Data from: Habitat formation prevails over predation in influencing fouling communities

Coastal human-made structures, such as marinas and harbours, are expanding worldwide. Species assemblages described from these artificial habitats are novel relative to natural reefs, particularly in terms of the abundance of non-indigenous species (NIS). Although these fouling assemblages are clearly distinctive, the ecosystem functioning and species interactions taking place there are little understood. For instance, large predators may influence the fouling community development either directly (feeding on sessile fauna) or indirectly (feeding on small predators associated with these assemblages). In addition, by providing refuges, habitat complexity may modify the outcome of species interactions and the extent of biotic resistance (e.g. by increasing the abundance of niche-specific competitors and predators of NIS). Using experimental settlement panels deployed in the field for 2.5 months, we tested the influence of predation (i.e. caging experiment), artificial structural complexity (i.e. mimics of turf-forming species), and their interactions (i.e. refuge effects) on the development of sessile and mobile fauna in two marinas. In addition, we tested the role of biotic complexity – arising from the habitat-forming species that grew on the panels during the trial – on the richness and abundance of mobile fauna. The effect of predation and artificial habitat complexity was negligible, regardless of assemblage status (i.e. native, cryptogenic and non-indigenous). Conversely, habitat-forming species and associated epibionts, responsible for biotic complexity, had a significant effect on mobile invertebrates (richness, abundance and community structure). In particular, the richness and abundance of mobile NIS were positively affected by biotic complexity, with site-dependent relationships. Altogether, our results indicate that biotic complexity prevails over artificial habitat complexity in determining the distribution of mobile species under low predation pressure. Facilitation of native and non-native species thus seems to act upon diversity and community development: this process deserves further consideration in models of biotic resistance to invasion in urban marine habitats.

全球范围内，滨海人工构筑物（如游艇码头、海港）的建设规模持续扩张。相较于自然礁体，此类人工生境中记录的物种组合独具特色，尤其体现在非本土物种（non-indigenous species, NIS）的丰度特征上。尽管这些污损生物组合特征显著，但其中的生态系统功能与物种互作机制仍鲜为人知。
例如，大型捕食者可通过两种途径影响污损群落的发育：直接捕食固着动物（sessile fauna），或是通过捕食与该类组合共生的小型捕食者产生间接效应。此外，生境复杂度可通过提供庇护所，改变物种互作的结果与生物抵抗（biotic resistance）的强度——例如通过提升针对非本土物种的生境特化竞争者与捕食者的丰度。
本研究通过在野外部署时长为2.5个月的实验附着板，在两座游艇码头中开展了相关实验：探究捕食作用（即笼养实验）、人工结构复杂度（即垫状丛生物种模拟物）及其交互作用（即庇护效应）对固着与移动动物群落发育的影响；此外还检验了试验期间附着板上滋生的生境构建物种所形成的生物复杂度，对移动动物类群物种丰富度与丰度的调控作用。
无论物种组合属于本土种、隐存种（cryptogenic species）还是非本土种，捕食作用与人工生境复杂度的影响均微乎其微。
与之相反，构成生物复杂度的生境构建物种及其附生生物（epibionts），对移动无脊椎动物的物种丰富度、丰度及群落结构均产生了显著影响。具体而言，移动性非本土物种的丰富度与丰度随生物复杂度提升呈显著正相关，且该效应存在位点依赖性。
综合来看，本研究结果表明，在低捕食压力下，相较于人工生境复杂度，生物复杂度对移动物种分布格局的调控作用更为显著。
由此可见，本土与外来物种的促进作用似乎会作用于群落多样性与发育过程，这一机制在城市海洋生境的生物抵抗入侵模型中值得进一步探讨与完善。