Table_2_From the shallow to the mesophotic: a characterization of Symbiodiniaceae diversity in the Red Sea NEOM region.xlsx

IntroductionThe northern Red Sea has been coined a refuge for reef corals due to the exceptional thermal tolerance of these organisms. With ocean warming threatening coral reefs worldwide, a panoptic characterization of corals living in extreme conditions may provide insights into future responses of corals to environmental change. Among other factors, the genotype of the endosymbiotic algae in the family Symbiodiniaceae has been shown to have major implications on the distribution and resilience of their coral hosts. In this study, we aim at genotyping the Symbiodiniaceae communities associated with three depth generalist and one depth specialist coral species, characterized by the ability to withstand environmental conditions that are apparently limiting for other corals and occurring in a unique geographical region.
MethodsWe sampled 50 corals from the northern Saudi Arabian Red Sea and the Gulf of Aqaba, covering a 97 m bathymetric gradient. We used high-throughput ITS2 gene sequencing and recovered different patterns of host–algal associations.
Results and discussionThe majority of the recovered algal genotypes appeared host- and environment-specific, while others were more widely distributed. At large, coral specimens were overwhelmingly associated with symbionts from the genus Cladocopium and specifically with many previously undescribed genotypes. This suggests the selection of specific genotypes, which might confer resistance and/or resilience to their host counterparts. Interestingly, we found a limited association with Durusdinium spp. and other known tolerant taxa in mesophotic corals in the northern Red Sea, but not in the Gulf of Aqaba. The broad absence of Durusdinium spp., typically ascribed to be stress tolerant, warrants further investigation into Symbiodiniaceae species that convey environmental resilience. Our data will serve as a baseline to explore the occurrence of specific symbionts that might be contributing to coral acclimation and adaptation and to assay how biodiversity might be impacted if subjected to increasing stressors.

引言
红海北部因造礁珊瑚具备卓越的耐热性，被称为造礁珊瑚的庇护所。当前全球海洋变暖正持续威胁世界各地的珊瑚礁生态系统，对栖息于极端环境中的珊瑚开展全面详尽的表征研究，或可为理解珊瑚对环境变化的未来响应提供关键见解。除其他影响因素外，虫黄藻科（Symbiodiniaceae）的基因型已被证实对其珊瑚宿主的分布范围与抗逆恢复力具有显著调控作用。本研究旨在对四种珊瑚物种所关联的虫黄藻科群落进行基因分型：其中三种为广深分布种（depth generalist），一种为狭深分布种（depth specialist），这些珊瑚均能耐受其他珊瑚生存所需的极限环境条件，且其栖息区域具备独特的地理特征。

方法
我们从沙特阿拉伯北部红海海域及亚喀巴湾采集了50份珊瑚样本，覆盖了97米的水深梯度范围。采用高通量ITS2基因测序技术，成功解析出宿主与共生藻的多种关联模式。

结果与讨论
本次研究获得的多数共生藻基因型兼具宿主特异性与环境特异性，其余基因型则具备更广泛的分布范围。整体来看，绝大多数珊瑚样本均与枝孢藻属（Cladocopium）的共生藻形成关联，且其中多数为此前未被报道的全新基因型。这表明珊瑚宿主会选择性招募特定的共生藻基因型，此类基因型或可赋予宿主抗逆性与恢复力。值得关注的是，我们仅在红海北部的中光层珊瑚中发现了少量与杜氏藻属（Durusdinium）物种及其他已知耐受型共生类群的关联，此类关联并未出现在亚喀巴湾的珊瑚样本中。通常被认为具备胁迫耐受能力的杜氏藻属类群在本次研究中广泛缺失，这一现象有待针对具备环境适应能力的虫黄藻科物种展开进一步研究。本研究所得数据将作为基准参考，用于探究可能参与珊瑚驯化与适应过程的特定共生藻类群的分布情况，同时可用于评估当珊瑚生态系统暴露于日益加剧的环境胁迫时，其生物多样性将受到何种影响。