The ecosystem dynamics of benthic communities depend on the relative importance of organism reproductive traits, environmental factors, inter-specific interactions, and mortality processes. The fine-scale community ecology of sessile organisms can be investigated using spatial analyses because the position of the specimens on the substrate (their spatial positions) reflects the biological and ecological processes that they were subject to in-life. Consequently, spatial point process analyses (SPPA) and Bayesian network inference (BNI) can be used to reveal key insights into the ecological dynamics of these deep-sea communities. Here we use these analyses to investigate the ecology of deep-sea glass sponge dominated community “The Forest of the Weird” (2,442 m depth, Ridge Seamount, Johnston Atoll, Pacific Ocean). A 3D reconstruction was made of this community using photogrammetry of video stills taken from high-resolution ROV video. The community was dominated by two genera of Hexactinellids: Farreidae Aspidoscopulia sp. and Euplectellidae Advhena magnifica with octocorals Narella bowersi, Narella macrocalyx, and Rhodaniridogorgia also present in large proportions. SPPA of the dead vs. alive organisms revealed a random distribution of dead amongst the living, showing a non-density dependent cause of death for the majority of taxa. However, in the high-density ridge crest region there was non-random aggregation of dead specimens, revealing density-dependent mortality for Aspidoscopulia. SPPA showed that the glass sponges and octocorals were each most strongly influenced by different underlying processes, and reacted to the environmental conditions differently. The octocorals responded to higher density areas with increased intra-specific competition, whilst the glass-sponges seemed impervious to a doubling of specimen density. BNI found that mutual habitat associations between different taxa resulted in inter-specific competition at larger (2–4 m) spatial scales, with instances of competition at small-spatial scales (<0.75 m) in the higher-density ridge crest section. To our knowledge, this study is the first to analyze the mortality, population and community dynamics of a deep-sea sponge community using SPPA. Our results provide the first insight into the variety of ecological behaviors of these different glass sponges and octocorals, and show how these different organisms have developed diverse responses to the biological and environmental gradients within their habitat.

中文翻译：

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来自太平洋约翰斯顿环礁海脊海山的玻璃海绵主导社区“怪异森林”的死亡率、人口和社区动态

底栖群落的生态系统动态取决于生物体生殖特征、环境因素、种间相互作用和死亡过程的相对重要性。由于标本在基质上的位置（它们的空间位置）反映了它们在生活中所经历的生物和生态过程，因此可以使用空间分析来研究固着生物的精细尺度群落生态。因此，空间点过程分析 (SPPA) 和贝叶斯网络推理 (BNI) 可用于揭示对这些深海群落生态动态的关键见解。在这里，我们使用这些分析来调查深海玻璃海绵为主的群落“怪异森林”（2,442 m 深，海岭海山，约翰斯顿环礁，太平洋）的生态。使用从高分辨率 ROV 视频拍摄的视频静止图像的摄影测量法对该社区进行了 3D 重建。该群落主要由两个 Hexactinellids 属主导：Farreidae Aspidoscopulia sp。和 Euplectellidae Advhena magnifica 与八珊瑚 Narella bowersi、Narella macrocalyx 和 Rhodaniridogorgia 也大量存在。死生物与活生物的 SPPA 揭示了死在活生物中的随机分布，显示了大多数分类群的非密度依赖性死亡原因。然而，在高密度脊嵴区域有死标本的非随机聚集，揭示了 Aspidoscopulia 的密度依赖性死亡率。SPPA 表明，玻璃海绵和八珊瑚都受不同的潜在过程影响最大，并且对环境条件的反应不同。八珊瑚对高密度区域的反应增加了种内竞争，而玻璃海绵似乎不受样本密度加倍的影响。BNI 发现，不同分类群之间的相互栖息地关联导致了更大（2-4 m）空间尺度上的种间竞争，在高密度山脊顶部有小空间尺度（<0.75 m）的竞争实例。据我们所知，这项研究是首次使用 SPPA 分析深海海绵群落的死亡率、种群和群落动态。我们的研究结果首次洞察了这些不同玻璃海绵和八珊瑚的各种生态行为，