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

crab Crabs are decapod crustaceans of the infraorder Brachyura (meaning "short tailed" in Greek language, Greek), which typically have a very short projecting tail-like abdomen#Arthropoda, abdomen, usually hidden entirely under the Thorax (arthropo ...

of the

family Family (from ) is a Social group, group of people related either by consanguinity (by recognized birth) or Affinity (law), affinity (by marriage or other relationship). It forms the basis for social order. Ideally, families offer predictabili ...

Grapsidae The Grapsidae are a family (biology), 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 Taxon, taxa may belong in other families. They are found al ...

, found in

New Zealand New Zealand () is an island country in the southwestern Pacific Ocean. It consists of two main landmasses—the North Island () and the South Island ()—and List of islands of New Zealand, over 600 smaller islands. It is the List of isla ...

and the

Juan Fernández Islands The Juan Fernández Islands () are a sparsely inhabited series of islands in the South Pacific Ocean, reliant on tourism and fishing. Situated off the coast of Chile, they are composed of three main volcanic islands: Robinson Crusoe Island, R ...

Chile Chile, officially the Republic of Chile, is a country in western South America. It is the southernmost country in the world and the closest to Antarctica, stretching along a narrow strip of land between the Andes, Andes Mountains and the Paci ...

Description

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

family. The adult males average 28 mm and females average 26 mm. The shell, or

carapace A carapace is a 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 tortoises, the unde ...

, 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 In celestial mechanics, an orbit (also known as orbital revolution) is the curved trajectory of an physical body, object such as the trajectory of a planet around a star, or of a natural satellite around a planet, or of an satellite, artificia ...

, 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. ''C. lavauxi'' is agile and alert, resulting in a very mobile and versatile crab. A number of different color morphs have been observed in ''C. lavauxi''. Their

can vary in color 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 color than the

. The legs display the same coloring as the

with brighter speckled colouring.

Distribution and habitat

The smooth shore crab's natural range is

and

in the

Juan Fernandez Islands ''Juan'' is a given name, the Spanish and Manx versions of ''John''. The name is of Hebrew origin and has the meaning "God has been gracious." It is very common in Spain and in other Spanish-speaking countries around the world and in the Philipp ...

. ''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. ''C. lavauxi'' can be found in a variety of environments, including boulders, under stones, and on beaches ranging from exposed shores to protected bays. It is a common crab on

beaches, outnumbering the larger common rock crab species. It is found near the

littoral The littoral zone, also called litoral or nearshore, is the part of a sea, lake, or river that is close to the shore. In coastal ecology, the littoral zone includes the intertidal zone extending from the high water mark (which is rarely i ...

sea margin, where it is only barely or not at all wetted. It has also been discovered on

mudflats Mudflats or mud flats, also known as tidal flats or, in Ireland, slob or slobs, are coastal wetlands that form in intertidal areas where sediments have been deposited by tides or rivers. A global analysis published in 2019 suggested that tidal ...

estuaries An estuary is a partially enclosed coastal body of brackish water with one or more rivers or streams flowing into it, and with a free connection to the open sea. Estuaries form a transition zone between river environments and maritime environm ...

, and rocky coastlines. Younger crabs prefer the lower lines of the shoreline and mudflats, whereas older crabs prefer the higher lines of the foreshore and mudflats. During the summer, all ''C. lavauxi'' migrate to the lower foreshore line.

Life cycle/phenology

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. During mating, males approach a female and hold on to her carapace for an hour, after which there is a two-hour-long copulation. Oftentimes females will resist males and try to escape. Females 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 The ovipositor is a tube-like organ used by some animals, especially insects, for the laying of eggs. In insects, an ovipositor consists of a maximum of three pairs of appendages. The details and morphology of the ovipositor vary, but typical ...

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 is stored in the

spermatheca The spermatheca (pronounced : spermathecae ), also called ''receptaculum seminis'' (: ''receptacula seminis''), is an organ of the female reproductive tract in insects, e.g. ants, bees, some molluscs, Oligochaeta worms and certain other in ...

after mating. Females only lay eggs once per mating season. The eggs initially are a dark purple colour, but grow paler and develop 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. ''C. lavauxi'' tend to

moult In biology, moulting (British English), or molting (American English), also known as sloughing, shedding, or in many invertebrates, ecdysis, is a process by which an animal casts off parts of its body to serve some beneficial purpose, either at ...

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 Corpse decomposition, 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 he ...

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

herbivore A herbivore is an animal anatomically and physiologically evolved to feed on plants, especially upon vascular tissues such as foliage, fruits or seeds, as the main component of its diet. These more broadly also encompass animals that eat ...

. 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' inhabiting the area where the tide does not often reach. Their main predators are generalist birds such as

Gulls Gulls, or colloquially seagulls, are seabirds of the subfamily Larinae. They are most closely related to terns and Skimmer (bird), skimmers, distantly related to auks, and even more distantly related to waders. Until the 21st century, most gul ...

and

Kingfisher Kingfishers are a family, the Alcedinidae, of small to medium-sized, brightly coloured birds in the order Coraciiformes. They have a cosmopolitan distribution, with most species living in the tropical regions of Africa, Asia, and Oceania, ...

s. Fish species including the Smooth Hound Fish,

Spiny Dogfish The spiny dogfish (''Squalus acanthias''), spurdog, mud shark, or piked dogfish is one of the best known species of the Squalidae (dogfish) family of sharks, which is part of the Squaliformes order. While these common names may apply to several ...

, 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 Triglidae, the gurnards and sea robins. This fish is found in the eastern Atl ...

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''. 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.'' Studies also suggest that females do 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 and often more successfully than others within its genus. ''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. The common body posture of C. lavauxi is being flat with pincers folded and lying on the ground with its walking legs close and side-by-side. When in a raised position, it places 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 Artillery consists of ranged weapons that launch Ammunition, munitions far beyond the range and power of infantry firearms. Early artillery development focused on the ability to breach defensive walls and fortifications during sieges, and l ...

. 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 Crabs of the Pacific Ocean Marine crustaceans of New Zealand Crustaceans described in 1853 Taxa named by Henri Milne-Edwards