2.7 RELEASE - BALLAST WATER DISCHARGE, MARINE FOULING AND IN-WATER HULL CLEANING
The discharge of ballast water necessarily releases organisms and sediment that have been carried in the tanks from source locations. The volume of this release is highly variable. Vessels from international ports may visit only one, or multiple, Australian ports. Coastal vessels may make regular voyages between two domestic ports only, or visit multiple ports. In each case, ballast water and sediment may be discharged, and, with the possible uptake of new ballast water in a number of ports, the number of sources of ballast increases.
Further, when a vessel is berthed, it may bump against the wharf, dislodging fouling organisms from its hull. Larvae emanating from encrustations on a fouled vessel may settle on nearby pylons or other vessel hulls, and vice versa18 Organisms may also be released from other areas of the ship such as pipes, anchor chains and wells.
The transfer of organisms by marine fouling may be facilitated by underwater or in-water cleaning of hulls. During in-water cleaning, divers use semi-hydraulic equipment to remove fouling encrustations from the hulls of berthed vessels. The debris is allowed to sink to the bed where some species may survive and successfully establish new populations. Hull cleaning may also encourage the release of spores and gametes from crushed organisms.
