Department of Biology, Coastal and Marine Institute, San Diego State University, 5500 Campanile Drive, San Diego, California, 92182, USA.
Tennenbaum Marine Observatories Network, Smithsonian Institution, Edgewater, Maryland, 20013-7012, USA.
Ecology. 2021 May;102(5):e03316. doi: 10.1002/ecy.3316. Epub 2021 Apr 8.
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.
人类活动会破坏和分割沿海海洋栖息地，降低其结构复杂性，使栖息地边缘成为常见的景观特征。尽管栖息地边缘经常与动物存活率和生物多样性降低有关，但有关边缘效应的实验结果并不一致，因此需要采用一种机制方法来研究边缘，这种方法明确包括在生物地理梯度上多个尺度上对栖息地进行改变的间接和交互影响。我们使用了一个横跨大西洋、太平洋和地中海的 17 个鳗草（Zostera marina）地点的实验网络，以确定：（1）鳗草边缘是否一致增加了动物捕食风险；（2）边缘对捕食风险的影响是否因栖息地退化（分枝变薄）而改变；（3）站点之间边缘效应强度的变化是否可以用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，与鳗草斑块内部相比，拴系甲壳类动物（螃蟹或虾类）的捕食风险在斑块边缘更低，无论栖息地退化的程度如何。然而，与斑块内部相比，边缘降低捕食风险的程度与边缘相对于斑块内部支持更高的鳗草结构复杂性和猎物生物量的程度相关。这表明边缘效应存在间接成分，边缘对捕食风险的影响是由边缘对其他关键生物因素的影响介导的。我们的研究结果表明，边缘效应的研究应考虑斑块边缘的结构特征，这些特征可能会因地理位置而异，以及人类破坏栖息地的多种方式。
