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   Mytilus galloprovincialis (mollusc)     
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      M. galloprovincialis in "Lido" Island, Venice (Photo:  Anna Occhipinti) - Click for full size   M. galloprovincialis scraped off a "bricola" in Venice (Photo:  Anna Occhipinti) - Click for full size
    Taxonomic name: Mytilus galloprovincialis (Lamarck, 1819)
    Common names: bay mussel (English), blue mussel (English), Mediterranean mussel (English), Mittelmeer-Miesmuschel (German)
    Organism type: mollusc
    Mytilus galloprovincialis (blue mussel or the Mediterranean mussel) is native to the Mediterranean coast and the Black and Adriatic Seas. It has succeeded in establishing itself at widely distributed points around the globe, with nearly all introductions occurring in temperate regions and at localities where there are large shipping ports (Branch and Stephanni 2004). Ship hull fouling and transport of ballast water have been implicated in its spread and its impact on native communities and native mussels has been suggested by a number of studies and observations (Carlton 1992; Robinson and Griffiths 2002; Geller 1999).
    Mytilus galloprovincialis is dark blue or brown to almost black. The two shells are equal and nearly quadrangular. The outside is black-violet coloured; on one side the rim of the shell ends with a pointed and slightly bent umbo while the other side is rounded, although shell shape varies by region. It also tends to grow larger than its cousins, up to 15cm, although typically only 5-8cm.
    Similar Species
    Mytilus spp., Mytilus edulis, Mytilus trossulus

    Occurs in:
    estuarine habitats, marine habitats
    Habitat description
    In its native range, M. galloprovincialis can be found from exposed rocky outer coasts to sandy bottoms (Ceccherelli and Rossi 1984). As an invader it typically requires rocky coastlines with a high rate of water flow. In fact, unlike the other 26 Asian and Atlantic molluscs introduced into Pacific regions only one introduced species, the Mediterranean mussel M. galloprovincialis, occurs in open coast, high energy environments on the Pacific coast; all remaining species are restricted to bays and estuaries (Carlton 1992).
    General impacts
    The alteration of benthic community dynamics by introduced bivalves on the Pacific coast remains largely uninvestigated including the impact of such invasives as M. galloprovincialis, but also Geukensia demissa, Musculista senhousia, Mya arenaria, Crassostrea virginica, Venerupis philippinarum, and Gemma gemma. It is known that M. galloprovincialis is able to outcompete and displace native mussels and become the dominant mussel species in certain localities. This is because M. galloprovincialis may grow faster than native mussels, be more tolerant to air exposure and have a reproductive output of between 20% and 200% greater than that of indigenous species (Van Erkom Schurink and Griffiths 1993, in Branch and Stephanni 2004). In a experiment to test the tolerance of the three native South African species to aerial exposure (in comparison to M. galloprovincialis) mussels were held for 42 weeks at the high-tide level where they experienced up to 7 days of continuous exposure to air. Under these conditions, survivorship of M. galloprovincialis was 92%, but 78% for Perna perna, 37–46% for Choromytilus meridionalis and 0–10% for Aulacomya ater (Hockey and van Erkom Schurink 1992, in Branch and Stephanni 2004). In South Africa the indigenous ribbed mussel A. ater was progressively displaced from semiexposed and exposed shores as the cover of M. galloprovincialis rose there. At sites where M. galloprovincialis was experimentally removed, there were no declines of A. ater (G.M. Branch Unpub. Data, in Branch and Stephanni 2004). Similarly, in southern California the introduction of M. galloprovincialis has been associated with a decline in the closely related native mussel M. trossulus (Geller 1999).
    Since the 1980s the introduced Mediterranean mussel (M. galloprovincialis) has successfully invaded the southern African coastline and has become the dominant species on rocky intertidal shores of the west coast. A comparative study by Robinson and Griffiths (2002) to investigate differences between M. galloprovincialis invaded areas and non-invaded areas was conducted in Langebaan Lagoon, South Africa, and highlighted the affect M. galloprovincialis has on naturally-occurring communities. Communities in invaded areas differed significantly from non-invaded areas with figures indicating that naturally-occurring sandbank communities were being replaced with communities more typical of rocky shores. To conserve the natural biota of the centre banks, which lie within a national park, the mussel beds should to be removed (Robinson and Griffiths 2002).
    Mytilus galloprovincialis is widely cultivated in Japan and China (Morton 1996).
    Geographical range
    Native range: Mediterranean Sea, Black Sea, and Adriatic Sea. It is unclear whether it is native to the outer coasts of France, Britain, and Ireland.
    Known introduced range: Southern Africa, east and west North America, Hawaii, and north-eastern Asia (Branch and Steffani 2004).
    Introduction pathways to new locations
    Live food trade: M. galloprovincialis is sometimes transferred through mariculture as a food source and because it is confused with other Mytilus species
    Ship: Shipping is held to be the most probable original mode of introduction of M. galloprovincialis to South Africa (Grant et al. 1984, in Branch and Stephanni 2004) and to Mexico (Carlton 1992).
    Ship ballast water: Late twentieth century distribution od M. galloprovincialis was probably enhanced by ballast water transport as well as ship fouling (Carlton 1992).
    Ship ballast water:
    Ship/boat hull fouling:

    Local dispersal methods
    Natural dispersal (local): A realistic estimate of the rate of spread of mussel beds (as opposed to individual mussels or solitary clumps) is 5 km year-1 (T. Phillips Pers. Comm., in Branch and Stephanni 2004).
    On animals (local): Mussel larvae are dispersed like passive particles matching the speed and direction of surface currents generated by the wind. For example the predominant winds on the stretch of coast in South Africa invaded by the mussel come from the southwest and as a consequence M. galloprovincialis was spread primarily to the east (a yearly average distribution increase of 42 km to the east compared with only 19 km to the west) (McQuaid and Phillips 2000).
    Water currents:
    Management information
    Ballast water management could stop the spread of its larvae.

    A new technique used in the aquaculture industry is the production of triploid and tetraploid mussels, which are functionally sterile, thereby eliminating the risk of wild populations establishing (McEnnulty et al. 2001).

    A filter-feeding bivalve that eats a wide range of planktotrophic organisms. This species prefers fast moving water that is free of sediment and thrives in regions where nutrient-rich upwelling occurs.
    Gonochoristic reproduction where males and females spawn simultaneously. M. galloprovincialis also has high fecundity and spawns at the time of year with the highest water temperature (Bayne 1976).
    Lifecycle stages
    Adult mussels spawn gametes, after which fertilization of an egg occurs. The egg undergoes gametogenesis, forming a larvae. The larva forms into a juvenile which settles and attaches itself using byssal threads after 2 to 4 weeks (Matson 2000).
    This species has been nominated as among 100 of the "World's Worst" invaders
    Principal sources: Branch, G.M. and 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.
    Compiled by: IUCN/SSC Invasive Species Specialist Group (ISSG)
    Last Modified: Tuesday, 9 May 2006

ISSG Landcare Research NBII IUCN University of Auckland