Thesis Defense Seminar - Casey Gallagher

MARINE BIOLOGY PROGRAM
DEPARTMENT OF LIFE SCIENCES
TEXAS A&M UNIVERSITY-CORPUS CHRISTI

SUBJECT: Capturing Carribean Colors: A Comparative Color Analysis Of Two Carribean Coral Species Along A Temperature Gradient

MAJOR ADVISOR: Dr. Keisha Bahr

ABSTRACT

Scleractinian corals are the foundation of reef ecosystems, yet they are increasingly threatened by ocean warming and other environmental stressors, leading to widespread bleaching and mortality. While color-health cards have been developed and successfully implemented for reef monitoring in some Pacific regions, colorimetry in Caribbean corals have not been assessed. This study investigates the disturbance and recovery dynamics in visual coloration of two Caribbean species, Acropora cervicornis and Orbicella faveolata, under ex-situ controlled bleaching conditions. Photosynthetic efficiency (Fv/Fm) was used as a health proxy to assess physiological responses, revealing species-specific differences. Acropora cervicornis, which was uniform in color among genotypes, exhibited gradual paling but no full bleaching and did not recover Fv/Fm values by two months after heat disturbance. In contrast, some individuals of O. faveolata, which had many genotypes varying in color, experienced full bleaching and recovered Fv/Fm values to pre-experimental rates. Color analysis indicated that the camera color channel red and brightness value were most correlated with bleaching in A. cervicornis. Magenta and blue color channels were most correlated in O. faveolata, but trends showed notable hue shifts potentially linked to changes in symbiont composition. Despite the physiological recovery indicated by Fv/Fm, color recovery lagged in O. faveolata, suggesting a complex relationship between pigmentation and coral health. These findings highlight the importance of species-specific and even genotype-specific considerations when assessing coral coloration, and the need to adapt current color card methodology to changing ocean conditions. Therefore, applying suggestions to color card methodology discussed in this study will ensure that color cards for more regions can be developed, increasing global scope of coral colorimetry-based monitoring.