PSL Research University, EPHE-UPVD-CNRS, USR 3278 CRIOBE, 98729 Moorea, French Polynesia; PSL Université Paris: EPHE-UPVD-CNRS, USR 3278 CRIOBE, Université de Perpignan, 66860 Perpignan Cedex, France.
California Academy of Sciences, San Francisco, CA 94118, USA.
Sci Total Environ. 2022 Oct 20;844:157049. doi: 10.1016/j.scitotenv.2022.157049. Epub 2022 Jul 1.
The rapid decline of shallow coral reefs has increased the interest in the long-understudied mesophotic coral ecosystems (MCEs). However, MCEs are usually characterised by rather low to moderate scleractinian coral cover, with only a few descriptions of high coral cover at depth. Here, we explored eight islands across French Polynesia over a wide depth range (6 to 120 m) to identify coral cover hotspots at mesophotic depths and the co-occurrent biotic groups and abiotic factors that influence such high scleractinian cover. Using Bayesian modelling, we found that 20 out of 64 of studied deep sites exhibited a coral cover higher than expected in the mesophotic range (e.g. as high as 81.8 % at 40 m, 74.5 % at 60 m, 53 % at 90 m and 42 % at 120 m vs the average expected values based on the model of 31.2 % at 40 m, 22.8 % at 60 m, 14.6 % at 90 m and 9.8 % at 120 m). Omitting the collinear factors light-irradiance and depth, these 'hotspots' of coral cover corresponded to mesophotic sites and depths characterised by hard substrate, a steep to moderate slope, and the dominance of laminar corals. Our work unveils the presence of unexpectedly and unique high coral cover communities at mesophotic depths in French Polynesia, highlighting the importance of expanding the research on deeper depths for the potential relevance in the conservation management of tropical coral reefs.
浅水珊瑚礁的迅速减少增加了人们对长期研究不足的中光珊瑚生态系统 (MCE) 的兴趣。然而，MCE 通常以较低到中等的珊瑚覆盖率为特征，只有少数描述了在深度处具有高珊瑚覆盖率。在这里，我们在法属波利尼西亚的八个岛屿上进行了广泛的深度调查，以确定中光深度下的珊瑚覆盖率热点，以及影响这种高光珊瑚覆盖率的共生生物群体和非生物因素。使用贝叶斯模型，我们发现，在研究的 64 个深点中，有 20 个点的珊瑚覆盖率高于中光范围内的预期值（例如，在 40 米处高达 81.8%，在 60 米处高达 74.5%，在 90 米处高达 53%，在 120 米处高达 42%，而基于模型的平均预期值分别为 31.2%、22.8%、14.6%和 9.8%）。在排除光辐照度和深度这两个共线性因素后，这些珊瑚覆盖率的“热点”与中光区域以及具有硬底质、陡峭到中等坡度和层状珊瑚占主导地位的深度相对应。我们的工作揭示了在法属波利尼西亚的中光深度存在出乎意料且独特的高光珊瑚覆盖率群落，这突显了扩大对更深深度的研究的重要性，因为这可能与热带珊瑚礁的保护管理有关。
