Field study of compensatory changes in UV-absorbing compounds in the mucus of the solitary coral Fungia repanda (Scleractinia:Fungiidae) in relation to solar UV radiation, sea-water temperature, and other coincident physico-chemical parameters

The relationship between coral UV-absorbing compounds (mycosporine-like amino acids, or MAAs) and solar UV radiation in the shallow coral reef environment has been much debated. The presence of these compounds in the mucus of Fungiidae allowed the measurement of weekly compensatory changes in the amount and composition of these compounds together with shifts in the wavelength of maximum absorbance (λ(max)) in the mucus of 11 specimens of Fungia repanda (Scleractinia:Fungiidae) during 18 months of monitoring in situ in Tahiti. The corals received full sunlight within a topless cage (specimen depth, 1 m) located at the Arue lagoon (northern coast of Tahiti). The amount of UV-absorbing compounds was found to be significantly and positively related to solar UV radiation, with a lag time of one week and with a corresponding long-wavelength shift in the maximum absorbance without lag, but was not significantly related to sea-water temperature or to the volume of mucus secreted. Analysis of mucus MAAs by high-performance liquid chromatography showed that the shift in λ(max), could be related to an increase in three components: mycosporine-2-glycine, palythine and mycosporine-glycine.