Habitats as Surrogates of Taxonomic and Functional Fish Assemblages in Coral Reef Ecosystems: A Critical Analysis of Factors Driving Effectiveness

Species check-lists are helpful to establish Marine Protected Areas (MPAs) and protect local richness, endemicity, rarity, and biodiversity in general. However, such exhaustive taxonomic lists (i.e., true surrogate of biodiversity) require extensive and expensive censuses, and the use of estimator surrogates (e.g., habitats) is an appealing alternative. In truth, surrogate effectiveness appears from the literature highly variable both in marine and terrestrial ecosystems, making it difficult to provide practical recommendations for managers. Here, we evaluate how the biodiversity reference data set and its inherent bias can influence effectiveness. Specifically, we defined habitats by geomorphology, rugosity, and benthic cover and architecture criteria, and mapped them with satellite images for a New-Caledonian site. Fish taxonomic and functional lists were elaborated from Underwater Visual Censuses, stratified according to geomorphology and exposure. We then tested if MPA networks designed to maximize habitat richness, diversity and rarity could also effectively maximize fish richness, diversity, and rarity. Effectiveness appeared highly sensitive to the fish census design itself, in relation to the type of habitat map used and the scale of analysis. Spatial distribution of habitats (estimator surrogate’s distribution), quantity and location of fish census stations (target surrogate’s sampling), and random processes in the MPA design all affected effectiveness to the point that one small change in the data set could lead to opposite conclusions. We suggest that previous conclusions on surrogacy effectiveness, either positive or negative, marine or terrestrial, should be considered with caution, except in instances where very dense data sets were used without pseudo-replication. Although this does not rule out the validity of using surrogates of species lists for conservation planning, the critical joint examination of both target and estimator surrogates is needed for every case study.

物种名录（Species check-lists）在建立海洋保护区（Marine Protected Areas, MPAs）以及总体上保护本地物种丰富度、特有性、稀有性与生物多样性方面颇具助益。然而，这类详尽的分类学名录（即生物多样性的真实替代物）需开展大规模且成本高昂的普查，故而采用估算替代物（estimator surrogates，例如栖息地）便成为颇具吸引力的替代方案。事实上，现有文献表明，替代物的有效性在海洋与陆地生态系统中均存在极大差异，这使得难以向管理者提供普适性的实用建议。本研究旨在评估生物多样性参考数据集及其固有偏差会如何对替代物的有效性产生影响。具体而言，本研究依据地貌、粗糙度、底栖覆盖物与结构标准对栖息地进行界定，并通过卫星图像为新喀里多尼亚的一处研究区域绘制了栖息地分布图。研究基于水下视觉普查（Underwater Visual Censuses）构建了鱼类分类学与功能名录，并依据地貌与暴露程度对普查进行了分层设计。随后，本研究检验了以最大化栖息地丰富度、多样性与稀有性为目标设计的海洋保护区网络，是否同样能够有效提升鱼类的丰富度、多样性与稀有性。研究结果显示，替代物的有效性对鱼类普查设计本身极为敏感，这与所采用的栖息地地图类型以及分析尺度密切相关。栖息地的空间分布（即估算替代物的分布）、鱼类普查站点的数量与位置（即目标替代物的采样），以及海洋保护区设计中的随机过程，均会对替代物的有效性产生影响，其影响程度之深，足以令数据集的微小改动便得出截然相反的研究结论。本研究认为，此前有关替代物有效性（无论为正向或负向结论、针对海洋或陆地生态系统）的研究结论，均需谨慎对待，仅在使用极高密度数据集且未出现伪重复的场景下除外。尽管本研究并未否定利用物种名录替代物开展保护规划的合理性，但针对每一项案例研究，均需对目标替代物与估算替代物开展关键性的联合审查。