造礁石珊瑚对富营养化和高温胁迫的响应机制及适应潜力

Although it is well established that nutrient enrichment can increase the susceptibility of reef corals to bleaching, the mechanism(s) underpinning this etiology have not been well attributed. Enrichment of seawater results in an enlarged, fast‐growing symbiont population that is ultimately a net carbon sink for the energetic resources of the coral, which increase the susceptibility of corals to bleaching. While reef corals exist ‘optimum’ Symbiodinium density maximizing autotrophic capacity (P:R) to resist thermal stress. However, lack of mechanistic understanding limits the identification of biologically‐relevant, eutrophication thresholds that are needed for the region‐specific design of effective management strategies. In this project, massive, plating and branching corals across five dominant coral species are investigated seasonally at Luhuitou fringing reef in Sanya, Hainan Island, northern South China Sea (SCS), and their physiological indicators are measured to evaluate species‐specific ‘optimum’ Symbiodinium density in northern SCS. On the basis of this field investigation, experimental study is designed to disentangle the effects of eutrophication on the physiological response of species‐specific corals subject to normal and to a short-term temperature increase (Coral health→Coral Bleaching→Recovery/Death). Additionally, three different inorganic nutrient ratios are tested to assess the influence of nutrient stoichiometry on coral physiology, and to explore physiological thresholds of coral bleaching, as well as to assess the resilience of corals.

海水富营养化会抑制珊瑚对其内共生藻种群生长的控制能力，引起共生藻过度增殖、共生体自养能力下降，导致珊瑚在高温胁迫时更容易发生白化。珊瑚体内存在“最佳”的共生藻密度使珊瑚自养能力最大化、白化抵抗力增强。目前国际上关于珊瑚“最佳”共生藻密度的研究非常有限，富营养化影响珊瑚热白化的生理机制仍不清楚。本项目拟以块状、叶片状和枝状造礁石珊瑚（热白化敏感性依次增高）为研究对象，通过野外调查——考察其在自然环境下的生理动态变化特征，以及室内模拟实验——系统研究富营养化条件下不同热白化敏感性珊瑚种类由健康→热白化→恢复/死亡的生理动态变化过程，从而揭示敏感性不同的珊瑚种类抵抗白化的“最佳”共生藻密度和发生热白化的关键生理阈值，阐明富营养化对珊瑚热白化的影响机制，评估热胁迫结束后珊瑚种类的恢复潜力。研究结果可为量化珊瑚礁白化的水质富营养化阈值提供数据支持，为珊瑚礁白化预警、珊瑚礁保护和管理提供科学依据。

目前国际上关于造礁石珊瑚抵抗热胁迫的最佳共生藻密度的研究非常有限，高温和富营养胁迫下珊瑚热白化的机制机理仍不清楚。本研究通过对包括三亚在内的南海珊瑚礁区热白化敏感性不同的主要造礁石珊瑚种类的生理指标（共生藻密度、叶绿素a和组织生物量）变化特征进行分析，初步估算了南海不同区域主要造礁石珊瑚种类的最佳共生藻密度范围；同时，通过对南海北部珊瑚礁热白化事件和室内模拟升温及富营养胁迫实验中不同热白化敏感性珊瑚种类的健康、半白化和白化状态的生理和分子动态变化特征进行分析，初步揭示了敏感性不同的造礁石珊瑚种类对高温和富营养胁迫的响应特征及适应潜力。研究结果为进一步探索气候变化背景下普适性的珊瑚礁科学规律、以及珊瑚礁保护和管理提供数据基础和科学参考。