Abstract
Sea-level rise (SLR) will produce unprecedented changes in tidal marsh systems that already cope with daily tidal perturbations, disturbances from storms, and salinity changes from droughts and runoff events. Additionally, negative impacts from non-native invasive species may alter marsh plants’ susceptibility to SLR stressors like inundation and salinity. Increasingly, tidal marsh communities must tolerate both changes in the physical environment from SLR and invasive species impacts. To assess the response of a threatened tidal marsh cordgrass (Spartina foliosa) to both stressors, we implemented a field experiment in San Francisco Bay, CA, USA, exposing cordgrass to a treatment that extended tidal inundation projected with SLR using a recently developed in situ method. At one of two field sites, we also enclosed the cordgrass with or without the invasive European green crab, Carcinus maenas. We found that cordgrass responded negatively to longer inundation, although these effects varied by site and year. In higher inundation treatments, cordgrass survival increased with increasing surface elevation of the plot. Cordgrass survival was lower in the presence of invasive crabs relative to controls. We did not find interacting effects of increased inundation and green crab presence on any response variables, which highlights the need to consider how latent or sequential effects of multiple stressors may affect ecosystems. This study demonstrates significant biological responses to invasive species and inundation. Evaluating relative effects and timing of multiple stressors, especially those induced by climate change and invasive species, will help us to manage threatened ecological communities in a changing world.