Declines in habitat structural complexity have marked ecological outcomes, as currently observed in many of the world's ecosystems. Coral reefs have provided a model for such changes in marine ecosystems; still our understanding has been centered on corals and fishes at broad spatial scales when metazoan diversity on coral reefs is dominated by small cryptic taxa (herein: “cryptofauna”). Given the paucity of studies and high taxonomic complexity of the cryptofauna, both of which limit a priori hypotheses, we asked whether hierarchical structuring theory provides a compelling framework to impose order and quantify patterns. In general terms, we explored whether cryptic communities are sufficiently described by broad seascape parameters or limited by a set of processes operating at their distinctly nested microhabitat scale. To address this theory and gaps in knowledge for the cryptofauna, we characterized community structure in coral rubble, an eroded coral condition where biodiversity proliferates. Rubble was sampled along a depth and exposure gradient at Heron Island on the Great Barrier Reef, Australia, to parameterize environmental and morphological indicators of sessile taxa and motile cryptofauna communities. We used a hierarchical study framework from microhabitat to seascape scales, which were evaluated using nonstructured multivariate analyses and Bayesian structural equation modeling. While the nonstructured analyses showed the effects of seascape on the cryptobenthos and its community, this approach overlooked the finer hierarchical patterns in rubble ecology revealed only in the structured model. Seascape parameters (exposure and depth) influenced microhabitat complexity (i.e., rubble branchiness), which determined the cover of sessile organisms on rubble pieces, which shaped the motile cryptofauna community. Rubble is likely to be increasingly prevalent on coral reefs in the Anthropocene and is typically associated with low seascape-level complexity and reduced macrofaunal richness. Parallel with hierarchical structuring theory, we showed a similar response operating at the microhabitat scale whereby low rubble complexity (i.e., branchiness) reduced cryptobenthic structure, diversity and size spectra. In a future ocean, we expect there may be an initial increase in biodiversity and trophodynamic processes derived from branching rubble, but a delay in ecosystem-scale outcomes if coral, and thus rubble, generation and complexity is not sustained.

中文翻译：

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珊瑚礁隐秘生物多样性的层次驱动因素

正如目前在世界许多生态系统中观察到的那样，栖息地结构复杂性的下降已带来显着的生态后果。珊瑚礁为海洋生态系统的这种变化提供了一个模型；当珊瑚礁上的后生动物多样性以小型隐秘类群（本文：“隐秘动物群”）为主时，我们的理解仍然集中在广泛空间尺度上的珊瑚和鱼类。鉴于研究的缺乏和加密动物分类学的高度复杂性，这两者都限制了先验假设，我们询问层次结构理论是否提供了一个令人信服的框架来强加秩序和量化模式。一般来说，我们探讨了隐秘群落是否可以通过广泛的海景参数来充分描述，或者是否受到一组在其明显嵌套的微生境规模下运行的过程的限制。为了解决这一理论和加密动物知识的空白，我们描述了珊瑚碎石中的群落结构，这是一种生物多样性激增的受侵蚀的珊瑚条件。在澳大利亚大堡礁赫伦岛沿深度和暴露梯度对碎石进行了采样，以参数化固着类群和活动的隐动物群落的环境和形态指标。我们使用了从微生境到海景尺度的分层研究框架，并使用非结构化多元分析和贝叶斯结构方程模型对其进行了评估。虽然非结构化分析显示了海景对隐底栖动物及其群落的影响，但这种方法忽略了仅在结构化模型中揭示的碎石生态学中更精细的层次模式。海景参数（暴露度和深度）影响微生境复杂性（即碎石分支），这决定了碎石碎片上固着生物的覆盖，从而形成了能动的隐动物群落。在人类世，碎石在珊瑚礁上可能越来越普遍，通常与海景复杂度低和大型动物丰富度降低有关。与层次结构理论并行，我们在微生境尺度上表现出类似的反应，即低碎石复杂性（即分支度）减少了隐底栖结构、多样性和尺寸范围。在未来的海洋中，我们预计，由于分支碎石而产生的生物多样性和营养动力学过程可能会出现初步增加，但如果珊瑚和碎石，生态系统规模的结果会出现延迟。