Enviroment

Invasive marine species constitute one of the four greatest threats to the world's oceans. Unlike other forms of marine pollution such as oil spills - where ameliorative action can be taken and from which the environment will eventually recover - the impact of invasive marine species is most often irreversible.

There are thousands of marine species that may be carried in ships' ballast water; basically anything that is small enough to pass through ships' ballast water intake and pumps. These include bacteria and other microbes, small invertebrates and the eggs, cysts and larvae of various species.

The problem is compounded by the fact that virtually all marine species have life cycles that include a planktonic stage or stages. Even species in which the adults are unlikely to be taken on in ballast water, for example because they are too large or live attached to the seabed, may be transferred in ballast during their planktonic phase.

It is estimated that at least 7,000 different species are being carried in ships' ballast tanks around the world.

The vast majority of marine species carried in ballast water do not survive the journey, as the ballasting and de-ballasting cycle and the environment inside ballast tanks can be quite hostile to organism survival. Even for those which do survive a voyage and are discharged, the chances of surviving in the new environmental conditions, including predation by and/or competition from native species, are further reduced. However, when all factors are favourable, introduced species may survive to establish a reproductive population in the host environment - it may even become invasive - out-competing native species and multiplying into pest proportions.