太阳紫外（UV）辐射增强严重影响着海洋珊瑚礁生态系统。本项目拟选择南海北部受陆源输入影响较大的三亚湾（近岸）和较小的西沙永兴岛（远海）热带珊瑚礁海区为研究对象，以连接微食物环和传统食物链的溶解有机物(DOM)光降解为切入点，以珊瑚礁海区低营养盐却维持高生产力的现象为突破口，通过现场调研、原位培养和受控模拟实验，综合分析UV和DOM（DOC、DON）在近岸和远海珊瑚礁海区的时空分布特征及差异，揭示UV辐射下不同系统DOM（近岸陆源输入和远海自身循环产生）光降解对细菌和藻类营养盐（C、N）吸收的贡献，探索DOM光降解对细菌生长效率（BGE）的影响及其与季风的耦合关系，这对深入分析珊瑚礁海区微食物环的结构功能及"高效营养生态泵"过程有重要的生态意义。本研究不仅为阐明珊瑚礁维持高生产力机制和营养动力学过程打下基础，还可为深化珊瑚礁生态系生物─光学驱动理论提供依据。

Increasing Ultraviolet Radiation (UV) intensity in the atmosphere caused by ozone depletion results in significant impacts on the marine ecosystem, especially in the oligotrophic sea waters such as a coral reef region. The project plans to study two contrasting tropical coral reef ecosystems in the northern South China Sea, i.e. near-shore Sanya Bay and offshore Yongxin Islands in Xisha area. Based on the former projects, we will study the photodegradation of dissolved organic matter (DOM), as it links the microbial loop with the traditional food chains, and is the mechanism that low-nutrients sustain high productivity in coral reef area. We will conduct field researches and in situ incubations to comprehensively analyze the following aspects: 1) UV penetration in water column, spatial-temporal distribution and the sources of different components of DOM (e.g. DOC and DON) in near-shore and offshore coral reef ecosystems cases; 2) DOM photodegradation and its effect on the nutrient availability (e.g. C and N) to bacteria and algae at different systems (the near-shore with terrigenous input and offshore with self-cycling); 3) Coupled with seasonal monsoon, the effects of DOM photodegradation on bacterial growth efficiency (BGE). It is significant to investigate the structure and function of microbial loop and the process of efficient nutrition-ecological pump in coral reef ecosystem. This study may not only to clarify the mechanism of coral reef waters maintaining high productivity and the dynamics of nutrients cycling, but also to provide a theoretical basis on which the model of coral reef ecosystem dynamics and bio-optical theory could be established and further studied.