Testing the efficacy of heated seawater for managing biofouling in ship’s sea chests

Biofouling within sea chests may be more important than ballast water and hull fouling for dispersing certain non-indigenous marine species (NIMS). Despite this current Australian guidelines remain costly, ineffective or may increase the biosecuirty risk of sea chests. This thesis tested the efficacy of a new heated seawater biofouling treatment technique on managing the biosecurity risks posed by sea chests. Chapter 2 provides a baseline assessment of time and temperature regimes required to achieve 100% mortality of secondary biofouling assemblages on Perspex settling plates placed in Port Kembla Harbour. Perspex plates were used because of relative ease to which fouling organism settle such artificial surfaces. Seawater heated to 40⁰C for 15 minutes was the minimum temperature and time required to achieve 100% biofouling mortality (F = 508.805, p \u3c 0.0001). Interestingly 30⁰C had no significant impact on organism mortality (F = 2.6, p = 0.115). In total 1619 organisms were quantified, Bryozoans were the most prevalent group making up over 57% (935) of organisms/colonies identified. Other taxa included polychaeta (648), cirripedia (12), bivalvia (4), ascidians (8) and porifera (12). These findings show that moderately elevated seawater temperatures (\u3e 40⁰C) are capable of treating 3 months of temperate marine biofouling. Future work might test temperatures between 30°C and 40°C determine minimum temperature and time regimes to achieve 100% biofouling mortality. Chapter 3 tests the efficacy of Hull Surface Treatment (HST), a new biofouling treatment technology, for treating secondary and tetiary biofouling within sea chests. A mock sea chest (1 x 1 x 0.75m) was constructed for the HST trials. As was shown in the trials from Chapter 2 treatments of 40⁰C for 15 minutes were enough to ensure 100% mortality of secondary biofouling within sea chests. 40⁰C treatments however, did not show any significant difference from control treatments for tertiary biofouling (f = 3.000, p = 0.114). Both 60 and 70⁰C treatments were observed to cause 100% tertiary biofouling mortality (f = 13.102, p \u3c 0.0001). These results show that HST is a viable option for treating the biosecuirty risks associated with biofouling within sea chests. Currently HST cannot treat other vessel niche areas (without diver intervention), as such HST should be used in association other antifouling and defouling measures and maritime regulatory practices. Future Studies should focus on larger sea chests and on tropical assemblages