Sea level rise, drought and the decline of Spartina patens in New England marshes

- Climate change impacts on S. patens were examined in a growth experiment.
- Changes in S. patens distribution were monitored in coastal marshes (2000-2014).
- High inundation reduced S. patens growth and persistence.
- Short-term drought conditions in a laboratory setting had no detectable effects on S. patens.
- Conservation of flood-intolerant marsh taxa should focus on landward migration.

Already heavily impacted by coastal development, estuarine vegetated habitats (seagrasses, salt marshes, and mangroves) are increasingly affected by climate change via accelerated sea level rise, changes in the frequency and intensity of precipitation and storms, and warmer ocean temperatures. Conservation of these sensitive and vulnerable habitats requires the recognition of climate change effects so environmental managers can develop and apply appropriate intervention and adaptation strategies where possible. Here we focus on Spartina patens (saltmeadow cordgrass), a foundation species of New England (USA) coastal marshes. A growing body of evidence suggests this species is disappearing rapidly from wetlands in the region, leading to reductions in habitat quality, plant diversity, carbon sequestration, erosion resistance and coastal protection. We grew S. patens under five inundation and three precipitation regimes, monitored changes in its extent within two Southern New England coastal marshes (2000-2014), and used water level and precipitation data to detect changes in environmental conditions affecting these marshes. Our results suggest that current inundation patterns have reduced the persistence of S. patens, while short-term drought did not appear responsible for vegetation changes or habitat conversion. We conclude that accelerated sea level rise is incompatible with the long-term survival of S. patens within the current landscape footprint of Southern New England's coastal wetlands. We suggest that conservation actions focused on high marsh preservation concentrate on facilitating the process of marsh migration onto uplands by prioritizing buffer conservation, conducting barrier removal and allowing for retreat where feasible.