Increase of harmful radiation to the Earth’s surface due to ozone depletion results in higher exposure to harmful ultraviolet- B radiation (UV), while fluctuations in seawater salinity may alter water density, ionic concentration, nutrient uptake, and osmotic pressure. This study evaluated the effects of salinity and UV on metabolism and morphology of Acanthophora spicifera (M.Vahl) Børgesen. Water with 30 and 37 psu [g(salt) kg-1(sea water)] was used for experiments during 7 d of exposure to UV (3 h per day). We demonstrated that UV treatment predisposed, irrespective of salinity, A. spicifera to a decrease in its growth rate and cell viability, as well as affected its morphological parameters. After exposure to PAR + UVA + UVB (PAB), samples showed structural changes and damage, such as increasing cell wall thickness and chloroplast disruption. Our results indicate that UV led to dramatic metabolic changes and cellular imbalances, but more remarkable changes were seen in samples exposed to high salinity., D. T. Pereira, C. Simioni, L. C. Ouriques, F. Ramlov, M. Maraschin, N. Steiner, F. Chow, Z. L. Bouzon, É. C. Schmidt., and Obsahuje bibliografii