Mesophotic coral ecosystems (MCEs; reefs 30–150 m depth) are poorly studied, with existing research heavily geographically biased away from the most species-rich reef regions. Yet, MCEs are of high interest because of their unique species and potential to act as refuges from the impacts of fishing. Using baited remote underwater video systems, we surveyed reef fish communities from 2 to 85 m depths throughout the Raja Ampat archipelago in West Papua, Indonesia—an area considered the heart of the Coral Triangle where coral reef biodiversity is greatest. We sought to provide the first assessment of fish communities across this depth gradient in the region and identify whether human population density and market access differently affected fish abundance based on depth. Here we show that—similar to shallow reefs—Raja Ampat MCEs are exceptionally diverse, with 152 fish species recorded at depths greater than 40 m. We found that fish community structures were highly depth driven, with declines in fish abundance at increased depth. In contrast to previous studies elsewhere in the world, we found that the proportion of planktivores declined across the shallow reef to MCE depth gradient. While greater human population density correlated with lower Epinephelidae and Lutjanidae abundance (two key fisheries families), we did not find evidence that MCEs provide a depth refuge from fishing. Surprisingly, we also found that fish abundance declined at greater distances from the major regional market—likely caused by historical fisheries pressure in more remote areas. These results both expand upon and contrast some previously established MCE-depth patterns and human impact patterns on fish communities, suggesting that regional context and historical pressures matters. Our findings highlight the need for future MCE studies within the Coral Triangle region.

中文翻译：

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西巴布亚拉贾安帕的高度多样化的中光礁鱼群落

中光珊瑚生态系统（MCE；30-150 m 深的珊瑚礁）的研究很少，现有的研究在地理上严重偏向于远离物种最丰富的珊瑚礁区域。然而，MCEs 因其独特的物种和作为免受捕鱼影响的避难所的潜力而备受关注。我们使用带诱饵的远程水下视频系统调查了印度尼西亚西巴布亚四王群岛的 2 至 85 m 深处的珊瑚礁鱼类群落，该地区被认为是珊瑚礁生物多样性最丰富的珊瑚三角区的中心。我们试图对该地区跨该深度梯度的鱼类群落进行首次评估，并确定人口密度和市场准入是否会根据深度对鱼类丰度产生不同的影响。在这里，我们表明——与浅礁相似——四王群岛 MCE 异常多样，在大于 40 m 的深度记录了 152 种鱼类。我们发现鱼类群落结构高度受深度驱动，随着深度增加，鱼类丰度下降。与世界其他地方以前的研究相比，我们发现浮游生物的比例在浅礁到 MCE 深度梯度下降。虽然较高的人口密度与较低的 Epinephelidae 和 Lutjanidae 丰度（两个主要渔业科）相关，但我们没有发现证据表明 MCE 提供了一个远离捕鱼的深度避难所。令人惊讶的是，我们还发现，在距主要区域市场较远的地方，鱼类丰度下降——这可能是由于更偏远地区的历史渔业压力造成的。这些结果既扩展又对比了一些先前建立的 MCE 深度模式和人类对鱼类群落的影响模式，表明区域背景和历史压力很重要。我们的研究结果强调了在珊瑚三角地区进行未来 MCE 研究的必要性。