There is a wide range of tolerance by marine and freshwater organisms to UVR. For example, different strains of free-living and symbiotic dinoflagellates [1,2] demonstrate markedly variable tolerances to exposure to UVR, as do corals [3]. Resistance to exposure to UVR will depend not only on the extent of damage incurred by these damaging wavelengths, but also on the efficiency and availability of various screening mechanisms both physical and chemical, on compounds able to quench photochemically produced toxins and on mechanisms to repair damage to sensitive cellular components such as proteins and DNA [4,5], Assessment of the tolerance of different species will not only depend on their ability to overcome damage but also on what parameters are used to assess sensitivity; normally photosynthetic parameters are monitored for autotrophic organisms and some kind of growth or survival parameter for heterotrophic organisms. Even within the same species, sensitivity to UVR can vary depending on factors such as light history and nutrient status [6]. Because autotrophic organisms must be exposed to adequate photosynthetically active radiation (PAR) so as to perform photosynthesis, they are also exposed to UVR, therefore, photoprotective mechanisms must be wavelength specific to protect against UVR while allowing for transmission of PAR.

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