Reef Corals: Symbiotic Dinoflagellate/Host Combinations and their Physiological Response to Environmental Change

礁珊瑚和相关刺胞动物的生长、钙化、营养、繁殖、健康以及在许多情况下的形态是它们与共生甲藻共生的结果，共生甲藻通常被称为“虫黄藻”。在过去的30年中，已经描述了几种不同的共生藻物种，以及至少五个分子“分支”中的数十种遗传上不同的类型，至少四分之一的珊瑚物种能够在其胃皮细胞中携带一种以上的共生藻。新的分子技术使珊瑚礁生物学家在区分共生藻共生体之间的基因组相似性和差异方面取得了快速进展，但对藻类生理学差异及其对宿主珊瑚生理学（光合作用，生长速率，繁殖和宿主的一般健康状况）的影响的研究远远落后。没有这些信息，就不可能预测共生体（或珊瑚宿主）从共生藻的特定组合中获得什么好处。珊瑚礁包括世界上最多样化的生态系统之一，无论是在物种数量还是在属间相互作用的复杂性方面。然而，全世界的珊瑚礁正在恶化：为众多鱼类和无脊椎动物提供珊瑚礁框架和栖息地的珊瑚群落的覆盖率正在下降，经历了前所未有的疾病事件，并显示出明显的压力迹象，主要是为了应对海洋变暖。特别令人震惊的是，珊瑚白化现象日益增多，共生体丧失了作为宿主生长、繁殖和发育所需碳（来自光合作用）的主要贡献者。在严重漂白时，当白色骨骼通过动物组织显示共生体密度下降时，珊瑚组织生物量和能量储存减少，宿主生长停止，繁殖受损，部分或整个群体可能死亡。人们还认为，受到压力（即漂白）的珊瑚更容易受到疾病的影响。对珊瑚减少的原因和可能促进其恢复的过程的了解非常少。特别是很少有人知道的复杂性和特异性的整合不同类型的共生藻与它们的主机，特别是共生体的组合导致更大的主机的增长，繁殖和生存，以及如何建立和维持这种最佳组合。这项研究旨在解决珊瑚宿主/共生体关系的复杂性，记录不同共生体的能力：（1）为宿主提供营养（共生体的光合作用和光合产物从宿主到宿主的转运），（2）影响宿主的生长，（3）稳定地栖息（=感染）不同的宿主，（4）通过生产各种“防晒霜”来提供紫外线保护，（5）在高于正常温度的时期内生存，（6）适应不同的光照条件。实验的总体目标是能够模拟共生体-宿主组合的季节性和长期变化，特别是在完整系统响应环境变化的变化方面，这可能导致完整协会的生理性能（包括生存）增加或减少。 这些数据将使我们能够预测哪些协会能够在未来50-100年的全球变暖中在世界热带海洋中生存，以及“切换”到具有更高耐受水平的藻类类型是否可能是一个可行的结果。

The growth, calcification, nutrition, reproduction, health and, in many cases, morphological form of reef corals and related cnidarians is the result of their mutualism with symbiotic dinoflagellates of the genus Symbiodinium, often referred to as "zooxanthellae". Several different species of Symbiodinium, as well as dozens of genetically different types within at least five molecular "clades" have been described within the past 30 years, with at least a quarter of coral species able to harbor more than one type of Symbiodinium within their gastrodermal cells. New molecular techniques have enabled coral reef biologists to make rapid progress in distinguishing genomic similarities and differences among Symbiodinium symbionts, but research on differences in algal physiology and its repercussions on host coral physiology (photosynthesis, growth rates, reproduction, and general health of the host) lags far behind. Without such information, it is impossible to project what benefits to the symbiosis (or coral host) come from having which specific combinations of Symbiodinium. Coral reefs comprise one of the world's most diverse ecosystems, both in terms of number of species and complexity of interactions among genera. Yet, coral reefs worldwide are deteriorating: the coral colonies that provide reef framework and habitat to multitudes of fish and invertebrates are decreasing in percent cover, experiencing unprecedented incidents of disease, and showing obvious signs of stress largely in response to ocean warming. Especially alarming is the increased occurrence of coral bleaching in which symbionts are lost as the principal contributors of carbon (from photosynthesis) for host growth, reproduction and development. Upon severe bleaching, when the white skeleton shows through the animal tissue as symbiont densities decline, coral tissue biomass and energy stores decrease, host growth ceases, reproduction is impaired, and portions or entire colony may die. It is also thought that stressed (i.e. bleached) corals are more susceptible to disease. Understanding of the causative factors for the decline of corals and the processes that might promote their recovery is very poor. Particularly little is known the of the complexity and specificity of the integration of the different types of Symbiodinium with their hosts, especially which combinations of symbionts lead to greater host growth, reproduction and survival and how such optimal combinations are established and maintained. This research is designed to resolve the complexities of the coral host/symbiont relationship, in terms of documenting the ability of different symbionts: (1) to provide nutrition to their host (photosynthesis of symbiont and translocation of photosynthate from alga to host), (2) to influence growth of the host, (3) to stably inhabit (=infect) different hosts, (4) to provide protection from ultra-violet light by the production of various 'sun screens', (5) to survive periods of higher-than-normal temperatures, (6) to photoadapt to different light conditions. The overall goal of the experiments is to be able to model seasonal and long-term changes in symbiont-host combinations, especially in regard to changes in the intact system in response to environmental change that might lead to greater or diminished physiological performance (including survival) of the intact association. The data will allow us to predict which associations are capable of surviving conditions expected in the world's tropical oceans over the next 50-100 years of global warming, and whether "switching" to algal types with higher tolerance levels might be a viable outcome.