Morpho-functional traits of the coral Stylophora pistillata enhance light capture for photosynthesis at mesophotic depths

The morphological architecture of photosynthetic corals modulates the light capture and functioning of the coral-algal symbiosis on shallow-water corals. Since corals can thrive on mesophotic reefs under extreme light-limited conditions, we hypothesized that microskeletal coral features enhance light capture under low-light environments. Utilizing micro-computed tomography scanning, we conducted a novel comprehensive three-dimensional (3D) assessment of the small-scale skeleton morphology of the depth-generalist coral Stylophora pistillata collected from shallow (4-5 m) and mesophotic (45-50 m) depths. We detected a high phenotypic diversity between depths, resulting in two distinct morphotypes, with calyx diameter, theca height, and corallite marginal spacing contributing to most of the variation between depths. To determine whether such depth-specific morphotypes affect coral light capture and photosynthesis on the corallite scale, we developed 3D simulations of light propagation and photosynthesis. We found that microstructural features of corallites from mesophotic corals provide a greater ability to use solar energy under light-limited conditions; while corals associated with shallow morphotypes avoided excess light through self-shading skeletal architectures. The results from our study suggest that skeleton morphology plays a key role in coral photoadaptation to light-limited environments. Micro-computed tomography scanning and 3D light simulation models reveals distinct morphotypes of the coral species Stylophora pistillata depending on depth, and suggest that coral skeletal micromorphology plays a key role in coral photoadaptation.

Automated summary

The morphological architecture of corals plays a crucial role in their adaptation to light-limited environments. Through micro-computed tomography scanning and 3D simulations, this study reveals distinct morphotypes of the coral species Stylophora pistillata depending on depth, indicating that coral skeletal micromorphology is key to coral photoadaptation.