Vulnerability of Key Sea Turtle Nesting Beaches to Future Erosion and Sea Level Rise

Abstract

Threatened sea turtles rely on sandy beaches for nesting, linking their long-term survival to global beach availability. However, beaches worldwide are increasingly threatened by anthropogenic stressors and sea level rise (SLR). Reliable vulnerability assessments require understanding beach dynamics across multiple time scales, informed by long-term coastal change records. While many nesting beaches lie in remote, data-poor environments, recent advances in coastal remote sensing now allow us to monitor coastal change worldwide. Here, we combine satellite-derived shorelines (CoastSat), shoreline modeling (CoSMoS-COAST), and global data sets to investigate shoreline evolution and future vulnerability at nine globally important sea turtle nesting sites. We investigate seasonal and long-term shoreline change, hindcast (1980–2024) and forecast (2025–2100) shoreline positions under various SLR scenarios, and quantify available accommodation space based on backbeach elevation and infrastructure footprints. We find that shoreline evolution and vulnerability vary considerably, with three sites showing historical accretion trends and four sites showing erosion. This demonstrates that the previously widely applied bathtub approach—adding SLR to a static beach profile—is not suitable to assess the vulnerability of sea turtle nesting beaches to erosion. Three eroding beaches emerge as particularly vulnerable due to projected shoreline retreat coupled with limited accommodation space. Despite significant uncertainties arising from long-term shoreline projections, our results provide important insights into seasonal and long-term morphodynamics, identify vulnerable nesting sites, and offer a comprehensive, transferable framework for assessing shoreline evolution and relative erosion vulnerability at other sites. Understanding these dynamics is crucial to inform conservation and management strategies to future-proof these critical nesting habitats.

Plain Language Summary
Sea turtles depend on sandy beaches for nesting, which means their survival is closely linked to how these beaches change over time. Today, many beaches are increasingly pressured by human activity and rising sea levels, putting turtle nesting habitats at risk. To better understand which beaches are most vulnerable, we used satellite images, computer models, and global data to study nine of the world's most important nesting sites. We looked at how the shoreline has moved since 1980, how it might change through 2100 under different sea level rise (SLR) scenarios, and how much space may remain for turtles to nest given local terrain and development. Our results show that some beaches are naturally building up while others are eroding, and that vulnerability is not the same everywhere. In particular, three beaches appear especially at risk because they are eroding and have little room for turtles to nest further inland. These findings highlight the importance of moving beyond simple “bathtub” estimates of SLR, and instead considering the complex, long-term behavior of beaches. This approach can help identify priority sites for conservation and guide strategies to protect sea turtle nesting habitats in a changing world.