This project describes long-term zooplankton trajectories in the San Francisco Bay-Delta, in terms of the amount of carbon available for higher trophic levels. Findings are of relevance to understanding whether shortages in zooplankton populations, or shifts in their community structure, may be at least partially to blame for the region’s pelagic organism decline. To date, the Delta Science Fellow reports that several non-native copepod and mysid species appear to have been introduced between 1987 and 1994—a period of prolonged drought. These species seem to have displaced the larger local calanoid and rotifer species. The sudden drop in fish populations in 2000 did not coincide with a similar decrease in the quantity of carbon from zooplankton. In the last year of the project, the fellow will be investigating the effects of the species composition of zooplankton on the quality of food for fishes.