Incident ultraviolet irradiances infuence physiology, development and settlement of larva in the coral Pocillopora damicornis

Ultraviolet radiation (UVR, 280-400 nm) is one of the potential factors involved in the induction of coral bleaching, loss of the endosymbiotic dinoflagellate Symbiodinium or their photosynthetic pigments. However, little has been documented on its effects on the behavior and recruitment of coral larvae, which sustains coral reef ecosystems. Here, we analyzed physiological changes in larvae of the scleractinian coral Pocillopora damicornis and examined the photophysiological performance of the symbiont algae, following exposure to incident levels of UVR and subsequently observed the development of coral larvae. The endosymbiotic algae exhibited a high sensitivity to UV-B (295-320 nm) during a 6 h exposure, showing lowered photosynthetic performance per larva and per algal cell, whereas the presence of UV-A (320-395 nm) significantly stimulated photosynthesis. UVR decreased chlorophyll a concentration only at higher surface temperature or at the higher doses or intensities of UVR. Correlations between UV-absorbing compound (UVAC) contents or UVR sensitivity and temperature were identified, implying that UVACs might act as a screen or antioxidants in Pocillopora damicornis larvae. Larvae reared under UVR exposures showed lower levels of survivorship, metamorphosis and settlement, with inhibition by UV-A being much greater than that caused by UV-B.