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Cyclograpsus granulosus (Family Grapsidae)

Smooth Shore Crab

Distribution:

The Smooth Shore Crab has a restricted distribution range from Vic to SA, including Tas (VIC, TAS, SA).

Features:

The Smooth Shore Crab has a carapace that has both the sides and the front edge smooth, and it does not have edge spines. Its carapace is four-fifths more broad than it is long. The carapace surface is granular both at the front and at the sides. It grows to a carapace width of 20-35 mm The species name 'Cyclograpsus' describes its rounded chelae. Its legs are partly flattened and are fairly long and strong. The top segments of the sternum are weakly haired. It is similar in appearance to the Purple Shore Crab, C. audouinii, but lacks the tufts of long hair between the leg bases.

The Smooth Shore Crab has mottled colouration with varying patterns of brown, purple, red and yellow.

Ecology/Way of Life:

The Smooth Shore Crab occurs at mid to high tide levels on rocky ocean shores, usually under rocks. In Tasmania they are consistently found on boulder beaches, usually semi-exposed ones, and may be found on both fully exposed or in sheltered areas. They are occasionally found on stony beaches.

Moulting takes place twice each year at the end of the breeding season in March and again at the beginning of the next breeding season. Males moult a little earlier than females. Small adults moult at the beginning of the breeding season while all adults moult at the end of the season. The number of juveniles fluctuates through the year with a peak of abundance near March and possibly in December. Juvenile crabs appear to range more widely than adults, who prefer habitats with stones and boulders. Large adults may be three years of age.

Interaction with Humans/Threats:

Because of its limited distribution range confined to south-eastern Australia, any environmental disaster such as a large oil spill in Bass Strait could have a severe effect on this species.

Other Comments:

Cyclograpsus granulosus, H. Milne-Edwards. Cyclograpsus is made up from two Greek words; kyclos meaning circle, while grapsus may come from graptos, meaning written. Granulosus comes from the Latin word granulum, which means grain. H. Milne-Edwards was a French carcinologist (crab researcher) from around the middle of the 19th Century.

Further Reading:

Campbell, B. M. & Griffin, D. J. G. (1966). The Australian Sesarminae (Crustacea, Brachyura) genera Helice, Helograpsus nov. Cyclograpsus and Paragrapsus. Mem. Qld. Mus. v.14 127-174.

Davey, K. (1998) A Photographic Guide to Seashore Life of Australia. p.53, New Holland Press, Sydney.

Edgar, G.J. (1997). Australian Marine Life: the plants and animals of temperate waters. p.213, Reed.

Griffin, D. J. G. (1969). Breeding and moulting cycles of two Tasmanian Grapsid Crabs (Decapoda, Brachyura). Crustaceana, v.16, 88-94.

Griffin, D. J. G. (1969). The Ecological Distribution of Grapsid and Ocypodid Shore Crabs (Crustacea: Brachyura) in Tasmania. J. Anim. Ecol. V.40 597-621.

Acknowledgments:

Text, map & photograph by Keith Davey.

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