UVR can cause injuries to freshwater organisms that can lead to mortality. Freshwater fish and amphibians are especially susceptible to the harmful effects of UVR. Sunburn in cultured fish has been the most frequently reported UV-induced injury in freshwater organisms. The wavelengths typically responsible for UV-induced injuries are in the UV-B wavelength range (280-320 nm). Sunburn-like injuries have also been observed in certain amphibian life stages and probably occur to some degree in other aquatic organisms. Sunburn in nature has not been widely reported, probably because aquatic organisms often succumb to opportunistic infections shortly after acquiring this injury, and thus are not readily observed. UV sensitivity exhibited by an organism can be linked to the concentration and distribution of photoprotective pigments contained in the integument in addition to efficiency of photorepair mechanisms. A number of climatic conditions can contribute to UV-induced injuries, including extended periods of elevated UV associated with ozone depletion, changes in cloud cover or extent of sunny conditions, and global warming that may give rise to increased water clarity because of water column stratification. Habitat characteristics, in turn, also play a role in the risk of UV-induced injuries. These characteristics include not only latitude and altitude of the organism's habitat, but also the degree of shading provided by canopy or substrate cover. In addition, the chemical composition of the aquatic habitat (particularly the composition and concentration of DOC) can influence UV penetration into the water column. Moreover, UVR in the aquatic habitat is considerably more dynamic than at the Earth's surface, and can vary by orders of magnitude depending on water clarity. The presence of certain chemical contaminants can additively or synergistically increase UV injury in organisms, even in habitats having low UVR. Reports of UV-induced injuries in aquatic organisms will probably increase with ozone depletion and global warming. Thus, further research is needed in this area, especially research on sublethal UV-induced effects including behavior, growth, and reproduction.
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