Reef location has a greater impact than coral bleaching severity on the microbiome of Pocillopora acuta

The composition of the microbial communities in the coral Pocillopora acuta were examined following the 2016 bleaching event on the Great Barrier Reef (GBR). Corals located within two reefs of the Palm Island archipelago on the Central GBR experienced moderate heat stress,In-water bleaching surveys were conducted at two depths (2 m and 5 m) on the 4th and 6th of April 2016. Five 10 × 1 m belt transects were used with observers capturing 1 m × 1 m square continuous images. Observers counted each coral colony > 5 cm in diameter within each 1 m × 1 m image, recorded:genus level identification categorical bleaching score based upon the proportion of living coral tissue visibly bleached white: No bleaching Pale 1–50% tissue bleached white 51–99% bleached white 100% bleached white with or without intense fluorescence partial or complete mortality of the colony (recently dead regions of tissue).Bleaching severity categories at the reef community level were based on the percentage of corals bleached as follows: no bleaching (0% bleached corals); minor bleaching (1–10%), moderate (10–30%); major (30–60%); severe (> 60%)Coral fragments were collected from 22 colonies at Pandora on the 4th April 2016 and from 25 colonies at Havannah on the 12th April 2016Samples were prepared for DNA extraction and Symbiodiniaceae cell counts as described in (Botte et al. 2021). Surface area of the coral skeletons was estimated using established protocol (Veal et al. 2010). Statistical analysis of DNA sequencing data was conducted using R.This study was conducted to identify the impact of bleaching severity on the microbiome of the P. acuta coral during the mass bleaching event of summer 2016, at two sampling sites within the Palm Island group (Central GBR). A significant impact of sampling site was found and no effect of bleaching severity, demonstrating the importance of fine-scale sampling when investigating large scale bleaching events.本研究针对2016年大堡礁（Great Barrier Reef, GBR）白化事件后，尖棘鹿角珊瑚（Pocillopora acuta）的微生物群落组成展开分析。位于大堡礁中部棕榈岛群岛两处礁体的珊瑚曾遭受中度热应激。 2016年4月4日与4月6日，研究人员在2米与5米两个水深开展水下白化调查。本次调查共设置5条10×1米的带状样带，通过拍摄1米×1米的连续正方形影像采集数据。调查人员对每幅1米×1米影像中直径大于5厘米的珊瑚群体进行计数，并记录以下信息： 属水平鉴定结果；基于可见白化变白的活珊瑚组织占比划定的分类白化评分，具体分级如下：无白化、浅白化、1–50%组织白化变白、51–99%组织白化变白、100%白化变白（伴或不伴强荧光）、珊瑚群体部分或完全死亡（组织区域近期坏死）。 礁群落水平的白化严重程度分级基于白化珊瑚的占比划定，具体标准如下： 无白化（白化珊瑚占比0%）、轻度白化（1–10%）、中度白化（10–30%）、重度白化（30–60%）、极重度白化（>60%） 2016年4月4日，研究人员于潘多拉礁（Pandora）的22个珊瑚群体中采集珊瑚碎片样本；同年4月12日，于哈瓦那礁（Havannah）的25个珊瑚群体中采集样本。 样本制备、DNA提取及虫黄藻科（Symbiodiniaceae）细胞计数流程参照Botte等（2021）的研究方案。珊瑚骨骼表面积的估算采用Veal等（2010）发布的标准规程。DNA测序数据的统计分析采用R语言完成。 本研究旨在明确2016年夏季大规模白化事件期间，棕榈岛群（大堡礁中部）两处采样点的P. acuta珊瑚的白化严重程度对其微生物组的影响。研究发现采样地点对微生物组存在显著影响，而白化严重程度无显著效应，这表明在开展大规模白化事件相关研究时，精细化采样具有重要意义。