Heterogeneous dissolved organic nitrogen supply over a coral reef: first evidence from nitrogen stable isotope ratios

• Published in: Coral reefs 2013-12, Vol.32 (4), p.1103-1110
• Main Authors: Thibodeau, B., Miyajima, T., Tayasu, I., Wyatt, A. S. J., Watanabe, A., Morimoto, N., Yoshimizu, C., Nagata, T.
• Format: Article
• Language: English
• Subjects: Biomedical and Life Sciences; Coral reefs; Freshwater & Marine Ecology; Geochemistry; Heterogeneity; Isotopes; Life Sciences; Marine biology; Nitrogen; Nitrogen fixation; Oceanography; Organic nitrogen; Stable isotopes; Water column
• ISSN: 0722-4028; 1432-0975
• DOI: 10.1007/s00338-013-1070-9

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 15 N isotopic composition of total dissolved nitrogen (δ 15 N TDN ), reflecting the isotopic signature of DON, in the water column over a coral reef. The uniformity in δ 15 N TDN during high tide (3.2 ± 0.3 ‰) indicated that the DON was mainly derived from offshore waters. In contrast, higher spatial heterogeneity of δ 15 N TDN (3.1 ± 0.9 ‰) and DON concentrations during low tide indicated the existence of local DON sources patchily distributed over the reef. Low δ 15 N TDN values located mid-reef were indicative of DON release from organisms that obtained their N via N 2 fixation, whereas high δ 15 N TDN appeared to reflect localized release of DON by organisms exposed to dissolved inorganic nitrogen with elevated 15 N, 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.