Isotopic Determination of Food Web Origins in Restoring and Ancient Estuarine Wetlands of the San Francisco Bay and Delta |
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Authors: | Emily R Howe Charles A Simenstad |
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Institution: | (1) School of Aquatic and Fishery Sciences, University of Washington, P.O. Box 355020, Seattle, WA 98195-5020, USA |
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Abstract: | We compared the extent to which ancient and restoring wetlands in three estuary regions of San Francisco Bay support estuarine
ecosystems through food web contributions. In comparison to mature marshes, we hypothesized that food webs of increasingly
younger restoration sites would display increased dependency upon allochthonous subsidies due to nominal internal production.
Using multiple stable isotopes (δ13C, δ15N, δ34S) in a mixing model, we traced links among primary producers and estuarine consumers. Results indicate that food webs of
estuarine marshes are heavily dependent upon autochthonous marsh materials (76 ± 17%), even within the youngest restoration
marshes (11 years). Nearly all sampled organisms relied upon autochthonous marsh materials, with the exception of Neomysis kadiakensis, a mysid shrimp, which derived the majority of its support from freshwater-produced phytoplankton. Marsh-derived organic
matter (OM) support was consistent both temporally throughout the year and spatially along the three estuary regions, but
evidence suggests that the specific type of OM supporting estuarine consumers depends on position along the estuarine gradient
and on seasonal shifts in freshwater flow. These results indicate that wetland restoration rapidly provides important contributions
to marsh consumers and potentially bolsters food web linkages in shallow-water ecosystems. |
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