Data from: Habitat collapse due to overgrazing threatens turtle conservation in marine protected areas

Marine protected areas (MPAs) are key tools for combatting the global overexploitation of endangered species. The prevailing paradigm is that MPAs are beneficial in helping to restore ecosystems to more ‘natural’ conditions. However, MPAs may have unintended negative effects when increasing densities of protected species exert destructive effects on their habitat. Here, we report on severe seagrass degradation in a decade-old MPA where hyper-abundant green turtles adopted a previously undescribed below-ground foraging strategy. By digging for and consuming rhizomes and roots, turtles create abundant bare gaps, thereby enhancing erosion and reducing seagrass regrowth. A fully parametrized model reveals that the ecosystem is approaching a tipping point, where consumption overwhelms regrowth, which could potentially lead to complete collapse of the seagrass habitat. Seagrass recovery will not ensue unless turtle density is reduced to nearly zero, eliminating the MPA's value as a turtle reserve. Our results reveal an unrecognized, yet imminent threat to MPAs, as sea turtle densities are increasing at major nesting sites and the decline of seagrass habitat forces turtles to concentrate on the remaining meadows inside reserves. This emphasizes the need for policy and management approaches that consider the interactions of protected species with their habitat.海洋保护区（Marine protected areas, MPAs）是对抗全球濒危物种过度开发的核心工具。当前主流学术范式认为，海洋保护区有助于将生态系统恢复至更接近“自然”的状态。然而，当受保护物种的种群密度升高并对其栖息地造成破坏时，海洋保护区可能会产生非预期的负面效应。本文报道了一处已建成十年的海洋保护区内出现的严重海草退化现象：该区域内高密度绿海龟采用了此前未被记录的地下觅食策略。绿海龟通过挖掘并食用海草的根茎与根系，形成大面积裸露斑块，进而加剧海岸侵蚀并抑制海草再生。经全参数化模型分析显示，该生态系统正逼近临界点——海龟的摄食压力已超过海草的再生能力，这可能最终导致海草栖息地完全崩溃。除非将海龟种群密度降至近乎为零，否则海草将无法实现自然恢复，这将彻底消解该海洋保护区作为海龟庇护所的价值。本研究结果揭示了海洋保护区此前未被关注却迫在眉睫的威胁：主要海龟筑巢地的种群密度持续上升，而海草栖息地的衰退迫使海龟聚集于保护区内残存的海草床中。这凸显了需制定兼顾受保护物种与栖息地间相互作用的政策与管理方案的必要性。