Effect of UV radiation on photoinhibition of marine macrophytes in culturesystems

The present study examined the effect of UV and photosynthetically active r adiation (PAR) on photoinhibition and recovery in the Phaeophyte Macrocysti s pyrifera, the Rhodophyte Chondrus crispus and the Chlorophyte Ulva lactuc a under outdoor culture conditions. There was an increase in photoinhibitio n as a consequence of high exposure to UV-B radiation in M. pyrifera, howev er, high levels of PAR accounted for most of the photoinhibition in C. cris pus and U. lactuca. Photodamage by UV-A, UV-B and PAR was completely repair ed within 5 h and effective quantum yield reached pretreatment values in th e three species studied. Species were less susceptible to photoinhibition a fter being incubated for 5 d under high exposures of natural irradiance sug gesting a photoadaptive process. The recovery of the effective quantum yiel d was impaired by long exposure to high levels of UV-B in C. crispus and UV -A, UV-B and PAR in M. pyrifera. This suggests a different kind of damage b y UV-A and PAR radiation, one to the photosynthetic apparatus and another w hich affects the repair mechanism of some species. There was an increase in UV-absorption (lambda 330 nm) in M. pyrifera and C. crispus within four da ys of the initiation of the experiment suggesting that these species photop rotect their photosynthetic system when exposed to elevated UV and PAR leve ls.