PARENT SESSION
Oral Session # 71: Trophic Structure I: Theory; Aquatic Systems.
Presiding: D Chalcraft
Thursday, August 7. 8:00 AM to 11:30 AM, SITCC Meeting Room 202.
Nutrients disrupt trophic coherence in aquatic ecosystems.
Ballantyne, Ashley*,1, Brett, Michael 2, Muller-Navarra, Doerthe3, 1 Duke University, Durham, NC2 University of Washington, Seattle, WA3 University of California, Davis, CA
ABSTRACT- Nutrient availability is a strong determinant of species growth and assemblage. Thus alterations to the biogeochemical cycling of such nutrients as phosphorus can have major implications for primary productivity, growth of consumers and ultimately water quality. Herein we present results from a series of consumer growth experiments and a numerical model that suggest an increase in phosphorus supply may cause a phase shift between phytoplankton and zooplankton populations in freshwater ecosystems, thereby reducing the transfer of mass and energy between trophic levels. Empirical results show that zooplankton growth was correlated with algal biomass (i.e. chlorophyll-a) in all three lakes of differing states of productivity; however, zooplankton growth was positively correlated in the mesotrophic lakes and negatively correlated in the eutrophic lake. Results from a coupled phytoplankton-zooplankton model were consistent with observations in that ecosystems with increased phosphorus levels and reduced zooplankton growth rates experienced greater time lags between maxima in algal biomass and zooplankton production. Thus coherence between trophic levels is important in governing the flow of biomass through ecosystems and phase changes between trophic levels may contribute to eutrophication in aquatic ecosystems.
Key words: stoichiometry, eutrophication, trophic dynamics, aquatic ecology