Encapsulating yachts to manage the transfer of marine alien species
Thesis (MSc)--Stellenbosch University, 2019.
ENGLISH ABSTRACT: In marine systems, the introduction and spread of alien species occurs predominantly through shipping, with hull fouling a dominant vector. Vessel fouling is primarily managed through the application of antifouling paints. However, the most effective of these paints, those containing TBT, were banned in the early 2000s and no equally effective alternative has become commercially available. This study looked at the potential use of encapsulation, the wrapping of a structure in plastic to deprive fouling organisms of oxygen and food to ultimately cause their death, as a tool for managing hull fouling, with the aim of reducing the biosecurity risk posed by fouling on recreational yachts. The aims of this study were to: (1) assess encapsulation under laboratory conditions to determine a timeframe for encapsulation of yachts in the field, (2) test this timeframe in the field, and (3) provide guidelines for implementation of a national encapsulation programme. In the laboratory, ascidians, mussels and fouling communities were exposed to four treatments: an aerated control in seawater, encapsulation in seawater, aerated seawater with a 4% acetic acid solution and encapsulation in seawater with a 4% acetic acid solution. All organisms and communities in acetic acid died in 24 hours regardless of encapsulation, while in encapsulated seawater, mortality of all taxa occurred within three days. Due to the implications of disposing of acetic acid in the field, this treatment was not considered in the field experiments. An encapsulation berth was constructed and four yachts were encapsulated in the field before a storm destroyed the berth. Walkway pontoons were then encapsulated as proxies for yachts, providing an opportunity to consider the effect of high (80-100%) and low (30-50%) fouling cover on encapsulation. On average, yachts required 4.25 (± 0.5 SD) days for fouling biota to reach total mortality, while pontoons with high and low fouling cover required 3.7 (± 0.48 SD) days and 3.8 (± 0.42 SD) days respectively. Field tests showed that the three days suggested by laboratory experiments was not sufficient in the field. This likely reflects an unavoidable higher ratio of water to fouling biomass in encapsulation systems in the field. A national encapsulation program could be useful for addressing the biosecurity risk posed by foreign yachts entering South African waters. It is recommended that vessels be treated for five days at their port of entry. This could be aligned with customs processes that are already in place. Importantly, mortality of fouling biota should be confirmed before removal of the encapsulation system. It is concluded that the application of an evidence-based management approach will support continual improvement of this emerging technique, and under these circumstances, encapsulation has the potential to considerably reduce the biosecurity risk posed by yachts visiting South African harbours.
AFRIKAANSE OPSOMMING: Geen opsomming