Biological invasions can have manifold effects on native biota, including impacts on species interactions in invaded ecosystems. Among those are effects on parasite-host interactions, for example in cases where invaders serve as a new host for native parasites, leading to an amplification of the parasite population which may ultimately result in increased infection levels in the original native hosts (parasite spillback). In this study, we investigated the potential spillback of the native shell-boring polychaete Polydora ciliata from invasive Pacific oysters (Crassostrea (Magallana) gigas) to native mussels (Mytilus edulis) in the Dutch Wadden Sea. A field survey in the intertidal revealed that the majority of P. ciliata can nowadays be found in the shells of live but also dead Pacific oysters and much less in shells of other potential host species: mussels and periwinkles (Littorina littorea). Using a unique historical shell collection based on long-term sampling programmes in the intertidal and subtidal of the western Dutch Wadden Sea, we compared P. ciliata infections in mussels before and after the invasion of the Pacific oyster by means of x-ray scans. Both for the intertidal and subtidal, we did not detect differences in prevalence of P. ciliata in mussels between pre- and post-invasion periods. This suggests that the invasion of the Pacific oyster may not have caused a strong spillback to mussels regarding P. ciliata and thus the invasion probably had little indirect infection-mediated effects on the condition and fitness of native mussels. Instead, the acquisition of native P. ciliata by the invasive oysters suggests that they may themselves be affected by the new infections and this may warrant further research.

生物入侵会对本地生物群产生多种影响，包括对入侵生态系统中物种相互作用的影响。其中包括对寄生虫-宿主相互作用的影响，例如在入侵者作为本地寄生虫的新宿主的情况下，导致寄生虫种群扩大，最终可能导致原始本地宿主的感染水平增加（寄生虫溢出） . 在这项研究中，我们调查了来自侵入性太平洋牡蛎（Crassostrea (Magallana) gigas）的原生贝壳多毛类Polydora ciliata向荷兰瓦登海的原生贻贝（Mytilus edulis）的潜在回溢。在潮间带进行的实地调查显示，大多数P. cilata现在可以在活的和死的太平洋牡蛎的壳中找到，而在其他潜在宿主物种的壳中则更少：贻贝和长春花（Littorina littorea）。我们使用基于荷兰瓦登海西部潮间带和潮下带长期采样计划的独特历史贝壳收集，通过 X 射线扫描比较了太平洋牡蛎入侵之前和之后贻贝中的纤毛虫感染。对于潮间带和潮下带，我们没有检测到入侵前和入侵后贻贝中纤毛虫流行率的差异。这表明太平洋牡蛎的入侵可能没有对P. ciliata造成对贻贝的强烈回溢因此，入侵可能对本地贻贝的状况和适应性几乎没有间接感染介导的影响。相反，侵入性牡蛎获得的原生P. cilata表明它们本身可能受到新感染的影响，这可能需要进一步研究。