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   Carcinus maenas (crustacean)    
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         General Impact

    Carcinus maenas is a voracious predator. It is able to crush mussels and shows a clear potential to negatively threaten mussel farms. In its native range, as well as in invaded regions, this species has been considered responsible for significant impacts on epibenthic and infaunal species, such as bivalves, other mollusks, and crustaceans, through predation, competition, and burrowing activities (Bravo, 2007). This species competes with other decapods for food or structure as well as resource competition, which may affect their geographic distribution (deRivera et al, 2005). The collapse of the soft-shell clam industries, in both New England and Nova Scotia, have been attributed to this species, which is causing concern for other local fisheries and economies (Breen & Metaxas, 2008). In the United States alone, C. maenas causes approximately $22 million dollars worth of damage each year (Williams, 2008). In areas in which the green crab has been introduced, it has the potential for significant impacts on fisheries, aquaculture, and the ecosystem. In fact, numerous studies have shown the potential for green crab to adversely affect many ecosystem components, directly and indirectly, by predation, competition and habitat modification (Klassen & Locke, 2007). This species has been documented as being a potential facilitator of Styela, which is an invasive club tunicate is some areas. They could facilitate the invasions by preying on tunicate predators. Green crabs are known to comsume prey from at least 158 genera and have been widely documented to decrease the diversity and biomass of estuarine communities (Locke et al 2007).

         Location Specific Impacts:
    Bras d'Or Lakes (Canada) English 
    Competition: Carcinus maenas and Cancer irroratus are found in close proximity as their habitat requirements overlap. Competition between these two species is inevitable (Klassen, 2007).
    San Francisco Bay (Estuary) (United States (USA)) English 
    Human nuisance: By entering and filling traps, Carcinus maenas has sometimes been a pest of trap fisheries for eels in eastern Canada and for bait fish (gobies and sculpin) in San Francisco Bay.

    Physical disturbance: When searching for prey, Carcinus maenas can dig about 15cm down in sand or mud, and this disturbance can affect the populations of small organisms living in the sediment. Carcinus maenas can also increase the populations of some species by eating their predators or competitors.
    Pacific Coast (USA) (United States (USA)) English 
    Competition: The Dungeness crab in Washington state and Oregon could potentially be threatened by further invasion of Carcinus maenas because of its similar food base and direct predation (Lafferty, 1996).

ISSG Landcare Research NBII IUCN University of Auckland