JGR: δ¹⁵N revealing the differences in trophic status between nearshore and offshore corals in the South China Sea

Recently, Xu Shendong, one visiting researcher of Guangxi Laboratory on the Study of Coral Reefs in the South China Sea (associate researcher of Yantai Institute of Coastal Zone Research, Chinese Academy of Sciences), published a research paper entitled "Significant Differences in Coral Trophic Status Between Nearshore and Offshore Reefs Recorded by δ¹⁵N of Coral Symbiotic Zooxanthellae and Host Tissue in the South China Sea" in a classic geological journal: Journal of Geophysical Research: Biogeosciences.

Based on the δ¹⁵N tracer technology, this study studied the nutritional pattern of coral in the nearshore Sanya reefs, and offshore Xisha, Nansha reefs in the South China Sea. The basic principle of this study is that the stable nitrogen isotopes (δ¹⁵N_z, δ¹⁵N_h) of coral symbiotic algae, the host, and the difference between the two (△^{h-z 15}N) can effectively indicate the intensity of physiological activities, such as autotrophic photosynthesis and heterotrophic predation of coral symbiotic algae. The study found that the density of zooxanthellae and δ¹⁵N_z of corals in nearshore Sanya Luhuitou reefs were higher than those of corals in the offshore Xisha and Nansha reefs (p<0.001); the δ¹⁵N of marine particulate organic matter (δ¹⁵N_POM) are relatively low in the offshore Xisha and Nansha reefs, but the corals in these area are significantly higher in δ¹⁵N_h and △^{h-z 15}N than that in Sanya Luhuitou (δ¹⁵N_h: p<0.05; △ ^{h-z 15}N: p<0.001). Based on these results, we conclude that corals in nearshore Sanya have higher autotrophic abilities than corals from offshore Xisha and Nansha reefs. By contrast, corals in offshore reefs are more dependent on heterotrophic feeding of the host to obtain energy. This study demonstrate that corals can adjust their trophic status to meet energy needs under different environmental conditions in the South China Sea. This dynamic adjustment of energy supply patterns is of great significance to improve coral's environmental adaptability. This study extends the application of stable nitrogen isotope δ¹⁵N tracing technology in the study of coral nutrition patterns in the South China Sea.

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Xu S., Mo H., Men Z., Yu K., Zhang Z., & Chen H. Significant differences in coral trophic status between nearshore and offshore reefs recorded by δ¹⁵N of coral symbiotic zooxanthellae and host tissue in the South China Sea in the SCS. Journal of Geophysical Research: Biogeosciences, 2024, 129, e2023JG007432. https://doi.org/10.1029/2023JG007432.