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Tuesday, January 23, 2007

THE INVASION OF MEDITERRANEAN MUSSEL (Mytilus galloprovincialis) IN THE WEST COASTAL PARK OF SOUTH AFRICA

The Mediterranean mussel (Mytilus galloprovincialis) is a native species in the Mediterranean Sea, Black Sea and Adriatic Sea. It dominates the out coast of France, Britain and Ireland but still unclear whether it is native to these countries. Mytilus galloprovincialis is dark blue or brown to almost black in colour. It possesses two shells which are equal and quadrangular in shape. (Branch and Stephanie 2004).


In the late 1970s the Mytilus galloprovincialis invaded South African coast. It was intentionally introduced for the purpose of aquaculture. It arrived in South Africa and occupies the Langebaan Lagoon. A Lagoon is a body of water cut off from a large body by a reef, sand or coral. The West Coast national park is a home to the Langebaan Lagoon which is recognised as a RAMSAR wetland site of international importance, and these wetlands are designed like sand beds. As a marine global invader Mytilus galloprovincialis was introduced via marine transport, it has been transported by ship ballast water to South Africa.

The introduced species started to out-compete the indigenous black mussel (choromytilus meridionalis) and also threatens the indigenous Perna perna. Its rapid spread has resulted in a decline of this endemic species. Ironically the Mediterranean mussel has become the stronghold of the mussel mariculture industry in Saldahna Bay.

Mytilus galloprovincialis grow so faster in the Lagoon than native mussels because the Lagoon provides more food which enables it to produce more offspring. The species is more air tolerant and have a reproductive output of between 20% and 200% greater than that of indigenous species. (Branch and Stephanie 2004). The problem with its rapid growth and reproduction is that access faeces are released in the Lagoon; these faeces contain organic material and sulphides which lead to the smothering, lack of oxygen and pollution in the sand beds. This makes the sand beds unsuitable to other species.

According to the studies conducted by Robinson and Griffiths (2002) a comparison was done to investigate the differences between Mytilus galloprovincialis invaded areas and non-invaded areas in Langebaan Lagoon highlighting the effect it has on naturally-occurring communities. Communities in invaded areas differed more importantly from non-invaded areas because the figures were indicating that naturally occurring sandbank communities were being replaced with communities more typical of rocky coasts. To conserve the natural biota of the centre banks the mussel beds should be removed (Robinson and Griffiths 2002).

Mytilus galloprovincialis has not yet completely replaced Perna perna. Since Perna perna occupies the lower shore and Mytilus galloprovincialis occupies the higher shore. It can be concluded through the experiment by Shea and Chesson (2002) that M. galloprovincialis suffers high mortality due to wave action on the low shore especially in monospecific beds. In the absence of strong wave P. perna exclude M. galloprovincialis completely.
Though it is the most dominant mussel species today its introduction has not caused major extinction in South African marine species as compared to other invasive species and it has been widely beneficial as food.

Reference list


Branch, G. M. and Stephani, C. N. (2004). Spatial comparisons of populations of an indigenous limpet Scutellastra argenvillei and an alien mussel Mytilus galloprovincialis along a gradient of wave energy. [Internet]. 22 January 2007, 14:04 UTC [Cited 22 Jan 2007]. Available From:
http://www.nisc.co.za/oneAbstract?absId=993

Department of Environmental Affairs ad Tourism. (1999). Driving forces affecting marine and coastal systems and resources. [Internet]. 23 January 2007, 09:44 UTC [Cited 23 Jan 2007]. Available From:
http://www.ngo.grida.no/soesa/nsoer/issues/coast/driver.htm

Griffiths, C. L. and Robinson, T. B. (2003). Status and Impacts of Marine Alien Species in South Africa. [Internet]. 23 January 2007, 11:42 UTC [Cited 23 Jan 2007]. Available From:
http://www.sgnis.org/publicat/grifrobi.htm

Shea and Chesson, 2002. Community ecology theory as a framework for biological invasion, [Internet]. 22 January 2007, 08:16 UTC [Cited 22 Jan 2007]. Available From:
http://eprints.ru.ac.za/466/01/McQuaid_Will_the_invasive_mussel_Mytilus_galloprovincialis_Lamarck.pdf

Dianah Nangammbi
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Email: dnangammbi@csir.co.za
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