The shape and the idea: 106 — Asian paddle crab, Charybdis japonica

Asian paddle crab, Long Bay marine reserve,
Auckland, 24/3/17.

The Asian paddle crab, Charybdis japonica * is a medium-large green-coloured crab (to ~12cm carapace width), which has become established in northeastern New Zealand. At present they are known from the Waitemata Harbour north to Whangarei Harbour, and Opua/Waitangi in Northland.

Asian paddle crabs were first detected in the Waitemata Harbour near the end of 2000. They prefer sheltered estuarine conditions and are very aggressive, with a strong and painful nip (personal experience). They reach maturity at around ~46 mm carapace width (for females) and can reproduce frequently, possibly several times a year, meaning they could become established in a new area quite quickly. However, they need the water temperature to be at least 20˚C to breed and this will probably limit their southward advance.

The invasive asian paddle crabs are of a similar size to the commercially exploited local species of paddle crab (Ovalipes catharus). Asian paddle crabs feed on a variety of benthic species including gastropods, bivalves, and other crabs; so there is the potential for competition with local species for resources. Recently I was told that in areas where these two species co-occur, asian paddle crabs now predominate: having out-competed the local species.

* (A. Milne-Edwards, 1861)