Depth-dependent photoacclimatization to solar ultraviolet radiation in theCaribbean coral Montastraea faveolata

The importance of solar ultraviolet radiation (UVR, 290 to 400 nm), and UVB (290 to 320 nm) in particular, as an environmental factor affecting the bi ology and ecology of coral reefs has taken on renewed interest since the de monstration of global stratospheric ozone loss through human activities. Th e hermatypic coral Montastraea faveolata occurs over a wide bathymetric ran ge in the Florida Keys reef tract. The bathymetric range of M, faveolata an d its role in reef community structure make it an important species for whi ch to assess the effects of present day UVR irradiances. Both UVR irradianc es and UVR-absorbing mycosporine-like amino acids (MAAs) decreased signific antly with increasing depth in M, faveolata. WE irradiances were measured t o a depth of 30 m during this study and maximum rates of productivity in M, faveolata were significantly affected by the presence of UVR. Action spect ra (= biological weighting function) for the photoinhibition of photosynthe sis by WR were measured for samples of M, faveolata at 3, 10, 18, 23, and 3 0 m. Using these action spectra, radiation amplification factors (RAFs) wer e calculated for corals at the same depths. RAFs for M, faveolata suggest t hat corals at depths greater than 3 m will be more sensitive to increases i n WE irradiance, such as might be caused by ozone depletion, than their sha llow-water counterparts. Despite this increase in sensitivity to UVB, calcu lations incorporating continued ozone depletion suggest that at the present rate of stratospheric ozone depletion corals deeper than 5 m in the Florid a Keys will be affected very little, if at all, by increases in UVR. These results, however, do not incorporate the interacting and synergistic effect s of UVR with other physical parameters (e.g. temperature) that will be ess ential to understanding and predicting the fate of coral reefs under condit ions of global change.