Data from: A cross-scale trophic cascade from large predatory fish to algae in coastal ecosystems

Trophic cascades occur in many ecosystems, but the factors regulating them are still elusive. We suggest that an overlooked factor is that trophic interactions (TIs) are often scale-dependent and possibly interact across spatial scales. To explore the role of spatial scale for trophic cascades, and particularly the occurrence of cross-scale interactions (CSIs), we collected and analysed food-web data from 139 stations across 32 bays in the Baltic Sea. We found evidence of a four-level trophic cascade linking TIs across two spatial scales: at bay scale, piscivores (perch and pike) controlled mesopredators (three-spined stickleback), which in turn negatively affected epifaunal grazers. At station scale (within bays), grazers on average suppressed epiphytic algae, and indirectly benefitted habitat-forming vegetation. Moreover, the direction and strength of the grazer–algae relationship at station scale depended on the piscivore biomass at bay scale, indicating a cross-scale interaction effect, potentially caused by a shift in grazer assemblage composition. In summary, the trophic cascade from piscivores to algae appears to involve TIs that occur at, but also interact across, different spatial scales. Considering scale-dependence in general, and CSIs in particular, could therefore enhance our understanding of trophic cascades.营养级联（trophic cascades）广泛分布于各类生态系统中，但其调控机制迄今尚未明确。我们提出，一个长期被忽视的影响因素是：营养相互作用（trophic interactions, TIs）往往具有尺度依赖性，且可能在不同空间尺度间发生交互作用。为探究空间尺度对营养级联的影响，尤其是跨尺度相互作用（cross-scale interactions, CSIs）的发生规律，我们收集并分析了波罗的海32个海湾内共计139个采样点的食物网数据。 研究结果显示，存在一条四级营养级联，其关联的营养相互作用跨越两个空间尺度：在海湾尺度下，食鱼性鱼类（鲈鱼与白斑狗鱼）对中营养级捕食者（三刺棘鱼）产生调控作用，而后者又会对底表植食者造成负面影响。在海湾内部的采样点尺度上，植食者平均能够抑制附生藻类，并间接促进造境植被的生长。 此外，采样点尺度下植食者与藻类的关系方向与强度，会随海湾尺度的食鱼性鱼类生物量发生变化，这表明存在跨尺度交互效应，其潜在驱动机制可能是植食者类群组成发生了改变。 综上，从食鱼性鱼类到藻类的营养级联，其涉及的营养相互作用既存在于不同空间尺度之内，也在不同尺度间产生了交互影响。因此，在研究中充分考虑尺度依赖性，尤其是跨尺度相互作用，将有助于进一步深化我们对营养级联的理解。