Vulnerability of sea turtle nesting sites to erosion and inundation: a decision support framework to maximize conservation

Sandy beaches provide essential nesting habitat for sea turtles but are threatened globally by a rapidly changing climate. Identifying which nesting sites are at greatest risk from erosion and inundation remains an important goal of sea turtle conservation globally. Yet, efforts to identify at-risk sites have been hindered by the ability to model complex processes and incomplete information on nesting distribution and abundance. To assess the erosion and inundation risk to the reproductive success of a discrete genetic stock of flatback turtles (Natator depressus) across its nesting range in the Pilbara region of Western Australia, we used the Integrated Valuation of Ecosystem Services and Trade-offs (InVEST) Coastal Vulnerability Model. A relative exposure index was calculated for 402 nesting beaches in terms of six geophysical variables: wind and wave exposure, surge potential, relief, observed sea level rise and coastal geomorphology, and coupled with published information on the distribution and abundance of turtle tracks in the region. The majority of beaches (74%) had an intermediate to high exposure. In particular, 36% of beaches with a high abundance of flatback tracks (the top 25% of the frequency distribution) had a high exposure (the top 25% of the frequency distribution). This suggests that coastal exposure is a key vulnerability to the reproductive success of sea turtles that nest in this region. Promisingly, five beaches with a high abundance of turtle tracks also had a low exposure (bottom 25% of the frequency distribution) and these beaches may be critical for the long-term resilience of the stock against sea level rise and severe storms. Exposure varied across nesting sites and the approach presented here allows for a rapid and broadscale assessment of relative erosion and inundation risks at a scale most relevant to management.

沙质海滩是海龟赖以生存的核心筑巢生境，却在全球范围内面临快速气候变化带来的威胁。明确哪些筑巢地最易遭受侵蚀与淹没，仍是全球海龟保护工作的核心目标之一。然而，此前的高危筑巢地识别工作始终受限：一方面难以对复杂海岸过程开展建模，另一方面筑巢分布与种群丰度的相关信息存在缺失。为评估西澳大利亚州皮尔巴拉地区离散遗传种群的平背海龟（Natator depressus）在其全部筑巢分布范围内，繁殖成功率所面临的侵蚀与淹没风险，本研究采用了生态系统服务与权衡综合评估（Integrated Valuation of Ecosystem Services and Trade-offs, InVEST）海岸脆弱性模型。研究针对该区域内的402处筑巢海滩，基于风浪暴露度、风暴潮潜能、地形起伏、实测海平面上升速率、海岸地貌共6项地球物理变量计算了相对暴露指数，并结合了已发表的该区域海龟筑巢足迹的分布与丰度数据。绝大多数海滩（74%）的暴露指数处于中等至高水平。具体而言，在平背海龟足迹丰度位列前25%的海滩中，有36%的海滩暴露指数同样处于最高的25%区间（即高暴露水平）。这表明海岸暴露程度是影响本区域筑巢海龟繁殖成功率的关键脆弱性因子。值得欣喜的是，共有5处海龟筑巢足迹丰度较高的海滩处于低暴露水平区间（即频率分布最低的25%），这些海滩对于该海龟种群抵御海平面上升与极端风暴的长期存续能力至关重要。不同筑巢地的暴露程度存在显著差异，本研究提出的评估方法可快速开展大范围相对侵蚀与淹没风险评估，其评估尺度与管理决策需求高度适配。