Interactive Effects of UV Radiation and Temperature on Pelagic Foodwebs


National Science Foundation
09/02/02 - 08/31/07
PI: Wade H. Jeffrey

One of the most challenging questions in environmental biology is how human-accelerated changes in multiple environmental variables are influencing natural communities and ecosystems. One of the more pervasive of these changes is the increase in ultraviolet radiation (UV) related to stratospheric ozone depletion. In aquatic ecosystems, changes in chromophoric (color-absorbing) dissolved organic matter (CDOM) related to changes in climate, land use, and hydrology, are also of key importance in regulating changes in the exposure of aquatic organisms to UV. Complex environmental gradients in temperature and UV combine with concerns about future trends toward increasing regional and global UV and temperature to argue for the need to understand the interactive effects of temperature and UV in natural ecosystems. The fact that DNA is the primary target for UV damage argues for the need for studies of UV effects to be integrated across levels of biological organization from the molecular to the ecosystem level. The proposed project will examine the regulation of UV impacts on pelagic food webs in lakes with an integrated study of two opposing, but interrelated hypotheses - regulation of UV impacts at the molecular level (photoprotection vs DNA repair) versus regulation at the ecosystem level (CDOM-mediated attenuation of UV and associated indirect effects). It is argued that climate change will regulate UV damage at both the molecular level (by altering temperature), and at the ecosystem level (by altering CDOM). More specifically it is hypothesized that environments with high UV and low temperature (high UV:T ratio) will favor more plant-based food webs while environments with low UV:T ratios will favor more microbial, bacteria-based food webs with consequently different zooplankton grazers.

The proposed study will integrate a carefully focused set of analytical and experimental approaches and apply them across a wide range of pelagic organisms. During the first two years the project will look at UV damage and the effectiveness of different molecular mechanisms of UV defense in phytoplankton, bacteria, protozoa, zooplankton, and fish at a range of temperatures. A novel solar simulator apparatus and protocol will be used to estimate temperature-dependent changes in UV tolerance and its components: photorepair, dark repair, and photoprotection. The effects of temperature on UV impacts on primary productivity and bacterial productivity will be examined, with particular attention to the importance of nutrient limitation and acclimation. During years 3 and 4 a series of in situ mesocosm experiments, combined with direct-effect bioassays like those in years 1 and 2, will examine mechanisms that underlie community and ecosystem level responses. The mesocosms and associated bioassays will test whether the strong effects often observed in past small-scale bag and bottle experiments actually translate to meaningful changes at the community and ecosystem level in the surface mixed layer of lakes. The research will center on four low elevation lakes in Pennsylvania and in high elevation lakes in the Beartooth Mountains of Wyoming where very high UV:T ratios are observed. By applying a diverse set of experimental and analytical tools to multiple trophic levels within the same study, the proposed research will advance our understanding of how pelagic communities are likely to respond to future changes in UV related to climate change and ozone depletion. The complexity of the project requires an integrative approach and as such, it will be undertaken by a consortium of scientists from seven institutions led by Lehigh University (total project budget: $2,750,000). Other members include the University of West Florida (CEDB), MD Anderson Cancer Center, University of Wisconsin-LaCross, Temple University, and Franklin and Marshall College. The twelve co-PIs bring in expertise on ultraviolet radiation effects on different trophic levels, photobiology, optics, modeling, lake ecosystems, organic carbon dynamics, and molecular biology.

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