Distribution of dissolved organic carbon and nitrogen in a coral reef
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Dissolved organic matter (DOM) concentrations in a fringing coral reef were measured for both carbon and nitrogen with the analytical technique of high-temperature catalytic oxidation. Because of high precision of the analytical system, not only the concentrations of dissolved organic carbon and nitrogen (DOC and DON, respectively) but the C:N ratio was also determined from the distribution of DOC and DON concentrations. The observed concentrations of DOC and DON ranged 57–76 and 3.8–5.6 μmol l−1, respectively. The C:N ratios of the DOM that was produced on the reef flat were very similar between seagrass- and coral-dominated areas; the C:N ratio was 10 on average. The C:N ratio of DOM was significantly higher than that of particulate organic matter (POM) that was produced on the reef flat. Production rates of DOC were measured on the reef flat during stagnant periods and accounted for 3–7% of the net primary production, depending on the sampling site. The production rate of DON was estimated to be 10–30% of the net uptake of dissolved inorganic N in the reef community. Considering that the DOM and POM concentrations were not correlated with each other, a major source of the reef-derived DOM may be the benthic community and not POM such as phytoplankton. It was concluded that a widely distributed benthic community in the coral reef released C-rich DOM to the overlying seawater, conserving N in the community.
KeywordsDOM POM Coral reef C:N ratio Primary production
We would like to thank Y. Maeda and Y. Motomura (Tokyo Institute of Technology) and K. Fujii (The University of Tokyo) for assistance with the sample collection. We are also grateful to two anonymous reviewers and M. Warner (topic editor) who provided helpful comments to improve this article. This work was supported by the Grant-in-Aid for Scientific Research on Innovative Areas “Coral reef science for symbiosis and coexistence of human and ecosystem under combined stresses” (No. 20121007) of the Ministry of Education, Culture, Sports, Science and Technology (MEXT), Japan.
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