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

RAPID：八珊瑚共生体多样性在不同季节的变化以及预测的白化事件

• 批准号: 1552949
• 负责人: Mary Alice Coffroth
• 金额: $ 5.63万
• 依托单位: SUNY at Buffalo
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2015
• 资助国家: 美国
• 起止时间: 2015-10-01 至 2017-09-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1552949&HistoricalAwards=false
• 关键词: RAPID; Variations; symbiont; diversity; octocoral

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.

在海洋环境中，微生物形成了世界上最重要的海洋共生体之一：珊瑚和光合单细胞藻类共生体之间的共生。在营养贫乏的热带沃茨，这种共生关系维持了珊瑚的高生产力，使珊瑚得以蓬勃发展，并为珊瑚礁生态系统提供了基础。 然而，这些珊瑚礁目前正受到生物成因引起的扰动的威胁（即，全球变暖，过度捕捞，污染）。 事实上，珊瑚礁上的珊瑚及其相关的生物多样性正在以惊人的速度消失，特别是在加勒比地区，那里的珊瑚覆盖率在过去30年中下降了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丧失。 相比之下，珊瑚礁没有出现这种下降，随着石珊瑚的下降，它们在加勒比的相对丰度和重要性正在增加。这部分归因于珊瑚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）中，许多珊瑚宿主物种都报告了漂白现象。虽然人们对硬珊瑚的白化现象有很多了解，但对珊瑚虫（海扇、海鞭、海羽等）的白化现象几乎一无所知。它们对加勒比海珊瑚礁的重要性日益增加，而且对它们对“漂白”的反应缺乏了解，这就迫切需要了解这些藻类共生体种群在石珊瑚漂白期间的动态。 漂白敏感性因宿主物种而异，这部分归因于它们所含的藻类共生体类型。 在该项目中，将在一年内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胞藻共生的理解。 珊瑚礁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了解这些共生体的功能，并允许与其他刺胞动物之间的漂白进行比较研究。 这项工作将包括培训本科生和研究生，通过与尼亚加拉水族馆合作向公众传播研究结果，并与科学界分享大量共生体文化收藏，珊瑚漂白是过去30年来珊瑚礁动态的一个重要组成部分。虽然我们对石珊瑚的白化现象有很多了解，但实际上对珊瑚中的这种现象一无所知。 随着石珊瑚数量的减少，珊瑚的相对数量保持不变。 部分成功可能是由于这些刺胞动物对漂白条件的敏感性似乎较低。 然而，20世纪事件和最近几年的事件之间的对比表明，频率和/或强度增加的热事件也会影响珊瑚，珊瑚的敏感性确实因物种而异。 因此，要预测珊瑚群落将如何发展，就需要更好地了解它们对漂白的敏感性的变化以及这种变化的基础。 这种变化的一个潜在来源是这些物种所携带的藻类共生体类型。加勒比海珊瑚的共生体多样性低于石珊瑚物种，绝大多数加勒比海珊瑚的共生体都是由多个共生藻物种组成的B1-ITS 2谱系。 该项目的目的是确定共生体的变化在珊瑚物种之前，期间和之后的预测漂白事件，并比较共生体类型与漂白敏感性。 为此，将在一年的时间内跟踪特定的珊瑚群落，并确定共生体密度和共生类型。 将对三种宿主物种Plexaurella dichotoma、Muricea muricata和Eunicea flexuosa的菌落进行标记（2个珊瑚礁中每个物种20个），并每3个月进行一次采样。共生体密度将通过使用血细胞计数器的细胞计数来确定，并且共生体类型将使用在B1谱系中的不同共生体物种之间分辨的标记来鉴定（即，Sym 15侧翼序列、ITS和叶绿体23 SrDNA）。如果在这些菌落中没有观察到漂白，这些数据将告知一个未充分研究的群体内的多样性，并提供有关这些共生体的季节变化和宿主物种内和宿主物种之间的变化的信息。了解珊瑚白化的动力学是重要的。如果珊瑚礁对漂白的抵抗力更强，这可能解释了丰度增加的观察结果。 随着珊瑚覆盖面的减少，这些物种代表了更多的生物覆盖面，并且往往是珊瑚礁上视觉上的主导生物。 此外，珊瑚礁生长迅速，有可能在开放空间定居，并通过为其他珊瑚生物提供栖息地来帮助稳定生态系统。