Effect of UV radiation on photoinhibition of marine macrophytes in culture systems

The present study examined the effect of UV and photosynthetically active radiation (PAR) on photoinhibition and recovery in the Phaeophyte Macrocystis pyrifera, the Rhodophyte Chondrus crispus and the Chlorophyte Ulva lactuca under outdoor culture conditions. There was an increase in photoinhibition as a consequence of high exposure to UV-B radiation in M. pyrifera, however, high levels of PAR accounted for most of the photoinhibition in C. crispus and U. lactuca. Photodamage by UV-A, UV-B and PAR was completely repaired within 5 h and effective quantum yield reached pretreatment values in the three species studied. Species were less susceptible to photoinhibition after being incubated for 5 d under high exposures of natural irradiance suggesting a photoadaptive process. The recovery of the effective quantum yield 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 by UV-A and PAR radiation, one to the photosynthetic apparatus and another which 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 days of the initiation of the experiment suggesting that these species photoprotect their photosynthetic system when exposed to elevated UV and PAR levels.