When seawater is pumped into a ship’s ballast tanks, millions of tiny and microscopic marine plant and animal become ‘stowaways’. During the voyage, the ballast water receives no light, fresh oxygen or food so most of the marine life will die. In the past when ships arrived in port, they would dump the ballast water that they had taken on board in their previous port, which could have been in a foreign country. Any unwelcome ‘survivors’ would be able to escape. In a new environment some species can become serious pests to other marine species and ecosystems.
It is estimated that about 10 billion tonnes of ballast water is transferred globally each year. Studies report that around 250 species have been introduced into our Australian seas from foreign regions.
Some of Australia’s least welcome of the marine pest species include Japanese seaweed, northern Pacific seastar, Mediterranean fan worm, European shore crab, Asian bivalve, Pacific oyster, Asian date mussel and a range of marine dinoflagellates.