Ecology of UV
UV introduction and basic optics
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Increases in UVR associated with stratospheric ozone depletion have been suggested as a cause of broad-scale declines in fish populations (Walters and Ward 1998). In general, fish are most susceptible to the damaging effects of UVR during the egg and larval stages (Hunter et al. 1979, 1981). This susceptibility is in part the result of high surface area to volume ratios that increase the proportion of cells at risk of exposure. In addition, eggs and larvae are limited in their ability to behaviorally avoid UV exposure, unlike older life history stages (Kelly and Bothwell 2002).
One mechanism of UV defense in fish is a change in spawning behavior. For example, yellow perch (Perca flavescens) in high UV environments spawn in deeper water where UVR is more attenuated (Williamson et al. 1997). However, lower temperatures associated with increasing depth can slow development rates, which can potentially decrease survival and recruitment (Huff 2000). In this case, UVR can have a strong indirect effect on fish populations.
Like other organisms, fish can also minimize effects of UV on eggs and larvae at the cellular level through two mechanisms: photoprotection and photorepair. Photoprotective defenses involve the production of pigments such as melanin and carotenoids that absorb UV-B radiation and prevent molecular damage. Photorepair defenses involve enzymes that reverse DNA damage caused by UV-B radiation. This enzymatic repair is temperature dependent and requires UV-A radiation for optimal activity.
Although many fishes possess both defenses, the effectiveness of these mechanisms varies widely among species. Consequently, species differ in overall tolerance to current and future UV damage. In addition, species differ in the relative importance of photoprotection vs. photorepair. Although phylogenetic differences likely explain some of this variation, differences in spawning time may also be important. Because enzyme activity is temperature dependent, species that spawn at low temperature may be ineffective at repairing DNA damage. These species may rely more heavily on photoprotective compounds, and may be more vulnerable to UV damage than species that spawn at higher temperatures.
References
Huff, D. D. 2000. The indirect effects of solar ultraviolet radiation on the early life stages of yellow perch (Perca flavescens) in lakes of different trophic status. Masters Thesis, Lehigh University, Bethlehem, PA.
Hunter, J. R., S. E. Kaupp, and J. H. Taylor. 1981. Effects of solar and artificial ultraviolet-b radiation on larval northern anchovy, Engraulis mordax. Photochemisttry and Photobiology 34:477-486.
Hunter, J. R., J. H. Taylor, and H. G. Moser. 1979. Effect of ultraviolet irradiation on eggs and larvae of the northern anchovy, Engraulis mordax, and the pacific mackerel, Scomber japonicus, during the embryonic stage. Photochemistry and Photobiology 29:325-338.
Kelly, D. J., and M. L. Bothwell. 2002. Avoidance of solar ultraviolet radiation by juvenile coho salmon (Oncorhynchus kisutch). Canadian Journal of Fisheries and Aquatic Sciences 59: 474-482.
Walters, C., and B. Ward. 1998. Is solar ultraviolet radiation responsible for declines in marine survival rates of anadromous salmonids that rear in small streams? Canadian Journal of Fisheries and Aquatic Sciences 55: 2533-2538.
Williamson, C. E., S.E. Metzgar, P.A. Lovera, and R.E. Moeller. 1997. Solar
ultraviolet radiation and the spawning habitat of yellow perch, Perca flavescens.
Ecological Applications 7: 1017-1023.