TY - JOUR TI - Nitrogen isotopic baselines and implications for estimating foraging habitat and trophic position of yellowfin tuna in the Indian and Pacific Oceans AU - Lorrain, Anne AU - Graham, Brittany S. AU - Popp, Brian N. AU - Allain, Valerie AU - Olson, Robert J. AU - Hunt, Brian P. V. AU - Potier, Michel AU - Fry, Brian AU - Galvan-Magana, Felipe AU - Menkes, Christophe E. R. AU - Kaehler, Sven AU - Menard, Frederic T2 - Deep-Sea Research Part Ii-Topical Studies in Oceanography AB - Assessment of isotopic compositions at the base of food webs is a prerequisite for using stable isotope analysis to assess foraging locations and trophic positions of marine organisms. Our study represents a unique application of stable-isotope analyses across multiple trophic levels (primary producer, primary consumer and tertiary consumer) and over a large spatial scale in two pelagic marine ecosystems. We found that delta N-15 values of particulate organic matter (POM), barnacles and phenylalanine from the muscle tissue of yellowfin tuna all showed similar spatial patterns. This consistency suggests that isotopic analysis of any of these can provide a reasonable proxy for isotopic variability at the base of the food web. Secondly, variations in the delta N-15 values of yellowfin tuna bulk-muscle tissues paralleled the spatial trends observed in all of these isotopic baseline proxies. Variation in isotopic composition at the base of the food web, rather than differences in tuna diet, explained the 11 parts per thousand variability observed in the bulk-tissue delta N-15 values of yellowfin tuna. Evaluating the trophic position of yellowfin tuna using amino-acid isotopic compositions across the western Indian and equatorial Pacific Oceans strongly suggests these tuna occupy similar trophic positions, albeit absolute trophic positions estimated by this method were lower than expected. This study reinforces the importance of considering isotopic baseline variability for diet studies, and provides new insights into methods that can be applied to generate nitrogen isoscapes for worldwide comparisons of top predators in marine ecosystems. (C) 2014 Elsevier Ltd. All rights reserved. DA - 2015/03// PY - 2015 DO - 10.1016/j.dsr2.2014.02.003 DP - Web of Science VL - 113 SP - 188 EP - 198 J2 - Deep-Sea Res. Part II-Top. Stud. Oceanogr. LA - English SN - 0967-0645 UR - http://www.sciencedirect.com/science/article/pii/S0967064514000472 DB - fdi:010064079 KW - ACL KW - Amino acids KW - Barnacles KW - DISCOVERY KW - E3 KW - IRD KW - ISOZOO_EC:FP7:PEOPLE_302010 KW - Lepas anatifera KW - Marine top predators KW - Nitrogen stable isotopes KW - SUD KW - Thunnus albacares KW - aa-csia KW - amino-acids KW - delta-n-15 KW - diet KW - eastern tropical pacific KW - ecology KW - food-web structure KW - fractionation KW - global patterns KW - pom KW - subtropical gyre KW - thunnus-albacares ER -