Department of Biology, California State University, 18111 Nordhoff Street, Northridge, CA, 91330-8303, USA.
Department of Environment and Sustainability and Department of Geology, University at Buffalo, Buffalo, NY, 14260, USA.
Sci Rep. 2022 May 2;12(1):7106. doi: 10.1038/s41598-022-10478-4.
Declines in abundance of scleractinian corals on shallow Caribbean reefs have left many reefs dominated by forests of arborescent octocorals. The ecological mechanisms favoring their persistence require exploration. We quantified octocoral communities from 2014 to 2019 at two sites in St. John, US Virgin Islands, and evaluated their dynamics to assess whether portfolio effects might contribute to their resilience. Octocorals were identified to species, or species complexes, and their abundances and heights were measured, with height serving as a biomass proxy. Annual variation in abundance was asynchronous among species, except when they responded in similar ways to hurricanes in September 2017. Multivariate changes in octocoral communities, viewed in 2-dimensional ordinations, were similar between sites, but analyses based on density differed from those based on the biomass proxy. On the density scale, variation in the community composed of all octocoral species was indistinguishable from that quantified with subsets of 6-10 of the octocoral species at one of the two sites, identifying structural redundancy in the response of the community. Conservation of the relative colony size-frequency structure, combined with temporal changes in the species represented by the tallest colonies, suggests that portfolio effects and functional redundancy stabilize the vertical structure and canopy in these tropical octocoral forests.
加勒比海浅滩地区造礁石珊瑚数量的减少，使得许多珊瑚礁由树状柳珊瑚林主导。需要探索有利于它们持续存在的生态机制。我们从 2014 年到 2019 年在美属维尔京群岛圣约翰的两个地点量化了柳珊瑚群落，并评估了它们的动态，以评估投资组合效应是否有助于它们的恢复力。柳珊瑚被鉴定为物种或物种复合体，并测量了它们的丰度和高度，高度作为生物量的替代指标。物种之间的丰度年度变化不同步，除非它们对 2017 年 9 月的飓风以相似的方式做出反应。在二维排序中观察到的柳珊瑚群落的多变量变化在两个地点之间相似，但基于密度的分析与基于生物量替代指标的分析不同。在密度尺度上，所有柳珊瑚物种组成的群落的变化与在两个地点之一的 6-10 个柳珊瑚物种的子集进行量化的变化无法区分，这确定了群落响应中的结构冗余性。相对殖民地大小频率结构的保护，加上由最高殖民地代表的物种的时间变化，表明投资组合效应和功能冗余性稳定了这些热带柳珊瑚林的垂直结构和树冠。
