Anthropogenic practices that facilitate species introductions need to be identified and modified to improve management and help control the spread of non-native taxa in many environments. In marine ecosystems, maintenance routines that remove dense epifaunal invertebrates attached to offshore oil platforms (cleaning) create a disturbance that may facilitate the establishment of non-native species.

We evaluated the effect of disturbance on the abundance (percent cover) of a non-native bryozoan, Watersipora subatra, on an offshore platform in the Santa Barbara Channel, U.S.A. by removing the existing epifaunal community in experimental plots and comparing Watersipora cover in these plots to that in undisturbed control plots. We explored the importance of larval supply and the existing epifaunal community in driving observed patterns using measurements of Watersipora larval availability and colony recruitment and growth in the disturbed and control plots. We also examined the effect of disturbance on Watersipora establishment at the larger, platform-scale with comparative surveys of cleaned and uncleaned portions of another platform before and after a maintenance cleaning. Both the disturbance experiment and the larger platform cleaning facilitated the establishment of Watersipora, with cover increasing from ∼5% -- to >50% at shallower (≤12m) depths, and these effects persisted for over a year. Larval availability was highly seasonal, and successful recruitment to disturbed areas was highest when disturbance coincided with recruitment season. One year after the experimental disturbance, sessile invertebrates occupied all available settlement space, reducing recruitment of Watersipora. Performance of Watersipora colonies was elevated in disturbed areas compared to undisturbed areas.

Anthropogenic disturbance that removed existing epifauna on offshore structures enabled the establishment of a non-native species. The timing of disturbance relative to the reproductive season of this species was an important driver of this pattern. Timing maintenance practices to occur after the reproductive period of Watersipora could allow adequate time for native species to recruit and occupy the available bare space, thereby reducing the potential for establishment of non-native species in the following season.