Environmental DNA (eDNA) has increasingly been used to detect rare species (e.g., newly introduced nonindigenous species) in both terrestrial and aquatic ecosystems, often with distinct advantages over traditional methods. However, whether water eDNA signals can be used to inform invasion risks remains debatable owing to inherent uncertainties associated with the methods used and the varying conditions among study systems. Here, we sampled eDNA from canals of the central route of the South-to-North Water Diversion Project (hereafter SNWDP) in China to investigate eDNA distribution and efficacy to inform invasion risks in a unique lotic system. We first conducted a total of 16 monthly surveys in this system (two sites in the source reservoir and four sites in the main canal) to test if eDNA could be applied to detect an invasive, biofouling bivalve, the golden mussel Limnoperna fortunei. Second, we initiated a one-time survey in a sub-canal of the SNWDP using refined sampling (12 sites in ~22 km canal) and considered a few environmental predictors. We found that detection of target eDNA in the main canal was achieved up to 1100 km from the putative source population but was restricted to the warmer months (May-November). Detection probability exhibited a significant positive relationship with average daily minimum air temperature and with water temperature, consistent with the expected spawning season. eDNA concentration in the main canal generally fluctuated across months and sites and was generally higher in warmer months. Golden mussel eDNA concentration in the sub-canal decreased significantly with distance from the source and with increasing water temperature and became almost undetectable at ~22 km distance. Given the enormity of the SNWDP, golden mussels may eventually expand their distribution in the main canal, with established "bridgehead" populations facilitating further spread. Our findings suggest an elevated invasion risk of golden mussels in the SNWDP in warm months, highlighting the critical period for spread and, possibly, management.
环境DNA(eDNA)已被越来越多地用于检测陆地和水生生态系统中的稀有物种(例如:新引入的外源物种)，相较于传统方法，其通常表现出明显优势。然而，由于所用方法固有的不确定性和不同研究系统的差异，水体eDNA信号是否可用于揭示入侵风险仍有争议。本研究中，我们从中国南水北调中线工程(以下简称南水北调工程)的渠道中提取eDNA样本，研究eDNA在这样一个独特的动水系统中的分布及其揭示入侵风险的效果。首先，我们在这一系统中进行了16次月度调查(涵盖源水库2个站点和干渠4个站点)，以测试eDNA是否可以用于检测入侵生物沼蛤Limnoperna fortunei，一种生物污损双壳贝类。其次，我们在干渠的一个支渠中，采用更加精细的取样方法(在约22公里的渠道中设置12个样点)，开展了一次考察多个环境因子的调查。我们发现，在距离假定源种群1100公里的干渠中可以检测到目标eDNA，但仅限于温暖的月份(5-11月)。目标eDNA的检出概率与日平均最低气温和水温呈显著正相关，这与预期的产卵季节一致。在支渠中，沼蛤eDNA浓度随着与源头的距离增加和水温的升高而明显下降，在约22公里处变得几乎无法检出。鉴于南水北调工程的巨大规模，沼蛤最终可能无法避免地扩张其在干渠的分布，已定殖的 “桥头堡 “种群会促进其进一步传播。我们的研究揭示了南水北调工程在温暖月份中升高的沼蛤入侵风险，凸显了其扩散和潜在管理的关键窗口期。.
Keywords: Limnoperna fortunei; biological invasions; early detection; invasion management; seasonal effect; temperature; water canal.
© 2023 The Ecological Society of America.