Cyclograpsus lavauxi

Cyclograpsus lavauxi is a small, temperate crab in the Grapsidae family.^[2] The adult males average 28 mm and females average 26 mm.^[1] The shell, or carapace, is polished^[3] and is wider than it is long.^[4] On average, the crab is 9 mm long and has a width of 11 mm.^[5] The brim of the C. lavauxi carapace is smooth.^[3] The anterior of the carapace 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.^[6] 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.^[5] The first, second, and third legs also have small tufts of hair between them.^[4] Its long legs enable it to run at rapid speeds. C. lavauxi is agile and alert, resulting in a very mobile and versatile crab.^[7]

A number of different color morphs have been observed in C. lavauxi. Their carapace can vary in color between slate blue, bluish-grey, fawn, and yellowish-brown.^[1] C. lavauxi carapaces can also contain several shades of grey, green, and brown, often with dark brown and red speckles.^[5] The underside of the crab is a lighter plain color than the carapace.^[1] The legs display the same coloring as the carapace with brighter speckled colouring.^[4]

The smooth shore crab's natural range is New Zealand and Chile in the Juan Fernandez Islands.^[1][8] C. lavauxi has been found to reside in a number of New Zealand sites from the Hohoura Harbour to Westland^[1] with significant populations in the North Island.^[5]

C. lavauxi can be found in a variety of environments,^[9] including boulders, under stones, and on beaches ranging from exposed shores to protected bays.^[1] It is a common crab on New Zealand beaches, outnumbering the larger common rock crab species.^[1] It is found near the littoral sea margin, where it is only barely or not at all^[10] wetted. It has also been discovered on mudflats, estuaries, and rocky coastlines.^[11] 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.^[2]

The mating season of C. lavauxi is during the summer months from mid-October to late December.^[12] 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.^[13] 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.^[13] Likely due to this competition, mating pairs can be found under rocks to hide from other males who might interfere.^[13]

During mating, males approach a female and hold on to her carapace for an hour, after which there is a two-hour-long copulation.^[13] Oftentimes females will resist males and try to escape.^[13]

Females carry eggs between November and February^[14] and have a short reception time of fewer than 24 hours, or almost a week in captivity.^[13] They oviposit their eggs in synchronization with others in the population within a four-week period,^[13] laying thousands of eggs in each batch.^[14] Females who are unable to mate during the breeding season are able to lay fertile eggs by storing sperm from the previous breeding season.^[13] This extra sperm is stored in the spermatheca after mating.^[13] Females only lay eggs once per mating season.^[12]

The eggs initially are a dark purple colour, but grow paler and develop black eyespots as they mature.^[12] The eggs are 0.25-0.3 mm in diameter and hatch in about two months.^[14] Once hatched, the larvae are just over 1 mm in length.^[12]

C. lavauxi tend to moult soon after the breeding season has ended, in late summer to early autumn.^[13]

C. lavauxi is a scavenger crab, foraging on deceased animals and plants,^[3] although in most cases it is a herbivore.^[5] Its general diet includes algae, drift and seaweed.^[1] 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.^[9]