Thames Catchment Under Threat From Invasive Species

sunset-2946289An invasive species is defined as an organism that causes harm, both ecologically and economically, to an area where it is not native. One such example of an invasive species is the Chinese Mitten Crab, Eriocheir sinensis, which has become a problem within the Thames Catchment (UK).

Marine invasive species are introduced to an environment through human actions and activities. In the UK, over half of marine invasive species are introduced through shipping (the dominant mechanism being fouling), while the rest were introduced unintentionally. The Chinese Mitten Crab was introduced to the Thames Catchment, London, in 1935 from the ballast water of ships that had travelled from Asia. In the 1980’s the range of the Chinese Mitten Crab grew rapidly, proving an issue for the economy and the environment in the rivers where they’d settled.

The Chinese Mitten Crab has impacted river ecosystems across the UK; this is because there is no natural predator in the UK. The Thames catchment has been damaged severely by the Chinese Mitten Crab – it eats everything including weeds, fish eggs and snails which can significantly alter aquatic food chains. This also means it is in competition with local species such as the white-clawed crayfish, Austropotamobius pallipes. As well as competing against native species, the Chinese Mitten Crab has caused damage to river banks (due to burrowing) which has also become an economical issue. As a result of the burrowing and damage to the river banks, there a risk of the river bank collapsing, this could affect local businesses and homes that are located on the river bank around these areas.

The Common Shore Crab (Carcinus Maenas) can be compared to the Chinese Mitten Crab because it too has become a marine invasive species (in America and Australia). Like the Chinese Mitten Crab, the Common Shore Crab has become a threat to local ecosystems, wildlife and economies. The Common Shore Crab predates on epibenthic and infaunal species, such as mussels, which has the potential to threaten mussel farms in the area. However, unlike the Chinese Mitten Crab, the Common Shore Crab is being predated on by a crab native to North America, Callinectes sapidus, which has been proven to have a significant effect on the abundance of the Common Shore Crab.

Controlling a marine invasive species can be a challenging task – knowledge of distribution, abundance, rate of spread and impacts all have to be taken into consideration when choosing the best method of control. The most effective method of controlling and preventing is to treat the ballast water of ships – this prevents the introduction of new marine invasive species in the first place. When a marine invasive species enters an alien habitat, a predating animal can also be introduced to control the population numbers, however there is the risk that that animal could also become a problem itself.

To conclude, marine invasive species are introduced to an area through preventable means (such as cleaning ballast water) and cause several problems to local ecosystems and economies. Control methods are being put into place, however most invasive species (such as the Chinese Mitten Crab) are still not under control.




Epibenthic – Organisms that live on the top layer of the benthic layer.

Infaunal – Infaunal species are benthic animals that live in the substrate of the water column.


  1. National Ocean Service. What Is An Invasive Species?. [online] Available at [Accessed 03/11/2016]
  2. Bax, N., Williamson, A., Aguero, M., Gonzalez, E. And Geeves, W. (2003) Marine invasive alien species: a threat to global biodiversity. Science Direct. 27(4), pp. 313-323
  3. Morelle, R. (2008). Aquatic alien ‘thugs’ set to meet. BBC News [online]. Available at: [Accessed 21/11/2016]
  4. Sewell, J. (2016). Chinese Mitten Crab, Eriocheir Sinensis. [pdf]. Available at: [Accessed 21/11/2016]
  5. Global Invasive Species Database (2016). Species Profile: Carcinus maenas. [Online] Available at: [Accessed 08/12/2016]
  6. Toole, G. and Toole, S. (2014) AQA A2 Biology. Oxford: Oxford University Press, pp. 76-77.

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