Carcinus maenas was one of the three established marine pest species in Australia declared as a species of national significance (Australian Priority Marine Pest List Report 2019). An updated Australian rapid response manual for crabs will be completed in 2020. Genetic evidence confirmed hybridisation between C. maenas and C. aestuarii in Japan, and likely for South Africa (Darling et al., 2008). A separate genetic cline of C. maenas was identified in Nova Scotia (Jeffery et al., 2017).

Individual sightings of Carcinus in new areas still occur at subtropical and tropical latitudes, such as a sighting of an individual found in Indonesia on iNaturalist in 2018. No new establishments of C. maenas outside of the five introduced biogeographic regions have occurred (east and west coasts of North America, Patagonian coast of South America, southern Africa, southeast Japan, and southeast Australia). In Australia, several individuals of C. maenas were located in the Fremantle Marine Area in Western Australia, however no evidence of establishment has occurred (Wells et al., 2010). C. maenas have the potential to establish in southern WA, and Spencer Gulf in SA,. Localised range expansions have been recorded, including to the western coast of Tasmania. In Washington State, USA, citizen science programs detected range expansion of C. maenas in two inland areas of the Salish Sea in 2016 (Grason et al., 2018). In southern Africa, C. maenas individuals are now being found in Namibia as recorded on iNaturalist.

Summary Description

In Australia there are established populations in NSW, VIC, TAS and SA, while crabs have also been detected in WA.  It is now established in temperate estuaries and embayments in these four States. Carcinus maenas was detected in the Swan River, WA, in 1965, but no establishment is apparent.

Carcinus maenas is a medium-sized crab that attains a width across the carapace of up to 90 mm for males and 75 mm for females, but more typically 65 mm. The crab has five distinct spines on the outside edge of the carapace on either side of the eyes. The colour of the upper surface in adults is distinctively green, however adults can also be green with black/brown/red colour combinations. It is an omnivorous and opportunistic marine predator that feeds extensively on benthic fauna such as bivalves, gastropods and other crustaceans. This species eats the same foods as other native and commercially important crustaceans, and burrowing and feeding activity by this crab can alter the structure of benthos, eelgrass and bivalve reef communities. It is found in sheltered estuaries and bays within the intertidal zone. Common habitats of this species include mudflats, rocky shores, bivalve and rocky reefs, mangroves, saltmarsh and artificial structures.