FA values decline.It is further demonstrated that ¹³C/¹²C ratios of individual fatty acids in potential prey(diet) and consumers allow identifying carbon fluxes and trophic links.Highly unsaturated fatty acids(PUFAs)are often used as dietary indicators since they cannot be created de novo,are seldom modified by marine organisms due to biochemical limitations,and are typically the most common fatty acids in marine ecosystems.