Here, we utilise a unique, 70-year-long (1949–2017), high-resolution historical aerial imagery dataset to track changes to coral reef structures in Bill’s Bay on the Ningaloo coast. Reef habitat was distinguished from sand and rubble substrates based on imagery greyscale values and autoclassified using unsupervised image analysis in ArcMap. This approach was validated through comparison of reef structure (defined by bathymetric LiDAR imagery), greyscale values of aerial photography taken during the same survey, and in-water ground-truthed photographs. Long-term (1990–2015) live coral cover data were then compared with changes in reef structure. Reef structure increased from 11 to 38% within Bill’s Bay between 1949 and 1990. A coral spawn-induced hypoxia event in 1989 caused a loss of live coral cover from 50 to 7%, a 25% reduction in reef structure by 2002, and a switch from branching to massive coral-dominated reef. From 2002, reef structure recovered and continued to expand, peaking at 41% of total area (2017). Live coral cover in 2015 (46%) matches this measured increase in reef structure, despite a drop in coral cover in 2008. Discrepancies observed between live coral cover and reef structure during the 2002–2010 period reflect the persistence of the massive dominated coral community and in situ dead reef framework. Across the entire study period, reef growth was most prominent along the south-western edge of the bay, possibly due to an increase in the availability of hard substrate for coral recruitment. This study provides new insights into reef health over decadal timescales by capturing changes in reef geomorphology that go beyond the spatial scale and scope of traditional in-water assessments. These data further highlight that coral reef structure in Bill’s Bay has expanded even with frequent natural disturbances affecting the region over the last 70 years.

中文翻译：

---

通过高分辨率的多年代航图对珊瑚礁结构进行长期（70 年）监测

在这里，我们利用一个独特的、长达 70 年（1949-2017）的高分辨率历史航拍图像数据集来跟踪宁格鲁海岸比尔湾珊瑚礁结构的变化。基于图像灰度值将珊瑚礁栖息地与沙子和碎石基质区分开来，并使用 ArcMap 中的无监督图像分析进行自动分类。通过比较珊瑚礁结构（由测深 LiDAR 图像定义）、同一调查期间拍摄的航空摄影灰度值和水中地面真实照片，验证了该方法。然后将长期（1990-2015）活珊瑚覆盖数据与珊瑚礁结构的变化进行比较。1949 年至 1990 年间，比尔湾内的珊瑚礁结构从 11% 增加到 38%。 1989 年珊瑚产卵引起的缺氧事件导致活珊瑚覆盖率从 50% 增加到 7%，到 2002 年珊瑚礁结构减少了 25%，并且从分支珊瑚礁转变为以珊瑚为主的大型珊瑚礁。从 2002 年开始，珊瑚礁结构恢复并继续扩大，达到总面积的 41%（2017 年）。尽管 2008 年珊瑚覆盖率有所下降，但 2015 年的活珊瑚覆盖率 (46%) 与珊瑚礁结构的增加相匹配。 2002-2010 年期间观察到的活珊瑚覆盖率和珊瑚礁结构之间的差异反映了大规模占主导地位的珊瑚群落的持续和原位死礁框架。在整个研究期间，海湾西南边缘的珊瑚礁生长最为突出，这可能是由于增加了用于珊瑚补充的硬质基质的可用性。这项研究通过捕捉超出传统水下评估空间尺度和范围的珊瑚礁地貌变化，为十年时间尺度的珊瑚礁健康提供了新的见解。这些数据进一步突出表明，即使在过去 70 年里，该地区受到频繁的自然干扰，比尔湾的珊瑚礁结构仍在扩大。