Cart driver crab

Ocypode gaudichaudii is a ghost crab of the family Ocypodidae, described in 1843 by H. Milne Edwards and Lucas ^[1]. It lives in burrows on sandy beaches of the eastern Pacific, from Guatemala to Chile ^[2]. Its name recorded for Peru is cangrejo carretero ^[3]. Populations have been measured at Salaverry, at Chancayllo and near Lima ^[4],[5],[2].

Crabs that feed on sediment develop claws with a truncated tip, which they use like a shovel ^[6]. On beaches near Lima, males weighed 14 g on average and females 17 g ^[2].

Measured size differs between studies. On three beaches at Salaverry, mean cephalothorax length was 28.8 mm, with a standard deviation of 5.6 mm ^[4]. At Chancayllo beach, the most frequent adult size class measured 37.5 to 42.5 mm in carapace width ^[5].

The species occurs along the Pacific coast of the Americas, from Guatemala to Chile ^[2]. It lives on sandy beaches, where it digs burrows in the sand banks and stays hidden while the tide is high ^[3].

On 10 beaches in northern Chile, between 20 and 23° S, the burrow zone mostly covered the dry part of the beach and the retention zone. Burrow density changed within each beach and between beaches, and was better explained by the height of the drift line and by the width and slope of those zones than by the morphodynamic type of the beach ^[7].

Along northern Peru there are dissipative, desert-backed beaches under different degrees of human pressure, including those at Salaverry, where the species was studied ^[4].

The population sex ratio is 1 to 1, although it varies with the part of the beach that is sampled: in the upper third, near the burrows, males outnumbered females 2 to 1, and away from the burrows there were twice as many females as males. Reports of skewed ratios may therefore reflect biased sampling ^[8]. At Chancayllo, the full year gave a ratio close to 1 to 1 ^[5].

Size at morphometric maturity (CW50, carapace width) was 19.8 mm in females and 18.0 mm in males, estimated from cephalothorax length ^[5]. At Salaverry, 56 % of the crabs were males, breeding appears to depend on temperature, and the instantaneous mortality rate was estimated at 0.84 per year ^[4].

In Panama, of 88 crabs examined, 44 had identifiable material in the foregut: 30 with animal remains, 12 with diatoms and 2 with both. Individuals under 12.3 mm cephalothorax length and with non-truncated claws ate only animals; larger ones, with truncated claws, ate animals, diatoms or both ^[6].

Crabs of the genus Ocypode are mostly nocturnal, live in deep burrows in the intertidal zone, and are generalist scavengers and predators of small animals ^[2]. In this species, in Panama, animal remains and diatoms have been found in the foregut ^[6].

Population density measured in Peru was 0.76 individuals per m² at Chancayllo, with no significant seasonal differences ^[5], and 0.15 burrows per m² at Salaverry ^[4].

The crab hosts a parasite, the acanthocephalan Neoandracantha peruensis, described from its larvae. From 1069 crabs examined on beaches near Lima, 12 larvae were obtained in total. The adults have not been found in the birds checked, although in most species of a related genus the final host is a cormorant ^[2].

No extinction-risk assessment is cited here for this species. What exists is a reading of its local condition: at Salaverry, estimated instantaneous mortality was 0.84 per year and few specimens approached the asymptotic length, data the authors say indicate a high level of ecosystem disturbance ^[4]. An Ecuadorian study notes that the species' populations can be affected by human activities on beaches ^[9].

The species has been described as an indicator of ecosystem disturbance on beaches of northern Peru ^[4]. In Ecuador, 832 burrows were counted on 4 beaches of Guayas and their opening diameter was measured as an indirect estimate of crab size, as a first step toward assessing the ecological state of those beaches ^[9].

Peruvian literature records it on sandy beaches at Salaverry, sampled from September 2021 to February 2022 ^[4], on Chancayllo beach on the central coast ^[5], and on beaches of Lima, Callao and Barranca studied between 2011 and 2017 ^[2].