Encapsulation as a biosecurity tool for managing fouling on recreational vessels.
Hull fouling is a dominant vector in marine systems, with recreational vessels playing an important role in intra-regional transfer of biota. Encapsulation (i.e. the wrapping of a structure in plastic to deprive biota of oxygen and food, ultimately causing their death), offers promise as a tool for treating vessel fouling in situ. However, there is currently no standardised approach with detailed field application recommendations. In recognition of this gap this study aimed to: (1) use laboratory experiments to establish a timeframe for the effective encapsulation of yachts, (2) test this approach in the field and (3) consider the practicalities associated with implementing an encapsulation program. Laboratory experiments exposed the ascidian Ciona robusta, the mussel Semimytilus algosus and fouling communities to four treatments: aerated control in seawater, encapsulation in seawater, aerated seawater with 4% acetic acid and encapsulation in seawater with 4% acetic acid. All biota in acetic acid died in 24 hours regardless of encapsulation, while in encapsulated seawater mortality of all taxa occurred within three days. In the field four yachts and five pontoons with high (80–100%) and low (30–50%) fouling cover were encapsulated. It took more than three days to achieve mortality on all structures (pontoons high cover 3.7 days (±0.48 SD); pontoons low cover 3.8 days (±0.42 SD) and yachts 4.3 days (±0.5 SD)). The discrepancy between laboratory and field results likely reflects an unavoidably higher water to fouling biomass ratio in field systems. These results suggest that five days may be sufficient for successful encapsulation of yachts. However, in recognition of the limited sample size of yachts in this study, it is recommended that these findings be used as a basis for further developing region specific protocols through adaptive management. Logistical considerations around the implantation of national encapsulation programs are also discussed.