Biological invasions are occurring at increasing rates since the onset of the twentieth century. While ports and marinas have been identified as a major point-of-entry for the spread of marine non-indigenous species (NIS), their relationships with wild habitats however needs further scrutiny. We had the rare opportunity to monitor the real-time colonization dynamics of a newly-built marina by the notorious invasive kelp Undaria pinnatifida in the Bay-of-Morlaix, Brittany (France). Field surveys (> 20,000 individuals geo-localized) were combined with genetic analyses (10 microsatellite loci, N = 890 individuals) over 3 years (i.e., 6 generations in the study area). Regarding the colonization dynamics, a dramatic snow-ball effect was documented over time, with local density reaching up to 50 individuals per m after 2 years. Assignment tests showed that the primary colonizers came from neighboring populations established in natural rocky reefs. A shift towards a self-sustaining population was however observed the following year, with 44% of self-assignment. These processes are best explained by (i) life history traits, notably rapid growth and selfing, and (ii) natural dispersal within the marina combined with human-mediated dispersal—through leisure boating- over longer distances. Spill-over effects have been previously documented, and here also reported, to explain the expansion of U. pinnatifida from marinas to the wild. We showed that the on-going ocean sprawl also offers a perfect arena for spill-back events (i.e., spread from natural habitats to artificial structures), highlighting the need for careful surveillance of newly built infrastructures.

中文翻译：

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自我保护后发生的溢出事件解释了臭名昭著的入侵性海藻对新建成的码头的快速殖民

自二十世纪初以来，生物入侵的发生率正在上升。虽然港口和码头已经被确定为海洋非本地物种（NIS）传播的主要切入点，但是它们与野生生境的关系仍需进一步审查。我们难得有机会通过臭名昭著的侵入性海带Undaria pinnatifida来监视新建码头的实时殖民动态在法国布列塔尼的莫莱湾。在三年（即研究区域的第6代）中，将现场调查（> 20,000个人进行了地理定位）与遗传分析（10个微卫星基因座，N = 890个人）相结合。关于定植动力学，随着时间的推移，记录到了戏剧性的雪球效应，两年后局部密度达到每m多达50个人。分配测试表明，主要的殖民者来自天然岩石礁中建立的邻近种群。然而，第二年观察到向自给自足人口的转变，占自我分配的44％。这些过程可以用（i）生命历史特征，尤其是快速的成长和自交，以及（ii）码头内的自然分散与人类介导的分散（通过休闲划船）在更长的距离上得到最好的解释。裙带菜从码头到野外。我们表明，持续的海洋蔓延还为溢流事件（即从自然栖息地扩散到人工结构）提供了一个完美的舞台，强调需要仔细监视新建基础设施。