Predators regulate communities through top‐down control in many ecosystems. Because most studies of top‐down control last less than a year and focus on only a subset of the community, they may miss predator effects that manifest at longer timescales or across whole food webs. In southeastern US salt marshes, short‐term and small‐scale experiments indicate that nektonic predators (e.g., blue crab, fish, terrapins) facilitate the foundational grass, Spartina alterniflora, by consuming herbivorous snails and crabs. To test both how nekton affect marsh processes when the entire animal community is present, and how prior results scale over time, we conducted a 3‐year nekton exclusion experiment in a Georgia salt marsh using replicated 19.6 m2 plots. Our nekton exclusions increased densities of plant‐grazing snails and juvenile deposit‐feeding fiddler crab and, in Year 2, reduced predation on tethered juvenile snails, indicating that nektonic predators control these key macroinvertebrates. However, in Year 3, densities of mesopredatory benthic mud crabs increased threefold in nekton exclusions, erasing the tethered snails' predation refuge. Nekton exclusion had no effect on Spartina biomass, likely because the observed mesopredator release suppressed grazing snail densities and elevated densities of fiddler crabs, whose burrowing alleviates soil stresses. Structural equation modeling supported the hypotheses that nektonic predators and mesopredators control invertebrate communities, with nektonic predators having stronger total effects on Spartina than mud crabs by controlling densities of species that both suppress (grazers) and facilitate (fiddler crabs) plant growth. These findings highlight that salt marshes can be resilient to multiyear reductions in nektonic predators if mesopredators are present and that multiple pathways of trophic control manifest in different ways over time to mediate community dynamics. These results highlight that larger scale and longer‐term experiments can illuminate community dynamics not previously understood, even in well‐studied ecosystems such as salt marshes.

中文翻译：

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Meopredator 释放缓和了佐治亚州盐沼中植物生物量的营养控制


在许多生态系统中，捕食者通过自上而下的控制来调节群落。由于大多数关于自上而下控制的研究持续不到一年，并且只关注群落的一个子集，因此他们可能会错过在较长时间尺度上或在整个食物网中表现出的捕食者效应。在美国东南部的盐沼中，短期和小规模实验表明，坏死捕食者（例如蓝蟹、鱼、水龟）通过食用食草性蜗牛和螃蟹来促进基础草 Spartina alterniflora。为了测试当整个动物群落存在时 nekton 如何影响沼泽过程，以及之前的结果如何随着时间的推移而扩展，我们使用复制的 3 m2 图在佐治亚州盐沼进行了一项为期 19.6 年的 nekton 排除实验。我们的 nekton 排除增加了植物放牧蜗牛和幼年存款喂养招潮蟹的密度，并且在第 2 年，减少了对拴系幼年蜗牛的捕食，这表明 nektonic 捕食者控制了这些关键的大型无脊椎动物。然而，在第 3 年，中层底栖泥蟹的密度在 nekton 排除中增加了三倍，消除了拴系蜗牛的捕食避难所。Nekton 排除对 Spartina 生物量没有影响，可能是因为观察到的 mesopredator 释放抑制了放牧蜗牛的密度和招潮蟹的密度增加，它们的穴居缓解了土壤压力。结构方程模型支持坏死捕食者和中生捕食者控制无脊椎动物群落的假设，坏死捕食者通过控制既抑制（食草动物）又促进（招潮蟹）植物生长的物种密度，对 Spartina 的总体影响比泥蟹强。 这些发现强调，如果存在中间捕食者，盐沼可以适应 nektonic 捕食者的多年减少，并且随着时间的推移，营养控制的多种途径以不同的方式表现出来，以介导群落动态。这些结果强调，更大规模和更长期的实验可以阐明以前不了解的群落动态，即使在盐沼等经过充分研究的生态系统中也是如此。