Efficacy of acetic acid treatments in the management of marine biofouling

The expansion of artificial habitats and aquaculture activities in coastal environments has been accompanied by an increased demand for tools to mitigate the effects of biofouling pests. One approach is to manage anthropogenic pathways to prevent the spread of established pest organisms to uninfected localities that are beyond their natural dispersal capacity. This paper describes the efficacy of acetic acid treatments against a variety of cosmopolitan fouling taxa, and evaluates a potential application in the treatment of foulers transported with movements of shellfish seedstock between mussel fanning areas in New Zealand. Laboratory and field experiments demonstrated that immersion in 4% acetic acid (in seawater) for as little as 1 min can eliminate many soft-bodied fouling organisms, with lower concentrations requiring longer immersion times. The effects of immersion treatment were enhanced when combined with a 24-h air exposure phase to simulate the inter-regional transport of mussel seedstock. We demonstrate that it is possible to cost-effectively treat mussels to eliminate the majority of problematical foulers without resulting in significant adverse effects to the stock either by: (i) a 4% treatment followed by a rinse to remove the acetic acid residue before transport, or (ii) application of the 4% treatment at the end of the transport phase. A concentration of 4% is equivalent to the acetic acid content of domestic vinegar, hence does not represent a significant environmental or occupational risk provided appropriate measures are put in place for handling and waste disposal. Acetic acid concentrations remain stable over time in the presence of organic matter, but may change during repeated use of treatment solutions. To ensure treatment criteria are being achieved, field determination of acetic acid levels can be made using simple titration-based approaches. Because of an apparent buffering effect in the case of sequential shellfish seedstock immersion, pH could not be used to estimate acetic acid concentrations in this instance, but may provide a simple and reliable field-based indicator for other fouling treatments. Further work to refine the treatment method should seek to maximise the 'window' between pest mortality and mussel survival, to provide assurance that high-risk species can be eliminated with minimal risk of adverse effects on seedstock. Where treatments that are completely effective against all pest organisms result in unavoidable mussel mortality, decisions about whether or not to apply them must balance treatment costs and benefits against the unmanaged risks and consequences of pest incursion. (c) 2006 Elsevier B.V. All rights reserved.