SOLAR DAMAGE IN INTERTIDAL CORALS

Solar irradiation has been cited as a possible cause of bleaching in c orals, either acting alone or in conjunction with other environmental factors. However, evidence of a solar involvement in naturally occurri ng bleaching is still largely conjectural. We have recorded a particul ar 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 irradianc e measurements have enabled us to show that this bleaching directly co rresponds 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. Furthermo re, on-site measurements of solar irradiance mitigate against the biol ogically damaging effect of shorter wavelength ultraviolet radiation ( UVR) as a major causative factor. Desiccation, heating, or photochemic al reactions by photosynthetically active radiation (PAR) (400 to 700 nm) remain possible candidates for further investigation