Estimation of accurate trophic positions of marine organisms using compound-specific nitrogen isotope ratios of amino acids

Abstract

Stable carbon and nitrogen isotope analyses of bulk organic materials have been widely used to understand marine food web structure in a number of ecological investigations. In particular, nitrogen isotopic composition (δ15N) can be used to determine the trophic level of target organism because this value tends to increase with increasing trophic level. However, large variations in trophic fractionation factor (i.e., isotopic discrimination between diets and consumers) among the animals and in δ15N values for primary producers (spatially and/or temporally) have made it difficult to estimate trophic levels of consumers in some ecosystems. Recently, compound-specific stable isotope analysis (CSIA) of nitrogen within amino acids has been proposed as a more powerful tool to determine the trophic position of organisms. It can be possible to estimate the trophic level of target animal using δ15N values of trophic (e.g., glutamic acid) and source amino acids (e.g., phenylalanine) in their tissue. Furthermore, the δ15N values of source amino acids in the organisms can be applicable to estimate the background nitrogen source in the ecosystems. This is possible because of little 15N enrichments in source amino acid with each trophic level. Therefore, compound-specific stable nitrogen isotope analysis of amino acids could be used to characterize food web structure and to understand nitrogen dynamics. This presentation will o determine the trophic level of target organism because this value tends to increase with increasing trophic level. However, large variations in trophic fractionation factor (i.e., isotopic discrimination between diets and consumers) among the animals and in δ15N values for primary producers (spatially and/or temporally) have made it difficult to estimate trophic levels of consumers in some ecosystems. Recently, compound-specific stable isotope analysis (CSIA) of nitrogen within amino acids has been proposed as a more powerful tool to determine the trophic position of organisms. It can be possible to estimate the trophic level of target animal using δ15N values of trophic (e.g., glutamic acid) and source amino acids (e.g., phenylalanine) in their tissue. Furthermore, the δ15N values of source amino acids in the organisms can be applicable to estimate the background nitrogen source in the ecosystems. This is possible because of little 15N enrichments in source amino acid with each trophic level. Therefore, compound-specific stable nitrogen isotope analysis of amino acids could be used to characterize food web structure and to understand nitrogen dynamics. This presentation will