Human activities degrade and fragment coastal marine habitats, reducing their structural complexity and making habitat edges a prevalent seascape feature. Though habitat edges frequently are implicated in reduced faunal survival and biodiversity, results of experiments on edge effects have been inconsistent, calling for a mechanistic approach to the study of edges that explicitly includes indirect and interactive effects of habitat alteration at multiple scales across biogeographic gradients. We used an experimental network spanning 17 eelgrass (Zostera marina) sites across the Atlantic and Pacific oceans and the Mediterranean Sea to determine (1) if eelgrass edges consistently increase faunal predation risk, (2) whether edge effects on predation risk are altered by habitat degradation (shoot thinning), and (3) whether variation in the strength of edge effects among sites can be explained by biogeographical variability in covarying eelgrass habitat features. Contrary to expectations, at most sites, predation risk for tethered crustaceans (crabs or shrimps) was lower along patch edges than in patch interiors, regardless of the extent of habitat degradation. However, the extent to which edges reduced predation risk, compared to the patch interior, was correlated with the extent to which edges supported higher eelgrass structural complexity and prey biomass compared to patch interiors. This suggests an indirect component to edge effects in which the impact of edge proximity on predation risk is mediated by the effect of edges on other key biotic factors. Our results suggest that studies on edge effects should consider structural characteristics of patch edges, which may vary geographically, and multiple ways that humans degrade habitats.

中文翻译：

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斑块边缘和生境退化对广泛的海洋基础物种中动物捕食风险的共同影响

人类活动使沿海海洋生境退化并破碎，降低了其结构复杂性，并使生境边缘成为普遍的海景特征。尽管栖息地边缘经常牵涉到减少的动物生存和生物多样性，但边缘效应的实验结果却不一致，需要一种研究边缘的机械方法，该方法明确包括跨生物地理梯度的多个尺度上的栖息地变化的间接和交互作用。我们使用了一个跨越17个鳗el（Zostera marina的实验网络）遍及大西洋，太平洋和地中海的地点，以确定（1）鳗gra边缘是否持续增加动物捕食风险，（2）栖息地退化是否会改变边缘对捕食风险的影响（射击变稀），以及（3）是否地点之间边缘效应强度的变化可以通过变化的鳗草栖息地特征的生物地理变异性来解释。与预期相反，在大多数地点，不管栖息地退化的程度如何，沿斑块边缘的被束缚的甲壳类（蟹或虾）的捕食风险都比斑块内部的低。但是，与贴片内部相比，边缘降低捕食风险的程度与与贴片内部相比，边缘支持较高的鳗草结构复杂性和猎物生物量的程度相关。这表明边缘效应的间接成分，其中边缘接近度对捕食风险的影响由边缘对其他关键生物因子的影响介导。我们的结果表明，对边缘效应的研究应考虑斑块边缘的结构特征（可能会因地理位置而异）以及人类退化栖息地的多种方式。