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Marine Ecology Progress Series

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MEPS 516:239-250 (2014)  -  DOI:

Nitrogen isotope fractionation and amino acid turnover rates in the Pacific white shrimp Litopenaeus vannamei

Eileen E. Downs1, Brian N. Popp2, Carolyn M. Holl1,*

1College of Natural and Computational Sciences, Hawai’i Pacific University, 45-045 Kamehameha Highway, Kaneohe, Hawai’i 96744, USA
2Department of Geology and Geophysics, University of Hawai’i at Manoa, POST Building, 1680 East-West Road, Honolulu, Hawai’i 96822, USA
*Corresponding author:

ABSTRACT: Fluctuations in an animal’s trophic position (TP) can indicate changes within an ecosystem. Traditionally, bulk tissue or whole animal nitrogen (N) isotope analysis has been used to determine an animal’s TP, but there are limitations to the application of this approach. Amino acid compound-specific isotope analysis (AA-CSIA) can be used to determine TP based on the difference between the δ15N values of certain amino acids, commonly glutamic acid and phenylalanine. The rate at which 15N is incorporated into amino acids is largely unknown, and this may affect the accuracy of relative TP estimates especially during periods of ecosystem change or ontogenetic changes in diet. To study amino acid turnover rates, the diet of the Pacific white shrimp Litopenaeus vannamei was changed in the laboratory from an unlabeled diet (7.2‰) to a 15N-enriched diet (24‰), and animals were sampled over the course of 7 wk. AA-CSIA revealed that turnover times of amino acids vary considerably, with some amino acids having much more rapid turnover than others. The TP of L. vannamei (using δ15N values of glutamic acid and phenylalanine) over the course of the experiment remained constant, and shrimp TP averaged 2.14 ± 0.15 (mean ± SD, n = 7) relative to its diet, which was as expected. Our results indicate that the δ15N values of glutamic acid and phenylalanine can be used to accurately determine TP even while shrimp are undergoing a change to a diet with a different δ15N value.

KEY WORDS: Compound-specific isotope analysis · Diet change · Trophic position · Crustacean

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Cite this article as: Downs EE, Popp BN, Holl CM (2014) Nitrogen isotope fractionation and amino acid turnover rates in the Pacific white shrimp Litopenaeus vannamei. Mar Ecol Prog Ser 516:239-250.

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