9520884 Carrick This research will examine the effect of upper food web configuration on pelagic ecosystem structure, carbon flow, and productivity in Castle Lake, California. This research builds on a whole lake food web manipulation, and augments the value and importance of a well-developed long term data set emphasizing biological and climatic determinants of primary productivity. In this project, food web configuration in Castle Lake will be manipulated by varying the stocking rates of rainbow trout. The manipulation will reduce rainbow trout, thus increasing the abundance of golden shiners, copepods, and micrograzers of bacteria. By measuring rates of microbial and primary production and assessing population and growth dynamics of metazoans and fish, this research will estimate patterns of production and carbon flow through the food web under different food web configurations. The response of the Castle Lake food web to trophic structure manipulation will be compared to concurrent dynamics in an unperturbed reference site, Cliff Lake. In addition to the whole lake manipulation, a series of meso- and microcosm experiments to address mechanisms determining food web structure will be conducted. This research will be summarized and synthesized within a quantitative simulation model. This quantitative framework will allow integration from investigations spanning a variety of spatial and temporal scales, and will allow interpretation of microbial and classic-based food web dynamics within the context of the long-term data record for the Castle Lake ecosystem.
