WILL SEAWALLS DAMAGE CRITICAL HABITAT FOR ENDANGERED SPECIES IN HAWAII AS SEA LEVEL RISES?

The Northwestern Hawaiian Islands (NWHI) consist of low-lying atolls used by Neomonachus schauinslandi , the critically endangered Hawaiian monk seal, to bask and pup. Preserving habitat, which includes sandy shorelines of the Main Hawaiian Islands (MHI), is critical to protecting this species. Although migrating between the NWHI and the MHI is rare for monk seal populations today, this movement may become necessary if there is habitat loss among the low-lying sandy shoals of the NWHI due to sea level rise. Oʻahu, as a high volcanic island, has wide sandy coastal plains that provide enhanced potential for habitat preservation. However, narrowing and loss due to shoreline armoring threaten beaches in the MHI. Thus, modeling future beach vulnerability to armoring provides important data for developing species and resource management plans. We employ spatial analysis of monk seal critical habitat on Oʻahu to identify when and which beaches are most vulnerable to erosion. Using ArcGIS we model future erosion for 0, 0.15, 0.3, 0.6, and 0.92 meters sea level rise. Results show near-term sea level rise of 0.15 to 0.3 m triggering a cascade of seawall applications, risking sensitive beach resources. We conclude that current and near-term sea level rise, not future sea level rise, poses the greatest threat to critical habitat and therefore the greatest priority for management planning exists now.