MYTILIDAE, Rafinesque, 1815

Mead, A., Carlton, J. T., Griffiths, C. L. & Rius, M., 2011, Introduced and cryptogenic marine and estuarine species of South Africa, Journal of Natural History 45 (39 - 40), pp. 2463-2524 : 2495-2496

Family MYTILIDAE

Mytilus galloprovincialis Lamarck, 1819 Introduced

The Mediterranean mussel forms dense beds in the high to mid intertidal zones ( Rius and McQuaid 2009). It is easily confused with the indigenous mussel, Choromytilus meridionalis , but is fatter, has a pitted resilial ridge and differs in habitat (occurring higher on the shore and away from sand-inundated sites). It is now globally distributed as a result of ship fouling and ballast water ( Branch and Steffani 2004). It was first collected in Saldahna Bay, South Africa in 1979 with genetic confirmation of the identification published 5 years later ( Grant et al. 1984). It is now the most significant marine introduction on rocky intertidal shores in this region, ranging from central Namibia (west coast) to East London on the east coast ( Robinson, Griffiths, McQuaid et al. 2005). There have been several studies into a variety of ecological impacts ( Branch and Steffani 2004; Rius and McQuaid 2009) and it is commercially cultured and exploited by recreational and subsistence fishers ( Robinson, Griffiths, McQuaid et al. 2005, 2007).

Perna viridis (Linnaeus, 1758) Introduced

We identified large green mussels collected from East London Harbour in 2010 as Perna viridis , based on shell colour and shape, shape of the posterior adductor muscle and shape of the pallial line ( Siddall 1980). However, we await confirmation via genetic studies, as this species is closely related to the endemic and highly variable Perna perna . To date there is no evidence of spread onto the open coast but if this occurs there is potential for hybridization with native Perna perna . Perna viridis is native to India and Southeastern Asia, but it has been widely introduced to Australia, Japan, the Caribbean, Gulf of Mexico and southeast United States. Hull fouling and ballast water are the most likely vectors.

Semimytilus algosus (Gould, 1850) Introduced

This small reef-forming mussel was first reported from South Africa only in 2010 and an initial survey has shown that it already forms dense and extensive beds in the lower intertidal and shallow subtidal on exposed rocky shores between Cape Town and the Namibian border. The species has long been known from Namibia, from where it was first reported in a somewhat obscure publication by Lamy (1931), under the name Modiola pseudocapensis . We have been unable to detect any later use or formal synonomy of that name. For example, it is not mentioned in the extensive taxonomic monograph of Soot-Ryan (1955). However, only Semimytilus algosus is currently recognized within the genus and this name has been the only one used by all local researchers (for example, Branch et al. 1994) subsequent to Lamy (1931). The species originates from the Pacific coast of South America and it is not clear whether its sudden appeareance in South Africa represents a dramatic southerly range extension of a newly introduced population.