*** Malloy 9614892 Recent decreases in stratospheric ozone have resulted in dramatic increases in the flux of mid-ultraviolet light (UVB) reaching the earth's surface, especially over Antarctica and, to a lesser extent, in temperate zones. Ozone depletion is expected to continue well into the next century, and to worsen at lower latitudes over time. Recent evidence suggests that present intensities of UVB are sufficient to produce significant impacts on phytoplankton communities in the Southern Ocean, as well as to negatively impact tropical marine communities and populations of temperate amphibians. The abbreviated trophic structure of the Antarctic marine ecosystem places an increased importance on primary and secondary consumers, especially on many species of zooplankton which form a critical link between primary production and top predators such as adult fish, marine mammals and birds. Although these zooplankton species and other heterotrophs, which include larval and adult fish, krill, and copepods, are important components of the trophic structure in the Antarctic ecosystem, there is no information regarding the effects of increased UVB on natural populations of these organisms. However, laboratory and field studies on non-polar species suggest that the impact of increased UV on Antarctic heterotrophs, and therefore on the Antarctic ecosystem, could be substantial. The proposed research will use established methods: 1) to measure the vulnerability of Antarctic zooplankton to UVB damage in the field and in the laboratory; 2) to measure DNA repair rates of Antarctic heterotrophs at ambient temperatures (-2 to +40C); and 3) to determine the relationship between UVB exposure and decreases in organismal fitness (measured as RNA:DNA ratios and transcription rates). The field component of this research is a unique effort to determine the in situ vulnerability of natural populations of Antarctic heterotrophs during normal and depleted ozone conditions. Laboratory experiments will deter mine dose:response (UVB fluence:DNA photoproducts) relationships for the zooplankton taxa which are most abundant during ozone depletion in order to determine species-specific vulnerabilities to increased UVB. However, DNA damage measured in natural populations represents both the net damage added by UVB and that removed by DNA repair. Therefore, DNA repair rates of several abundant pelagic heterotrophs will be measured to facilitate a more complete understanding of the potential vulnerability of each taxa. Photolyase genes from Antarctic fishes that have already been cloned will be sequenced and the deduced amino acid sequences will be compared to other photolyase sequences to better understand the underlying mechanisms of DNA repair at low temperatures. Finally, the sub-lethal impacts of UVB exposure, and the associated DNA damage, on fitness will be evaluated by measuring long-term (RNA:DNA ratios) and short-term (nuclear run-on assays) measures of biochemical condition. Together, these studies are critical for developing predictive models of the relative impact of increased UVB on Antarctic marine heterotrophs and for relating ozone depletion on decreased fitness, survival, and population dynamics of these species. ***
