Invasion
Invasion Description
1st Record: Lockeport/Nova Scotia/Atlantic Ocean (1960, Audet et al. 2003)
Geographic Extent
Keji/ Nova Scotia/Atlantic Ocean (Williams et al. 2015, 43.86, 64.82, souther and northern (Scandinavian haplotypes); Lockeport/Nova Scotia/Atlantic Ocean (1960, Audet et al. 2003); Halifax/Nova Scotia/Atlantic Ocean (1966, Introduced, Established, Audet et al. 2003; 2008, Choi et al. 2016); Tor Bay/Nova Scotia/Atlantic Ocean (Audet et al. 2003); Cape Breton/Nova Scotia/Strait of Canso (1991, introduced, established, Audet et al. 2003); Nova Scotia/Bras d'Or Lakes (Cameron 2005); Sydney/Nova Scotia/Atlantic Ocean (2008, Choi et al. 2016); Burnt Island/Newfoundland/Cabot Strait (2010, Fisheries and Oceans Canada 2011); Newfoundland/Placentia Bay (2007, Canadian Broadcasting Company News 2007; Best et al. 2017); Come by Chance Harbour/Newfoundland/Placentia Bay (2007, Blakeslee et al. 2010); North Harbour/Newfoundland/Placentia Bay (2007, Blakeslee et al. 2010); Fox Harbour/Newfoundland/Placentia Bay (2010, Fisheries and Oceans Canada 2011); Spanish Room/Newfoundland/Placentia Bay (2010, Fisheries and Oceans 2011); Petty Harbour/Newfoundland/Atlantic Ocean (Matheson and Gagnon 2012)
Vectors
| Level | Vector |
|---|---|
| Alternate | Natural Dispersal |
| Alternate | Hull Fouling |
| Alternate | Ballast Water |
| Alternate | Discarded Bait |
Regional Impacts
| Ecological Impact | Predation | |
| Breen and Metaxas (2008) measured predation rates of juvenile and adult C. maenas on mussels (Mytilus sp.) and compared them to two species of native crabs (Cancer irroratus and Dyspanopeus sayi). Rates of mussel consumption were similar to or lower than native species. However, warm years can result in high recruitment, causing juvenile C. maenas to greatly outnumber native crabs, resulting in increased predation impacts (Breen and Metaxas 2008). Matheson and Gagnon (2012) compared feeding rates of C. maenas and C. irroratus and found that C. maenas had a preference for smaller mussels, compared to C. irroratus. In Kejimkujik National Park Seaside, Nova Scotia, modeling of a removal of Green Crabs from a sandflat resulted in a prediction of increased abundance of a variety of benthic invertebrates. However, these changes were predicted to be small, compared to the impact of migrating shorebirds (Wong and Dowd 2014). In citizen science field samples at 29 sites in the southern Gulf of St. Lawrence, there was a negative correlation between C. maenas and Say's Mud Crab (Dyspanopeus sayi). Large (70-80 mm diameter) Green Crabs fed on Mud Crabs at about twice the rate as on similarly sized juvenile Green Crabs (25-30 mm) in unstructured sand habitats, but preyed on both types of small crabs at about the same rate in oyster beds. Habitat complexity appears to affect the impact of Green Crab predation (Gehrels et al. 2016). In sandy and muddy sediments on Prince Edward Island, Carcinus maenas digs numerous pits in sandy and muddy sediments. Pits in muddy sediiment have reduced numbers of polychaetes and small bivalves (Lutz-Collins et al. 2016). | ||
| Ecological Impact | Competition | |
| In laboratory experiments, juvenile C. maenas initially reduced the growth rate of small (below 19-22 mm carapace width) Cancer irroratus (Rock Crabs) (Breen and Metaxas 2009). In experiments, Green Crabs reduced foraging of Rock Crabs, especially at warmer temperatures (Matheson and Gagnon 2012). Modelling of the impacts of removal of Green Crabs in Kejimkujik National Park Seaside, Nova Scotia,predicted an an increase of small shorebirds (eg. Black-bellied Plover, Pluvialis squatarola), because the increase in small prey (polychaetes, bivalves, small crustaceans) offset the decreased availabilty of Green Crabs as prey. However, these impacts were predicted to be small (Wong and Dowd 2014). | ||
| Ecological Impact | Food/Prey | |
| Breen and Metaxas (2009) found that when C. maenas and Cancer irroratus of similar size (above 19-22 mm carapace width) were reared together, the growth rate of C. irroratus increased, as a result of feeding on green crabs (Breen and Metaxas 2009). In modeling of the foodweb inl ejimkujik National Park Seaside, Nova Scotia, potential removal of Green Crabs resulted in a decreased in gull (Larus spp.) biomass due to the decrease of a major prey item (Wong and Dowd 2014). | ||
| Ecological Impact | Habitat Change | |
| In sandy and muddy sediments on Prince Edward Island, Carcinus digs numerous pits. The pits in sandy sediment fill rapidly, and do not differ from undisturbed areas, while pits in muddy sediments fill more slowly, and differ in their infauna, mostly in having smaller numbers of small polychaetes (Lutz-Collins et al. 2016). In Placentia and Bonaventure Bays, Newfoundland, disturbance due to foraging Green Crabs, has resulted in a reduction of Eelgrass (Zostera marina) cover, up to 50% removal, based on Before-After-Control Impact studies (Matheson et al. 2016). | ||
| Ecological Impact | Trophic Cascade | |
| In Placentia and Bonaventure Bays, Newfoundland, disturbance due to foraging Green Crabs, has resulted in a reduction of Eelgrass (Zostera marina), up to 50% removal. The loss of eelgrass has led to a sharp reduction in fish biomass and abundance, probably due both to the loss of shelter and the associated invertebrate community (Matheson et al. 2016). | ||