Climate Impacts on Zooplankton Grazing in Alpine Lakes: UV and Temperature.

1. Cold: 8oC Warm: 12oC Craig Williamson1, Courtney Salm2, Sandra Cooke3, Jasmine Saros2, David Mitchell4 1 Department of Zoology, Miami University, Oxford, OH 45056 2Climate Change Institute, University of Maine, Orono, ME 04469 3Division of Ecology & Conservation Science, Illinois Natural History Survey, Champaign, IL 61820 4M.D. Anderson Cancer Center, Science Park/Research Division, University of Texas, Smithville, Texas 78957 Introduction: Previous laboratory microcosm studies suggest that climate warming will impact higher trophic levels more than lower trophic levels (Petchey et al. 1999). Consumers may also be more susceptible to UV damage than are primary producers because the latter require exposure to sunlight for photosynthesis and thus are more likely to be acclimated to high UV. Here we examine the effects of UV radiation and temperature on phytoplankton growth rates and zooplankton grazing rates in a subalpine lake where climate change is expected to be strong. Methods: Results: Experimental Design Climate Impacts on Zooplankton Grazing in Alpine Lakes: UV and Temperature. Natural assemblages of phytoplankton were collected from subalpine Beartooth Lake and incubated at the very surface of a nearby cool (8oC) lake and warm (12oC) pond in the presence and absence of UV and zooplankton grazers (6 Leptodiaptomus ashlandi for 7 days) in a 3-way factorial design. Incident UV was reduced to 62% of surface values with mesh. Phytoplankton growth and zooplankton grazing rates were estimated with standard exponential growth models. Figure 1. Warmer temperatures significantly increased the growth rates of all four dominant phytoplankton species, while UV had a negative impact on all species except Dinobryon. • Conclusions: • The direct effects of temperature and UV on phytoplankton growth rates were greater than on zooplankton grazing rates. • We did not assess the longer term effects of temperature and UV on zooplankton, but a coordinated study did find that UV significantly depressed reproduction and recruitment rates of L. ashlandiunder these exposure conditions (Cooke et al. 2006). Results of 3-way ANOVA Din = Dinobryon sp. Frag = Fragilaria crotonensis Ast = Asterionella formosa Cyc = Cyclotella stelligera* * Recently renamed Discotella stelligera? Field Incubation Sites Acknowledgements: We thank Ryan Lockwood, Kirsten Kessler, Lindsay ?, Shaina Keseley and Caren Scott for field assistance. This work was supported by NSF Grant DEB-IRCEB-0210972. DNA Dosimeters verified strong differences in DNA damage due to UV exposure among UV +/- treatments (means and S.E.). Figure 2. Warmer temperatures significantly increased zooplankton grazing rates only on Fragilaria and Cyclotella, while exposure to UV had no effect on zooplankton grazing rates. Literature Cited: Petchey, McPhearson, Casey & Morin 1999. Nature.402:69 Cooke, Williamson & Saros 2006. Freshwat. Biol. 51: 1827.