Seasonal Variations in Coral Lipids and Their Significance for Energy Maintenance in the South China Sea

Abstract

The degradation of coral reef ecosystems caused by coral bleaching has been increasing in recent years. Coral bleaching implies a decrease in the symbiodinianceae, such as endosymbiotic zooxanthellae, which in turn affects the energy supplied to coral hosts. However, as an alternative energy source, the energy supply mechanism of lipids during seasonal changes in zooxanthellae density (ZD) was not well explored and validated. In this study, 66 coral samples of Acropora millepora and Pocillopora damicornis were collected in March, June and October 2020 in Xisha Islands in the South China Sea. The response of lipids to the seasonal variations of ZD and photosynthetic rate was explored by combining physiological parameters (ZD) with geochemical indicators (δ¹³C of zooxanthellae δ¹³C_z, host tissues δ¹³C_h and total lipids δ¹³C_TL). The ZD and δ¹³C_z of Acropora millepora and Pocillopora damicornis (ZD: 28.7% and 28.8%; δ¹³C_z: 0.47 and 0.57‰ respectively) decreased in summer compared to that in spring indicate a decrease in photosynthetic rate of zooxanthellae. Correspondingly, δ¹³C_h decreased by 0.50 and 0.61‰, lipid content decreased by 60.82% and 53.56%, δ¹³C_TL decreased by 2.1 and 2.07‰ respectively. This means that corals can maintain stable energy supply by increasing heterotrophic predation and consuming more lipid when autotrophic photosynthesis decreases in summer. We emphasize that the level of lipid reserves may be an important factor affecting the resistance to environmental stress. Coral species with higher lipid reserves could have a selective advantage and higher resistance to bleaching.