Stable N and C isotopes in the organic matrix of fish otoliths: Validation of a new approach for studying spatial and temporal changes in the trophic structure of aquatic ecosystems

TY - JOUR

T1 - Stable N and C isotopes in the organic matrix of fish otoliths: Validation of a new approach for studying spatial and temporal changes in the trophic structure of aquatic ecosystems

AU - Grønkjær, P.

AU - Pedersen, J.B.

AU - Ankjærø, Torben

AU - Nielsen, J.M.

AU - Christensen, J.T.

AU - Kjeldsen, H.

AU - Heinemeier, J.

AU - Steingrund, P.

PY - 2013/4/1

Y1 - 2013/4/1

N2 - Stable isotope studies of long-term ecosystem change are often hampered by lack of archived tissue samples. Here, we provide a reliable method for extracting the organic matrix from fish otoliths, demonstrate differences in isotope values between the soluble and insoluble organic fractions, and provide the trophic enrichment factors (ε). The analyses were performed on otoliths from wild-caught adult Atlantic cod (Gadus morhua) and otoliths from a 6-month diet-switch experiment with juvenile cod. Acid hydrolysis of otolith powder followed by ultrafiltration enabled us to purify and separate the soluble and insoluble organic material. There was a significant 1.72‰ and 0.15‰ difference in δN and δ C, respectively, between the soluble and insoluble organic fraction of the otolith. This emphasizes the need for separation of the two fractions before analysis. The diet-specific trophic enrichment (ε ) in the soluble fraction varied between -0.20‰ and 0.31‰ for nitrogen and between 0.09‰ and 0.23‰ for carbon. In conclusion, the organic matrix of otoliths provides an attractive archive of organic material for ecological stable isotope analysis that has the potential to provide important insights into historic changes in the trophic structure of aquatic ecosystems.

AB - Stable isotope studies of long-term ecosystem change are often hampered by lack of archived tissue samples. Here, we provide a reliable method for extracting the organic matrix from fish otoliths, demonstrate differences in isotope values between the soluble and insoluble organic fractions, and provide the trophic enrichment factors (ε). The analyses were performed on otoliths from wild-caught adult Atlantic cod (Gadus morhua) and otoliths from a 6-month diet-switch experiment with juvenile cod. Acid hydrolysis of otolith powder followed by ultrafiltration enabled us to purify and separate the soluble and insoluble organic material. There was a significant 1.72‰ and 0.15‰ difference in δN and δ C, respectively, between the soluble and insoluble organic fraction of the otolith. This emphasizes the need for separation of the two fractions before analysis. The diet-specific trophic enrichment (ε ) in the soluble fraction varied between -0.20‰ and 0.31‰ for nitrogen and between 0.09‰ and 0.23‰ for carbon. In conclusion, the organic matrix of otoliths provides an attractive archive of organic material for ecological stable isotope analysis that has the potential to provide important insights into historic changes in the trophic structure of aquatic ecosystems.

UR - http://www.scopus.com/inward/record.url?scp=84874760962&partnerID=8YFLogxK

U2 - 10.1139/cjfas-2012-0386

DO - 10.1139/cjfas-2012-0386

M3 - Journal article

AN - SCOPUS:84874760962

SN - 0706-652X

VL - 70

SP - 143

EP - 146

JO - Canadian Journal of Fisheries and Aquatic Sciences

JF - Canadian Journal of Fisheries and Aquatic Sciences

IS - 2

ER -