Impacts of invasive species and increased inundation on salt marsh plants in San Francisco Bay

Julie Gonzalez, Environmental Science & Policy, University of California, Davis, Davis, CA and Edwin Grosholz, Environmental Science and Policy, University of California, Davis, Davis, CA

Background/Question/Methods
Interspecific interactions determine the structure of marsh communities, and may change as salt marshes are exposed to novel stressors like sea-level rise and invasive species. Negative impacts from invasive species may alter marsh plants’ susceptibility to sea-level rise stressors like inundation and salinity. We used field experiments to examine how increased inundation from flooding or projected sea-level rise and invasive crabs impact marsh plants and physical factors associated with sediment structure and nutrient cycling in San Francisco Bay. We implemented an experiment where we caged the European green crab Carcinus maenas with the native cordgrass Spartina foliosa, and exposed crab treatments to increased inundation time in situ using experimental weirs that extended the period of immersion to simulate effects of rising sea levels.
Results/Conclusions
We found that increased inundation alone significantly decreases cordgrass shoot density relative to inundation controls. Crab treatments also negatively impacted shoot density, but these results were confounded by strong cage effects and crab burrowing. This work suggests that increased inundation will likely impact establishing cordgrass, but further work is necessary to disentangle the interacting impact of invasive crabs and inundation on S. foliosa growth and establishment. This and future work will increase our understanding of how effects of invasive species will interact with sea-level rise to impact important foundation species like salt marsh plants.