DETERMINING THE VULNERABILITY OF MARINE HABITATS AT CUMBERLAND ISLAND NATIONAL SEASHORE TO CLIMATE CHANGE STRESSORS

Climate change, the varied effects of increasing global temperature and atmospheric carbon, is already affecting coasts and is anticipated to worsen in the coming century. Sea-level rise (SLR) and changes in ocean chemistry make coastal regions among the most threatened habitats. The National Park Service (NPS), managing almost 12,000 km of shoreline, has an urgent need to characterize and predict the effects of climate change for mitigation and management purposes. The goal of this project is to develop a methodology framework for assessing the vulnerability of marine habitats within NPS, beginning with a pilot project at Cumberland Island National Seashore (CUIS). This framework employs a vulnerability assessment (VA) approach in which vulnerability is the sum of exposure (the magnitude of the stressor), sensitivity (how strongly a system is affected by the stressor), and adaptive capacity (the potential to adjust in response to the stressor).

Four climate-change-related stressors were analyzed: SLR, temperature change, salinity change, and ocean acidification (OA). Within CUIS, the marine habitats of interest include subtidal and intertidal environments such as beach, salt marsh, shellfish beds, and tidal creeks. For each habitat-stressor combination, the exposure, sensitivity, and adaptive capacity were rated on a qualitative scale of low-medium-high.

Preliminary results show the most vulnerable marine habitat at CUIS to be high-fringing salt marsh (HFSM), a narrow and sporadic zone between the expansive low salt marsh and the uplands. Topography, environmental conditions, cultural resources, and the encroaching low salt marsh make the HFSM sensitive to SLR and salinity, as well as reduce its potential to adapt (i.e., migrate inland). The changes in salinity and sea level would likely reduce the overall suitability for the growth of HFSM species (i.e., Juncus roemerianus) as well as increase competition, particularly with the ubiquitous low marsh species Spartina alterniflora. Preliminary field analysis at the site shows S. alterniflora growing sporadically in the HFSM at many locations within CUIS. Of the four stressors, SLR is of the greatest concern, given the immediacy of the threat and its high potential to disrupt sensitive habitats.