Sand Bubbler Crab
The Sand Bubbler Crab occurs on the east coast of Australia from southern New South Wales to northern Queensland. (NSW, QLD)Features:
The squat, compact Sand Bubbler Crab resembles its relatives, the Ghost Crabs, though it is much smaller in size, and its body is distinctly bubble-like in shape. Adults measure about 12 mm across the carapace. Unlike Ghost Crabs, the claws of the Sand Bubbler Crab are equal in size, although larger in males than in females. A flattened membrane, called the tympanic membrane, occurs on the inner surface of the thigh on each leg. This species is grey-brown in colour, and usually well-matched to the colour of the sand where it lives. The claws are white externally, and are a rich red on their inner margins. The mouth and surrounds are bluish.Ecology/Way of Life:
The Sand Bubbler Crab occurs on sheltered sandy ocean beaches and bays. It normally hides in vertical burrows in a narrow zone almost at high water mark. During daytime periods of low tide it burrows up to the surface, emerging to feed on detritus and other organic matter stranded by the retreating water. It may take up to 3 hours most to emerge, and 5-6 hours for the last few to appear. The first sign of an emerging crab is a near circular hole - the opening of the burrow - from which the crab checks several times to see if it is safe to emerge. Once satisfied, it re-enters the burrow and begins clearing it of sand. The sand is packed into rough balls and pushed out of the burrow from beneath, using the walking legs. The crab then picks it up by hugging it to its mouth with its claws, and takes it up to 20 cm away before dropping it. This clearing continues until the burrow reaches the water table in the sand.
When the burrow is clear, the crab cleans itself and smoothes the sand around the entrance hole. It then begins to feed by scraping the surface sand with each chela (claw) alternately. The sand is spooned into the mouth and rotated, forming a net round pellet. Once the organic matter is taken from the sand, the pellet is pushed down into the tunnel formed by the walking legs, and pushed toward the back of the crab. In this way the crab moves away from its burrow in a straight line, marked by discarded pellets for 20-30 cm, before returning to the hole and repeating the same action on a different angle; the result is a very characteristic pattern of shallow trenches lined by small pellets of sand alongside, that form a star-like pattern radiating out from its burrow. While in its burrow, this crab stores water in its gill cavities beneath the carapace, to keep its gills moist, and also to assist in feeding. It has been suggested that the tufts of hairs between the leg bases may absorb moisture from the sand surface and help to replenish the crab's water supply.
These crabs feed on organic material sifted out from the sand pellets by using its mouthparts. Sand Bubbler Crabs, especially males, defend their feeding area against other individuals. When defending, the crab straightens its legs to near vertical and then stretches up its claws above the body, and then drops its claws and body rapidly in front of the attacker, thus displaying the red inner margin of the claws and the blue mouthparts. The outcome usually depends on size, and well-matched pairs may spar and lock claws; the subordinate crab may retreat into its burrow.Interaction with Humans/Threats:
This crab does not appear to be under threat from human activities.Other Comments:
named by Alphonse Milne Edwards, 1873, a prominent French crustacean biologist, and son of Henri Milne Edwards; the genus name comes from the Latin: scopa = twigs or broom, and mera = thigh, referring to the tuft of tightly packed hairs which protrude from beneath the carapace between the second and third walking legs, and into the gill cavities; the species name is from the Latin: inflata = puffed up, and describes the crab's bubble-like shape.Further Reading:
Bennett, I. 1987). W.J. Dakin's classic study: Australian Seashores. P.226. Angus & Robertson.
Davey, K. (1998). A Photographic Guide to Seashore Life of Australia. p. 63. New Holland Press.
Davie, P.J.F. (1985). The Biogeography of Littoral Crabs (Crustacea: Decapoda: Brachyura) Associated with Tidal Wetlands in Tropical and Sub-tropical Australia. in Bardsley, K.W. , Davie, J.D.S. and Woodroffe, C.D. (edds). Coasts and Tidal Wetlands of the Australasian Monsoon Region, Mangrove Monograph No.1, Australian Natiuonal University, North Australia Research Unit, Darwin, 259-75.
George, R.W. & Knott, M.E. (1965), The Ocypode Ghost Crabs of Western Australia (Crustacea, Brachyura). Journal of the Royal Society of Western Australia, v.48(1): 15-21.
Jones, D. & Morgan, G. (1994). A Field Guide to Crustaceans of Australian Waters. p.201. Reed.
McCulloch, A.R. & McNeill, F.A. (1923). Notes on Australian Decapoda. Records of the Australian Museum, V. 14(1): 49-59.
Text, map & photograph by Keith Davey.Sponsorship welcomed:
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