1 Department of Biological Sciences, Macquarie University , Sydney, New South Wales 2109 , Australia.
2 Hawaii Institute of Marine Biology, University of Hawaii , Manoa, HI 96744 , USA.
Proc Biol Sci. 2019 Apr 24;286(1901):20190053. doi: 10.1098/rspb.2019.0053.
Marine reserves can effectively restore harvested populations, and 'mega-reserves' increasingly protect large tracts of ocean. However, no method exists of monitoring ecological responses at this large scale. Herbivory is a key mechanism structuring ecosystems, and this consumer-resource interaction's strength on coral reefs can indicate ecosystem health. We screened 1372, and measured features of 214, reefs throughout Australia's Great Barrier Reef using high-resolution satellite imagery, combined with remote underwater videography and assays on a subset, to quantify the prevalence, size and potential causes of 'grazing halos'. Halos are known to be seascape-scale footprints of herbivory and other ecological interactions. Here we show that these halo-like footprints are more prevalent in reserves, particularly older ones (approx. 40 years old), resulting in predictable changes to reef habitat at scales visible from space. While the direct mechanisms for this pattern are relatively clear, the indirect mechanisms remain untested. By combining remote sensing and behavioural ecology, our findings demonstrate that reserves can shape large-scale habitat structure by altering herbivores' functional importance, suggesting that reserves may have greater value in restoring ecosystems than previously appreciated. Additionally, our results show that we can now detect macro-patterns in reef species interactions using freely available satellite imagery. Low-cost, ecosystem-level observation tools will be critical as reserves increase in number and scope; further investigation into whether halos may help seems warranted. Significance statement: Marine reserves are a widely used tool to mitigate fishing impacts on marine ecosystems. Predicting reserves' large-scale effects on habitat structure and ecosystem functioning is a major challenge, however, because these effects unfold over longer and larger scales than most ecological studies. We use a unique approach merging remote sensing and behavioural ecology to detect ecosystem change within reserves in Australia's vast Great Barrier Reef. We find evidence of changes in reefs' algal habitat structure occurring over large spatial (thousands of kilometres) and temporal (40+ years) scales, demonstrating that reserves can alter herbivory and habitat structure in predictable ways. This approach demonstrates that we can now detect aspects of reefs' ecological responses to protection even in remote and inaccessible reefs globally.
海洋保护区可以有效地恢复已捕捞的种群，而“超级保护区”越来越多地保护大片海洋。然而，目前还没有监测这种大规模生态响应的方法。食草作用是构建生态系统的关键机制，这种消费者-资源相互作用在珊瑚礁上的强度可以指示生态系统的健康状况。我们使用高分辨率卫星图像，结合远程水下录像和对一部分的分析，对澳大利亚大堡礁的 1372 个和 214 个珊瑚礁进行了筛选，以量化“放牧光环”的流行程度、大小和潜在原因。光环被认为是食草作用和其他生态相互作用的景观尺度足迹。在这里，我们表明，这些类似光环的足迹在保护区中更为普遍，特别是在较老的保护区（约 40 年）中，这导致了从太空中可见的尺度上对珊瑚礁生境的可预测变化。虽然这种模式的直接机制相对清楚，但间接机制仍未经过测试。通过将遥感和行为生态学相结合，我们的研究结果表明，保护区可以通过改变食草动物的功能重要性来塑造大规模的生境结构，这表明保护区在恢复生态系统方面的价值可能比以前认识到的更大。此外，我们的研究结果表明，我们现在可以使用免费的卫星图像检测珊瑚物种相互作用的宏观模式。随着保护区数量和范围的增加，低成本、生态系统水平的观测工具将是至关重要的；进一步研究光环是否有助于保护区似乎是有必要的。
