The amount of UV-B radiation reaching the earth’s surface is increasing due to attenuation of the stratospheric ozone. Although the release of ozone-depleting material has declined significantly in the past decade, there is a considerable lag in the recovery of the ozone layer.Cyanobacteria are the oldest photosynthetic prokaryotes and play an important role in the aquatic ecosystem. UV-B can penetrate water to a depth sufficient to disrupt aquatic ecosystems. For example, the depth of water required to remove 90% of the solar radiation at 310 nm is about 20 m in the clearest ocean. Thus, a large number of cyanobacteria populate aquatic habitats that are exposed to UV-B radiation. UV-B radiation is known to affect cyanobacteria biomass by disrupting physiological and biochemical processes. have developed mechanisms to counteract the damaging effects of UV-B, including production of UV-screening pigments [(e.g., mycosporine-like amino acids (MAAs)] and downward migration. We evaluated the effects of short-term enhanced UV-B radiation onS. platensis were exposed to 240 UV-B for 3.5 h. By compared with untreated cyanobacteria cells, exposure to increased levels of UV-B radiation was associated with a reduction in chlorophyll a, carotenoid and phycobiliprotein Our results suggest that increased levels of UV-B radiation causes bleaching of the photosynthetic pigment. Exposure to higher levels of UV-B was also associated with increased synthesis of MAAs and accumulation of proline. We hypothesize that this is a mitigation strategy to reduce the damaging effects of UV-B.