An Overview of the Socio-Ecological System of Cays and Islets in the US Caribbean and Their Vulnerability to Climate Change

The offshore cays around the main islands of Puerto Rico, St. Thomas, St. John, and St. Croix are largely uninhabited and provide habitat for threatened, endangered, at-risk, and species of greatest conservation need including many resident and migratory species of seabirds, shorebirds, endemic reptiles, and plants. Management is limited by insufficient resources, capacity, and a mixture of ownership (federal, Commonwealth, Territorial, private NGO, and private), making regional planning a challenge. Invasive species are the dominant short- and long-term threats to these systems including invasive plants that alter habitat conditions and invasive mammals (e.g., mice, rats, goats) that kill native fauna and degrade habitats. Recreational and commercial uses by humans, as well as marine debris and accumulations from harmful algal blooms, pose a significant threat to crucial habitats and key conservation species, especially in the coastal zone. In the longer term, the cays ecosystems and fauna are expected to show high exposure and sensitivity with limited adaptive capacity, depending on the type of island, to the impacts of climate change. Current projections highlight substantially altered rainfall patterns and extensive drought, as well as extreme sea level rise (beyond 3 m by 2100 under the worst scenarios) and more frequent or intense hurricanes. The impacts of sea level and precipitation in particular were used to develop future scenarios to compare and contrast effects on focal species and coastal habitats. The scenarios and impacts were then used to suggest potential adaptation strategies.