Colouration of coral Xenia umbellata in a aquarium experiment

One colony per tank (n = 3 per treatment) was photographed every 7 days in a 25°C tank using an Olympus TG6 (ISO 100, f/1.4, 4x magnification). Images were analysed in Photoshop, selecting the opening of the gastrovascular cavity and tentacles of three polyps. RGB pixel values were measured and converted to inverted luminosity, where lower values indicate bleaching and higher values indicate darkening. Xenia umbellata originates from the Red Sea.