Food Webs of the Delta, Suisun Bay, and Suisun Marsh: An Update on Current Understanding and Possibilities for Management

Abstract

This paper reviews and highlights recent research findings on food web processes since an earlier review by . We conduct this review within a conceptual framework of the DeltaSuisun 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.

Effects of Extreme Hydrologic Regimes on Juvenile Chinook Salmon Prey Resources and Diet Composition in a Large River Floodplain

“…Consequences of the Asian clam's invasion along with physicochemical drivers resulted in an ecological “regime shift” that is most pronounced in the SFE's low‐salinity zone (see Figure ; Brown et al. ). In addition, introduction of at least 10 non‐indigenous zooplankton species in the estuary after the Asian clam invasion resulted in a nearly complete change in species composition that further altered the food web (Brown et al.…”

“…In addition, introduction of at least 10 non‐indigenous zooplankton species in the estuary after the Asian clam invasion resulted in a nearly complete change in species composition that further altered the food web (Brown et al. ). These invasions extended to the tidal freshwater estuary, such as the Cache Slough complex and the Yolo Bypass, where several introduced copepod species are now abundant and often dominant (Kimmerer ).…”

“…Consequences of the Asian clam's invasion along with physicochemical drivers resulted in an ecological "regime shift" that is most pronounced in the SFE's low-salinity zone (see Figure 1; Brown et al 2016). In addition, introduction of at least 10 non-indigenous zooplankton species in the estuary after the Asian clam invasion resulted in a nearly complete change in species composition that further altered the food web (Brown et al 2016). These invasions extended to the tidal freshwater estuary, such as the Cache Slough complex and the Yolo Bypass, where several introduced copepod species are now abundant and often dominant (Kimmerer 2004).…”

Evidence of a Shift in the Littoral Fish Community of the Sacramento-San Joaquin Delta

“…Since 1987, phytoplankton biomass in the upper San Francisco Estuary declined substantially due to the invasion of the “overbite” clam Potamocorbula amurensis [62,63,64]. Further spread of submerged and floating aquatic macrophytes in recent years may have exacerbated the pelagic fish food deficiency by limiting light availability for phytoplankton in the Delta [65]. However, we note that Delta pelagic and littoral fish species possess fairly diverse life histories and as such, it is likely that the expansion of aquatic macrophytes is just one of several factors responsible for changes in fish biomass in pelagic and littoral habitats.…”

Factors and Processes Affecting Levee System Vulnerability

“…Since reclamation, agriculture and urban areas replaced the large expanse of approximately 365,000 acres of tidal freshwater emergent wetlands and over 1,600 km of associated tidal channels (Whipple et al 2012;Brown et al 2016, Figure 12). Interrelated changes included loss of ecological function; reduction in habitat extent and heterogeneity; loss of connectivity within and among habitat types; degradation of habitat quality; disconnection of habitats from sustaining physical processes; and invasive species (SFEI-ASC 2014).…”