Nitrogen and carbon isotope values of individual amino acids: a tool to study foraging ecology of penguins in the Southern Ocean
Lorrain, A.; Graham, B.; Menard, F.; Popp, B.; Bouillon, S.; van Breugel, P.; Cherel, Y. (2009). Nitrogen and carbon isotope values of individual amino acids: a tool to study foraging ecology of penguins in the Southern Ocean. Mar. Ecol. Prog. Ser. 391: 293-306. dx.doi.org/10.3354/meps08215
We determined the d15N and d13C values of individual amino acids (AAs) isolated from chick blood of 4 penguin species that forage in different oceanic regions (from the subtropics of the Indian Ocean to Antarctica) to test if: (1) the d15N values of phenylalanine (d15N phe) revealed different foraging areas among the species; (2) the difference between glutamic acid and phenylalanine d15N values (?d15Nglu-phe) accurately predicted trophic levels; and (3) the d13C value of AAs could resolve species foraging locations, similar to bulk d13C values. The d13C values of all AAs decreased with latitude, were positively correlated with bulk d13C data, and, therefore, tracked the isotopic baseline. However, we were not able to discern additional ecological information from these d13C values. In contrast, the d15N values of AAs distinguished the isotopic value of the nitrogen at the base of the food web from the trophic level of the consumer, providing new insight for the study of the trophic ecology of seabirds. The difference in the bulk d15N values of northern and southern rockhopper penguins Eudyptes chrysocome ssp. was due to both a difference in their foraging location (different d15N phe) and their trophic levels (different ?d15Nglu-phe). The d15N phe values of king Aptenodytes patagonicus and Adélie penguins Pygoscelis adeliae were higher than those of rockhoppers, which could reflect a foraging on mesopelagic prey for king penguins and, in the highly productive Antarctic shelf waters, for Adelie penguins. The ?d15Nglu-phe accurately reflected the relative trophic level of penguins, but further work is required to determine the trophic enrichment factors for compound-specific isotope analysis.
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