Heterogeneous dissolved organic nitrogen supply over a coral reef: first evidence from nitrogen stable isotope ratios
- 520 Downloads
Dissolved organic nitrogen (DON) potentially plays a major role in sustaining the high productivity and biological diversity of coral reefs. However, data are scarce regarding sources and sinks of DON. This study, for the first time, determined the 15N isotopic composition of total dissolved nitrogen (δ15NTDN), reflecting the isotopic signature of DON, in the water column over a coral reef. The uniformity in δ15NTDN during high tide (3.2 ± 0.3 ‰) indicated that the DON was mainly derived from offshore waters. In contrast, higher spatial heterogeneity of δ15NTDN (3.1 ± 0.9 ‰) and DON concentrations during low tide indicated the existence of local DON sources patchily distributed over the reef. Low δ15NTDN values located mid-reef were indicative of DON release from organisms that obtained their N via N2 fixation, whereas high δ15NTDN appeared to reflect localized release of DON by organisms exposed to dissolved inorganic nitrogen with elevated 15N, such as from terrestrial and offshore inputs. Collectively, the results highlight the importance of spatial patterns in DON release from reef communities in the N cycling of coral reefs.
KeywordsGeochemistry Stable isotopes Nitrogen cycle Dissolved organic nitrogen Dinitrogen fixation Coral reefs
This work was funded by the Japan Society for the Promotion of Sciences through Grants-In-Aid for Scientific Research awarded to T.N and B.T and through Fellowship to Foreign Researcher awarded to B.T. We are grateful to two anonymous reviewers for their comments.
- Atkinson M (2011) Biogeochemistry of nutrients. In: Dubinsky Z, Stambler N (eds) Coral reefs: An ecosystem in transition. Springer, pp 199-206Google Scholar
- Atkinson M, Falter J (2003) Coral reefs. In: Black K, Shimmield G (eds) Biogeochemistry of marine systems. Sheffield Academic Press, pp 40-64Google Scholar
- Grasshoff K, Kremling K, Ehrhardt M (1999) Methods of seawater analysis. Weinheim, TorontoGoogle Scholar
- Haas AF, Wild C (2010) Composition analysis of organic matter released by cosmopolitan coral reef-associated green algae. Aquat Biol 10:131–138Google Scholar
- Johannes RE, McCloske Lr, Marsh JA, Marshall N, Maragos J, Alberts J, Betzer S, Clutter RI, Crabtree D, Helfrich P, Telek G, Wells JM, Webb KL, Wiebe W, Roth A, Sottile W, Smith S, Pomeroy LR, Pilson MEQ, Meyer J, Delia C, Dupaul WD, Kinzie RA (1972) Metabolism of some coral reef communities - team study of nutrient and energy flux at Eniwetok. Bioscience 22:541–543CrossRefGoogle Scholar
- Kendall C, Elliott EM, Wankel SD (2007) Tracing anthropogenic inputs of nitrogen to ecosystems, Chapter 12. In: Michener RH, Lajtha K (eds) Stable isotopes in ecology and environmental science, 2nd edition. Blackwell Publishing, pp 375- 449Google Scholar
- Knapp AN, Sigman DM, Lipschultz F, Kustka AB, Capone DG (2011) Interbasin isotopic correspondence between upper-ocean bulk DON and subsurface nitrate and its implications for marine nitrogen cycling. Global Biogeochem Cycles 25 (4), GB4004, doi: 10.1029/2010GB003878
- Suzuki Y, Casareto BE (2011) The role of dissolved organic nitrogen (DON) in coral biology and reef ecology. In: Dubinsky Z, Stambler N (eds) Coral reefs: An ecosystem in transition. Springer, pp 207-214Google Scholar
- Thibodeau B, Hélie JF, Lehmann MF (2013) Variations of the nitrate isotopic composition in the St. Lawrence River caused by seasonal changes in atmospheric nitrogen inputs. Biogeochemistry, 10.1007/s10533-013-9834-4
- Wiedenmann J, D’Angelo C, Smith EG, Hunt AN, Legiret FE, Postle AD, Achterberg EP (2012) Nutrient enrichment can increase the susceptibility of reef corals to bleaching. Nat Clim Change doi: 10.1038/nclimate1661