Effect of low concentrations of Irgarol 1051 on RGB (R, red; G, green; B, blue) colour values of the hard-coral Acropora tenuis

Colour change in Acropora tenuis, a representative species of Indo-Pacific hard coral, in response to low concentrations of Irgarol 1051 was examined in the laboratory. Branches of A. tenuis were exposed to 0, 1, and 10 μg Irgarol 1051/L for 14 days, and photographed daily using digital camera. These Irgarol 1051 concentrations were similar to those recorded at a number of sea ports. Red, green and blue (RGB) coral colour values were quantified from the photographs, with black represented by R = G = B = 0 and white as R = G = B = 255. Exposure to Irgarol 1051 caused RGB values to increase, moving towards the 'white' end of the spectrum as Irgarol 1051 concentration increased. These results suggest that the ambient levels of Irgarol 1051 recorded from port environments could be implicated in coral bleaching, if concentrations over nearby reef ecosystems are similar.