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Representative ballast capacities
Representative ballast capacities
Courtesy of IMO/Global Ballast Water Management Programme


The world's oceans are under threat, under threat from marine pollution, from over-fishing and from physical destruction. As if this is not enough, they are also under threat from alien invaders, marine species transported beyond their natural range and dispersed across the globe by shipping.

Shipping moves over 80% of the world's commodities and transfers around 10 billion tonnes of ballast water each year. Ballast is absolutely essential to the safe and efficient operation of ships, providing balance and stability when empty of cargo. However, it may also pose a serious ecological, economic and health threat.

The problem arises when ballast water contains marine life. There are literally thousands of species that may be carried in ships' ballast - anything small enough to pass through a ship's ballast water intake pumps. This includes bacteria, small invertebrates and the eggs, cysts and larvae of various species.

The development of larger, faster ships combined with rapidly increasing world trade means that the natural barriers to the dispersal of species across the oceans are being reduced. As a result, whole ecosystems are being changed and economic impacts can be massive. In one example from North America, the introduced European Zebra Mussel has infested over 40% of internal waterways and has required over US$5 billion in expenditure on control measures since 1989. In several countries, introduced, microscopic, 'red-tide' algae have been absorbed by filter-feeding shellfish, such as oysters. When eaten by humans, these contaminated shellfish can cause paralysis and even death. The list goes on, hundreds of examples of major ecological, economic and human health impacts across the globe. It is even feared that cholera may be transported in ballast water.

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