Depth-dependent microskeletal features modify light harvesting in Turbinaria reniformis corals

Area of Science:

• Marine Biology
• Coral Reef Ecology
• Biophotonics

Background:

• Coral skeletal morphology plays a crucial role in modulating light exposure for symbiotic algae.
• Light availability is a critical factor for coral health, particularly in light-limited mesophotic reef environments.
• Quantifying light capture within complex coral structures presents significant challenges.

Purpose of the Study:

• To investigate the depth-dependent bio-optical properties of *Turbinaria reniformis* corals.
• To explore how skeletal micro-architectures influence light scattering and penetration.
• To quantify the light-harvesting efficiency of corals at different depths.

Main Methods:

• Utilized optical coherence tomography and high-resolution X-ray scanning to analyze coral skeletal structure.
• Characterized depth-dependent bio-optical properties of shallow and mesophotic coral specimens.
• Performed light simulations to determine light fluence rates at the skeleton-water interface.

Main Results:

• Identified two distinct skeletal layers: a superficial scattering layer and a deeper light-penetrating layer.
• Mesophotic corals exhibited higher scattering coefficients and increased reflectivity.
• Coenosteum grooves promoted forward scattering, while spines and septa enhanced surface reflectivity.

Conclusions:

• Coral microskeletal heterogeneity is key to fine-tuning light capture at the microenvironmental scale.
• Mesophotic corals can enhance available light up to 2.7-fold through skeletal adaptations.
• These adaptations improve light-harvesting efficiency, supporting coral survival in deeper, light-limited environments.