Global Trophic Position Comparison of Two Dominant Mesopelagic Fish Families (Myctophidae, Stomiidae) Using Amino Acid Nitrogen Isotopic Analyses

Abstract

The δ15N values of organisms are commonly used across diverse ecosystems to estimate trophic position and infer trophic connectivity. We undertook a novel cross-basin comparison of trophic position in two ecologically well-characterized and different groups of dominant mid-water fish consumers using amino acid nitrogen isotope compositions. We found that trophic positions estimated from the δ15N values of individual amino acids are nearly uniform within both families of these fishes across five global regions despite great variability in bulk tissue δ15N values. Regional differences in the δ15N values of phenylalanine confirmed that bulk tissue δ15N values reflect region-specific water mass biogeochemistry controlling δ15N values at the base of the food web. Trophic positions calculated from amino acid isotopic analyses (AA-TP) for lanternfishes (family Myctophidae) (AA-TP ∼2.9) largely align with expectations from stomach content studies (TP ∼3.2), while AA-TPs for dragonfishes (family Stomiidae) (AA-TP ∼3.2) were lower than TPs derived from stomach content studies (TP∼4.1). We demonstrate that amino acid nitrogen isotope analysis can overcome shortcomings of bulk tissue isotope analysis across biogeochemically distinct systems to provide globally comparative information regarding marine food web structure.

Opportunism on the High Seas: Foraging Ecology of Olive Ridley Turtles in the Eastern Pacific Ocean

“…For example, TPs of tuna, adult leatherbacks, lanternfishes, dragonfishes, and zooplankton do not change across ocean basins Olson et al, 2010;Choy et al, 2012;Hetherington et al, 2017). This underscores the uniqueness of detecting a potential trophic shift on the Costa Rica Dome.…”

“…All samples had values for Glu and Phe. We propagated error to calculate SD (see Dale et al, 2011;Choy et al, 2012;Bradley et al, 2015 for details). The two approaches were compared with a two-sided, paired Wilcoxon Signed-Rank test.…”

Methylmercury production below the mixed layer in the North Pacific Ocean

“…39 assuming the difference between δ 15 N glu and δ 15 N phe in marine algae (β) is 3.4 ± 0.9 and the 15 N enrichment in glutamic acid relative to phenylalanine during trophic transfer ( ) is 7.6 ± 1.1 . Uncertainty in trophic position was calculated by propagation of errors 38 and is treated quantitatively using the analytical solution of differentiation of equation 7 Table S3). Routine bulk tissue C and N isotopic compositions were determined using an online C-N analyser coupled with an isotope ratio mass spectrometer.…”

Hagfish feeding habits along a depth gradient inferred from stable isotopes

“…1 could simply be explained by a diet containing an increased amount of benthic prey. The analysis of δ 15 N from additional taxa in this food web or the use of compound-specific nitrogen isotope analysis of individual amino acids (Choy et al 2012) could improve our understanding of these patterns.…”