NASA SOHO Mission,Yohkoh
science team
Ecological impacts of
UV-B radiation
Organismal effects and responses
The common frog (Rana temporaria)
(Funet)Animals
Direct exposure to UV-B has been shown to cause molecular damage to proteins and nucleic acids, inhibition of metabolic processes, and blockage of genome replication and expression in animals. Like plants, animals are more susceptible to UV-B damage during particular life cycle stages and their exposure varies with their mobility. Responses to UV-B vary within species, between populations of a particular species, and among species. Karentz and Bosch (2001) point out that many animals, such as seals, birds, adult fish, and whales are protected from UV-B damage by their fur, feathers, scales, and thick skin.Amphibians
Most research on responses and effects of UV-B on animals has been conducted on amphibians (and people) because many amphibians live at high altitudes, lay their eggs in relatively shallow water, and many species have been suffering recent declines. UV-B radiation has been shown to reduce hatching success, increase embryonic mortality, cause deformities, slow growth and development, and change behavior in some species of amphibians (Bridges and Boon 2003). Pahkala et al. (2002) found that some populations of the common frog (Rana temporaria ) were more tolerant to UV-B than others and that embryonic sub-lethal exposure to UV-B may cause reduced fitness for the frogs later in life. Research by Blaustein et al. (1994, 1998) suggest that photolyase activity (a DNA repair mechanism) can explain differences in tolerance to UV-B, especially between species at high altitudes with repair mechanisms and those at sea level which are not adapted to high UV-B exposure. Bridges and Boon (2003) and Blaustein et al. (1998) attribute levels of UV-B exposure in amphibians to mobility of amphibians at different life stages and their egg laying behaviors, respectively. Amphibian eggs laid in shallow water have the potential to be exposed to high levels of UV-B while tadpoles can swim to shaded areas (Bridges and Boon 2003) and some amphibians lay there eggs under leaves or logs and in muddy water or crevices (Blaustein et al. 1998). Kiesecker et al. (2001) also observed that the depth of the water in which amphibian eggs are laid determines their exposure to UV-B and their vulnerability to infection by a pathogenic oomycete ( Saprolegnia ferax ). Many researchers agree that UV-B is one of many stressors that are responsible, either alone or in combination, for amphibian population declines. For instance, Pahkala et al. (2002) observed that low pH and UV-B acted synergistically to decrease survival rates and increase malformations in the common frog.Pelagic zooplankton and fish
Hessen (2003) reviews the direct and indirect effects of UV-B on pelagic zooplankton and vertebrates and the adaptive and repair responses of these organisms to UV-B exposure. Direct damage includes membrane and DNA damage, intracellular photoproducts, immunosuppression, skin lesions, cancers, and eye damage. These effects can in turn can cause death or reduced fitness later in life. Some pelagic animals produce UV-screening compounds, or derive them from consuming photosynthetic organisms. These screening compounds absorb UV-B and protect the animals tissues from damage. Animals also employ DNA repair mechanisms, such as those described in the molecular photobiology section, when suffering from increased UV-B exposure. Indirect effects of UV-B include reduced productivity of photosynthetic organisms and bacteria exposed to UV-B which translates to less and less nutritious food for animals and the release of toxic metals into the water as a result of macromolecules breaking down with UV exposure. Fish larvae and early stages of other pelagic vertebrates, especially those with floating eggs are more susceptible to UV-B damage than are adults because of their small surface to area ratios and longer exposure to UV-B (as reviewed by Karentz and Bosch 2001).
