The smooth shore crab (''Cyclograpsus lavauxi'') is a marine large-eyed

crab Crabs are decapod crustaceans of the infraorder Brachyura, which typically have a very short projecting "tail" (abdomen) ( el, βραχύς , translit=brachys = short, / = tail), usually hidden entirely under the thorax. They live in all the ...

of the family

Grapsidae The Grapsidae are a family of crabs known variously as marsh crabs, shore crabs, or talon crabs. The family has not been confirmed to form a monophyletic group and some taxa may belong in other families. They are found along the shore among rocks ...

, found in New Zealand and the Juan Fernández Islands of Chile.

Description

''Cyclograpsus lavauxi'' is a small, temperate crab in the

family. The crab is roughly the size of a coin, with the adult males averaging 28 mm and females averaging 26 mm. The shell, or

carapace A carapace is a Dorsum (biology), dorsal (upper) section of the exoskeleton or shell in a number of animal groups, including arthropods, such as crustaceans and arachnids, as well as vertebrates, such as turtles and tortoises. In turtles and tor ...

, is polished and is wider than it is long. On average, the crab is 9 mm long and has a width of 11 mm. The brim of the ''C. lavauxi''

is smooth. The anterior of the

is linear-edged, with two eye orbits, which are curved and situated in the two frontal corners. The antennae are well-developed and are used for sensing texture, food, and sound. ''C. lavauxi'' has eight legs and two large frontal pincers. Its legs are compressed, slender, and long, and have six lines of hair running the full 4mm length of the legs, which are fairly robust. The first, second and third legs also have small tufts of hair between them. Its long legs enable it to run at rapid speeds. ''Cyclograpsus spp''. is agile and alert, resulting in a very mobile and versatile crab. ''A number of different

colour morphs In biology, polymorphism is the occurrence of two or more clearly different morphs or forms, also referred to as alternative ''phenotypes'', in the population of a species. To be classified as such, morphs must occupy the same habitat at the s ...

have been observed in C. lavauxi''. Their

can vary in colour between slate blue, bluish-grey, fawn, and yellowish-brown. ''C. lavauxi'' carapaces can also contain several shades of grey, green, and brown, often with dark brown and red speckles. The underside of the crab is a lighter plain colour than the

. The legs display the same colouring as the

with brighter speckled colouring.

Distribution

Natural global range

The smooth shore crab's natural range is New Zealand and Chile in the Juan Fernandez Islands.

New Zealand range

''C. lavauxi'' has been found to reside in a number of New Zealand sites from the Hohoura Harbour to Westland with significant populations in the North Island.

Habitat preferences

''C. lavauxi'' occurs in a multitude of habitats including boulders, under stones and on beaches ranging from exposed coasts to sheltered bays. It is a fairly common crab on New Zealand shores and typically outnumbers the larger common rock crab species. It can be found near the littoral sea fringe where it is wetted only slightly or not at all. It has also been found in intertidal levels, mudflats, estuaries and rocky shores. Older individuals are often found higher on the foreshore or mudflats than younger individuals while younger crabs prefer the lower lines of the foreshore and mudflats. During the summer months, all ''C. lavauxi'' move down into the lower foreshore line.

Life cycle/phenology

Reproduction

The mating season of ''C. lavauxi'' is during the summer months from mid-October to late December. This mating season is highly synchronous within the population. The crabs are not monogamous and both females and males will mate multiple times during the breeding season. During this reproduction season, male-male competition is frequently displayed. Bigger males will often attack other males in the process of mating with a female, frequently giving the female an opportunity to escape. Likely due to this competition, mating pairs can be found under rocks to hide from other males who might interfere. Brockerhoff and McLay found that males approach a female and hold on to her carapace for an hour, after which there was a two-hour-long copulation. Oftentimes females will resist males and try to escape. Females only carry eggs between November and February and have a short reception time of fewer than 24 hours, or almost a week in captivity. They oviposit their eggs in synchronization with others in the population within a four-week period, laying thousands of eggs in each batch. Females who are unable to mate during the breeding season are able to lay fertile eggs by storing sperm from the previous breeding season. This extra sperm was stored in the spermatheca after mating. Females only lay eggs once per mating season. The eggs initially are a dark purple colour after laying, but grow paler and have obvious black eyespots as they mature. The eggs are 0.25-0.3 mm in diameter and hatch in about two months. Once hatched, the larvae are just over 1 mm in length.

Moulting

''C. lavauxi'' tend to moult soon after the breeding season has ended, in late summer to early autumn.

Diet and foraging

''C. lavauxi'' is a

scavenger Scavengers are animals that consume dead organisms that have died from causes other than predation or have been killed by other predators. While scavenging generally refers to carnivores feeding on carrion, it is also a herbivorous feeding b ...

crab, foraging on deceased animals and plants, although in most cases it is a

herbivore A herbivore is an animal anatomically and physiologically adapted to eating plant material, for example foliage or marine algae, for the main component of its diet. As a result of their plant diet, herbivorous animals typically have mouthpart ...

. Its general diet includes algae, drift and seaweed. The crabs feed only during high tides, and are able to synchronize or modify their feeding pattern to ensure they feed under optimal conditions, maximizing their feeding hours and nutrition intake.

Predators, parasites, and diseases

A number of species predate on ''C. lavauxi'', particularly bird species due to the crabs' habiting the area where the tide does not often reach. Their main predators are generalist birds such as Seagulls or Kingfisher. Fish species including the Smooth Hound Fish, Spined Dogfish, Terakihi, Sea Perch, Moki and

Red Gurnard The red gurnard (''Chelidonichthys cuculus''), also known as the East Atlantic red gurnard or soldier, is a benthic species of ray-finned fish belonging to the family (biology), family Triglidae, the gurnards and sea robins. This fish is found ...

also occur. ''C. lavauxi'' are at times able to evade predators by using their quick reactions and speed. The nematode ''Ascarophsis sp.'' and the parasitic isopod ''Portunion sp.'' are found in ''C. lavauxi''. Brockerhoff found the majority of ''C. lavauxi'' are infected by the internal parasite ''Portunion sp.'' Brockerhoff's study showed the reproduction of female ''C. lavauxi'' was remarkably reduced by the parasite ''Portunion sp.'', this was believed to be because all parasitized females were castrated, although there were no visible signs of this parasite affecting mating behaviour in the males. The male verse male competition was also not seen to affect the crab that was infected with the parasite ''Portunion sp.'' Brockerhoff's study also suggests that females did not avoid either the unparasitized and parasitized males due to there being no visible disadvantages to either.

Other features

''C. lavauxi'' has the ability to live successfully under large amounts of sediment. Bacon found that ''Cyclograpsus insularum'' was only able to tolerate 18% of sediment underneath boulders while ''C.lavauxi'' can withstand up to 63% of sediment. ''C. lavauxi'' displays a number of other unique behavioural traits including its aggressiveness when cornered, raising its pincers to accentuate its size along with showing their paleness. Its major body postures include being flat with its pincers folded and lying on the ground with its walking legs close and side-by-side. When in a raised position it place its body at a 45 degree angle with its back part still lying on the ground with pincers resting still either flat or poised at the midway mark. Its final position is the tiptoe position with its body angled and lifted off the ground and in the air, pincers still folded but held off the ground with its walking legs fully extended. ''C. lavauxi'' are usually found under stones, with their hind legs grasping stones which pushes the back half of the crab up onto the stone clasping it with its talons with the crab using its other legs to support its weight. This is in order to increase its mobility and stabilize the crab against the effects of tidal action. They also use their pincers and talons to dig burrows and push stones away. These holes have been found to be between 20 and 40 mm deep under the cover of rock. Further, ''C. lavauxi'' can make clicking noises with the sound acting as a sort of distant artillery. It is one of the only crabs in New Zealand that can perform such an action. ''C. lavauxi'' has evolved to become a versatile and robust species that is able to cope in extreme conditions that many species of crab in New Zealand cannot. This has resulted in an overall greater abundance and success in its population, leading it to be one of New Zealand's most common crabs.

References

{{Taxonbar, from=Q5198705 Grapsoidea Crustaceans of the eastern Pacific Ocean Marine crustaceans of New Zealand Crustaceans described in 1853 Taxa named by Henri Milne-Edwards