Within-colony variations of UV absorption in a reef building coral

Concentration and composition of ultraviolet (UV) absorbing substances have been found to vary in corals found at different depths, between color morp hs of conspecifics and between coral species. In this study, spatial distri bution patterns of UV-absorbing compounds were found to differ within indiv idual colonies of the reef building coral Montastraea annularis. Extracts f rom coral cores were analyzed spectrophotometricaly to determine total conc entration of UV-absorbing compounds and HPLC analyses were performed to ide ntify specific mycosporine-like-amino-acids (MAAs) and their concentrations . The greatest UV absorbance was measured on the top of the colony with int ermediate values on the vertical sides and lowest absorbance near the base. Variations in UV absorbance corresponded to the expected incident UV radia tion regime along the surface of the coral with a five-fold increase in UV absorption on the top when compared with the base of the coral. HPLC analys is of M. annularis extracts demonstrated that the increase in UV absorption on the top of the colony was largely due to a higher concentration of the two dominant compounds, mycosporine-glycine and palythine. This study demon strates that individual coral colonies exhibit considerable plasticity in t heir capacity to absorb UV radiation, emphasizing that sampling location wi thin a colony must be a primary consideration when making comparisons of UV -absorbing capabilities between colonies, between species or along depth gr adients.