Evolution Systematics and Ecology Department, Life Sciences Institute, The Hebrew University of Jerusalem, Jerusalem 91904, Israel.
J Exp Biol. 2010 Dec 1;213(Pt 23):4084-91. doi: 10.1242/jeb.039891.
Depth zonation on coral reefs is largely driven by the amount of downwelling, photosynthetically active radiation (PAR) that is absorbed by the symbiotic algae (zooxanthellae) of corals. The minimum light requirements of zooxanthellae are related to both the total intensity of downwelling PAR and the spectral quality of the light. Here we used Stylophora pistillata colonies collected from shallow (3 m) and deep (40 m) water; colonies were placed in a respirometer under both ambient PAR irradiance and a filter that only transmits blue light. We found that the colonies exhibited a clear difference in their photosynthetic rates when illuminated under PAR and filtered blue light, with higher photosynthetic performance when deep colonies were exposed to blue light compared with full-spectrum PAR for the same light intensity and duration. By contrast, colonies from shallow water showed the opposite trend, with higher photosynthetic performances under full-spectrum PAR than under filtered blue light. These findings are supported by the absorption spectra of corals, with deeper colonies absorbing higher energy wavelengths than the shallow colonies, with different spectral signatures. Our results indicate that S. pistillata colonies are chromatically adapted to their surrounding light environment, with photoacclimation probably occurring via an increase in photosynthetic pigments rather than algal density. The spectral properties of the downwelling light are clearly a crucial component of photoacclimation that should be considered in future transplantation and photoacclimation studies.
珊瑚礁的深度分层主要受向下辐射的量以及珊瑚共生藻（虫黄藻）吸收的光合有效辐射（PAR）的影响。虫黄藻的最小光照要求与向下辐射 PAR 的总强度和光的光谱质量有关。在这里，我们使用从浅水区（3 米）和深水区（40 米）收集的石珊瑚属（Stylophora pistillata）的群体；将这些群体放在呼吸计中，同时接受环境 PAR 辐照度和仅透过蓝光的滤光片的照射。我们发现，当用 PAR 和过滤后的蓝光照射时，群体的光合速率有明显差异，与相同光强度和持续时间的全光谱 PAR 相比，深水区群体在蓝光下表现出更高的光合作用性能。相比之下，浅水区的群体则表现出相反的趋势，在全光谱 PAR 下的光合作用性能高于过滤后的蓝光下。珊瑚的吸收光谱支持了这些发现，较深的群体比浅水区的群体吸收更高能量的波长，具有不同的光谱特征。我们的结果表明，石珊瑚属群体对周围的光照环境具有颜色适应性，可能通过增加光合色素而不是藻类密度来进行光适应。向下辐射光的光谱特性显然是光适应的一个关键组成部分，在未来的移植和光适应研究中应该考虑到这一点。
