Coral shading experiment during a bleaching event

Here are shown a series of photographs of a rice coral (Montipora capitata) shaded with light filters during a natural “coral bleaching” event observed during anomalously high ocean temperatures in Autumn of 2004 on the island of Oʻahu, Hawaiʻi. The first image shows the coral, collected from the reef flat at the Hawaiʻi Institute of Marine Biology and placed in a flow-through holding tank, having already succumbed to heat stress as evidenced by its pale color. The coral is pale (i.e., “bleached”) because of the partial loss of symbiotic algae that normally give the coral its color and are responsible for the coral’s nutritional wellbeing. The image at the top right shows the experimental shade filters being placed over the coral to see if shading from visible sunlight and/or ultraviolet radiation could help the coral withstand and recover from bleaching. The plastic shades (clockwise, starting at top left) were ultraviolet transparent (UVT), dark shade, ultraviolet opaque (UV0, i.e., ultraviolet blocking), and light shade. The bottom row of images shows the same coral as time progressed with the shades still in place (though they were removed temporarily to take the photographs). By October 23, 2004, it appears that the areas of the coral shaded by both the light- and dark-shaded plastic have returned to the coral’s normal, brown color, suggesting the return of symbionts or at least partial recovery from bleaching. It is also apparent from the photographs that shading from ultraviolet radiation did not have the same potentially therapeutic effect as the shading from visible sunlight. While this was not a quantitative experiment, the images suggest that shading corals during a natural coral bleaching event could be investigated as a possible measure to mitigate temperature stress. The methodology for this experiment was adapted from prior research (Kuffner, 2001). This preliminary work was performed under an existing scientific research permit to Paul L. Jokiel at the University of Hawaiʻi, and the coral was returned to the reef after the observations.

Kuffner, I.B., 2001, Effects of ultraviolet (UV) radiation on larval settlement of the reef coral Pocillopora damicornis: Marine Ecology Progress Series, v. 217, 251-261 pp., https://doi.org/10.3354/meps217251.