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 n m) and B (UVB, 280 to 320 nm) radiation on planktonic planula larvae o f the reef-building coral Agaricia agaricites (Linnaeus) were investig ated through field experiments. Survival, chlorophyll concentrations, and solubilized protein concentrations were determined for larvae spaw ned from colonies at 3 and 24 m depth and subjected to one of three li ght regimes at 3, 10, or 24 m depth for 72 h: PAR (photosynthetically active radiation, 400 to 700 nm) only, PAR + UVA, or PAR + UVA + UVB. At 3 m depth, larvae in the PAR + UVA + UVB treatment showed lower sur vivorship than larvae exposed to either PAR alone or PAR + UVA. Within the PAR + UVA + UVB treatment at 3 m depth, larvae from colonies at 2 4 m depth suffered higher mortality than those from 3 m. Differences i n survivorship between larvae originating from 3 and 24 m depth corres ponded with tissue concentrations of UVB-protective mycosporine-like a mino acids: larvae from 3 m had higher concentrations of mycosporine-g lycine (lambda(max)=310nm) and palythine (lambda(max)=320 nm) than tho se from 24 m depth. Chlorophyll concentrations were inversely correlat ed with PAR intensities, but variation in this parameter did not appea r to be detrimental. These results show that sensitivity to high inten sities of UVB radiation may affect survivial of A. agaricites larvae i n shallow reef-waters.