RAPID: Variations in symbiont diversity in octocoral across seasons and a predicted bleaching event

在海洋环境中，微生物形成了世界上最重要的海洋共生关系之一：珊瑚与光合单细胞藻类共生关系。在营养贫乏的热带水域，这种共生关系维持了珊瑚的高生产力，使珊瑚茁壮成长，并为珊瑚礁生态系统提供了基础。然而，这些珊瑚礁目前受到人为干扰（即全球变暖、过度捕捞、污染）的威胁。事实上，珊瑚及其相关的珊瑚礁生物多样性正在以惊人的速度消失，特别是在加勒比地区，在过去30年里，那里的珊瑚覆盖率下降了80%。这种下降在很大程度上归因于珊瑚白化，即这些藻类共生体因海洋温度升高而减少。相比之下，在加勒比地区，随着核珊瑚的减少，八月珊瑚的数量和重要性却在增加。这在一定程度上归因于这样一个事实，即白化在八色珊瑚中比较罕见。然而，在最近的变暖事件中（2005年、2010年和2014年），许多八珊瑚宿主物种都出现了白化现象。虽然人们对硬珊瑚的白化现象了解很多，但对八角珊瑚（海扇珊瑚、海鞭珊瑚、海羽珊瑚等）的白化现象却一无所知。它们在加勒比海珊瑚礁上的重要性日益增加，而人们对它们对“白化”的反应缺乏了解，因此迫切需要了解在白化期间，这些藻类共生种群在八珊瑚体内的动态。对白化的敏感性因宿主物种而异，这部分归因于它们所含的共生藻类的类型。在这个项目中，将在一年的时间里跟踪特定的八珊瑚群落，并使用分子技术确定共生体类型。这些数据将用于确定漂白敏感性是否与共生类型有关。这个项目将大大增加对刺胞动物-藻类共生的理解，这是珊瑚礁生态系统的基础。八月珊瑚主宰着许多加勒比珊瑚礁，是许多鱼类和无脊椎动物的结构和栖息地。这些数据将有助于我们了解这些共生体的功能，并允许与其他刺胞动物的漂白进行比较研究。这项工作将包括对本科生和研究生的培训，通过与尼亚加拉水族馆的合作向公众传播研究结果，以及与科学界分享广泛的共生文化收藏。在过去的30年里，珊瑚白化一直是珊瑚礁动态的重要组成部分。虽然人们对核珊瑚的白化现象了解很多，但实际上对八角珊瑚的这种现象一无所知。随着硬核珊瑚丰度的下降，八月珊瑚的相对丰度保持不变。这一成功的部分原因可能是这些刺胞动物对漂白条件的敏感性似乎较低。然而，20世纪的事件与近年来的事件在八珊瑚白化方面的对比表明，频率和/或强度增加的热事件也会影响八珊瑚，而且八珊瑚的敏感性确实因物种而异。因此，预测八珊瑚群落将如何发展，需要更深入地了解它们对白化敏感性的变化及其变化的基础。这种变化的一个潜在来源是这些物种所拥有的藻类共生类型。加勒比地区八角珊瑚的共生体多样性低于硬核珊瑚，绝大多数加勒比八角珊瑚的共生体为B1-ITS2系，该系由多个共生体组成。该项目的目的是确定在预测的漂白事件之前，期间和之后，八珊瑚物种内的共生体变化，并比较共生体类型与漂白敏感性。为了做到这一点，将在一年的时间里跟踪特定的八珊瑚群落，并确定共生体密度和种型。将对三种寄主物种（Plexaurella dichotoma， Muricea muricata和Eunicea flexxuosa）的菌落进行标记（每个物种20个），并每3个月取样一次。共生体密度将通过使用血细胞计进行细胞计数来确定，并使用在B1谱系中不同共生体物种（即Sym15侧卫体，ITS和叶绿体23S rDNA）之间的标记来确定共生体的种型。如果在这些菌落中没有观察到白化现象，这些数据将告知未被研究群体内的多样性，并提供有关这些共生体的季节变化以及宿主物种内部和之间变化的信息。了解八珊瑚白化的动态很重要。如果八角珊瑚对白化的抵抗力更强，这也许可以解释观察到的数量增加。随着珊瑚覆盖面积的减少，这些物种代表了更多的生物覆盖面积，并且通常是珊瑚礁上视觉上的优势生物。此外，八爪珊瑚生长迅速，有可能在开放空间定居，并通过为其他珊瑚礁生物提供栖息地来帮助稳定生态系统。

Within the marine environment microorganisms form one of the most important marine symbioses in the world: the symbiosis between corals and photosynthetic single-celled algal symbionts. In nutrient poor waters of the tropics, this symbiosis maintains the coral's high productivity, allowing corals to flourish and provides the foundation of the coral reef ecosystem. However, these reefs are currently threatened by anthropogenic-induced perturbations (i.e., global warming, overfishing, pollution). In fact, corals and their associated biodiversity on reefs are being lost at an alarming rate, especially in the Caribbean, where coral cover has declined by 80% over the last thirty years. Much of this decline has been attributed to coral bleaching, a loss of these algal symbionts in response to increase ocean temperatures. Octocorals, in contrast, do not show this decline and are increasing in relative abundance and importance in the Caribbean as scleractinian corals decline. Part of this has been attributed to the fact that bleaching is rarer among octocorals. However, during recent warming events (2005, 2010 and 2014) bleaching was reported in many octocoral host species. Although a great deal is known about bleaching among scleractinian (hard) corals, virtually nothing is known of this phenomenon among octocorals (sea fans, sea whips, sea feathers, etc.). Their growing importance on Caribbean reefs and the lack of knowledge of their response to "bleaching" creates an urgency to understand the dynamics of these algal symbiont populations within octocorals during periods of scleractinian bleaching. Bleaching susceptibility varies among host species and this has been attributed in part to the type of algal symbiont that they contain. In this project, specific octocoral colonies will be followed over the course of a year and symbiont type determined using molecular techniques. These data will be used to determine if bleaching susceptibility is related to symbiont type. This project will significantly add to an understanding of cnidarian-algal symbioses that form the foundation of the coral reef ecosystem. Octocorals dominate many Caribbean reefs and serve as structure and habitat for numerous fish and invertebrates. These data will contribute to our understanding of how these symbioses function and allow for a comparative study with bleaching among other cnidarians. This work will include the training of undergraduate and graduate students, dissemination of the findings to the general public through a collaboration with the Aquarium of Niagara, and sharing of an extensive symbiont culture collection with the scientific community.Coral bleaching has been an important component of the dynamics on coral reefs for the past 3 decades. Although a great deal is known about bleaching among scleractinian corals, virtually nothing is known of this phenomenon among octocorals. As scleractinian abundance is declining, the relative abundance of octocorals has remained more constant. Part of that success is likely due to a seemingly lower sensitivity of these cnidarians to bleaching conditions. However, the contrast in octocoral bleaching between the 20th century events and those of more recent years suggests that thermal events of increasing frequency and/or intensity will affect octocorals as well and that octocoral sensitivity does vary between species. Thus projecting how octocoral communities will fare requires a greater understanding of variation in their sensitivity to bleaching and the basis of that variation. One potential source of that variation is in the algal symbiont type that these species harbor. Symbiont diversity among Caribbean octocorals is lower than that of scleractinian species with the vast majority of Caribbean octocorals harboring symbionts in the B1-ITS2 lineage which is composed of multiple Symbiodinium species. The aim of this project is to identify symbiont variation within octocoral species before, during and after a predicted bleaching event and to compare symbiont type with bleaching susceptibility. To do this, specific octocoral colonies will be followed over the course of a year and symbiont density and phylotype determined. Colonies from three host species, Plexaurella dichotoma, Muricea muricata and Eunicea flexuosa will be tagged (20 per species at each of 2 reefs) and sampled every 3 months. Symbiont density will be determined through cell counts using a hemocytometer and symbiont phylotype identified using markers that resolve among the different symbiont species in the B1 lineage (i.e., Sym15 flanker, ITS and chloroplast 23S rDNA). If bleaching is not observed in these colonies, these data will inform the diversity within an understudied group and provide information on seasonal change in these symbionts and variation within and between host species. Understanding the dynamics of octocoral bleaching is important. If octocorals are more resistant to bleaching, this may explain observations of increasing abundance. As coral cover declines, these species represent more of the living cover and are often the visually dominant organism on reefs. Furthermore, octocorals are fast growing and have the potential to colonize open space and help to stabilize the ecosystem by providing habitat for other reef organisms.