Untangling Natural Seascape Variation from Marine Reserve Effects Using a Landscape Approach

Distinguishing management effects from the inherent variability in a system is a key consideration in assessing reserve efficacy. Here, we demonstrate how seascape heterogeneity, defined as the spatial configuration and composition of coral reef habitats, can mask our ability to discern reserve effects. We then test the application of a landscape approach, utilizing advances in benthic habitat mapping and GIS techniques, to quantify this heterogeneity and alleviate the confounding influence during reserve assessment. Seascape metrics were quantified at multiple spatial scales using a combination of spatial image analysis and in situ surveys at 87 patch reef sites in Glover's Reef Lagoon, Belize, within and outside a marine reserve enforced since 1998. Patch reef sites were then clustered into classes sharing similar seascape attributes using metrics that correlated significantly to observed variations in both fish and coral communities. When the efficacy of the marine reserve was assessed without including landscape attributes, no reserve effects were detected in the diversity and abundance of fish and coral communities, despite 10 years of management protection. However, grouping sites based on landscape attributes revealed significant reserve effects between site classes. Fish had higher total biomass (1.5×) and commercially important biomass (1.75×) inside the reserve and coral cover was 1.8 times greater inside the reserve, though direction and degree of response varied by seascape class. Our findings show that the application of a landscape classification approach vastly improves our ability to evaluate the efficacy of marine reserves by controlling for confounding effects of seascape heterogeneity and suggests that landscape heterogeneity should be considered in future reserve design.

区分系统内的固有变异性与管理措施的效应，是评估海洋保护区（marine reserve）效能的核心考量因素。本文首先论证了：海洋景观异质性（seascape heterogeneity）——定义为珊瑚礁生境的空间配置与组成——会掩盖我们识别保护区效应的能力。随后，我们测试了景观学方法的应用效果：借助底栖生境（benthic habitat）制图与地理信息系统（GIS）技术的最新进展，量化该异质性，以缓解保护区效能评估中的混杂影响。

研究以伯利兹格洛弗礁环礁（Glover's Reef Lagoon）内87个斑礁（patch reef）点位为对象，结合空间影像分析与实地调查（in situ surveys），在多个空间尺度上量化海洋景观指标；这些点位覆盖了自1998年起实施保护的海洋保护区内外区域。随后，基于与鱼类和珊瑚群落观测变异显著相关的指标，将斑礁点位聚类为具有相似海洋景观属性的类别。

若评估海洋保护区效能时未纳入景观属性，尽管已实施10年管理保护，仍未在鱼类与珊瑚群落的多样性和丰度中检测到保护区效应。但基于景观属性对点位进行分组后，则在不同点位类别间检测到了显著的保护区效应：保护区内鱼类的总生物量（为对照区的1.5倍）与具有商业价值的生物量（为对照区的1.75倍）均更高，珊瑚覆盖率也较对照区提升1.8倍；不过不同海洋景观类别的响应方向与程度存在差异。

本研究结果表明，通过控制海洋景观异质性带来的混杂影响，应用景观分类方法可大幅提升我们评估海洋保护区效能的能力；同时也提示，未来的保护区规划应当纳入景观异质性考量。