The decrease of the stratospheric ozone layer has resulted in an increase in the amount of harmful ultraviolet radiation reaching both terrestrial and aquatic ecosystems. Recent data indicates that this phenomenon will also affect tropical ecosystems. Tropical ecosystems have a long evolutionary history of exposure to fluxes of UV radiation, and can provide considerable insight into evolved mechanisms of protection against the deleterious effects of UV radiation. We presently do not know with confidence the wave length-dependent efficiency (action spectrum) of UV radiation for any physiological function in symbiotic cnidarians. Widespread coral bleaching events have recently been observed following anomolously high sea surface temperatures around the world. If UV radiation synergistically interacts with increased sea water temperatures, action spectra will be required to predict what dose of UV radiation can induce bleaching, with or without an increase in sea water temperature. An important step in understanding the bleaching phenomenon is to determine the independent and synergistic effects of temperature, visible radiation, and UV radiation on the functional biology of symbiotic associations.
