We all know the problems caused by introduced plants and animals such as lantana, rabbits and cane toads. Some of these species have been deliberately introduced to Australia, while others have turned up uninvited!
But the problem of introduced pests isn't confined to land. The Great Barrier Reef and waters around Australia are now facing a serious environmental threat from marine organisms brought in by foreign ships, especially in ballast water - water carried in the empty hull to make the ship stable. Picked up overseas and then discharged in Australia, this water can bring unwelcome hitch-hikers that poison shellfish, compete with native species and cause serious environmental problems.
Ballast water and hull hitch-hikers
Ballast water is sea water taken on by large ships sailing to Australia without cargo. When they arrive in an Australian port they discharge this water as cargo is loaded. If the conditions in the harbour are right, whatever organisms are in that ballast water can grow, breed and spread.
At least 70 varieties of fish, worms, molluscs, seaweed and toxic algae have been introduced to Australia in the ballast water or on the hull of ships. Some of these have become pests.
Health checks have found some ballast water contains human diseases such as cholera.
Other ballast water contains toxic micro organisms, such as dinoflagellates, which get into shellfish and then cause illness or even death in humans who eat affected oysters or abalone. The Tasmanian shellfish industry lost millions of dollars after blooms of Gymnodinium catenatum algae shut down shellfish beds for months at a time. This industry is also under threat from the introduced Northern Pacific Seastar (Asterias amurensis), a ravenous shellfish feeder.
Several fish species have been introduced in ballast water. They compete with native fish for food and some, like the large Japanese sea bass (Lateolabrax japonicus), eat native fish.
Once organisms like these have been introduced they are almost impossible to remove.
How to control the problem
Researchers are trying to find ways to reduce the risks of ballast water introducing unwelcome organisms to Australia's waterways. Prevention is the best way to solve the problem, but where that's not possible, procedures to minimise the risk are being developed. Currently there is no practical, effective way of treating ballast water, so continued funding for research into safe, cheap, effective methods is needed.
Since 1990, ships entering Australian ports from overseas have been asked to comply with voluntary quarantine guidelines. These include preventing organisms being taken on board during ballasting, by taking on ballast water well out to sea and exchanging water several times in mid-ocean during the voyage to Australia.
The Australian Quarantine Inspection Service (AQIS) can test ballast water on a ship entering Australian waters from overseas and may prohibit discharge of ballast water if it is thought to be contaminated.
Australian Ballast Water Management Strategy by AQIS, Department of Primary Industry and Energy, Canberra 1995.
Australian Department of Agriculture.