Ecology of Selected Tidal Wetlands of the San Francisco Estuary

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Researachers study differences of tidal marsh restoration efforts throughout Bay-Delta ecosystem.

The CALFED Science Program funded a multi-party effort that worked from 2003-2005 to collect field data at six wetland sites spanning the estuarine salinity gradient from the western Delta to the North Bay. The project sought to address the question of how tidal marsh restoration efforts through the bay and delta affect ecosystem processes at different scales. The project, known as IRWM (Integrated Regional Wetlands Monitoring) consisted of seven teams' physical processes, landscape ecology, birds, plants, fish and invertebrates, primary production, and data management. Participants included Wetlands and Water Resources (Siegel), PRBO Conservation Science (Nur, Stralberg), San Francisco State University (Parker, Vasey, Bollens, Dugdale, Wilkerson, Carpenter), University of San Francisco (Callaway), UC Berkeley (Kelly), SFEI (Collins, May), University of Washington (Simenstad). Data collection took place mainly through 2004 and 2005. Study sites were west Delta/Suisun (tidal portion of Sherman Island, Browns Island), Napa River (Pond 2A, Coon Island, Bull Island), and Petaluma River (Carl's Marsh). The project web site is housed at SFEI and is available at The web site contains a public side and a login side that contains extensive project materials and data.

Aerial overview of locations of tidal wetlands sampled

Aerial overview of locations of tidal wetlands sampled. (Public domain.)

The original IRWM budget was centered around data collection with the intent to move on and develop integrative analytical papers and monitoring methodologies. It operated with two separate contracts, one for physical processes, landscape ecology, birds, plants, and data management and the second for fish and productivity. The CALFED Ecosystem Restoration Program did provide some additional funds for further papers that were centered around landscape ecology, birds, and plants; however, only two papers have been published relating to the aquatic ecology aspects of the IRWM effort. Emily Howe published a paper from her thesis under Si Simenstad on a mussel translocation experiment designed to identify energy (food) sources to benthic invertebrates using stable isotopes (Howe and Simenstad 2007). Sahrye Cohen published a paper from her thesis under Steve Bollens on diet content of Mississippi silversides and yellowfin gobies at the Napa River marshes (Cohen and Bollens 2008). A third paper has been under preparation for some time but has not been submitted to a journal; Bollens and his lead field staff Darren Gewant are describing the fish communities found at each study site. Thus, the larger integrative objective of understanding overall ecosystem function across a range of marsh types remains unaddressed.

The overall goal of this project is to address the question of how tidal marsh restoration efforts through the bay and delta affect ecosystem processes at different scales with an emphasis on the aquatic habitat and benefits of wetlands to fishes. Some more specific questions include:

  • What life stages of each fish species utilize each of the wetlands studied? What does this tell us about how tidal wetlands are being used by fishes for spawning, rearing, feeding or escaping from predation or unfavorably environmental conditions?
  • What specific types of resources produced within tidal marshes are being utilized by fishes either directly as food or indirectly, such as supporting production of food resources used by fishes? We will consider all types of data collected by the program including sources of primary production and abundances of phytoplankton, zooplankton, epibenthic and benthic invertebrates, terrestrial insects, and small fishes.
  • What do the answers to the previous questions imply about the value of tidal wetlands to various fish populations across the range of wetlands studied?

All data for this study has already been gathered and is available from a data repository maintained by the San Francisco Estuary Institute. The original Principal Investigators agreed that all data gathered by IRWM would be made available for public use by a fixed deadline, which has been exceeded. Therefore, all data being utilized are considered public data. The first step for this project will be downloading all appropriate data from the repository and preparing files for data analysis. Data analysis and integration of results will take the following approach.

The first step will be developing an understanding of the ecology of each wetland individually. Environmental and species data will be summarized for each wetland. Patterns in species composition for each taxa group (e.g., phytoplankton, benthic invertebrates, fish) will be analyzed with ordination techniques, primarily nonmetric multidimensional scaling. Patterns of abundance of individual taxa and in species composition will be correlated with environmental conditions to develop an understanding of the environmental factors affecting ecosystem structure. We will develop simple conceptual models of energy flow within each wetland (i.e., food webs). Links in the models will be determined from IRWM data whenever possible and from the scientific literature when no IRWM data are available.

The second step will be to compare and contrast the results from individual wetlands across the range of tidal wetlands studied by IRWM. Because the IRWM project selected wetlands along a salinity gradient, we expect to see differences in species composition based on salinity tolerances; however, other physical parameters collected will also be evaluated. The more critical comparisons will involve comparisons of energy flow through the wetlands and the types of fishes that would benefit. For example, if the model for a wetland highlights terrestrial insects as an important energy input, then fishes, such as juvenile salmon, may be able to derive substantial benefit from that type of wetland.