Estuary Food Web

San Francisco Estuary Food Web Dynamics

The Dugdale & Wilkerson Labs work together to use long-term data sets of nitrogen and carbon uptake rates by phytoplankton coupled with computer models to understand the San Francisco Estuary (SFE) ecosystem’s nutrient processes and productivity of phytoplankton, the base of the Estuary’s food web. Numerous SFE fish species are listed as threatened or endangered and management agencies are under legal pressure to take steps to protect these species from extinction, often by controlling fresh water flows, to enhance planktonic food. Dugdale and Wilkerson have applied a computer model in the SFE to assess consequences of flow actions on the ecosystem. This model can also be used to predict the likely outcomes of planned flow actions on the ecosystem. Another current project involves measuring productivity before and after a sewage treatment upgrade on the Sacramento River that will drastically alter the nutrient forms and concentrations entering the North Delta.

Dr. Michelle Jungbluth applies molecular methods to study lower trophic level food web interactions in the SFE. Results of her work provide information about valuable prey items in the larval fish diet that we did not know about previously, as well as indicate whether different areas of the Estuary provide different food resources to the fishes. Dr. Jungbluth has found that DNA sequencing gives a higher resolution view of the fish diets; there are many interesting prey items that we were not able to see with standard gut dissection-based diet analysis; and some DNA in the diet suggests different life history strategies for the larval longfin smelt and Pacific herring.

The Kimmerer Lab studies the zooplankton, especially copepods, of the SFE. They study zooplankton from their lives in an estuary where investigations are more practicable than in the open ocean; and learn about estuaries from the life histories and behaviors of these abundant organisms. To study zooplankton requires attention to dynamics of their physical environment such as transport processes and mixing, their food (phytoplankton, microzooplankton) and their predators (fish, macroinvertebrates). We have discovered the mechanisms by which copepods are able to remain in the estuary despite the net seaward flow of water; found regional variation in growth rates of copepods; and showed that both food limitation and losses to water diversions from the estuary are important contributors to the decline of the endangered delta smelt.