Comparing trophic position estimates using bulk and compound specific stable isotope analyses: applying new approaches to mackerel icefish Champsocephalus gunnari

• Published in: PeerJ
• Main Authors: Canseco, José Antonio, Niklitschek, Edwin J., Quezada-Romegialli, Claudio, Yarnes, Chris, Harrod, Chris
• Other Authors: Universidad de Los Lagos, Instituto Antártico Chileno
• Format: Article in Journal/Newspaper
• Language: unknown
• Published: PeerJ 2024
• Subjects: Euphausia superba; South Orkney Islands; Champsocephalus gunnari; Trophic ecology; Nitrogen isotope; Compound specific; Antarctic; Inach; Antarc*; Antarctic Krill; Icefish
• Online Access: http://hdl.handle.net/10261/366206; https://doi.org/10.7717/peerj.17372

Quantifying the tropic position (TP) of an animal species is key to understanding its ecosystem function. While both bulk and compound-specific analyses of stable isotopes are widely used for this purpose, few studies have assessed the consistency between and within such approaches. Champsocephalus gunnari is a specialist teleost that predates almost exclusively on Antarctic krill Euphausia superba. This well-known and nearly constant trophic relationship makes C. gunnari particularly suitable for assessing consistency between TP methods under field conditions. In the present work, we produced and compared TP estimates for C. gunnari and its main prey using a standard bulk and two amino acid-specific stable isotope approaches (CSI-AA). One based on the difference between glutamate and phenylalanine (TP), and the other on the proline-phenylalanine difference (TP). To do that, samples from C. gunnari, E. superba and four other pelagic invertebrate and fish species, all potential prey for C.gunnari, were collected off the South Orkney Islands between January and March 2019, analyzed using standard isotopic ratio mass spectrometry methods and interpreted following a Bayesian approach. Median estimates (CI) for C. gunnari were similar between TP (3.6; CI: 3.0-4.8) and TP (3.4; CI:3.2-3.6), and lower for TP (3.1; CI:3.0-3.3). TP differences between C. gunnari and E. superba were 1.4, 1.1 and 1.2, all compatible with expectations from the monospecific diet of this predator (1TP=1). While these results suggest greater accuracy for Glx-Phe and Pro-Phe, differences observed between both CSI-AA approaches suggests these methods may require further validation before becoming a standard tool for trophic ecology. Jose Canseco was supported by a doctoral fellowship from Universidad de Los Lagos (Chile). Edwin Niklitschek was supported by the Chilean Antarctic Institute (INACH) through grant RT_68-18 and by Universidad de Los Lagos through Research Grant RT 29/18. Chris Harrod and Claudio Quezada-Romegialli were supported by ...