Abstract Artificial structures can provide suitable space for invasive species through a colonisable surface and refuge against predators. Besides several physical factors, invasive species can present different colonization success and dominance on structures that are connected to the sea floor (i.e. fixed) compared to structures that are suspended, depending on the differential predation pressure that affect both structures. Benthic and nektonic predators can reach fouling communities on fixed structures, while only nektonic predators can affect communities growing on suspended structures, depending on the distance to the sea floor. Only few studies tested both communities of predators at the same time in different artificial structures. In this study, we evaluated the effect of benthic and nektonic predators on the cover, composition and diversity on fouling communities and on the dominance of invasive ascidians on these communities, in two different types of artificial structures. We performed an experiment in the port area of Puerto Madryn (Southwestern Atlantic, Argentina) to compare the fouling community development between fixed and suspended structures and among different predator exclusion treatments. Results showed that benthic predators exerted a higher predation pressure than nektonic predators on the cover, composition and diversity of the fouling communities. In the absence of benthic predators, and even where nektonic predators were not excluded, communities were greatly dominated by two invasive ascidians, Ascidiella aspersa (Muller, 1776) and Ciona robusta Hoshino and Tokioka, 1967. Our results suggest that in this type of cold temperate ports, fouling organisms find refuge from benthic predators growing on suspended structures, where nektonic predators exert low predation pressure. We propose that, since benthic predators in temperate latitudes have an essential role decreasing invasive ascidians dominance and the cover of fouling communities, future studies should consider both predator communities, i.e. nektonic and benthic, in experimental designs performed to test biotic resistance and predation pressure.

中文翻译：

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入侵海鞘：掠食者如何减少它们在寒冷温带地区人工结构中的主导地位

摘要 人工结构可以通过可殖民的表面和避难所来为入侵物种提供合适的空间来抵御捕食者。除了几个物理因素之外，入侵物种可以在连接到海底（即固定）的结构上与悬挂的结构相比呈现不同的殖民成功和优势，这取决于影响两个结构的不同的捕食压力。底栖和游动捕食者可以到达固定结构上的污染群落，而只有游动捕食者才能影响在悬浮结构上生长的群落，具体取决于与海底的距离。只有少数研究同时在不同的人造结构中测试了两个捕食者群落。在这项研究中，我们评估了底栖和游动捕食者对覆盖物的影响，在两种不同类型的人工结构中，污染群落的组成和多样性以及侵入性海鞘在这些群落上的优势。我们在马德林港（阿根廷西南大西洋）港区进行了一项实验，以比较固定和悬浮结构之间以及不同捕食者排除处理之间的污垢群落发展。结果表明，底栖捕食者在污损群落的覆盖、组成和多样性方面比游动捕食者施加更高的捕食压力。在没有底栖捕食者的情况下，即使不排除游动捕食者，群落也主要由两种入侵海鞘，Ascidiella aspersa (Muller, 1776) 和 Ciona Robusta Hoshino 和 Tokioka，1967 年主导。我们的结果表明，在这种类型的寒冷中温带港口，污损生物找到栖息在悬浮结构上的底栖捕食者的避难所，在那里，游动捕食者施加的捕食压力很低。我们建议，由于温带地区的底栖捕食者在减少侵入性海鞘优势和污染群落的覆盖方面发挥着重要作用，未来的研究应该在为测试生物抗性和捕食压力而进行的实验设计中考虑捕食者群落，即浮游群落和底栖生物群落。