From cells to reefs—fluorescent protein distribution reveals species‐specific photoadaptation in closely related Caribbean corals

Fluorescent proteins (FPs) are diverse and widespread pigments in reef‐building corals, assumed to modulate the internal light microenvironment within coral tissues. Yet, their precise distribution and organization at the tissue and cellular levels remain poorly understood, limiting our understanding of their functional roles. We examined the localization of FPs in three Madracis species ( M. decactis , M. pharensis , and M. senaria ) to identify species‐specific patterns and potential links to their ecological life‐history traits. Both cyan–green and orange–red fluorescent signals occurred across all species. Cyan–green fluorescence predominates in diffuse and granular forms, while orange–red fluorescence is exclusively diffuse in its distribution. Colocalization analyses showed a significantly greater spatial overlap between cyan–green fluorescence and photosymbionts in M. senaria than in M. decactis and M. pharensis . In M. senaria , colocalization increased with decreasing light exposure, suggesting a light‐driven modulation of protein localization. Linear Discriminant Analysis disclosed distinct species separation based on physiological and symbiotic traits, including colocalization of cyan–green fluorescence and photosymbionts, cyan–green‐to‐chlorophyll fluorescence intensity ratio, and symbiont photochemical efficiency. Our results revealed the spectral and structural complexity of FPs tissue distribution in Madracis , suggesting a role in species differentiation and adaptation to reef environments.