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

Abstract

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 biology and ecology of coral reefs has taken on renewed interest since the demonstration of global stratospheric ozone loss through human activities. The hermatypic coral Montastraea faveolata occurs over a wide bathymetric range in the Florida Keys reef tract. The bathymetric range of M. faveolata and its role in reef community structure make it an important species for which to assess the effects of present day UVR irradiances. Both UVR irradiances and UVR-absorbing mycosporine-like amino acids (MAAs) decreased significantly with increasing depth in M. faveolata. UVB irradiances were measured to 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 spectra (= biological weighting function) for the photoinhibition of photosynthesis by UVR were measured for samples of M. faveolata at 3, 10, 18, 23, and 30 m. Using these action spectra, radiation amplification factors (RAFs) were calculated for corals at the same depths. RAFs for M. faveolata suggest that corals at depths greater than 3 m will be more sensitive to increases in UVB irradiance, such as might be caused by ozone depletion, than their shallow-water counterparts. Despite this increase in sensitivity to UVB, calculations incorporating continued ozone depletion suggest that at the present rate of stratospheric ozone depletion corals deeper than 5 m in the Florida Keys will be affected very little, if at all, by increases in UVR. These results, however, do not incorporate the interacting and synergistic effects of UVR with other physical parameters (e.g. temperature) that will be essential to understanding and predicting the fate of coral reefs under conditions of global change.