Data from: Acclimatisation of symbiotic corals to mesophotic light environments through wavelength transformation by fluorescent protein pigments

The depth distribution of reef-building corals exposes their photosynthetic symbionts of the genus Symbiodinium to extreme gradients in the intensity and spectral quality of the ambient light environment. Characterising the mechanisms used by the coral holobiont to respond to low intensities and reduced spectral composition prevalent in deeper reefs (>20m) is fundamental to our understanding of the functioning and structure of reefs across depth gradients. Here, we demonstrate that host pigments, specifically photoconvertible red fluorescent proteins (pcRFPs), can promote coral adaptation / acclimatisation to deeper water light environments by transforming the prevalent blue light into orange-red light, which can penetrate deeper within zooxanthellae-containing tissues; this facilitates a more homogeneous distribution of photons across symbiont communities. The ecological importance of pcRFPs in deeper reefs is supported by the increasing proportion of red fluorescent corals with depth (measured down to 45m) and increased survival of colour morphs with strong expression of pcRFPs in long-term light manipulation experiments. In addition to screening by host pigments from high light intensities in shallow water, the spectral transformation observed in deeper water corals highlights the importance of GFP-like protein expression as an ecological mechanism to support the functioning of the coral-Symbiodinium association across steep environmental gradients.造礁珊瑚的深度分布特征，使其共生的虫黄藻属（Symbiodinium）光合共生体，暴露于环境光强与光谱品质均存在极端梯度变化的生境中。阐明珊瑚共生功能体（coral holobiont）应对水深>20m的深水区普遍存在的低光强与简化光谱组成的响应机制，是理解不同深度礁体生态功能与群落结构的核心基础。本研究证实，宿主色素尤其是光转化红色荧光蛋白（photoconvertible red fluorescent proteins, pcRFPs），可通过将主导性蓝光转化为橙红光，该波段光可更深入穿透含虫黄藻的珊瑚组织，从而助力珊瑚适应与驯化深水光照环境，使共生体群落内的光子分布更趋均匀。随着深度增加（本研究观测深度可达45m），红色荧光珊瑚的占比逐步升高；且在长期光照操控实验中，高表达pcRFPs的珊瑚颜色型个体存活率更高，这进一步佐证了pcRFPs在深礁生境中的生态重要性。除宿主色素可在浅水区过滤强光外，深水珊瑚所展现的光谱转化特性，进一步凸显了类绿色荧光蛋白（GFP-like）的表达作为一种生态机制，对支撑珊瑚-虫黄藻共生体在极端环境梯度下维持功能的重要性。