Pressurized seawater as an antifouling treatment against the colonial tunicates Botrylloides violaceus and Botryllus schlosseri in mussel aquaculture

The development of effective mitigation techniques against Botryllus schlosseri and Botrylloides violaceus colonizing blue mussel aquaculture operations has not been well studied. The objectives of our research were to determine the efficacy of using pressurized seawater in the mitigation of colonial tunicate fouling and to identify optimal treatment timing and frequencies in reducing tunicate biomass. Treatment trials using high- (similar to 700 psi) and low-pressure (similar to 40 psi) seawater spraying were conducted in St. Peters Bay and Savage Harbour, PEI, from May to November 2009. The use of high-pressure seawater was an effective anti-fouling measure for these species, causing significant reductions in tunicate biomass. In contrast, low-pressure seawater had no discernable effect. The timing of treatment was found to be the most important factor affecting efficacy, with reductions in tunicate biomass increasing in magnitude the closer the treatment occurred to harvest. Treatment frequency did not affect tunicate biomass. In addition, fewer treatments also resulted in less nuisance mussel spat fouling the mussel socks. Colonial tunicate fouling did not affect adult mussel growth and productivity, and no evidence of smothering or crop loss was observed.