Assessing the Vulnerability of Salt Marsh Habitats to Sea-Level Rise in California

Predicted sea-level rise (SLR) could have catastrophic impacts on the coastal zone. Salt marshes have evolved under low SLR, but their resilience to higher rates is uncertain. Assessing vulnerabilities of California’s salt marshes is a case study of the diversity and scale of problems that land managers will face. The major questions of this study were: 1) Are recent sediment budgets allowing southern California salt marshes to keep pace with SLR; 2) within its current range, how vulnerable are two sub-species of Ridgway’s rail (Rallus obsoletus; rails), a low elevation salt marsh specialist, to SLR; and 3) within its current range, how vulnerable are Belding’s savannah sparrows (Passerculus sandwichensis beldingi; sparrows), a high elevation salt marsh specialist, to SLR? To answer the first question, tidal creek sediment fluxes were measured in two sites with different levels of adjacent urbanization. To answer the second and third questions, original and pre-existing wildlife and habitat data were compiled at 17 sites to forecast habitat suitability. Storms and high tides led to sediment import in tidal creeks at Mugu and Seal. While sediment budgets were balanced during the dry study period, Seal’s elevation declined, and Mugu’s elevation plateaued, suggesting that only Mugu would persist if SLR rate stabilizes. For the Ridgway’s Rail study, under a SLR scenario of +166cm/100yr, suitable habitat for the San Francisco Bay Area’s (SF) sub-species will increase by 35% at mid-century, and current breeding habitat extent for Southern California’s (SC) sub-species will increase by 24%. However, by 2100, SF will lose 84% of suitable habitat and SC will lose 80% of its current habitat extent. Furthermore, six salt marshes will lose over 95% of suitable habitat. Under the same scenario, the current extent of Belding’s Savannah sparrow habitat will contract by 61% at mid-century before completely drowning by 2100. Results from the habitat suitability studies indicate that if no major adaptations, such as protecting the shoreline, increasing elevations, restoring marsh drainage, facilitating marsh migration, and restoring sediment delivery, are implemented soon, salt marsh-dependent wildlife in the majority of California coastal zones will be extirpated by 2100 under high SLR scenarios