Smooth Shore Crab

Cyclograpsus lavauxi is a small, temperate crab in the Grapsidae family. The adult males average 28 mm and females average 26 mm. The shell, or carapace, 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 carapace is smooth. 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. 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.

The smooth shore crab's natural range is New Zealand and Chile in the Juan Fernandez Islands. 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 New Zealand beaches, outnumbering the larger common rock crab species. It is found near the littoral sea margin, where it is only barely or not at all wetted. It has also been discovered on mudflats, estuaries, 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.

C. lavauxi is a scavenger crab, foraging on deceased animals and plants, although in most cases it is a herbivore. 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.

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.