Abstract

Stable carbon isotopic compositions of amino acids (δ¹³C_AA) in organisms potentially record information on carbon sources and flow in food webs. In this study, we report δ¹³C values of 16 proteinogenic amino acids in marine consumers and evaluate their changes associated with the trophic transfer by using a newly developed analytical method based on multidimensional preparative liquid chromatography and elemental analysis with isotope-ratio mass spectrometry. Our targets in this study are cultured black rockfish (Sebastes melanops) and its isotopically-known diet, as well as wild blue mackerel (Scomber australasicus) as a representative marine consumer. δ¹³C values of AAs in marine consumers have a variation as large as 30‰, with glycine, serine, and threonine being most ¹³C-enriched and leucine and phenylalanine being most ¹³C-depleted. On the other hand, the δ¹³C_AA variation among species is relatively small, showing that δ¹³C values of amino acids in marine organisms are mainly determined by their central biochemical pathways rather than species-specific processes. The δ¹³C_AA differences (Δ¹³C = δ¹³C_consumer − δ¹³C_diet) between the cultured fish and its diet are small for most amino acids (− 0.6‰ on average), with two amino acids synthesized from glycolytic intermediates, serine (+ 4.4‰) and alanine (− 2.6‰), having the largest positive and negative deviation, respectively. It indicates a larger extent of de novo synthesis of glycolytic amino acids in fish. Some essential amino acids also show small but significant Δ¹³C, like threonine (+ 1.7‰) and methionine (− 2.4‰). In summary, this study provides a new assessment of δ¹³C compositions of amino acids in marine consumers and their changes during the trophic transfer, covering a nearly complete set of proteinogenic amino acids. It should offer significant refinements for future studies.