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.

沙质海滩是海龟至关重要的筑巢栖息地，但在全球范围内正面临快速变化的气候带来的威胁。明确哪些筑巢地面临最严重的侵蚀与淹没风险，仍是全球海龟保护工作的重要目标之一。然而，当前对风险筑巢地的识别工作却受限于复杂过程建模能力不足，以及筑巢分布与种群丰度相关信息的不完备。为评估西澳大利亚州皮尔巴拉地区内，某一离散遗传种群的平背龟（Natator depressus）在其整个筑巢范围内的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（InVEST）海岸脆弱性模型。研究针对该区域内的402处筑巢海滩，基于风与波浪暴露、风暴潮潜势、地形起伏、实测海平面上升以及海岸地貌这六项地球物理变量，计算了相对暴露指数，并结合了该区域已发表的海龟爬行痕迹分布与丰度数据。其中74%的海滩处于中等至高暴露水平。尤为值得注意的是，在平背龟爬行痕迹丰度较高（处于频率分布前25%区间）的海滩中，有36%的海滩处于高暴露水平（同样处于频率分布前25%区间）。这表明海岸暴露水平是影响本区域筑巢海龟繁殖成功率的关键脆弱性因素。值得欣喜的是，有5处爬行痕迹丰度较高的海滩处于低暴露水平（处于频率分布后25%区间），这些海滩或许对该遗传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。不同筑巢地的暴露水平存在差异，本研究提出的方法能够以与管理实践高度适配的尺度，快速开展大范围的侵蚀与淹没相对风险评估。