Depth gradients are known to drive patterns of adult and juvenile coral distribution, but the influence on early successional communities and subsequent interactions with coral larvae settlement are poorly understood. We studied how early successional communities changed across a 40 m depth gradient to test whether patterns of coral larvae settlement could be explained by changes in preferred settlement substrates. Light decreased 83-fold from 3 to 40 m, and coral settlement orientation switched from tile undersides at 3 and 8 m to tile topsides at 25 and 40 m as expected. Regardless of the reduction in light, community composition on the topsides of settlement tiles did not change across depths, being dominated by turf algae (49%), crustose coralline algae (CCA; 29%), and biofilmed tile (12%). In contrast, settlement tile undersides were dominated by coralline and fleshy algae at 3 m, transitioning to ascidians and bryozoans at 8 m and 25 m, and biofilmed tile (80%) at 40 m. Following multiple regression analysis from an initial 21 bio-physical variables ( R 2 = 0.34), the optimal reduced model for predicting coral settlement included just five variables and explained most of the variability ( R 2 = 0.29). CCA contributed an R 2 of 0.14 to the model and was positively correlated with Acroporidae settlement, biofilmed tile contributed an R 2 of 0.09 to the model and was negatively correlated with Acroporidae settlement, while the other predictors explained nominal model variance. As assessed using electivity indices, Acroporidae switched settlement preference from CCA at shallower depths to biofilmed tile in deeper environments. In addition to the influence of light on larval settlement behaviour as described in previous research, our results show that CCA also provide an important facilitator of coral settlement behaviour across depth gradients. However, as in shallow reefs environments, further work is required to elucidate whether changes occurring at a finer taxonomic resolution within the CCA community can help to further explain switches in coral larval settlement behaviour in light-limited environments.

中文翻译：

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深度梯度驱动早期演替群落组成和相关珊瑚幼虫沉降相互作用的变化

已知深度梯度会驱动成年和幼年珊瑚分布的模式，但对早期演替群落的影响以及随后与珊瑚幼虫定居点的相互作用知之甚少。我们研究了早期演替群落如何在 40 m 深度梯度上发生变化，以测试珊瑚幼虫的沉降模式是否可以通过首选沉降基质的变化来解释。光从 3 到 40 m 减少了 83 倍，珊瑚沉降方向从 3 和 8 m 的瓷砖底面切换到 25 和 40 m 的瓷砖顶面，正如预期的那样。不管光照减少，定居地砖上部的群落组成在深度上没有变化，主要是草皮藻类（49%）、壳珊瑚藻（CCA；29%）和生物膜瓷砖（12%）。相比之下，沉降瓦底面在 3 m 处以珊瑚和肉质藻类为主，在 8 m 和 25 m 处过渡到海鞘和苔藓动物，在 40 m 处过渡到生物膜瓦 (80%)。在对初始 21 个生物物理变量 (R 2 = 0.34) 进行多元回归分析后，预测珊瑚沉降的最佳简化模型仅包括五个变量并解释了大部分可变性 (R 2 = 0.29)。CCA 为模型贡献了 0.14 的 R 2 并与 Acroporidae 沉降正相关，生物膜瓷砖对模型贡献了 0.09 的 R 2 并与 Acroporidae 沉降负相关，而其他预测因子解释了名义模型方差。使用选择性指数进行评估时，Acroporidae 将定居偏好从较浅深度的 CCA 转换为较深环境中的生物膜瓷砖。除了先前研究中描述的光对幼虫沉降行为的影响之外，我们的结果表明，CCA 还提供了跨深度梯度的珊瑚沉降行为的重要促进因素。然而，与浅礁环境一样，需要进一步的工作来阐明在 CCA 社区内以更精细的分类学分辨率发生的变化是否有助于进一步解释光限制环境中珊瑚幼虫定居行为的转变。