Efficient light-harvesting of mesophotic corals is facilitated by coral optical traits

1. Sustained light-dependent coral reef communities can be found at a wide range of light environments, extending from the sea level to as deep as 150 m (i.e. esophotic). How mesophotic corals thrive despite extremely limited light conditions still requires further investigation. 2. Here, we undertook a comprehensive ecophysiological and bio-optical study on four depth-generalist coral species aiming to delineate the functional role that optical trait properties have in light-harvesting, at contrasting light regimes. 3.We show that the optical traits of coral skeletons are adjusted to their ambient light conditions and complement the microalgal demands for sufficient light, thus exhibiting a spatially efficient photosymbiotic system. 4. In contrast to shallow corals, mesophotic corals absorbed up to three fold more light, resulting in excellent photosynthetic response under light conditions of only similar to 3% of the incident surface irradiance. The enhanced light-harvesting capacity of mesophotic corals was achieved by redistributing light in the coral skeleton through optical scattering, thereby facilitating light transport and absorption by densely pigmented host tissue. 5. Our findings provide fundamental insight into the light-harvesting mechanisms underlying the productivity of mesophotic coral reef ecosystems, yet also raise concerns regarding their ability to withstand prolonged environmental disturbances.

Automated summary

The study found that the optical traits of coral skeletons are adjusted to ambient light conditions and contribute to the microalgal demands for sufficient light, resulting in a spatially efficient photosymbiotic system. Mesophotic corals absorbed up to three times more light than shallow corals, showcasing excellent photosynthetic response under low light conditions. The enhanced light-harvesting capacity of mesophotic corals was achieved by redistributing light through optical scattering in the coral skeleton.