Concerns on the environmental disruption and ecosystem degradation due to the biological invasions are growing, with far-reaching consequences for the resilience of recipient ecosystems. While numerous studies mostly emphasized the negative impacts of invasive species on native species at a single time point, there is a lack of knowledge whether and how the invasion impacts vary with time. Here, we provide an empirical study on stage-dependent invasive impacts in an intertidal seagrass habitat (Zostera japonica), which is undergoing invasion of an invasive cordgrass (Spartina. alterniflora). Combining results from field surveys and experiments suggested that, impacts of cordgrass on seedling establishment of native seagrass species shift from facilitation at the initial stage of invasion to inhibition at the later stage when the invasive cordgrass become densely vegetated, causing density-dependent effects. In addition, at the later stage, patch expansion of cordgrass triggered degradation of seagrass-dominant habitats, showing the remnant patches of seagrass-dominant habitat have a strong patch-size dependent effect, with an optimal patch size of ~8 m² and ~1.5 cm detritus to the establishment of seagrass seedlings. These stage-dependent effects strongly linked to water movement and sedimentation rate. Both of them are modified by the abundance of the invasive cordgrass and patch formation through transforming native seagrass habitat with invasion. Our findings highlight the importance of unraveling stage-dependent impacts for assessing the consequences of biological invasion on native ecosystems degradation.

对由于生物入侵而造成的环境破坏和生态系统退化的担忧日益增加，对受援生态系统的复原力产生了深远的影响。尽管许多研究都着重强调了入侵物种在单个时间点对本地物种的负面影响，但仍然缺乏关于入侵影响是否以及如何随时间变化的知识。在这里，我们提供了对潮间带海草生境（Zostera japonica）的阶段依赖性侵入性影响的实证研究，潮间带海草生境正在侵袭侵入性草丛（Spartina。alterniflora））。野外调查和实验的综合结果表明，草皮草对本地海草树种幼苗建立的影响从入侵初期的促进作用转变为后来的侵入性草丛变得茂密的植被的抑制作用，从而引起密度依赖性效应。此外，在后期阶段，草cord的斑块扩展引发了以海草为主的生境的退化，这表明残留的海草为主要生境的斑块具有强烈的斑块大小依赖性，最佳斑块大小约为8 m ²和约1.5厘米的碎屑，以建立海草幼苗。这些与阶段有关的影响与水的流动和沉降速率密切相关。通过侵袭性转化原生海草生境，入侵性草丛的丰富性和斑块的形成都改变了它们。我们的发现强调了揭示阶段依赖性影响对于评估生物入侵对原生生态系统退化的后果的重要性。