Ballast Water

Points covered:

• What is ballast water?
• How does ballast water introduce exotic species?
• What is the impact of exotic species on our marine ecosystems?
• What measures are being taken to minimise the effects of exotic species?

Words to know:

• DINOFLAGELLATES - aquatic, single-celled organisms.
• EXOTIC SPECIES - introduced species.
• ESTUARY - semi-enclosed coastal water that is affected by both ocean and fresh water, such as the mouth of a river.

Ballast water is carried in unladen ships to provide stability. It is taken on board at the port before the voyage begins and tiny stowaways, in the form of marine organisms, are taken on board with it.

During the voyage, temperature changes in the ballast water and lack of food and light kill many, but not all, of these organisms. At the ships' destination, the cargo is loaded and the ballast water, with its surviving stowaway organisms, is pumped out. Some of these organisms then establish populations in the surrounding waters.

Over 100 species of marine organisms are known to have been introduced by ballast water. While some appear benign, others have become pests, threatening biodiversity, fisheries and aquaculture. Some introduced species severely deplete native populations or deprive them of food. Others form colonies which can smother existing fauna. Introduced toxic dinoflagellates cause red tides and algal blooms that can affect or even kill shellfish, fish, sea birds and humans.

About 60 million tonnes of ballast water are discharged annually into Australian ports. Many iron ore and coal carrying ships arrive empty of cargo and fully ballasted, so enormous volumes of foreign water are pumped into our ports.

Procedures have been implemented to control ballast water introductions. Since 2001, Australia has had a compulsory Ballast Water program for mid-ocean exchange, managed by AQIS. Under this system, ships exchange their ballast water for ocean water, which contains organisms that are less likely to survive in the estuarine environment of ports. Unfortunately, this practice is not always feasible because it is dangerous to empty a ship of all ballast. Furthermore, it is voluntary and difficult to monitor. Once a species is introduced into an Australian port it may be transported further by coastal shipping or recreational vessels. Certainly, once an introduced species has become established it is almost impossible to eradicate.

Introduced species can also be transported as hull-fouling organisms or when aquaculture stocks are moved.

Research is continuing in order to find better methods of reducing ballast water introductions. If the biodiversity of Australian waters is to be protected, it is vital that such research continues.

 

Pat Hutchings
Marine Invertebrates
Australian Museum