Experimental investigation of UV tolerance in hermatypic corals (Scleractinia)

Effects of artificial radiation on various species of coral from the Great Barrier Reef were studied.The corals were either exposed to artificial white light during and after UV-treatment or were kept In darkness subsequent to UV exposure.When not exposed to white light, the UV tolerance of corals taken from depths of up to 1.5 m was, on average, double that of those collected at 18 to 20 m.Under the ~nfluence of short wavelength visible light (max.effectiveness 450 to 500 n m ) , UV tolerance increased on average by a factor of 6.It is postulated that protection from UV light involves at least 2 different physiolog~cal mechanisms: screening by UV-absorbing compounds and recovery due to photoreact~vation.The most conspicuous symptom of serious radiation damage to polyps was extrusion of mesenterial filaments through the mouth opening and entire body surface Slmllar but less pronounced reactions could b e induced in non-irradiated polyps by exposing then1 to rad~ation-damaged polyps, In particular when the unexposed polyps were a different species.Such interactions never occurred, however, between polyps from the same colony.It is therefore conjectured that there is a specific protective mechanism that impedes the spread of secondary damage from damaged polyps to others in the same colony