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环境之一：珊瑚和光合单细胞藻类共生体之间的共生。在营养贫乏的热带水域，这种共生关系保持了珊瑚的高生产力，使珊瑚得以繁衍，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，珊瑚礁上的珊瑚及其相关生物多样性正在以惊人的速度消失，特别是在加勒比海地区，那里的珊瑚覆盖率在过去30年里下降了80%。这种下降在很大程度上归因于珊瑚漂白，即这些藻类共生体的丧失，以应对海洋温度的上升。相比之下，八角珊瑚没有出现这种下降，而且随着硬珊瑚的减少，它们在加勒比地区的相对丰度和重要性都在增加。这在一定程度上归因于这样一个事实，即在章鱼中，漂白现象较为罕见。然而，在最近的变暖事件(2005年、2010年和2014年)期间，据报道许多八珊瑚宿主物种出现了漂白。虽然人们对硬珊瑚(硬)珊瑚的漂白有很多了解，但在八珊瑚(海扇、海鞭、海羽等)中几乎没有人知道这种现象。它们对加勒比海珊瑚礁的重要性与日俱增，而且对它们对“漂白”的反应缺乏了解，因此迫切需要了解八珊瑚中这些藻类共生体在珊瑚礁漂白期的动态。不同寄主物种的漂白敏感性不同，这在一定程度上归因于它们所包含的藻类共生体的类型。在这个项目中，将对特定的八珊瑚群落进行为期一年的跟踪，并使用分子技术确定共生体类型。这些数据将被用来确定漂白敏感性是否与共生体类型有关。该项目将大大增加对构成珊瑚礁生态系统基础的刺齿动物-藻类共生的了解。八角珊瑚主宰着许多加勒比海珊瑚礁，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理解这些共生体是如何发挥作用的，并允许与其他蛇类中的白化动物进行比较研究。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微生物培养集。珊瑚漂白在过去30年里一直是珊瑚礁动态的重要组成部分。虽然关于硬珊瑚中的漂白现象人们已经知道很多，但在八目珊瑚中几乎没有人知道这种现象。随着珊瑚礁丰度的下降，八角珊瑚的相对丰度一直保持着更稳定的状态。这一成功的部分原因可能是这些驯鹿对漂白条件的敏感度似乎较低。然而，20世纪和最近几年发生的八珊瑚漂白事件之间的对比表明，频率和/或强度不断增加的热事件也会影响八珊瑚，并且八珊瑚的敏感度确实因物种而异。因此，预测八珊瑚群落将如何发展，需要更好地了解它们对漂白的敏感度的变化以及这种变化的基础。这种变异的一个潜在来源是这些物种所藏匿的藻类共生体类型。加勒比海八珊瑚的共生体多样性低于硬珊瑚物种，绝大多数加勒比海八珊瑚都含有B1-ITS2谱系的共生体，该谱系由多种共生虫组成。该项目的目的是确定八珊瑚物种在预测的漂白事件之前、期间和之后的共生体变化，并比较共生体类型与漂白敏感性。为了做到这一点，将对特定的八珊瑚群体进行为期一年的跟踪，并确定共生体密度和系统类型。将对来自三个寄主物种Plexaurella dichotoma、Muricea Muricata和Eunicea Fluosa的菌落进行标记(在两个珊瑚礁中每种20个)，并每3个月采样一次。共生体密度将通过使用血细胞分析仪的细胞计数来确定，并使用可分辨B1谱系中不同共生体物种(即Sym15侧翼、ITS和叶绿体23S rDNA)的标记来确定共生体的系统类型。如果在这些群体中没有观察到漂白，这些数据将告知研究不足的群体内的多样性，并提供关于这些共生体的季节性变化以及宿主物种内部和之间的变化的信息。了解八珊瑚漂白的动力学是重要的。如果八珊瑚对漂白的抵抗力更强，这可能解释了观察到的物种数量增加的原因。随着珊瑚覆盖率的下降，这些物种代表了更多的活着的覆盖物，通常是珊瑚礁上视觉上的优势生物。此外，八角珊瑚生长迅速，有可能在开阔空间定居，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.