Thousands of acres of land have been restored to tidal marsh in the San Francisco Bay and Delta (Bay-Delta) over the last two decades, often by breaching old dikes. Currently, several more large-scale, multiagency marsh restoration projects are planned or underway. Nevertheless, the extent to which dike breaching yields robust and diverse aquatic food webs remains unclear.
This study will compare samples from various restoration sites in the Bay-Delta, with a particular focus on their food webs. The samples, which were collected in 2019 and 2020, come from three paired sets of reference and restored sites. The structure of the food web at each site will be characterized using information gained from three stable isotopes: carbon (𝛿13C), which tells us whether plant eaters are consuming the aquatic or terrestrial vegetation, nitrogen (𝛿15N), which identifies whether an animal is a top predator or their prey, and finally, sulfur (𝛿34S), which differs in animal and plant tissues depending if they reside in freshwater or marine environments. The information gained from these isotopes is especially valuable in this study system, which spans a wide salinity gradient. These data will be modeled so that different hypotheses about food web structure can be analyzed. For example, to what extent are the differences attributed to variation in the amount of plants and other prey available, and what are the impacts of non-native species on native trophic niches?
By comparing tidal marsh food webs across multiple reference and restored sites along the salinity gradient, this study will help clarify what it means to successfully restore habitat for native fishes, a primary goal of tidal marsh restoration projects.