Abstract:
The importance of vessel biofouling as a vector for the dispersal of non-indigenous
marine species (NIMS) is only just beginning to receive international attention. At the
time of commencing this study, there was a considerable lack of knowledge surrounding
which vessels, hull locations, levels and types of biofouling pose the greatest
biosecurity risk. Therefore, the aim of this study was to investigate the nature, extent
and survivorship of biofouling organisms on various vessel types at different hull
locations and offers a pragmatic risk assessment approach for managing this threat.
The results of this thesis found that the recruitment, persistence, distribution, abundance
and species composition of biofouling on vessel hulls is influenced by many factors
including: 1) the presence/absence, age and type of anti-fouling coating; 2) voyage
duration and route; and 3) port residency period. Therefore, higher levels of biofouling
(species richness, percentage cover, and biomass), including NIMS are more likely to
accumulate and persist on vessels (and in hull locations) that: 1) lack and/or possess old,
ineffective, damaged, inappropriate or unsuitable anti-fouling coatings; 2) spend
prolonged periods stationary in ports; 3) travel at slow speeds (i.e. <10 knots); 4) have
short voyage durations; and 5) remain at similar latitudes.
Prevention is clearly better than a cure, hence the correct application and maintenance
of 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 unwanted
translocation of biofouling organisms and NIMS. However, the results of this thesis
demonstrate 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 defence
against the unwanted dispersal of NIMS. Clearly, the survivorship of biofouling
organisms was highest amongst vessels that travelled at slow and medium speeds (e.g.
<10 knots). Therefore, given that accumulation of biofouling follows a successional
process 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 risk
of translocating NIMS on a vessel by vessel scale. However, despite the observation
that faster vessels reduce the diversity, quantity and quality of sessile biofouling
organisms in laminar flow areas of the hull, a wide range of sessile, sedentary and
mobile organisms were still cable of survival in areas protected from harsh hydrodynamically forces commonly referred to as niche areas, particularly within sea-chests.
