Marine Biology

Rough Shore Crabs



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Rough shore crabs (Cyclograpsus granulosus) are fast moving crabs that are very active day or night and do not like to be disturbed. They are found in limited areas on the southern shoreline of Australia, Victoria and Tasmania.

Description and features

Rough shore crabs have a carapace of around 38 millimeters at adulthood. The carapace is the outer skeletal shell of the crab. The carapace comes in different colors but most are mottled purple and brown, red and brown or purple on yellow. They are similar in appearance to the purple shore crab (Cyclograpsus audouinii) referred to as the smooth shore crab but lack the long tufts of hair found between the base of the legs. The carapace surface is granular (rough and grainy) all the way around. The edges of its shell do not have teeth or spines. The rough shore crab has four sets of legs that are slightly flattened but strong and fairly long. They are able to live out of water for three to four hours at a time.

Habitat

The rough shore crab can be found at high tide levels and mid-tide levels on rocky shores. They are most prevalent in Tasmania where they can be found on boulder beaches either partially or fully exposed and under rock beds. They are sometimes found on stone beaches but prefer to hide under larger boulders. The younger crabs seem to wander and have a broader range while the adults stay near the large rocks.

Molting

Rough shore crabs molt twice a year. Molting is the process where the crab’s carapace is replaced by a new one that grows underneath the old. Molting happens at the end of the breeding season in March and again around September. The adults always moult after breeding while juveniles moult before the season. Male rough shore crabs moult earlier than females.

Diet

These crabs do not hunt but are scavengers. They use their claws to tear apart flesh and decaying plant matter. Rough shore crabs are not the pickiest eaters so they are a great benefit to their ecosystems cleaning up dead fish, birds and other animals as well as decaying seaweed and sea grass.

Conservation

Rough shore crabs are not an endangered or threatened species; however, due to their limited habitat any encroachment by man can put them in either category. Also, the risk of oil spills in the Bass Strait or other disasters could wipe out the species. Dredging is also a threat to this species of crab as the fine sediment that dredging creates will cause serious harm to the rough shore crab and other species as well.

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