Climate Impacts on Zooplankton Grazing in Alpine Lakes:
UV and Temperature.
Craig Williamson1, Courtney Salm2, Sandra Cooke3, Jasmine Saros2, David Mitchell4
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
1
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
8oC UV+
5.0
5.0
4.0
Growth Rate.
Growth Rate.
4.0
3.0
2.0
1.0
3.0
2.0
1.0
0.0
-1.0
5.0
Field Incubation Sites
Cold: 8oC
Warm: 12oC
0.0
Din
Fra
600
400
200
0
UV+
UV-
Fra
Ast
Cyc
12 C UV-
3.0
2.0
1.0
0.0
-1.0
Din
4.0
Growth Rate.
1.0
0.0
Din
Fra
Ast
Cyc
-1.0
Din
Fra
Ast
Cyc
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.
Din = Dinobryon sp.
Frag = Fragilaria crotonensis
Ast = Asterionella formosa
Cyc = Cyclotella stelligera*
* Recently renamed Discotella stelligera?
8oC UV+
Grazing Rate
Grazing Rate
2.0
1.5
1.0
0.5
0.0
Din
Fra
Ast
Cyc
1.5
1.0
0.5
0.0
-0.5
Ast
1.5
1.0
0.5
0.0
2.5
2.0
Fra
2.0
-0.5
12oC UV+
Din
8oC UV-
2.5
Grazing Rate
Grazing Rate
CPD MB DNA -1
8oC
12oC
5.0
2.0
2.5
800
-1.0
o
3.0
-0.5
DNA Dosimeters
verified strong
differences in
DNA damage due
to UV exposure
among UV +/treatments
(means and S.E.).
Cyc
12oC UV+
2.5
UV-induced
DNA Damage
Ast
4.0
Growth Rate.
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.
Results of 3-way ANOVA
8oC UV-
Cyc
Din
Fra
Ast
12oC UV-
1.5
1.0
0.5
0.0
Din
Fra
Ast
2) 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. ashlandi under
these exposure conditions (Cooke et al.
2006).
Cyc
2.0
-0.5
Conclusions:
1) The direct effects of temperature and
UV on phytoplankton growth rates were
greater than on zooplankton grazing
rates.
Cyc
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.
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.
Literature Cited:
Petchey, McPhearson, Casey & Morin 1999. Nature.402:69
Cooke, Williamson & Saros 2006. Freshwat. Biol. 51: 1827.