The distributions of the brachyuran crabsHelice crassaDana, 1851,Hemigrapsus crenulatus(Milne Edwards, 1837),Cyclograpsus lavauxiMilne Edwards, 1853,Macrophthalmus hirtipes(Jacquinot, 1853), andHalicarcinus whitei(Miers, 1876) (Crustacea: Decapoda), and of the common half crab,Petrolisthes elongatus(Milne Edwards, 1837) (Decapoda: Anomura), were recorded in the Avon‐Heathcote Estuary, Christchurch. Experiments on the effects of salinity and substrate showed thatH. crenulatusis euryhaline and has a wide tolerance of differing substrates, whereasP. elongatusis stenohaline and requires a rocky substrate. Low salinity and particle size of the substrate may limit the distributions of other crabs in the estuary.