Abstract
This paper reviews and highlights recent research findings on food web processes since an earlier review by Kimmerer et al. (2008). We conduct this review within a conceptual framework of the Delta–Suisun food web, which includes both temporal and spatial components. The temporal component of our framework is based on knowledge that the landscape has changed markedly from historical conditions. The spatial component of our framework acknowledges that the food web is not spatially static; it varies regionally and across habitat types within regions. The review highlights the idea of a changing baseline with respect to food web function. New research also indicates that interactions between habitat-specific food webs vary across the current landscape. For example, based on early work in the south Delta, the food web associated with submerged aquatic vegetation was thought to provide little support to species of concern; however, data from other regions of the estuary suggest that this conceptual model may not apply across the entire region. Habitat restoration has been proposed as a method of re-establishing historic food web processes to support species of concern. Benefits are likely for species that directly access such restored habitats, but are less clear for pelagic species. Several topics require attention to further improve the knowledge of food webs needed to support effective management, including: (1) synthesis of factors responsible for low pelagic biomass; (2) monitoring and research on effects of harmful algal blooms; (3) broadening the scope of long-term monitoring; (4) determining benefits of tidal wetland restoration to species of concern, including evaluations of interactions of habitat-specific food webs; and (5) interdisciplinary analysis and synthesis. The only certainty is that food webs will continue to change in response to the changes in the physical environment and new species invasions.
Highlights
The northern reaches of the San Francisco Estuary, including the Sacramento–San Joaquin Delta, Suisun Bay, and Suisun Marsh, have undergone substantial shifts over the last 150 years in configuration, hydrology, species composition, and the dominance of humans on the landscape (Nichols et al 1986; Whipple et al 2012)
From 1972 to 1980, the pelagic food web began changing for unknown reasons, as phytoplankton biomass and abundance of rotifers, E. affinis, and N. mercedis declined by greater than two-fold (Orsi and Mecum 1986, 1996; Kimmerer et al 1994; Kimmerer 2005)
As we have described in the previous sections, many factors have brought about the changes to the Delta food web
Summary
The northern reaches of the San Francisco Estuary (the estuary), including the Sacramento–San Joaquin Delta, Suisun Bay, and Suisun Marsh, have undergone substantial shifts over the last 150 years in configuration, hydrology, species composition, and the dominance of humans on the landscape (Nichols et al 1986; Whipple et al 2012). We start this review by presenting our conceptual framework of the Delta–Suisun food web, which includes both temporal and spatial components. We consider food web findings for different habitats and Delta–Suisun regions, using a twopart conceptual framework. We discuss the relevance of these findings for habitat management actions that have been proposed to increase food web support for species of concern (e.g., Herbold et al 2014). Our conceptual framework highlights food web differences among historical periods, habitats and geographic areas of the Delta–Suisun region. Understanding the history of ecological changes is important when actions intended to restore functions and services are considered (Lotze and Muir 2009; Lotze and Worm 2009), including food web functions.
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