Ballast water

Examples of animals and plants introduced from ballast water and shipping in the UK


The movement of vessels around the world requires the intake of ballast water to give them a safe degree of stability when light. This disposal of water, when it takes place within ports and harbours is classed as a waste product. The ballast water that is disposed of may contain a variety of harmful substances, including in certain cases oil contaminants (Section 6.3.1), non-native marine animals and plants, and disease causing organisms in sewage contaminated water.

This introduction of non-native species is considered to be one of the five major threats to marine biodiversity identified in the Convention of Biodiversity. The introduction of non-native species from ships’ ballast water, in addition to other sources, is a matter that is causing increasing concern and is a potentially serious, but highly unpredictable problem, in all coastal marine ecosystems (Carlton 1996). A JNCC review of non-native marine species in British waters estimates that around a third of the 51 non-native animals and plants found in British waters have been introduced by shipping, both in ballast waters and on ship’s hulls (Eno et al 1997).

The effects of introducing new animal and plants can be almost undetectable, or conversely they can completely dominate and displace native communities. Severe cases of introduced non-native organisms include the European zebra mussel into the North American lakes, causing billions of dollars worth of damage due to fouling, and a comb jelly into the Black Sea, causing the near extinction of anchovy and sprat fisheries. The bloom forming algae Gymnodimium, which causes paralytic shellfish poisoning, was introduced into Australian waters from Japan.

In general, the effects in British waters are not as bad as elsewhere in the world, with approximately 80% of introduced species in the UK having no effect on native species and ecosystems (Ribera & Bouderesque 1995). However, 20% of introduced species have had some effect on native communities, with severe results in some cases. Examples of actual and possible effects of non-native animals and plants which have been introduced to the UK from shipping are shown below (Eno et al 1997).

Examples of animals and plants introduced from ballast water and shipping in the UK (Eno et al 1997)

  • Various species of bloom forming phytoplankton are thought to have been introduced from ships’ ballast water and have in some cases displaced native species to the point of being dominant, including one species, which can produce a thick grey slime with toxic properties.
  • A number of fouling organisms have been introduced from ballast water and ships hulls, causing both economic problems associated with the fouling of ships, buoys and harbour structures, and environmental impacts, such as competing with native species of barnacle for example. Hydroides ezoensis is a severe fouling organism in Southampton Water, however it also potentially benefits other animals by providing food and shelter.
  • In the Tay Estuary a marine worm introduced in ballast competes with native benthic species.
  • The most well known non-native species probably introduced from ship’s ballast water is cordgrass Spartina introduced to Southampton Water from North America. This cordgrass, subsequently crossed with the native species and produced common cordgrass Spartina anglica which spread rapidly colonising mudflats throughout Britain, forming dense swards and out-competing native cordgrass and other saltmarsh species. The spread of common cordgrass is thought to have contributed to the decline of Zostera beds in some areas, such as Lindisfarne (Percival, Anderson & Denny 1996; Dee Davison Associates 1998).
  • Both introduced and native cordgrasses are considered of high conservation importance and the Spartina swards in which they can be found are designated coastal features of the Solent Maritime and Essex Estuaries SACs.

It is should be noted that ballast water has been disposed by ships in ports, harbours and coastal waters since the early 1900’s and that during this time many non-native species have been introduced. However, it is a highly unpredictable issue and the probability of a harmful species being introduced in any one port is low, but the potential for harm is high should it occur. Recognising that the possible severity of the consequences, the IMO has taken action by developing guidelines for preventing the introduction of non-native species which aim to minimise the effects and the Oslo and Paris convention are also considering action.

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