Controls on the nitrogen isotopic composition of shallow water corals across a tropical reef flat transect
- 422 Downloads
We tested the hypothesis that the nitrogen (N) isotopic signature (δ15N) of coral skeletal organic material (CS-δ15N) matches that of the coral tissue and also reflects the δ15N of water column fixed N, such that CS-δ15N can be used as a proxy for spatio-temporal oceanic N isotope distributions. Strong correlations between the δ15N of skeletal organic material and that of coral tissue in two scleractinian corals (Porites lutea and Favia stelligera) across a tropical coral reef flat support the use of CS-δ15N in reconstructing coral biomass δ15N changes. However, we observed a consistent and species-specific offset between the coral tissue δ15N and the skeletal CS-δ15N. As such, the CS-δ15N is not an absolute measure of tissue δ15N. The CS-δ15N of both coral species and three species of macroalgae increased across the reef flat in response to a natural gradient in water column δ15N. There was an apparent dampening of the water column δ15N gradient recorded in the coral tissue δ15N and the CS-δ15N, possibly caused by shifting trophic status of corals across the reef flat. The CS-δ15N therefore appears to robustly reflect the δ15N of the coral tissue, and the coral system is responsive to the δ15N of the water column N pools. The distortion of the true water column δ15N by corals requires further investigation and is an important consideration for the use of coral skeletons in temporal reconstructions of water column δ15N.
KeywordsCoral skeleton Organic material Nitrogen isotopes Tropical corals
This work was funded by Southern Cross University (Special Studies Leave program), the Australian Research Council (LP100200732, DP0878683), US NSF grants OCE-1234664 and OCE-1060947 (to D.M.S), and the Grand Challenges Program at Princeton University. We thank I. Alexander and M. Carvalho de Carvalho from SCU, and A. M. Weigand from Princeton University for technical assistance. We also thank I. Santos for assistance with Heron Island sample collection.
- D’Elia C, Webb K, Porter J (1981) Nitrate-rich groundwater inputs to Discovery Bay, Jamaica: a significant source of N to local coral reefs? Bull Mar Sci 31:903–910Google Scholar
- Fowler D, Coyle M, Skiba U, Sutton MA, Cape JN, Reis S, Sheppard LJ, Jenkins A, Grizzetti B, Galloway JN, Vitousek P, Leach A, Bouwman AF, Butterbach-Bahl K, Dentener F, Stevenson D, Amann M, Voss M (2013) The global nitrogen cycle in the twenty-first century. Philos Trans Roy Soc Lond B Biol Sci 368:20130164CrossRefGoogle Scholar
- Jones PD, Briffa KR, Osborn TJ, Lough JM, van Ommen TD, Vinther BM, Luterbacher J, Wahl ER, Zwiers FW, Mann ME, Schmidt GA, Ammann CM, Buckley BM, Cobb KM, Esper J, Goosse H, Graham N, Jansen E, Kiefer T, Kull C, Kuettel M, Mosley-Thompson E, Overpeck JT, Riedwyl N, Schulz M, Tudhope AW, Villalba R, Wanner H, Wolff E, Xoplaki E (2009) High-resolution palaeoclimatology of the last millennium: a review of current status and future prospects. Holocene 19:3–49CrossRefGoogle Scholar
- Knapp AN, Sigman DM, Lipschultz F (2005) N isotopic composition of dissolved organic nitrogen and nitrate at the Bermuda Atlantic time-series study site. Global Biogeochem Cycles 19:GB1018Google Scholar
- Wang XT, Sigman DM, Cohen AL, Sinclair DJ, Sherrell RM, Weigand MA, Erler DV, Ren H (2014) Isotopic composition of skeleton-bound organic nitrogen in reef-building symbiotic corals: a new method and proxy evaluation at Bermuda. Geochim Cosmochim Acta. doi: 10.1016/j.gca.2014.09.017
- Yamazaki A, Watanabe T, Tsunogai U (2011) Nitrogen isotopes of organic nitrogen in reef coral skeletons as a proxy of tropical nutrient dynamics. Geophys Res Lett 38:L19605Google Scholar