Spatial variations in the trophic status of Favia palauensis corals in the South China Sea: Insights into their different adaptabilities under contrasting environmental conditions

Scleractinian corals exhibit a dual trophic pattern of autotrophic photosynthesis and heterotrophic predation. However, whether corals can adjust their trophic status under contrasting environmental conditions remains unclear. In our study, 70 scleractinian corals (Favia palauensis) were collected from Sanya and the Xisha and Nansha Islands in the South China Sea. We measured the zooxanthellae density (ZD) and δ13C of zooxanthellae (δ13Cz) and host tissue (δ13Ch) and analyzed the difference between δ13Ch and δ13Cz (i.e., Δh−z 13C). The relatively high ZD and δ13Cz values in the samples from Sanya indicate that these corals might have higher photosynthetic rates and autotrophic abilities than those from Xisha and Nansha. In contrast, the relatively low δ13Ch and Δh−z 13C values in the samples from Xisha and Nansha suggest that these corals might have a higher heterotrophic ability than those from Sanya. In addition, we tested the coral tissue biomass and skeletal δ13C (δ13Cs) in the samples from Sanya and examined their correlations with Δh−z 13C. The results showed a negative correlation, indicating that the more the organic material produced by the coral, the stronger its heterotrophic ability. Our results show that corals can adjust their trophic status under different environmental and physiological conditions, which is essential for increasing their adaptability to different environmental conditions.