Solar damage in intertidal corals

Solar irradiation has been cited as a possible cause of bleaching in corals, either acting alone or in conjunction with other environmental factors. However, evidence of a solar involvement in naturally occurring bleaching is still largely conjectural. We have recorded a particular type of naturally occurring bleaching damage at intertidal sites at Phuket, Thailand for a number of years which has a strong directional component. Use of tidal data, sun track analysis, and solar irradiance measurements have enabled us to show that this bleaching directly corresponds to sun altitude and azimuth. Our work has shown that for the massive coral Goniastrea aspera, bleaching is induced during periods of subaerial exposure with high sun altitude and irradiance. Furthermore, on-site measurements of solar irradiance mitigate against the biologically damaging effect of shorter wavelength ultraviolet radiation (UVR) as a major causative factor. Desiccation, heating, or photochemical reactions by photosynthetically active radiation (PAR) (400 to 700 nm) remain possible candidates for further investigation