Variation in UVB sensitivity of planula larvae of the coral Agaricia agaricites along a depth gradient

The effects of natural intensities of ultraviolet A (UVA, 320 to 400 nm) and B (UVB, 280 to 320 nm) radiation on planktonic planula larvae of the reef-building coral Agaricia agaricites (Linnaeus) were investigated through field experiments. Survival, chlorophyll concentrations, and solubilized protein concentrations were determined for larvae spawned from colonies at 3 and 24 m depth and subjected to one of three light regimes at 3, 10, or 24 m depth for 72 h: PAR (photosynthetically active radiation, 40- to 700 nm) only, PAR+UVA, or PAR+UVA+UVB. At 3 m depth, larvae in the PAR+UVA+UVB treatment showed lower survivorship than larvae exposed to either PAR alone or PAR+UVA. Within the PAR+UVA+UVB treatment at 3 m depth, larvae from colonies at 24 m depth suffered higher mortality than those from 3 m. Differences in survivorship between larvae originating from 3 and 24 m depth corresponded with tissue concentrations of UVB-protective mycosporine-like amino acids: larvae from 3 m had higher concentrations of mycosporine-glycine (λ_max=310nm) and palythine (λ_max=320nm) than those from 24 m depth. Chlorophyll concentrations were inversely correlated with PAR intensities, but variation in this parameter did not appear to be detrimental. These results show that sensitivity to high intensities of UVB radiation may affect survival of A. agaricites larvae in shallow reef-waters.