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   Musculista senhousia (mollusc)   
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    Taxonomic name: Musculista senhousia (Benson, 1842)
    Synonyms: Brachidontes (Arcuatula) senhousia Kira, 1959 , Brachidontes (Musculista) senhousia Kira, 1962 , Brachidontes aquarius Grabau and King, 1928 , Modiola (Arcuatula) arcuatula Hanley, 1844 , Modiola bellardiana Tapparone-Canefri, 1874 , Modiola senhausii Reeve, 1857 , Modiola senhousia Benson in Cantor, 1842 , Modiolus senhousei Hanna, 1966 , Musculista senhausia Morton, 1974 , Musculus (Musculista ) senhousia Yammamoto & Habe, 1958 , Volsella senhausi Smith, 1944
    Common names: Asian date mussel (English), Asian mussel (English-USA), cuckoo mussel, date mussel, green bagmussel (English-USA), green mussel (English-USA), hototogisu, Japanese mussel (English-USA), senhouse mussel (English), Senhouse's mussel (English)
    Organism type: mollusc
    Musculista senhousia is a small, short-lived mytilid mussel native to east Asia which has successfully spread to New Zealand, Australia, the Mediterranean and the Pacific coast of the USA. It can grow rapidly and is capable of marked habitat alteration through the construction of byssal mats on the surface of soft sediments.
    Musculista senhousia is a small mussel with a maximum length of around 30mm, but most commonly 10-25mm in length and up to 12mm in width. It has a smooth, thin shell which is an olive green to brown in colour, with dark radial lines or zigzag markings. A well developed byssus is used to construct a cocoon which protects the shell. This cocoon is made up of byssal threads and sediment. M. senhousia burrows vertically down into the sand/mud leaving only its posterior end protruding, allowing its siphons access to the water to enable feeding (NIMPIS, 2002; CIESM, 2005).
    Similar Species
    Modiola arcuatula, Xenostrobus securis

    Occurs in:
    marine habitats
    Habitat description
    Musculista senhousia is an opportunistic species which can be found from intertidal to subtidal habitats (to a depth of 20m) and on soft or hard substrata. It prefers to settle in groups on soft substrata, but is capable of fouling wharf pilings and man made structures. When settled on hard substrata the mussel will not form a protective cocoon. When densities are high, individual byssal cocoons fuse to form continuous byssal carpets. Densities of "up to 2,500 mussels per square metre in Hong Kong, 2,600 per square metre in Western Australia, 2,800 per square metre in Japan, 3,300 per square metre in New Zealand, 8,600 per square metre in Mission Bay, 12,400 per square metre in San Diego Bay and 16,000 per square metre at Auckland, New Zealand have been reported. Crooks (2002) reported that densities of 5,000-10,000 per square metre are typical in mats in Mission Bay, with peak densities of over 150,000 mussels per square metre. Juveniles have been reported to settle on eelgrass at densities of 28,650 per square metre and on synthetic line at 126,000 per square metre; they later drop off these substrates to settle in mats on the bottom" (Cohen, 2005). M. senhousia is a highly adaptive species, and is able to tolerate low salinities (CSIRO, 2000; NIMPIS, 2002).
    General impacts
    Musculista senhousia can dominate benthic communities and potentially exclude native species. It settles in aggregations and is therefore able to reach high densities. Unlike most mussels, M. senhousia lives entirely within the sediments, surrounded by a bag of byssal threads. At mussel densities of greater than 1500 m2, individual byssal bags coalesce to form a continuous mat or carpet on the sediment surface. The presence of these mats dramatically alters the natural benthic habitat, changing both the local physical environment and the resident macroinvertebrate assemblage. Although this can result in increased species richness and abundance of some species, mussel mats reduce the densities of many common native bivalves and the growth of nearby eelgrass (NIMPIS, 2002; Allen and Williams, 2003). Crooks (1999) found that the effects of M. senhousia appear to be scale dependent. At larger scales, surface-dwelling, suspension-feeding clams are competitively inhibited. At smaller scales, however, the mussel benefits a variety of biota.
    M. senhousia deposits large amounts of organic matter in the sediment, which possibly results in the accumulation of toxic metabolites such as sulfide, which can have adverse effects on seagrass growth (Morton, 1974; Ito and Kajihara, 1981; in Reusch and Williams, 1998).
    Predation by native species contributes significantly to community resistance to invasion by Musculista senhousia in southern California, and may locally prevent the mussel from establishing dense, habitat-modifying beds with potential effects on native species. (Reusch, 1998).
    Geographical range
    Native range: Russian Federation, Democratic People's Republic of Korea, Republic of Korea, Japan, China (CSIRO, 2000), Singapore (OBIS, 2006).
    Known introduced range: USA (USGS, 2006), Canada, Mexico (Cohen, 2005), New Zealand, Australia (Allen and Williams, 2003), Israel, Egypt, France, Italy, Slovenia (CIESM, 2005), Tanzania, Madagascar (Mastrototaro et al. 2003).
    Introduction pathways to new locations
    Aquaculture: Musculista senhousia may have been introduced to Australia as an accidental importation with Pacific oysters (CSIRO, 2000). In the Mediterranean, invasion of M. senhousia has been strictly linked with shellfish farming and trading, and the initial invasion of the Pacific coast of the USA is attributed to transport with oysters imported from Japan (Mistri et al. 2004).
    Ship ballast water:
    Ship/boat hull fouling:

    Local dispersal methods
    Natural dispersal (local):
    Management information
    A two year study was undertaken for the Department of Environment and Heritage (Australia) by the Commonwealth Scientific and Industrial Research Organisation (CSIRO) to identify and rank introduced marine species found within Australian waters and those not found within Australian waters.
    All of the non-native potential target species identified in this report are ranked as high, medium and low priority, based on their invasion potential and impact potential. A hazard ranking of potential domestic target species based on invasion potential from infected to uninfected bioregions identifies Musculista senhousia as a 'medium priority species' - these species have a reasonably high impact/or invasion potential.
    For more details, please see Hayes et al. 2005.
    The rankings determined in Hayes et al. 2005 will be used by the National Introduced Marine Pest Coordinating Group in Australia to assist in the development of national control plans which could include options for control, eradication and/or long term management.

    McEnnulty et al. (2001) list four possible control options for M. senhousia: air exposure/dessication/freezing, commerical harvesting for food and fertiliser, dredging/beamtrawling/mopping, heated water treatment (baths, spray). Please see The Web-based Rapid Response Toolbox for more detailed information.

    Predation by native species contributes significantly to community resistance to invasion by M. senhousia in southern California, and may locally prevent the mussel from establishing dense, habitat-modifying beds with potential effects on native species. (Reusch, 1998).

    Musculista senhousia, like most mussels, is a suspension feeder. It lives endobenthically just below the sediment surface, where it filters phytoplankton from the water column with a short (<5mm) siphon (Morton, 1974; in Reusch and Williams, 1998; NIMPIS, 2002; Allen and Williams, 2003).
    Musculista senhousia is a species with high fecundity, rapid growth, a short life span and good dispersal ability, making it a successful invader. In the northern hemisphere it reproduces in the summer, larvae being most abundant through autumn and early winter. It has separate sexes, with males and females spawning at the same time. Spawning time varies within a limited spawning season (NIMPIS, 2002; CIESM, 2005).
    Lifecycle stages
    Musculista senhousia eggs and larvae are planktonic, and remain in the plankton for 45-55 days. It can reach adult size within 9 months, and up to 25mm within a year. Life span is thought to be between 18 and 24 months (Crook, 1996; CSIRO, 2000; NIMPIS, 2002; CIESM, 2005).
    Principal sources: NIMPIS. 2002. Musculista senhousia species summary. National Introduced Marine Pest Information System (Eds: Hewitt, C.L., Martin, R.B., Sliwa, C., McEnnulty, F.R., Murphy, N.E., Jones, T. and Cooper, S.).
    Compiled by: National Biological Information Infrastrcuture (NBII) & IUCN/SSC Invasive Species Specialist Group (ISSG)
    Last Modified: Thursday, 16 November 2006

ISSG Landcare Research NBII IUCN University of Auckland