UV-ABSORBING COMPOUNDS IN THE CORAL POCILLOPORA-DAMICORNIS - INTERACTIVE EFFECTS OF UV-RADIATION, PHOTOSYNTHETICALLY ACTIVE RADIATION, AND WATER-FLOW

A direct relationship exists between irradiance of solar ultraviolet ( UV) radiation and concentration of UV-absorbing compounds, know as myc osporine-like amino acids (MAAs), in the Hawaiian reef coral Pocillopo ra damicornis. However, MAA concentration is also influenced by flow r egime and the irradiance of photosynthetically active radiation (PAR). High irradiances of UV radiation in reef environments art: correlated with high PAR and high water velocity, because all three parameters d iminish exponentially with increased depth. This correlation can also be found along horizontal gradients on reefs. The dearest water is typ ically found on outer reefs growing in oceanic water. These ocean reef s typically experience high water velocities due to ocean swell when c ompared to the more turbid lagoon reefs exposed only to small wind-dri ven waves. Flow-modulated photosynthetic rate seems to be a major fact or affecting the observed changes in MAA concentration when P. damicor nis is grown under different flow regimes and identical irradiances of UV and PAR radiation. High PAR and high water velocity significantly enhance the effect of increased UV radiation on MAA concentration.