Freshwater megafauna, such as sturgeons, giant catfishes, river dolphins, hippopotami, crocodylians, large turtles, and giant salamanders, have experienced severe population declines and range contractions worldwide. Although there is an increasing number of studies investigating the causes of megafauna losses in fresh waters, little attention has been paid to synthesising the impacts of megafauna on the abiotic environment and other organisms in freshwater ecosystems, and hence the consequences of losing these species. This limited understanding may impede the development of policies and actions for their conservation and restoration. In this review, we synthesise how megafauna shape ecological processes in freshwater ecosystems and discuss their potential for enhancing ecosystem restoration. Through activities such as movement, burrowing, and dam and nest building, megafauna have a profound influence on the extent of water bodies, flow dynamics, and the physical structure of shorelines and substrata, increasing habitat heterogeneity. They enhance nutrient cycling within fresh waters, and cross‐ecosystem flows of material, through foraging and reproduction activities. Freshwater megafauna are highly connected to other freshwater organisms via direct consumption of species at different trophic levels, indirect trophic cascades, and through their influence on habitat structure. The literature documenting the ecological impacts of freshwater megafauna is not evenly distributed among species, regions, and types of ecological impacts, with a lack of quantitative evidence for large fish, crocodylians, and turtles in the Global South and their impacts on nutrient flows and food‐web structure. In addition, population decline, range contraction, and the loss of large individuals have reduced the extent and magnitude of megafaunal impacts in freshwater ecosystems, rendering a posteriori evaluation more difficult. We propose that reinstating freshwater megafauna populations holds the potential for restoring key ecological processes such as disturbances, trophic cascades, and species dispersal, which will, in turn, promote overall biodiversity and enhance nature's contributions to people. Challenges for restoration actions include the shifting baseline syndrome, potential human–megafauna competition for habitats and resources, damage to property, and risk to human life. The current lack of historical baselines for natural distributions and population sizes of freshwater megafauna, their life history, trophic interactions with other freshwater species, and interactions with humans necessitates further investigation. Addressing these knowledge gaps will improve our understanding of the ecological roles of freshwater megafauna and support their full potential for facilitating the development of effective conservation and restoration strategies to achieve the coexistence of humans and megafauna.

中文翻译：

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淡水巨型动物塑造生态系统并促进恢复

淡水巨型动物，如鲟鱼、巨型鲶鱼、河豚、河马、鳄鱼、大型海龟和大鲵，在全球范围内经历了严重的种群数量下降和活动范围缩小。尽管越来越多的研究调查淡水中巨型动物消失的原因，但很少有人关注综合巨型动物对淡水生态系统中非生物环境和其他生物的影响，以及失去这些物种的后果。这种有限的理解可能会阻碍其保护和恢复的政策和行动的制定。在这篇综述中，我们综合了巨型动物如何塑造淡水生态系统的生态过程，并讨论了它们增强生态系统恢复的潜力。通过运动、挖洞、筑坝和筑巢等活动，巨型动物对水体范围、水流动力学以及海岸线和地层的物理结构产生深远的影响，增加了栖息地的异质性。它们通过觅食和繁殖活动增强淡水内的养分循环以及跨生态系统的物质流动。淡水巨型动物与其他淡水生物密切相关通过不同营养级物种的直接消耗、间接营养级联及其对栖息地结构的影响。记录淡水巨型动物群的生态影响的文献在生态影响的物种、区域和类型之间分布并不均匀，缺乏关于南半球大型鱼类、鳄鱼和海龟及其对养分流和食物的影响的定量证据‐网络结构。此外，种群数量下降、活动范围缩小和大型个体的丧失降低了淡水生态系统中巨型动物影响的程度和程度，使得后验的评价比较困难。我们认为，恢复淡水巨型动物种群具有恢复干扰、营养级联和物种扩散等关键生态过程的潜力，这反过来又将促进整体生物多样性并增强自然对人类的贡献。恢复行动面临的挑战包括基线变化综合症、人类与巨型动物对栖息地和资源的潜在竞争、财产损失以及人类生命面临的风险。目前缺乏淡水巨型动物的自然分布和种群规模、它们的生活史、与其他淡水物种的营养相互作用以及与人类的相互作用的历史基线，因此需要进一步调查。解决这些知识差距将提高我们对淡水巨型动物的生态作用的理解，并支持它们充分发挥潜力，促进制定有效的保护和恢复战略，以实现人类与巨型动物的共存。