10 true crabs to spot in South Australia

10 true crabs to spot in South Australia

Find out about 10 true crabs you’re like­ly to see in SA waters and why we keep refer­ring to them as true’ crabs.

Crabs belong to the large group of ani­mals called Decapo­da, which means ten-foot­ed. Decapo­da is an all-encom­pass­ing term for about 8,000 species of crustaceans.

True’ crabs have ten legs – eight walk­ing legs and two grasp­ing claws and walk side­ways, where­as sev­er­al oth­er crab-like groups like her­mit crabs, squat lob­sters, and porce­lain crabs dif­fer in legs or movement. 

Here’s 10 species of true crabs you’re most like­ly to spot in South Australia. 

1. Black-fin­gered crab

This crab is the largest shore crab species in Aus­tralia. They can be found across south­ern Aus­tralia and north­ern New Zealand.

Research has shown that black-fin­gered crabs are strong­ly asso­ci­at­ed with their home’ rock and do not move far from it dur­ing their lifetime.

10 true crabs to spot in South Australia

2. Pur­ple mot­tled shore crab

This is a com­mon species found along SA’s rocky shores.

The hard shell cov­er­ing a crab body is known as a cara­pace. The cara­pace is shed reg­u­lar­ly, known as moult­ing, for the crab to grow.

The pur­ple mot­tled shore crab’s cara­pace is squar­ish with round­ed edges.

10 true crabs to spot in South Australia

3. Rough rock crab

This crab not only sounds rock’n’roll, but looks rock’n’roll.

At about 8 cm wide, they are coloured pur­ple or red-brown at the front, and grey or tan at the back. They have a straight, red rim along the front edge of their shell and between their eyes.

This crab has strong front and black claws, with tooth-like edges. Dur­ing breed­ing time, a male rough rock crab will car­ry the female around for a few days until she moults her hard shell.

(Image cour­tesy of D Monceaux)

4. Sand crab

The south­ern Aus­tralian sand crab can eas­i­ly be iden­ti­fied by the two dark red or pur­ple-coloured spots near its tail at the end of its shell. They can grow to more than 15 cm wide.

Sand crabs can be found along the beach­es of the Gulf St Vin­cent and the Spencer Gulf in SA.

(Image cour­tesy of Sunphlo)

5. Smooth shore crab

This is anoth­er com­mon species in SA waters and is close­ly relat­ed to the pur­ple mot­tled shore crab.

The smooth shore crab has dis­tinc­tive tufts of long hair between the bases of its legs.

There are some hybrid crabs that look like both the pur­ple mot­tled shore crab and smooth shore crab.

(Image cour­tesy of Richard Ling)

6. Lit­tle shore crab

This small crab, at about 2 cm wide, is usu­al­ly well cam­ou­flaged on rocky and mud­dy shores.

It comes in many colours from green to cream, but a dis­tin­guish­ing fea­ture is the three teeth behind its eyes and its 10 hairy legs.

(Image cour­tesy of J Baker)

7. Beard­ed crab

This cutie can be spot­ted across the south-east­ern coast of Aus­tralia from the shore­line to about 70 m deep.

Beard­ed crabs are a grey­ish-tan colour, with long hairs around the edges of its hard shell and on its legs.

They grow to about 3 cm wide and have a habit of bur­row­ing in the sand.

(Image cour­tesy of H Crawford)

8. Smooth peb­ble crab

The smooth peb­ble crab has a mar­ble-shaped, green­ish-grey hard shell, with four white dots.

This crab is often found in calmer water, such as in the sand and mud near the mouth of estu­ar­ies, and on shel­tered shores near sea­grass beds.

(Image cour­tesy of J Baker)

9. Dec­o­ra­tor crab

This crab grows to about 5 cm wide, with long legs and blue-and-orange claws.

The crab loves to cam­ou­flage by attach­ing sea­weed and sea­grass to its shell and legs.

Dec­o­ra­tor crabs belong to the spi­der crab family.

(Image cour­tesy of D Muirhead)

10. Euro­pean green shore crab

Last and prob­a­bly least, a crab that you’re like­ly to see but we wish you didn’t is the Euro­pean green shore crab – a pest crab. The Euro­pean shore crab is an intro­duced species, and is clas­si­fied as a pest in South Aus­tralia.

Euro­pean shore crabs car­ry par­a­sites that can hurt SA’s native marine species.

This crab is found in bays, estu­ar­ies, and tidal creeks across var­i­ous parts of the state.

(Image cour­tesy of D Frade)

This sto­ry and images were pre­pared with the help of Marine Ecol­o­gist and Edu­ca­tor Janine L. Baker. 

Love SA’s marine life? Check out this wrap-up of some of the unique species that call our state home.

Main image: Pur­ple mot­tled shore crab (image cour­tesy of Muse­ums Victoria)

This sto­ry was orig­i­nal­ly post­ed in June 2019.

This con­tent was pro­duced in part­ner­ship with  Good Living