2.9 SUMMARY

· Ballast water in ships confers stability and ensures that the structural integrity of ships is not compromised. It is essential for the safe, efficient and effective operation of sea-going vessels.

· Types of tanks and arrangement of tanks differ between classes of vessel and individual ships. Ballast discharge pumps are unable to remove all water and sediment from ballast tanks.

· There are four stages in the translocation of organisms: take-up;. transit; release; and establishment.

· Marine organisms may be taken on-board along with sea water and similarly discharged. Ballast is usually taken on-board and discharged in sheltered port waters.

· The survival rates of species during transit differ markedly in response to temperature, light intensity, salinity and food availability.

· The discharge of ballast water releases organism and sediment carried from source locations. Further, organisms may be released from vessel hulls.

· Factors influencing successful establishment of exotic organisms in a new environment include: temperature tolerance; salinity regimes; habitat; predators; and food sources. Just because a species may have been unsuccessful in establishing populations in a new environment in the past does not mean that it will not do so in the future.