Evaluation of nitrogen loading and its ecological consequences in the coastal marine ecosystem using compound-specific isotope analysis

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Compound-specific δ15N analysis has been employed to investigate ecological effects of anthropogenic nitrogen loading to the coastal marine ecosystems, particularly coral reefs. Spatial change in δ15N along environmental gradient of N loading was compared between the traditional bulk-δ15N and the amino acid δ15N measurements for both the host corals and the zooxanthellae. The mechanism for internal N exchange between the host coral and the zooxanthellae was investigated by comparing the amino acid δ15N pattern among corals incubated under different light and feeding conditions. To evaluate the detrital food chain using the amino acid δ15N, bacteria were incubated under several different nutritional conditions and compared for the amino acid δ15N pattern. We also evaluated the influence of atmospheric N deposition on coral reefs, which has been almost overlooked in previous works. The origin and the transport pathway were estimated using δ15N and δ18O of rainwater nitrate, δ18O and δ2H of meteoric water, and the backward trajectory analysis.