Supplementary and dataset for: <b>Species-specific vulnerability of northern Red Sea mesophotic corals to accelerated warming</b>

Mesophotic coral ecosystems have gained attention for their potential role as refugia from climate-driven coral bleaching, yet their resilience to prolonged marine heatwaves remains uncertain. Here, we experimentally assessed the thermal tolerance of two Red Sea corals with contrasting depth distributions: the mesophotic specialist <i>Leptoseris glabra</i> and the depth-generalist <i>Acropora squarrosa</i>. Through controlled thermal stress experiments simulating strong to extreme marine heatwave events, we quantified photophysiological, optical, and biochemical responses. Under thermal stress, <i>L. glabra</i> exhibited severe declines in photosynthetic efficiency and energy reserves, coupled by a three-fold increase in tissue reflectance, indicative of extensive symbiont loss. In contrast, mesophotic <i>A. squarrosa</i> maintained stable photophysiology and energy reserves, whereas its shallow conspecific showed marked declines in photosynthetic efficiency, symbiont density, and lipid stores. Skeletal optical analysis revealed that shallow <i>A. squarrosa</i> exhibited higher scattering coefficient and reflectance than its mesophotic counterpart, while <i>L. glabra</i> shared similar optical properties with mesophotic <i>A. squarrosa</i>. These findings suggest that enhanced skeletal light scattering may have exacerbated bleaching in shallow <i>A. squarrosa</i>, whereas reduced light exposure and greater lipid content contributed to mesophotic <i>A. squarrosa’s</i> resilience. Critically, 20-year <i>in situ </i>temperature analysis revealed accelerated warming across intermediate to upper mesophotic depths compared to shallow reefs. This dual threat of species-specific vulnerability combined with accelerated warming at presumed refuge depths, suggests that refugia capacity in mesophotic ecosystems may not be universal across all taxa, but instead depend on species-specific traits.中光珊瑚生态系统（Mesophotic Coral Ecosystems）因其作为气候驱动珊瑚白化避难所的潜在功能而受到广泛关注，但其对持续海洋热浪的耐受能力仍不明确。本研究通过实验评估了两种具有不同深度分布特征的红海珊瑚的热耐受能力：中光特化种*Leptoseris glabra*与广深分布种*Acropora squarrosa*。通过模拟强至极端海洋热浪事件的可控热胁迫实验，我们量化了珊瑚的光生理、光学及生化响应。在热胁迫条件下，*Leptoseris glabra*的光合效率与能量储备出现显著下降，同时组织反射率提升至原来的三倍，这表明其共生虫黄藻发生了大量流失。与之形成鲜明对比的是，中光环境下的*Acropora squarrosa*保持了稳定的光生理状态与能量储备；而其浅海同种种群则出现光合效率、共生体密度与脂质储备的显著下降。骨骼光学分析显示，浅海*Acropora squarrosa*的散射系数与反射率均高于其中光种群；而*Leptoseris glabra*与中光*Acropora squarrosa*具有相似的光学特性。上述研究结果表明，增强的骨骼光散射可能加剧了浅海*Acropora squarrosa*的白化现象；而更低的光暴露水平与更高的脂质含量则赋予了中光*Acropora squarrosa*的耐热韧性。尤为关键的是，为期20年的原位（in situ）温度分析显示，相较于浅海礁体，中光中层至上层深度的海水升温速率显著加快。这种兼具物种特异性脆弱性与假定避难所深度加速升温的双重威胁表明，中光珊瑚生态系统的避难所能力并非适用于所有生物类群，而是取决于物种自身的特异性性状。