Smooth Pebble Crab
The Smooth Pebble Crab has a temperate southern Australian distribution. It ranges from Vic and Tas, across SA to Albany, WA. (VIC, TAS, SA, WA)
The Smooth Pebble Crab is a cream or slaty-grey coloured crab that is almost globe- or pebble-shaped. The front of its carapace, with its eyes, sticks out slightly at the front. It grows to a carapace width of 20-25 mm. Its carapace regions are not well defined. It has extremely long, distinctive, spindly chelae and swollen hands. Its slightly gloss-sheen coloured walking legs are long and slender. The male is much larger than the female crab. The males' chelae are also larger than the females' are. It has very small eyes. On each side of the carapace are three slightly angled sharp bumps, and a short ridge above the hind-margin. The carapace and chelipeds are mostly smooth, dull in colour and marked with very small granules.
The carapace is grey-brown, grey or cream in colour. It sometimes has four white dots on its carapace. The legs often have bands.
Ecology/Way of Life:
The Smooth Pebble Crab prefers sea grass areas in muddy or sandy estuaries and bays. It occurs from low tide levels down to 10 metres depth.
The Smooth Pebble Crab has an unusual shaped mouth that narrows at the front. This adaptation allows it to breathe when it is buried into the soft sand substrate.
I was at Westernport Bay, Vic, when I saw the tide coming in over the large, expansive, gentle-graded sandflats, The water edge was moving in at a slow walking pace. Smooth Pebble Crabs were trundling along behind this edge of water, searching for titbits of detritus and dead animal fragments. As the crabs moved along, they pushed their hands down into the soft mud and under pebbles, feeling for something to eat. They were looking for marine worms, snapping prawn pincers and bits from other burrowing invertebrates.
The following quote comes from Herbert Hale in 1927-29. "During mating their courting behaviour is amazing. A male selects a female and moves around her in a clumsy sort of dance; after a time the female, as if fascinated, folds her legs and remains quiescent. The male then seizes his consort with one or other of his large chelipeds, and bears her off at arm's length, the female remaining all the time quite motionless. If a couple are disturbed during their elopement they at once commence to burrow, the male placing himself immediately behind the female, often with his arms half encircling her. The burrowing only occupies a few seconds."
Interaction with Humans/Threats:
This crab appears to be fairly common in estuaries across southern Australia. If there was an environmental disaster, such as an oil or chemical spill, local populations of the Smooth Pebble Crab could be at risk.
Davey, K. (1998) A Photographic Guide to Seashore Life of Australia. p.47, New Holland Press, Sydney.
Edgar, G.J. (1997). Australian Marine Life: the plants and animals of temperate waters. p.204, Reed.
Jones, D. and Morgan, G. (1994). A Field Guide to Crustaceans of Australian waters. p.145, Reed.
Marine Research Group of Victoria (1984). Coastal Invertebrates of Victoria: An atlas of selected species. p.124, Museum of Victoria.
Text, map and photograph by Keith Davey.
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