Mediterranean mussel

Mytilus galloprovincialis

Common names

Mediterranean mussel, bay mussel, blue mussel (English); Mediterreënse mossel (Afr.); Mittelmeer-Miesmuschel (German).

Mytilus galloprovincialis is from the Mediterranean and has colonised approximately 10 localities.  In South Africa it is found occupying the mid- to high rocky shore (Branch et al. 2010; Mead et al. 2011). One curious fact about M. galloprovincialis is that it is virtually absent from the subtidal areas despite the fact that when it is transplanted to ropes in aquaculture, its growth in the subtidal areas exceeds that in the intertidal areas (Branch et al. 2004).

How to recognise Mytilus galloprovincialis

Mytilus galloprovincialis are large, smooth-shelled black to blue mussels, typically 50 mm but up to 120 mm long. The two shells are equal in size and nearly quadrangular (four-sided) in shape. The outside of the shell is black–violet in colour. On one side the rim of the shell ends with a pointed and slightly bent umbo (beak of a bivalve shell) while the other side is rounded, although shell shape varies from region to region. Compared to the indigenous black mussel it is fat and usually has eroded shells. It occurs higher on the shore, away from sand (Picker & Griffiths 2011). The lifecycle of M. galloprovincialis includes a pediveliger (larval) stage – where the animal is able to crawl using its foot; and a plantigrade (spat, seed, juvenile) stage – the post-larval stage following metamorphosis (Carl et al. 2012).

Getting around

Adult Mytilus galloprovincialis is found firmly attached to rocks using strong byssal threads secreted by a mobile foot (Picker & Griffiths 2011). In the pediveliger (larval) stage M. galloprovincialis is able to crawl around using its foot. 

Communicating

M. galloprovincialis responds to chemical cues released by its nearby conspecifics (members of the same species) by crawling away from them (Nicastro et al. 2007).

Distribution

Indigenous to the Mediterranean and Black seas, M. galloprovincialis has colonised and formed naturalised populations at nine localities outside of its native range. These include Hong Kong, Japan, Korea, Australia, America, Mexico, Canada, Great Britain and Ireland (Branch & Nina Steffani 2004; Wonham 2004). In South Africa it is now abundantly distributed along the entire west coast, while on the south coast they form mixed beds with indigenous Brown mussel (Perna perna) (Picker & Griffiths 2011).

Habitat

M. galloprovincialis was first detected on the west coast of South Africa in the late 1970s (Bownes & McQuaid 2006; Picker & Griffiths 2011). Both recruitment and growth of M. galloprovincialis are documented as greatest on wave-exposed as opposed to sheltered shores (Steffani & Branch 2003; Branch & Nina Steffani 2004; Xavier et al. 2007). They have also been reported in subtidal habitats lower down on the sides and bottoms of floating docks (Rensel et al. 2005)

Food

M. galloprovincialis is a sedentary filter-feeder that feeds by pumping water through its enlarged sieve-like gills (Branch et al. 2010; Picker & Griffiths 2011). Its larvae were observed feeding on all red-tide dinoflagellates in a study by Jeong et al. (2004); thus demonstrating diverse prey species.

SEX and LIFE CYCLES

Sex

Mytilus galloprovincialis has separate sexes with gonads (which are cream in males and pink in females) that extend throughout the body. They produce millions of eggs and sperm at each spawning. Fertilised eggs develop into free-swimming larvae that disperse widely and grow rapidly, reaching a length of 70 mm in the first year within favourable sites (Griffiths et al. 1992; Bownes & McQuaid 2006; Picker & Griffiths 2011). These microscopic larvae drift with water currents for several weeks before settling down to the benthos (bottom of the sea bed) (Green 2014). They initially settle as pediveligers (larvae) and actively explore the substratum by crawling with a foot, which is a muscular and glandular organ with cilia (short hair-like structures) that are also used for byssus secretion. If they find a suitable substratum, they then deposit an adhesive plaque and byssal thread (Carl et al. 2012).

Family life

Mussels often grow into beds of individuals upon settling, coating any hard surface area. Colony sizes can reach numbers in the millions (Green 2014). The fast growth rate and large size of M. galloprovincialis and hybrids may make them less susceptible to predators and alter predator–prey relationships in the intertidal and subtidal zones (Rensel et al. 2005).

THE BIG PICTURE

Friends and Foes

Mytilus galloprovincialis forms dense, multi-layered beds that dominate the intertidal rocks. They displace indigenous mussels (e.g. ribbed mussel, Aulacomya ater) and large limpets (e.g. bearded limpet, Scutellastra argenvillei), but smaller species flourish within the beds (Hanekom & Nel 2002; Branch et al. 2004). In South Africa, the whelk Nucella cingulata is a predator of M. galloprovincialis (Branch et al. 2004). As such, these whelks have been found to increase in density where these mussels have established populations. Also in South Africa, the endangered African Black Oystercatcher has been observed to switch from feeding on native mussels to the invasive Mediterranean mussel. This is potentially due to the invasive mussel having taken over the habitat typically used by the native mussels, or because they grow larger in size and provide more energy per individual. As a result it has been reported that these birds’ reproductive potential has increased following the mussel establishment (Kohler et al. 2011; Green 2014).

Smart Strategies

M. galloprovincialis prefers warm, high salinity waters (Rensel et al. 2005). They also have a clear preference for more complex surfaces for settlement sites relative to the size of the individual – from the pediveliger stage through to the plantigrade stage (Carl et al. 2012). It also invades gaps in its beds by lateral expansion, and larval settlement seems to occur directly into mussel beds or crevices rather than on bare rock (Ruiz Sebastián et al. 2002).

Poorer world without me

M. galloprovincialis is one of the major contributors to the mussel aquaculture industry and is worth more than 1.2 billion US dollars per annum (Carl et al. 2012).

People & I

Mytilus galloprovincialis is a native species of the Mediterranean, hence its common name, the Mediterranean mussel (Wonham 2004). It has been introduced to countries such as South Africa and China where it is widely cultured. In Spain it is reported to produce above 3 000 tons per year (Galimany et al. 2011; Bolton et al. 2013). In Portugal it is harvested by humans in order to supplement their diet and also for commercial and bait use (Rius & Cabral 2004).

Conservation status and what the future holds

M. galloprovincialis was first recorded in South Africa in the 1970s and has since spread to cover about 2 000 km of the west coast of South Africa and Namibia; it has also become established in the south coast as a result of mariculture (Branch et al 2004). It is listed as an invasive species in the National Environmental Management: Biodiversity Act (NEMBA) under category 2. This means that its utilisation is only allowed under permit conditions within an area specified in the permit (Department of Environmental Affairs 2014).

Relatives

Genetic and geological data show that the genus Mytilus evolved in the north Pacific where M. trossulus stock migrated to the north Atlantic. This is also where M. edulis stock arose, subsequently giving rise to M. galloprovincialis in the Mediterranean (Wonham 2004). 

References and further reading

  • Bolton, J.J., Davies-Coleman, M.T. & Coyne, V.E. 2013. Innovative processes and products involving marine organisms in South Africa. African Journal of Marine Science 35, 449–464. doi:10.2989/1814232X.2013.830990.
  • Bownes, S.J. & McQuaid, C.D. 2006. Will the invasive mussel Mytilus galloprovincialis Lamarck replace the indigenous Perna perna L. on the south coast of South Africa? Journal of Experimental Marine Biology and Ecology 338, 140–151.
  • Branch, G.M., Nina Steffani, C. & Steffani, C.N. 2004. Can we predict the effects of alien species? A case-history of the invasion of South Africa by Mytilus galloprovincialis (Lamarck). Journal of Experimental Marine Biology and Ecology 300, 189–215. doi:10.1016/j.jembe.2003.12.007.
  • Branch, G.M., Odendaal, F. & Robinson, T.B. 2010. Competition and facilitation between the alien mussel Mytilus galloprovincialis and indigenous species: Moderation by wave action. Journal of Experimental Marine Biology and Ecology 383, 65–78. doi:10.1016/j.jembe.2009.10.007.
  • Carl, C., Poole, A.J., Williams, M.R. & De Nys, R. 2012. Where to settle — settlement preferences of Mytilus galloprovincialis and choice of habitat at a micro spatial scale. PLoS ONE 7, 1–10. doi:10.1371/journal.pone.0052358.
  • Department of Environmental Affairs. 2014. National Environmental Management: Biodiversity Act 2004 (Act No. 10 of 2004) Draft Alien and Invasive Species Lists, 2014. Government Gazette # 37320 3–62.
  • Galimany, E., Ramón, M. & Ibarrola, I. 2011. Feeding behavior of the mussel Mytilus galloprovincialis (L.) in a Mediterranean estuary: A field study. Aquaculture 314, 236–243. doi:10.1016/j.aquaculture.2011.01.035.
  • Green, A. 2014. Invasive Species Report: Mediterranean Mussel (Mytilus galloprovincialis), International Union for Conservation of Nature. doi:10.1111/ddi.12297.
  • Griffiths, C.L., Hockey, P.A.R., Van Erkom Schurink, C. & Le Roux, P.J., 1992. Marine invasive aliens on South African shores: implications for community structure and tropillic functioning. South African Journal of Marine Science 12: 713–722. doi:10.2989/02577619209504736.
  • Hanekom, N. & Nel, P. 2002. Invasion of sandflats in Langebaan Lagoon, South Africa, by the alien mussel Mytilus galloprovincialis: size, composition and decline of the populations. African Zoology 37: 197–208.
  • Jeong, H.J., Song, J.Y., Lee, C.H. & Kim, S.T. 2004. Feeding by larvae of the mussel Mytilus galloprovincialis on red-tide dinoflagellates. Journal of Shellfish Research 23: 185–195.
  • Kohler, S., Connan, M., Hill, J., Mablouké, C., Bonnevie, B., Ludynia, K., Kemper, J., Huisamen, J., Underhill, L., Cherel, Y., McQuaid, C. & Jaquemet, S. 2011. Geographic variation in the trophic ecology of an avian rocky shore predator, the African Black Oystercatcher, along the southern African coastline. Marine Ecology Progress Series 435: 235–249. doi:10.3354/meps09215.
  • 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: 2463–2524. doi:10.1080/00222933.2011.595836.
  • Nicastro, K., Zardi, G. & McQuaid, C. 2007. Behavioural response of invasive Mytilus galloprovincialis and indigenous Perna perna mussels exposed to risk of predation. Marine Ecology Progress Series 336: 169–175. doi:10.3354/meps336169.
  • Picker, M. & Griffiths, C.L. 2011. Alien & invasive animals: a South African perspective. Struik Nature, Cape Town.
  • Rensel, M., Elliott, J. & Wimberger, P. 2005. Will the introduced mussel Mytilus galloprovincialis outcompete the native mussel M. trossulus in Puget Sound? A study of relative survival and growth rates among different habitats, methods, survival and growth experiments. Proceedings of the 2005 Puget Sound Georgia Basin Research Conference 1–8.
  • Rius, M. & Cabral, H.N. 2004. Human harvesting of Mytilus galloprovincialis Lamarck, 1819, on the central coast of Portugal. Scientia Marina 68: 545–551.
  • Ruiz Sebastián, C., Steffani, C. & Branch, G. 2002. Homing and movement patterns of a South African limpet Scutellastra argenvillei in an area invaded by an alien mussel Mytilus galloprovincialis. Marine Ecology Progress Series 243, 111–122. doi:10.3354/meps243111.
  • Steffani, C. & Branch, G. 2003. Growth rate, condition, and shell shape of Mytilus galloprovincialis: responses to wave exposure. Marine Ecology Progress Series 246, 197–209. doi:10.3354/meps246197.
  • Wonham, M.J. 2004. Mini-review: distribution of the Mediterranean mussel Mytilus galloprovincialis (Bivalvia: Mytilidae) and hybrids in the North East Pacific. Journal of Shellfish Research 23: 535–543.
  • Xavier, B.M., Branch, G.M. & Wieters, E. 2007. Abundance, growth and recruitment of Mytilus galloprovincialis on the west coast of South Africa in relation to upwelling. Marine Ecology Progress Series 346: 189–201. doi:10.3354/meps07007.

Author

Siyasanga Miza

SANBI Marine Programme

February 2016

Official Common Name

Mediterranean mussel  

Scientific Name and Classification:

Kingdom

Animalia

Phylum

Mollusca

Class

Bivalvia

Subclass

Pteriomorphia

Order

Mytiloida

Family

Mytilidae

Genus

Mytilus

Species

M. galloprovincialis Lamarck, 1819

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