BACKGROUND The capacity of reef-building corals to tolerate (or adapt to) heat stress is a key factor determining their resilience to future climate change. Changes in coral microbiome composition (particularly for microalgal endosymbionts and bacteria) is a potential mechanism that may assist corals to thrive in warm waters. The northern Red Sea experiences extreme temperatures anomalies, yet corals in this area rarely bleach suggesting possible refugia to climate change. However, the coral microbiome composition, and how it relates to the capacity to thrive in warm waters in this region, is entirely unknown. RESULTS We investigated microbiomes for six coral species (Porites nodifera, Favia favus, Pocillopora damicornis, Seriatopora hystrix, Xenia umbellata, and Sarcophyton trocheliophorum) from five sites in the northern Red Sea spanning 4° of latitude and summer mean temperature ranges from 26.6 °C to 29.3 °C. A total of 19 distinct dinoflagellate endosymbionts were identified as belonging to three genera in the family Symbiodiniaceae (Symbiodinium, Cladocopium, and Durusdinium). Of these, 86% belonged to the genus Cladocopium, with notably five novel types (19%). The endosymbiont community showed a high degree of host-specificity despite the latitudinal gradient. In contrast, the diversity and composition of bacterial communities of the surface mucus layer (SML)-a compartment particularly sensitive to environmental change-varied significantly between sites, however for any given coral was species-specific. CONCLUSION The conserved endosymbiotic community suggests high physiological plasticity to support holobiont productivity across the different latitudinal regimes. Further, the presence of five novel algal endosymbionts suggests selection of certain genotypes (or genetic adaptation) within the semi-isolated Red Sea. In contrast, the dynamic composition of bacteria associated with the SML across sites may contribute to holobiont function and broaden the ecological niche. In doing so, SML bacterial communities may aid holobiont local acclimatization (or adaptation) by readily responding to changes in the host environment. Our study provides novel insight about the selective and endemic nature of coral microbiomes along the northern Red Sea refugia.

中文翻译：

---

红海北部的珊瑚微生物组组成表明细菌的高度可塑性和内共生甲藻群落的特异性。

背景技术造礁珊瑚耐受（或适应）热应激的能力是决定其对未来气候变化的适应能力的关键因素。珊瑚微生物组组成的变化（特别是微藻内共生体和细菌）是一种可能有助于珊瑚在温暖水域中茁壮成长的潜在机制。红海北部经历极端温度异常，但该地区的珊瑚很少白化，表明可能是气候变化的避难所。然而，珊瑚微生物组的组成，以及它与该地区温暖水域中繁衍生息的能力之间的关系，却是完全未知的。结果 我们对红海北部跨越 4° 纬度、夏季平均温度范围为 26.6 °C 的五个地点的六种珊瑚（Porites nodifera、Favia favus、Pocillopora damicornis、Seriatopora hystrix、Xenia umbellata 和 Sarcophyton trocheliophorum）的微生物组进行了研究至 29.3°C。总共 19 种不同的甲藻内共生体被鉴定为属于共生藻科 (Symbiodinium、Cladocopium 和 Durusdinium) 中的三个属。其中，86% 属于枝叶属，特别是有五种新类型（19%）。尽管存在纬度梯度，内共生菌群落仍表现出高度的宿主特异性。相比之下，表面粘液层（SML）（对环境变化特别敏感的隔室）的细菌群落的多样性和组成在不同地点之间存在显着差异，但对于任何给定的珊瑚来说都是物种特异性的。结论 保守的内共生群落表明具有较高的生理可塑性，可以支持不同纬度范围内的全生物生产力。此外，五种新型藻类内共生体的存在表明，半孤立的红海中某些基因型（或遗传适应）的选择。相比之下，与跨位点 SML 相关的细菌的动态组成可能有助于全生物功能并扩大生态位。在此过程中，SML 细菌群落可以通过轻松响应宿主环境的变化来帮助全生物适应当地环境。我们的研究提供了关于红海北部保护区珊瑚微生物组的选择性和地方性性质的新见解。