Crustaceans- Grapsidae

The family of grapsid crabs are those that look very much like 'normal' crabs, usually flat in shape, with long legs radiating outward, moving sideways, and having strong nippers. This family is widely spread all over the world and in New Zealand, and contains a high proportion of endemic species (marked in red). This family of crabs is interesting because many of its members can readily be observed in the intertidal.
  • Suborder Thoracotremata - (L: thorax= breast; trema=hole; hole-breasted)
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    Leptograpsus variegatus (Fabricius, 1793), purple rock crab, large shore crab, papaka nui

    Leptograpsus variegatus(L: leptos= fine, small, narrow; variegatus= varied in colour, marked with irregular patches) The purple rock crab is large, strong, and moves fast. When wedged into a crevice, it is not easily dislodged. Handling a ferocious crab like this requires skill, and risks painful nips. The purple rock crab is the largest native shore crab, exceeded in size only by paddle crabs Ovalipes catharus (on sand bottom) and the Australian mud crab Scylla serrata (on mud flats).
    It is found between high tide and above it, often occupying moist crevices up to two metres above high tide. It can remain out of the water for days, but equally happily can stay submerged. The crab measures up to 5cm across its back, and its long, flat legs  fold neatly together as in an oriental fan, giving it a very flat profile.
    The purple rock crab is active particularly by night, when it leaves its crevice, scaling the vertical rocks and navigating its way over the rock flats and into the water, in search of flea mussels, which it cracks without effort. At night it has no fear and can be approached and photographed from close up, even in bright lamp light. However, the crabs are inactive during the full moon phase. Towards the morning, the crab navigates flawlessly all the way back to its home crevice. Yet, by day, this large crab is extremely wary, scuttling away noisily, its legs grating the rocks. When a group of these forays by day, large males can be seen taking guard in a defensive posture, warning the others at the slightest disturbance. To see several of these beautiful purple and white crabs feeding off green seaweeds, is spectacular. This crab is an omnivore, feeding on both animal (flea mussels, barnacles) and plant matter (seaweeds, plankton slime).
    Large crabs migrate all the way down the shore to the sublittoral fringe where food is more abundant. Small crabs foray more in restricted areas.
    This crab runs fast and when cornered, can be very aggressive with its nippers, which makes it difficult to capture and handle.

    Colour: This crab is usually coloured as shown in the paintings and photographs, but two distinct colour morphs (blue and orange) have been distinguished in australia.

    Life history: the purple rock crab mates in October-November when the female is hard-shelled. Before mating, the crabs make leg contact, during which the legs are rapidly vibrated. The male crab may then mount the underside of the female. The female moults before laying her eggs. Females with eggs are found from November till January/February (Auckland/Wellington). The incubation period is about 6 weeks and the crab spawns only once a year. Newly laid eggs are about 0.36mm in diameter, and develop from a dark brown colour to light brown just before hatching. The female carries 55,000-144,000 eggs (depending on her size), attached to her pleopods under her broad abdomen. This crab can become five years old.

    Distribution: North Island, Kermadec Islands, Australia and the islands of the South Pacific. This crab is found in southern warm temperate (subtropical) Indian and Pacific Oceans from western Australia to western South America. In NZ from the top of the North Island to Kaikoura or Westport.


    Plagusia chabrus, red rock crab, (Plagusia capensis) (Linnaeus, 1758), papaka ura, red bait-crab (Australia)

    Plagusia capensis(L: plagusia=?; capensis= of Cape of Good Hope; chabrus=?) The red rock crab lives under water and seldom or never ventures outside. Small ones are found inside rock pools, but divers encounter these animals to depths of 25m (the photic zone where light is sufficient for plant growth). This crab feeds mainly on plants (brown and red algae, coralline turf), although it will scavenge as well on limpets, chitons, gastropods, mussels, brittle stars and barnacles. Small crabs are mainly herbivorous whereas large crabs are more carnivorousIts carapace can measure up to 7cm across, and its legs can span 20cm. Yet this animal is more placid than the purple rock crab, and can be handled with some skill. The painting shows a female, recognisable by her smaller nippers. Each nipper has three knobbly ridges. The red rock crab's carapace is covered in fine hairs, which gives it an advantage when attacked by octopus, their main predator (and shags).  Once lodged inside a crevice, an octopus won't be able to dislodge it. The red rock crab lives mainly on rocky reefs, but may venture on the sand to forage for food by night.
    This crab can run over the rocks, half by swimming with its flattened long legs. When approached cautiously by divers, it shows no fear.
    This crab does not seem to be territorial but may put up a fight when foraging or courting. It is aggressive to other species of crab, but not to crayfish with which it often shares a crevice. Studies with tagged crabs suggest that they spend about 50% of their time foraging, 25% feeding, 20% in agonistic (combative, contestant) encounters and 5% in reproductive behaviour.
    In Australia this crab is favoured by fishermen for use as bait. Groupers seem to relish it.

    Life history: Mating between hardshelled crabs lasts about 7 minutes, with the female on top. Small females carry eggs from September to February but large females from late October. Eggs are about 0.4mm in size and change colour from brick red to light green just before hatching. During the release of the hatched larvae, the female assists departure by flexing her body up and down, vibrating her abdomen and pulling the hatching eggs from her pleopods with her nippers. Juveniles and small crabs moult throughout the year but but large crabs mainly in winter from May to September, before the breeding season.

    Distribution: the southern Indo-Pacific from south Africa to Chile. Southern Australia, Tasmania, South Africa, Juan Fernandez, Chile, Tonga. In New Zealand from Parengarenga Hr to Lyttleton Hr.

    f003215: red rock crab Plagusia capense
    f003215: A female red rock crab (small nippers) is taking a break, not far from a wharf pile where she hides inside crevices between encrusting organisms. Here she is standing tall, not showing any fear for the photographer. Interestingly, she has perched herself on top of two cushion stars, one with five legs, which is the norm, the far one with six legs, which is unusual.


    Hemigrapsus edwardsi (Hilgendorf, 1882), (Hemigrapsus sexdentatus), common rock crab, marbled rock crab, rerere,

    Hemigrapsus edwardsi(L: hemi= half; Edwards= a taxonomist?) A common intertidal crab, occurring in a variety of habitat: under boulders, on the rocky reef, on sand and mud flats. They are rarely found outside the intertidal zone. They can reach 4cm across their backs, and their colour is often a reddish purple, mottled with dirty white patches. They are usually found sheltering underneath rocks, extending from the high tide mark down to about mid tide. It is recognisable by the six teeth, from the eyes half way down on its carapace (sexdentatus: L: sex=six; dentatus= toothed). It has a smooth skin. The males have enormous chelae (nippers) with great pads of muscle bulging at the angles of the nippers. The two nippers are equal in size and shape.
    There are two colour types: light and dark. The lighter crabs have either a grey or cream-coloured background with markings of light or dark chestnut-red. Darker crabs are marked with dark purple, sometimes almost purplish black, and their legs are banded. Usually the front half of the carapace is more deeply pigmented than the rest. The eyestalks are white, speckled with dark red. Basal antenna segments arebanded. antennules are pale green with dark red spots. Belly surface is white.
    Hemigrapsus edwardsii is a very agile, rapidly moving crab, although easy to handle. Males have very large nippers and are able to crush oyster borers (Lepsiella sp.). The crabs emerge from under boulders and crevices to forage for mainly plant food at night. This crab is most active when the tide is in. It lives in the middle region of the intertidal rocky shore.

    Life history: This crab is a late winter breeder, with females in berry from March to August. Females carry their 26,000 eggs (size 0.3mm) for about 6 weeks, during which time they change colour from light brown to transparent.

    Distribution: found abundantly throughout the North and South Islands, endemic in New Zealand. Not in Chatham Islands or southern islands. This crab is more abundant on southern shores than in the north, where its intertidal habitat is taken by the blackfinger crab Ozius truncatus.

    Hemigrapsus crenulatis (H Milne Edwards, 1837), hairy-handed crab, papaka huruhuru

    Hemigrapsus crenulatus(L: hemi= half; crena= notch; latus=wide) The hairy-handed crab is often found where the tunnelling mud crab is found, on mud flats and sand flats, but it may also occur under boulders on the rocky shore intertidal. It has a dull colour and slightly hairy legs. Its main distinguishing features are the two hairy pads on the inner/under side of its nippers, but a crab needs to be handled in order to be able to view this. These crabs are much less wary than the other mud crabs, often going about their business without taking much notice of observers.
    It is thought that the hairy pads on its nippers allow it to wipe the bottom and objects such that food particles such as diatoms are caught in it. With its mouth parts, it can then feed from its hairy hands. These crabs are quite sturdy and in the aquarium they have been seen hunting and eating the smaller mud crabs. They are also very effective scavengers.
    Males have larger nippers than females, but left and right hand nippers are similar. The colour of its back is greeny-yellow with white patches, covered with tiny dark purple or reddish spots. The upper sides of their forearms (cheliped carpus and prodopus) are marked with deep purple-brown. The fingers of their nippers are white with small brown tips. Legs are greeny yellow with dark purple spots.
    This crab occurs in a wide variety of habitats, under stones, burrowing insand and mud, but always in sheltered places.

    Life history:  Males mature in about 1 year and live for 5 years. Females mature earlier and die earlier. Large males mate with smaller females. Mating takes about 10 minutes. The females come in berry in spring, from October to December. They may spawn more than once each year (June-February). Their 8,000-30,000 eggs (0.27mm) change colour from brownish-yellow to almost transparent, and hatch after 8-12 weeks. When releasing her offspring, the female raises hereself on her legs, opening her tail wide and beating it in rhytmical fashion. The nippers were alternatively dug into the brood to propel the newly hatched larvae in the surrounding water.
    This crab is a great survivor, being able to live in brackish water. Its main predators are fish like rig, red cod, sea perch and red gurnard. When small, more types of fish eat it.

    Distribution: A New Zealand species, occurring along the coasts of North and South Islands and Stewart Island. It is possible that the Chilean species is identical. It is interesting that two so widely separated species, look so much alike, but the Chilean species is grey, grey-brown and black.

    f026934: Hemigrapsus crenulatus, hairy- handed crab
    f026934: A large hairy-handed crab seen blowing bubbles while posturing on its patch in the sandy eelgrass habitat. Its hairy patches on the insides of its nippers are only just visible.
    f215306: hairy-handed crab walking
    f215306: Hairy-handed crabs do not bother to burrow or run away in case of danger. They seem to be confident that they are inedible to birds and other predators. Roaming around over the sand, and following the tide in and out, they move fast to arrive timely on the scene of death of other creatures.
    f215302: hairy handed carb burrowing
    f215302: shying away from the photographer, this hairy-handed crab starts digging itself in, releasing bubbles of methane gas rising from the putrid sand below. Notice that the orange coloured 'hairs' on its exoskeleton are actually brown algae. The hairy pads after which it is named, lie on the insides of its nippers. 
    f215328: two hairy-handed crabs dissecting a casualty
    f215328: Two hairy-handed crabs have arrived on the scene of a casualty, but long after whelks beat them to it. With their strong nippers, these crabs are able to tear the flesh apart. The whelks however, can drill through skeletons and reach the smallest corners inside, by means of their flexible trunks (probosces).


    Helice crassa (Dana, 1851), tunnelling mud crab, kairau

    Helice crassa(Gk: elisso= to revolve; L: Helix/Helice= a spiral curve; crassus= dull) The tunnelling mud crab is found in large numbers on healthy mud flats, where they burrow. These small crabs, measuring up to 4cm across their backs, are very wary, scuttling and scurrying in hordes at the slightest sign of movement, making the mud flats seem to move for a fraction of a second. They take time to dig elaborate tunnels in the mud, often with more than one entrance. Active by day, the tunnelling mud crabs sleep by night, often closing their burrows with a plug of mud. 
    These mud crabs are actively preyed upon by birds and many other animals. Their survival depends on how quickly they can withdraw into their burrows, and how capricious and unpredictable such tunnels are formed. It will occupy its tunnel for a long period of time and will defend it against intruders. Competitors are warned off with a typical threatening posture.
    Burrows of tunnelling mud carbs (morton & Miller 1968)The tunnelling mud crab has a squarish back and two short stalked eyes, and is brownish in colour. But older specimens are beautifully coloured greenish orange. It cannot be confused with the stalk-eyed mud crab, because this one has an elongated carapace, long stalked eyes, and beautiful colours. The tunnelling mud crabs live from the mud, which is rich in diatoms, algae and bacteria. Even the spoils of their burrows are spread carefully for optimal productivity (see photo; how many crabs can you see?). With their flat, spade-like nippers, they till the mud, like farmers do. It takes up a scoop of mud on its nippers, and then sorts it out with its mouth parts. In this rich, sun-lit environment, small organisms like diatoms and bacteria grow profusely, particularly when the mud warms up during low tide in mid day. Only a very small area, the size of a hand, is sufficient to feed a mud crab for life. Mudcrabs grow at least 5-6 years old, but some may survive a decade or longer. The large ones are rare, but beautifully coloured. One finds these in the cleaner reaches of an estuary.
    The colour of these crabs is tawny brown in juveniles, becoming green to yellow in large adults. Small patches of bright orange can be seen in the joints. Its antennae are brown, antennules light purple, eyestalks pale green dorsally (on top) but white ventrally (below). Legs are dark green with pale yellow margins. Males grow to 21mm measured over the width of their carapace (CW), and females are slightly smaller. These crabs are larger in the South Island.
    The tunnelling mudcrab lives in sheltered places where it can burrow in the sand or mud, or well-drained sediment exposed to the air for more than six hours on each tidal cycle (upper intertidal region). In places, up to 500-1800 crabs can be counted per square metre! H crassa must return frequently to its burrow to wet its gills.
    Tunnelling mudcrabs become suddenly active as soon as the tide moves out around them. They start cleaning the area around their burrow, and also themselves. When feeding on mud, the crab walks slowly forward with the nippers held in front, while probing the surface. Small pinches of surface sediment (algae and detritus) are transferred to the mouth parts. Wastes (sand, silt) accumulate at the bottom of the mouth frame, and these are wiped off by the nippers. These wastes (pseudo-faeces) form small pellets. H. crassa seldom forages more than 200mm from its burrow, often defending its territory against other mudcrabs. H.crassa will scavenge when the opportunity arises.
    In mangrove swamps, where mangrove trees shade the mud underneath, resulting in lower algal productivity, crabs may climb up the trees to a height of 1m, feeding from the mud on branches and leaves.
    Their burrows have complicated shapes, often joining up with those of other mud crabs. The end of their burrow slopes down, holding 20-50mm of water at low tide. When the tide moves in again, the crabs plug up the entrances to their burrows.
    H crassa has many enemies, from wading shore birds to fish (parore, cod, flounder, yellow-eyed mullet), including eels.

    Life history: Female H crassa mate in hard-shell condition. Mating occurs August to May, with peak periods in October and May. Copulation occurs on the surface of the ground, or still partly covered by water, with the male flat on his back and the female uppermost. Males usually mate with smaller females. The female carries her eggs in early spring and summer (August to March). Females mature at CW of 10mm. A 16mm female will carry about 16,000 eggs of 0.3mm, which change colour from brownish-yellow to transparent green during 42 days of incubation. Females may reproduce more than once per season, and do not require to mate for this. H. crassa appear to reach maturity after 1 year, and they can live a 5-6 year life.

    Distribution: this is a New Zealand species, widely distributed over the North and South Islands and Stewart Island.

    f992725: mud crab holes
    f992724: tunnelling mudcrab in burrow
    f992724: above, a tunnelling mud crab in its burrow. This is a large and old one, beautifully coloured.

    f992725: on left the burrows of a community of old and large mud crabs, who survived to an old age, perhaps because the sand here is consolidated and hardened by iron leachates. 

    f215226: a mud crab postures near its burrow
    f215226: A tunnelling mudcrab postures near its burrow. Notice its wide but flat nippers, which are eminently suitable for moving soil, like a spade. This is a large specimen, perhaps over ten years old.
    f215237: top view of Helice crassa
    f215237: As this mudcrab is cautiously leaving its burrow, it affords us a view of its back, characterised by its square shape and three spines along the edge.
    f215229: mudcrab disappearing into the mud
    f215229: a mudcrab is disappearing sideways into the mud. This is how it starts a new tunnel.
    f215231: mudcrab disappearing
    f215231:mud crab disappearing in the sandy mud.
    f215227: frontal view of Helice crassa
    f215227: frontal view of a large specimen of Helice crassa. When mudcrabs grow old, their skins also become more colourful.
    f215227: closeup of Helice's face
    f215227: closeup of Helice's face. Its mouth parts are shaped for sieving mud and sand.


    Cyclograpsus insularumCyclograpsus insularum (Campbell and Griffin, 1966), northern smooth shore crab

     This species is easily confused with the smooth shore crab Cyclograpsus lavauxi, which has a wider range in New Zealand, but similar habitat and eating habits.In first instance, this crab is distinguished by its smoothly graded colour from brown/purple in front, to paler brown towards the back, whereas C lavauxi is distinctly speckled. The northern smooth shore crab is also smaller than C lavauxi (CW 22mm versus 28mm). Its legs are not pointed and sharp but end in a kind of nipple. Its nippers are smooth, and so are their cutting edges. The righthand claw shows a distinctive gape between fingers.
    This crab is found in the upper reaches of the intertidal on exposed shores in the presence of boulders, just lower than high tide level, and below C lavauxi when the two are found together. It can be found in densities of over 30/m2. For further specifics, see those of the smooth shore crab.

    Life history: This crab breeds in winter from June to August, in a very short season of 9 weeks. They produce only one brood. Eggs are relatively large, measuring 0.45mm across and they are dark purple. They hatch after 7 weeks.

    Distribution: Lord Howe Island, Norfolk Island, Kermadec Islands and in New Zealand from North Cape to East Cape.


    Cyclograpsus lavauxi (Milne Edwards, 1853), smooth shore crab 

    Cyclograpsus lavauxi(L: cyclo= circle; Lavaux= name of an explorer) The smooth shore crab is a New Zealand species, common on rocky shores all around new Zealand. It is also found in estuaries and mud flats. Usually hiding at high intertidal levels, under boulders, it looks at first sight like a young (15mm) common rock crab, but its carapace is smoother (missing the six teeth) and elegantly curved. The eye orbits (sockets) are curved. A rare species exists, Cyclograpsus whitei, which looks the same, but does not have the carved eye sockets.
    The colour of the smooth shore crab is distinctly speckled in dark reddish-brown on a background varying through slate blue, bluish grey, fawn to yellowish brown. Its underside is pale. Its nippers are white. This is a small crab, measuring only 28mm CW in adult males.
    This crab is claimed the most terrestrial of the common crabs, living in the upper intertidal area around the high tide level. It spends a great deal of time out of the water. It usually outnumbers the hairy handed crab H edwardsi which lives lower down the shore. It normally rests under stones, becoming active only once daily during the night high tide.
    The smooth shore crab is usually found under stones, and may be heard making clicking sounds. It has the curious habit of grasping stones with its rear legs, presumably to stabilise itself in the presence of wave action. When prodded, this crab takes a defensive posture, which is often explained as aggressive.
    This crab normally dines on tough seaweeds, but it will also scavenge and predate on worms.

    Life history: Females start breeding at around 11mm CW. Their egg-carying period runs from September to January. Their eggs are 0.32mm across, coloured dark purple, becoming paler as development proceeds. Incubation time is about 8 weeks. Some females can produce two clutches of eggs in a season. Most crabs die after 2-3 years but some may live up to 5 years.

    Distribution: This crab is found mainly in two places, very far apart: New Zealand and Juan Fernandez in Chile. It may well be that the one in Juan Fernandez is a different species, not capable of interbreeding with its NZ relative. For this reason we consider C lavauxi an endemic species (found in NZ only).

    Related species: Cyclograpsus granulosus is found in Tasmania, C punctatus in south Africa and C integer in Jamaica.


    Planes cyaneus, Blue Pacific weed crab 

    Planes cyaneus (Gk: planes/planetes= wanderer; cyaneus= blue; blue wandering crab) The Pacific weed crab is a small crab (12mm across its back, 25mm length), living in the open ocean, often clinging to seaweed and flotsam. In this way it is a frequent visitor to New Zealand waters, where it may get beached with its raft of flotsam, debris, fishing float, pumice, dead shell or rams horn shell. It is sometimes seen attached to sea turtles.
    This crab has a variable and protective colouration ranging from blue, bluish brown to yellowish, clouded with brown. It is likely that this crab is able to change its colours when moulting, in a similar manner as its relative P minutus. With its chromatophores, this crab can respond to white, black, blue, yellow and green backgrounds.

    Life history: Not much is known about this crab. Females start to breed at about 8mm CL, and like P minutus, may breed all year round. Crabs in berry have not been recorded from NZ.

    Distribution: Pacific Ocean.

    A related species is the Gulf-weed crab Planes minutus, which is found in the open Atlantic ocean, associated with the seaweed Sargassum (Spanish: sargasso= seaweed).

    Planes marinusPlanes marinus (Rathburn, 1914), Brown Pacific weed crab

    (L: planes= wanderer; marinus= of the sea; sea wanderer) The brown Pacific weed crab is an oceanic species, found attached to seaweed and flotsam, often between goose barnacles. It is a small crab (20mm CW) with a squarish back and dark reddish-brown colour. Very little is known about it. Ovigerous (in berry) females have been found in NZ.

    Distribution: Indo-Pacific, Japan, west coast of N America, Australia, Kermadec islands, in New Zealand from the Bay of Plenty to Chatham Islands.

    Grapsus grapsus, Sally Lightfoot crab 

    The Sally Lightfoot crab is found in south America and features on many shore photographs of the Galapagos Islands. It is not found in New Zealand. It resembles the purple rock crab in behaviour, feeding and habitat preference.

    Plagusia depressa tuberculataPlagusia depressa tuberculata (Lamarck, 1818)

    The depressed red rock crab is similar to the red rock crab Plagusia chabris and occupies a similar niche in the tropics. It is sometimes encountered in New Zealand, clinging to floating objects like driftwood. This crab is recognisable by its flat shape and slightly hollow (convex) back, which is covered with flattened tubercles. Its colour is reddish with darker blood-red spots and speckles.

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