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Coutts, A.D.M. and M.D. Taylor, 2001. An Investigation of High Risk Areas on The Hulls of Merchant Vessels for the Translocation of Exotic Fouling Organisms, Cawthron Institute. Proceedings of the Second International Conference on Marine Bioinvasions, New Orleans, La., April 9-11, 2001, pp. 25-27. An Investigation of High Risk Areas on The Hulls of Merchant Vessels for the Translocation of Exotic Fouling OrganismsOver the past two decades the importance of hull fouling as a major vector for the transfer of marine organisms to new locations has been overshadowed by the importance of ballast water. This has largely occurred due to the preconceived notion that hull fouling has been significantly reduced, if not eliminated, by significant improvements in antifouling paint technology, combined with an increase in vessel speeds and cargo loading times. Coutts (1999) concluded that while such improvements may have reduced the degree of fouling upon merchant vessels, there are still regions upon hulls that remain high-risk areas for the transportation of exotic marine organisms. One such region includes the inside dry docking support strips (InDDSS), which refers to those areas underneath large vessels where chocks are used during dry docking to support the vessel. Reapplication of new antifouling paint is precluded in such areas. Coutts (1999) also observed other regions of the hull with high levels of fouling. These were generally protected "nooks and crannies" or irregularities on the hull, which were commonly sheltered from harsh hydrodynamic forces (e.g. rudders, gratings, holes, etc). James and Hayden (2000) also recorded excessive fouling in protected areas upon vessels greater than 500 DWT. This study investigates the importance of protected areas on the hulls of merchant vessels as a mechanism for transferring exotic marine species, and compares these areas with other regions of the hull with respect to the level and diversity of fouling organisms. In July 1999 a request was made to two commercial diving companies to view their archives of videos of underwater hull inspections of merchant vessels visiting New Zealand. A total of 30 vessels were randomly selected for the study and the video footage was viewed at Cawthron over the following two months. The vessels plyed international and domestic shipping routes and ranged in size from 2,300 to 30,000 DWT. The hull inspections were carried out during visits to one of three New Zealand ports: Auckland, Tauranga and Wellington, between 1998 and 1999. Lloyds surveying regulations ensured that the following regions of the hull were inspected: bulbous bows; bilge keels; In DDSS, Outside DDSS; sea chest gratings; propellers; rudders; and rope guards. Video footage of the bow thruster region was restricted to two vessels only, therefore this region was excluded from quantitative analyses. The percentage cover of fouling organisms within each region was determined by freeze-framing the video at various random locations and recording the taxa that occupied each of 50 random points. A cost-benefit analysis indicated that five quadrats provided sufficient replication for estimating the mean percentage cover of fouling taxa per hull region. Fouling organisms were classified according to three successional categories: category 1 -bare metal, painted surfaces, encrusting brown algae, encrusting green algae, filamentous green algae; category 2-acorn barnacles, serpulids, coralline algae, encrusting bryozoans, hydroids; category 3-solitary ascidians, compound ascidians, mussels and oysters (Figure 1). The hulls of vessels with old (i.e. ineffective) antifouling paint were characterised by fouling organisms in successional categories 2 and 3. Conversely, vessels with new (i.e. effective) paint were characterised by organisms in successional category 1. As expected, the mean percentage cover of algal fouling was highest in the regions receiving the greatest amount of light such as on the bulbous bow, upper edges of the bilge keel, propeller, rudder and rope guards. Very little algae colonized the regions that receive the least amount of light, such as the Outside DDSS and sea chest gratings. Coralline algae were very common on the propeller, where antifouling paint was absent. Although the InDDSS was often colonized by some coralline algae, insufficient light levels appeared to limit their success. Corallines were also found on the rope guards and sea chest gratings, but in these regions they were epiphytic. In addition to algal fouling, the bulbous bow was dominated by compound ascidians, which was probably due to anchor chains removing the antifouling paint while the vessels were at anchor. Acorn barnacles and sometimes mussels colonized the sea chest gratings. The InDDSS were also dominated by acorn barnacles, and the rope guards were also sometimes colonized by mussels (Figure 1). The percentage cover of invertebrate taxa overall was highest on the InDDSS, rope guards and sea chests. These regions also had the highest richness of fouling taxa.Interestingly, Coutts (1999) found species richness, diversity and evenness amongst invertebrates to be highest on the InDDSS, which supports the findings from the present study. Coutts (1999) found that 89% of the taxa that were present were found on the InDDSS, and 55% of the taxa were found only on the InDDSS. The InDDSS were also found to be colonized by three exotic species) yet to be introduced to Tasmanian waters: Megabalanus rosa, M. tintinnabulum, Balanus reticulatus, and Watersipora arcuata. Interestingly, Coutts (1999) found species richness, diversity and evenness amongst invertebrates to be highest on the InDDSS, which supports the findings from the present study. Coutts (1999) found that 89% of the taxa that were present were found on the InDDSS, and 55% of the taxa were found only on the InDDSS. The InDDSS were also found to be colonized by three exotic species) yet to be introduced to Tasmanian waters: Megabalanus rosa, M. tintinnabulum, Balanus reticulatus, and Watersipora arcuata. Literature Cited: Coutts, A.D.M. 1999. Hull fouling as a modern vector for marine biological invasions: investigation of merchant vessels visiting northern Tasmania. M. App. Sci. Thesis, Australian Maritime College, Launceston, Tasmania, Australia. James, P. and B. Hayden. 2000. The potential for the introduction of exotic species by vessel hull fouling: A preliminary study. National Institute of Water and Atmospheric Research, Report June 2000./p>
Contact: Ashley Coutts, Biosecurity Scientist, Cawthron Institute, Private Bag 2, Nelson, NEW ZEALAND |
