Response of the soft coral Heteroxenia fuscescens to ultraviolet radiation regimes as reflected by mycosporine-like amino acid biosynthesis

Abstract

The variation in mycosporine-like amino acid (MAA) concentration in the soft coral Heteroxenia fuscescens in relation to changes in ultraviolet radiation (UVR) regimes was investigated at the Gulf of Eilat, northern Red Sea. Solar radiation (300–700 nm) was measured for different depths and seasons. The UVR irradiance was measured to a depth of 25 m on the reef. The mean attenuation coefficient for UV-B measured in winter was twofold that of the summer value. Separation of H. fuscescens extracts by reverse-phase isocratic high-performance liquid chromatography revealed a single MAA compound, palythine (λ_max = 320 nm). Possible seasonal changes in MAAs in colonies of H. fuscescens along a depth gradient were examined on different dates. Palythine concentrations in the colonies were significantly higher in summer than in the other seasons particularly in shallow water. Possible changes in MAA content in colonies of H. fuscescens as a result of UVR protection, were determined by experiments conducted for periods of 1 week, 1 month and 3 months, at a depth of 5 m. In these experiments colonies were removed from the natural substrate and placed underwater, protected from UVR by a PVC filter. Significant differences between UV-exposed and protected colonies of H. fuscescens were found only in the 3-month experiment conducted during the summer. These findings demonstrate that UVR is an important environmental factor regulating MAA biosynthesis in the soft coral H. fuscescens.