The Nature, Extent and Survivorship of Biofouling Organisms at Different Hull Locations on Various Vessel Types

The importance of vessel biofouling as a vector for the dispersal of non-indigenousmarine species (NIMS) is only just beginning to receive international attention. At thetime of commencing this study, there was a considerable lack of knowledge surroundingwhich vessels, hull locations, levels and types of biofouling pose the greatestbiosecurity risk. Therefore, the aim of this study was to investigate the nature, extentand survivorship of biofouling organisms on various vessel types at different hulllocations and offers a pragmatic risk assessment approach for managing this threat.

The results of this thesis found that the recruitment, persistence, distribution, abundanceand species composition of biofouling on vessel hulls is influenced by many factorsincluding: 1) the presence/absence, age and type of anti-fouling coating; 2) voyageduration and route; and 3) port residency period. Therefore, higher levels of biofouling(species richness, percentage cover, and biomass), including NIMS are more likely toaccumulate and persist on vessels (and in hull locations) that: 1) lack and/or possess old,ineffective, damaged, inappropriate or unsuitable anti-fouling coatings; 2) spendprolonged periods stationary in ports; 3) travel at slow speeds (i.e. <10 knots); 4) haveshort voyage durations; and 5) remain at similar latitudes.

Prevention is clearly better than a cure, hence the correct application and maintenanceof suitable anti-fouling coatings to the entire submerged hull surface of vessel hulls,including niche areas is the most cost-effective way of minimising the unwantedtranslocation of biofouling organisms and NIMS. However, the results of this thesisdemonstrate that if biofouling organisms colonise and establish on a vessel's hull,voyage speed alone is not capable of providing a reliable secondary level of defenceagainst the unwanted dispersal of NIMS. Clearly, the survivorship of biofoulingorganisms was highest amongst vessels that travelled at slow and medium speeds (e.g.

<10 knots). Therefore, given that accumulation of biofouling follows a successionalprocess and NIMS are more likely to be associated with higher levels of biofouling,vessels that travel at slow and medium speeds are more likely to pose the greatest riskof translocating NIMS on a vessel by vessel scale. However, despite the observationthat faster vessels reduce the diversity, quantity and quality of sessile biofoulingorganisms in laminar flow areas of the hull, a wide range of sessile, sedentary andmobile organisms were still cable of survival in areas protected from harsh hydrodynamically forces commonly referred to as niche areas, particularly within sea-chests.