Developing a Site-Specific Coral Health Assessment Tool: Photophysiological and Visual Indicators of Bleaching

1. Abstract 

Coral reefs worldwide face escalating threats from climate change-induced thermal stress, necessitating effective monitoring tools for conservation efforts. This study investigated coral bleaching responses in Moorea, French Polynesia, to develop methodological frameworks for color-based health assessment supporting regional monitoring initiatives.

Six hundred coral fragments representing ten species were subjected to controlled thermal stress over 32 days. Photosynthetic efficiency was measured using PAM fluorometry, while standardized color analysis was performed using RGB, HSB, and CMYK extraction methods.

Results revealed species-specific thermal tolerance hierarchies (Pocillopora > Acropora > Montipora > Porites), with significant linear decline in photosynthetic efficiency over time. Color analysis detected subtle bleaching changes, including increased red channel intensity and decreased black component indicating tissue brightening, but correlations between color parameters and photosynthetic efficiency were unexpectedly weak, challenging assumptions underlying visual monitoring approaches.

Moorean corals demonstrated greater thermal resilience compared to Hawaiian counterparts, potentially due to thermally resistant symbionts. The study reveals that coral color reflects multiple pigments, suggesting that color-based monitoring requires integration with quantitative physiological measurements for comprehensive assessment.

This research establishes baseline methodologies for developing site-specific coral health monitoring tools while highlighting the importance of species-specific calibration and multi-parameter approaches for effective coral reef conservation in the face of climate