Turbid coral reefs experience high suspended sediment loads and low-light conditions that vertically compress the maximum depth of reef growth. Although vertical reef compression is hypothesized to further decrease available coral habitat as environmental conditions on reefs change, its causative processes have not been fully quantified. Here, we present a high-resolution time series of environmental parameters known to influence coral depth distribution (light, turbidity, sedimentation, currents) within reef crest (2–3 m) and reef slope (7 m) habitats on two turbid reefs in Singapore. Light levels on reef crests were low [mean daily light integral (DLI): 13.9 ± 5.6 and 6.4 ± 3.0 mol photons m–2 day–1 at Kusu and Hantu, respectively], and light differences between reefs were driven by a 2-fold increase in turbidity at Hantu (typically 10–50 mg l–1), despite its similar distance offshore. Light attenuation was rapid (KdPAR: 0.49–0.57 m–1) resulting in a shallow euphotic depth of <11 m, and daily fluctuations of up to 8 m. Remote sensing indicates a regional west-to-east gradient in light availability and turbidity across southern Singapore attributed to spatial variability in suspended sediment, chlorophyll-a and colored dissolved organic matter. Net sediment accumulation rates were ∼5% of gross rates on reefs (9.8–22.9 mg cm–2 day–1) due to the resuspension of sediment by tidal currents, which contribute to the ecological stability of reef crest coral communities. Lower current velocities on the reef slope deposit ∼4 kg m2 more silt annually, and result in high soft-sediment benthic cover. Our findings confirm that vertical reef compression is driven from the bottom-up, as the photic zone contracts and fine silt accumulates at depth, reducing available habitat for coral growth. Assuming no further declines in water quality, future sea level rise could decrease the depth distribution of these turbid reefs by a further 8–12%. This highlights the vulnerability of deeper coral communities on turbid reefs to the combined effects of both local anthropogenic inputs and climate-related impacts.

中文翻译：

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光限制和深度可变的沉积驱动了混浊珊瑚礁上的垂直珊瑚礁压缩

浑浊的珊瑚礁经历高悬浮沉积物负荷和低光照条件，垂直压缩珊瑚礁生长的最大深度。尽管随着珊瑚礁环境条件的变化，垂直珊瑚礁压缩被假设会进一步减少可用的珊瑚栖息地，但其因果过程尚未完全量化。在这里，我们展示了环境参数的高分辨率时间序列，这些参数已知会影响两个浑浊礁石上的礁顶（2-3 m）和礁坡（7 m）栖息地内的珊瑚深度分布（光、浊度、沉积、洋流）。新加坡。珊瑚礁顶部的光照水平很低 [平均日光积分 (DLI)：在 Kusu 和 Hantu，分别为 13.9 ± 5.6 和 6.4 ± 3.0 mol 光子 m–2 day–1]，尽管离岸距离相似，但汉图的浊度增加了 2 倍（通常为 10-50 mg l-1），导致了珊瑚礁之间的光照差异。光衰减很快（KdPAR：0.49-0.57 m-1），导致浅的透光深度 <11 m，每日波动高达 8 m。遥感表明，由于悬浮沉积物、叶绿素-a 和有色溶解有机物的空间变异性，新加坡南部的光照可用性和浊度存在区域性从西到东的梯度。由于潮汐对沉积物的再悬浮，珊瑚礁上的净沉积物积累率约为总沉积率的 5%（9.8-22.9 mg cm-2 天-1），这有助于珊瑚礁群落的生态稳定性。礁坡沉积物的较低流速每年增加约 4 kg m2 的淤泥，并导致高软沉积物底栖覆盖。我们的研究结果证实，垂直珊瑚礁压缩是自下而上的，因为光带收缩，细沙在深处积聚，减少了珊瑚生长的可用栖息地。假设水质没有进一步下降，未来海平面上升可能会使这些浑浊珊瑚礁的深度分布进一步减少 8-12%。这凸显了混浊礁上更深的珊瑚群落对当地人为输入和气候相关影响的综合影响的脆弱性。未来海平面上升可能会使这些浑浊礁石的深度分布进一步减少 8-12%。这凸显了混浊礁上更深的珊瑚群落对当地人为输入和气候相关影响的综合影响的脆弱性。未来海平面上升可能会使这些浑浊礁石的深度分布进一步减少 8-12%。这凸显了混浊礁上更深的珊瑚群落对当地人为输入和气候相关影响的综合影响的脆弱性。