Giant crab – a goliath amongst crustaceans

No. 52

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The deep-water crab, Pseudocarcinus gigas, is a goliath amongst crustaceans. Weighing in at up to 17.6 kg and with a carapace (shell) width of up to 46 cm, it is one of the largest species of crab in the world, and much heavier than its close relatives. Adult males wield one massively oversized claw, which accounts for much of the crab’s weight. Females lack the enlarged claw and generally only attain a more modest 7 kg. The claws are strong enough to crush the thickest of shells, since molluscs and crustaceans make up much of the giant crabs’ diet.

Giant crabs are long-lived and slow-growing, as befits their life in the cool ocean depths. Juveniles shed their carapace every three to four years, but adult females probably only do so every nine years or so. Since their only opportunity to mate is when their new carapace is yet to harden, they can’t breed more frequently than this. However, when they do breed, they can release vast numbers of eggs, and the larvae drift in the plankton for many months – or even years – before settling on the sea floor.

The giant crab is found along Australia’s southern coastline, from New South Wales to Western Australia. Though young crabs are very occasionally washed ashore (dead), our main chance of encountering an adult is through the efforts of commercial fishing boats which, since the early 1990s, have been setting pots for giant crabs on the continental shelf-break off Tasmania’s east and west coasts, in waters at least 140 m deep.

The French explorer, Péron (an ecologist before that word was invented), procured the ‘type’ specimen, from a party of Aborigines encountered on Maria Island. It was taken to France and formally described by Jean-Baptiste Lamarck in 1818; it now resides in the Muséum national d’Histoire naturelle (MNHN), the National Museum of Natural History, in Paris.

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