KUFFNER, I.B.: Effects of ultraviolet radiation and water motion on the reef coral Porites compressa: A transplantation experiment

Ultraviolet radiation (UVR, 280 – 400 nm) is an important ecological variable affecting coral reef organisms, but UVR effects may be influenced by other factors such as water motion. In this study, the effects of ambient UVR and water motion on several physiological parameters of the reef coral Porites compressa were investigated in a factorial transplantation experiment. Branches from nine different colonies were transplanted from the windward side of Coconut Island (Kaneohe Bay, Hawaii) to a control area on the windward side (ambient water motion) and to an area on the leeward side (low water motion). Transplanted corals were placed under UV-opaque or UV-transparent filters fixed to the reef. Initially and at three and six weeks, coral branches were weighed to determine calcification rate, and tissues were extracted to analyze photosynthetic pigments and the concentration of the UV-absorbing compounds, mycosporine-like amino acids (MAAs) via HPLC. When UVR was screened from the corals’ environment, total MAA concentration decreased by 33 % over six weeks. The presence of UVR resulted in higher concentrations of MAAs in UVR-exposed colonies compared to colonies shielded from UVR. However, UVR-exposed corals moved to low water motion decreased MAAs while UVR-exposed corals moved to the control area retained initial levels. Photosynthetic pigments and calcification rate were also significantly lower in corals moved to low water motion. There was no UVR effect on photosynthetic pigments or calcification rate. This study provides evidence that water motion is important for the maintenance of MAAs. However, there were interesting colony-specific patterns in MAA composition in response to the UVR treatment, indicating a genetic (host, zooxanthellae or both) component to UVR resistance.