A community metabolism approach to examine the environmental regulation of coral growth

珊瑚礁的多样性和生产力直接取决于珊瑚的生态和生物地球化学动态（例如钙化，生长和补充），珊瑚是关键的生态系统建筑师。温度、光照（浊度和沉积）和风暴破坏等相对较小的变化都会对这些珊瑚造成压力，从而导致整个生态系统的物理和生物结构发生变化。进一步人为引起的压力，如过度捕捞和沿海土地利用的变化，加剧了这种压力；然而，现在人们普遍认识到，珊瑚面临的两个最大的环境威胁是热引起的漂白事件和海洋酸化。热白化是指珊瑚在经历高于平均温度的温度时色素脱色，而海洋酸化是指随着大气中升高的二氧化碳缓慢扩散到海水中，pH值降低。在这些较低的pH值条件下，珊瑚钙化率降低。研究现在已经开始关注这些因素是如何共同影响珊瑚生长的；不幸的是，这些研究在技术上仍然有限，无法完全控制酸化研究所需的海水复杂的碳化学成分。此外，光的可用性作为一个共同调节因素被忽视了，这是令人惊讶的，因为光不仅加剧了珊瑚白化，而且还提高了钙化的速度。我们最近发现，具有某些形态（类型，我们的术语）的珊瑚表现出不同的漂白反应，这反过来又是钙化模式和速率的函数。1型物种生长和钙化速度快，但对环境变化极为敏感。2型品种更健壮，生长缓慢，钙化率较低。因此，一个物种受气候变化影响的程度似乎与原始生长过程有关，并可能依赖于原始生长过程。珊瑚类型的这种相对易感性对珊瑚礁的生物和物理结构都有深远的影响。这里提出的工作建立在我们实验室的几项成功研究的基础上，这些研究检查了环境变化对钙化生物的影响。这些研究中现有的“pH值统计”技术将被改进，以提供对海水无机碳系统的完全控制。利用这项新技术，科学家们将进行一系列实验，研究珊瑚类型如何对调节珊瑚生长的主要因素——光线、温度和二氧化碳的同时变化做出反应。具体来说，我们关注珊瑚群落代谢，因为这代表了珊瑚宿主和相关细菌菌群的呼吸净活动，以及珊瑚共生微藻的光合作用，最终有助于生长（钙化）。我们将在实验室中应用这种群落代谢方法，以获得对气体交换的高水平控制，从而允许以高精度控制物理/化学环境条件，并以高时间分辨率测量代谢率。

Coral reef diversity and productivity are directly dependent on the ecological and biogeochemical dynamics (e.g. calcification, growth and recruitment) of corals, the key ecosystem architects. These corals can be stressed by relatively small modifications in temperature, light availability (turbidity and sedimentation) and storm damage, which in turn can lead to alterations of the physical and biological structure of the entire ecosystem. Further anthropogenic-induced stresses, such as over-fishing and coastal land use changes, compound this stress; however, it is now generally recognised that two of the greatest environmental threats to corals are thermal induced bleaching events and ocean acidification. Thermal bleaching refers to the dipigmentation of corals as they experience higher than average temperatures whist ocean acidification refers to the lowering of pH as elevated atmospheric CO2 slowly diffuses into seawater. Under these lower pH condiitons coral calcification rates are reduced. Research has now begun to focus on how these factors act in concert to affect coral growth; unfortunately, these studies are still technologically limited to enable full control over the complex carbon chemistry of seawater required for acidification studies. Furthermore, light availability has been ignored as a co-regulatory factor, which is surprising since light not only exacerbates coral bleaching but also enhances the rate of calcification. We have recently identified that corals with certain morphologies (Types, our terminology) exhibit alternative bleaching responses, which in turn are a function of calcification patterns and rates. Type 1 species have fast growth and calcification rates, but are extremely sensitive to environmental change. Type 2 species are more robust, slow growing and have reduced rates of calcification. Thus, the extent to which a species will be affected by climate change appears to be associated with, and potentially dependant upon, the primary growth processes. This relative susceptibility of coral Types has profound implications for both the biological and physical structure of coral reefs. Work proposed here builds on several successful studies from our laboratory examining the effect of environmental change on calcifying organisms. Existing 'pH stat' technology from these studies will be modified to provide full control of the inorganic carbon system of seawater. A series of experiments will be performed to examine, using this new technology, how coral Types respond to simultaneous changes in light, temperature and CO2, the primary factors regulating coral growth. Specifically, we focus on coral community metabolism since this represents the net activity of respiration, by the coral host and associated bacterial flora, and photosynthesis, by the coral's symbiotic microalgae, that ultimately contribute to growth (calcification). We will apply this community metabolism approach in the laboratory to obtain high levels of control upon gas exchange, thus allowing physical/chemical environmental conditions to be controlled with high precision and metabolic rates measured with high temporal resolution.