PARENT SESSION
Oral Session # 3: Fish Ecology.
Presiding: M Ford
Monday, August 4. 8:00 AM to 11:30 AM, SITCC Meeting Room 102.

Interactive effects of climate change and eutrophication on growth of a coldwater planktivore.

Koski, Marci^*,1, Johnson, Brett¹, ¹ Colorado State University, Fort Collins, CO, USA

ABSTRACT- Anthropogenic environmental change will have direct and indirect effects on aquatic ecosystems, including alteration of food web dynamics and trophic status of lakes and reservoirs. Climate change and eutrophication may affect lentic characteristics such as water quality and clarity, primary and secondary productivity, and zooplankton distributions that, in turn, can impact higher trophic levels. In this analysis we used an improved bioenergetics model fitted with a light-dependent functional response to predict growth of a planktivorous fish (kokanee salmon, Oncorhynchus nerka) in Blue Mesa Reservoir (BMR), CO. Inputs to the model included geographical location, kokanee foraging depth (diel vertical migration scenarios), time of day, and limnological data such as secchi depth, zooplankton density, and temperature profiles. We first simulated yearling kokanee growth using information collected from BMR in 2002 to predict growth under current conditions. We simulated climate warming scenarios by increasing epilimnetic temperatures by 2 and 4 degrees C. To simulate eutrophication scenarios, we decreased water clarity and increased zooplankton density in the epilimnion. We also created interaction scenarios by combining the effects of both eutrophication and climate warming. We found that increasing epilimnetic water temperatures by 2 and 4 degrees C decreased kokanee daily growth rate by 12% and 27% respectively; conversely, our eutrophication scenarios increased kokanee growth rate by approximately 30% due to increased food availability. When simulated eutrophication conditions were combined with warmer epilimnetic temperatures the benefits of higher food availability were limited by the increased energetic costs of inhabiting warmer water. We conclude that the interactive effects of climate change and eutrophication may force kokanee to feed for longer periods of time in the epilimnion, where temperatures are physiologically sub-optimal and predation risk may be greater.

Key words: climate change, trophic dynamics, planktivore growth, eutrophication