Cyclograpsus cinereus

Cyclograpsus cinereus Dana, 1851 is a marine crab of the family Varunidae, accepted under that name in the World Register of Marine Species ^[1]. It lives in the upper part of the intertidal zone on the south-eastern Pacific coast, and its northern limit reported in the literature is Ancón, in Peru ^[2]. The authors of a study in Antofagasta list it among the most abundant species on the rocky shores of Chile ^[3].

According to the survey cited by Costlow and Fagetti, adults occur from Ancón, in Peru, to Calbuco, in Chile, and there is also one isolated locality outside that range, in Panama ^[2]. Adults live in the upper level of the intertidal zone, under stones, in coarse sand ^[2].

In later studies, the Chilean populations have been described as belonging to the supratidal zone, with constant cycles of immersion and emersion ^[4]. In Antofagasta bay (23°27′ S) the species was counted in quadrats on rocky shores during the spring and summer of 2018 to 2020, at six sites, four urban and two inside a protected area ^[3].

At Montemar, on the central Chilean coast, ovigerous females were observed all year round except February. The main spawning period ran from July to November, when more than 60% of the population carried eggs and the water temperature rose from 12 °C to 14 °C ^[2].

The larva completes its development in 5 zoeal stages and 1 megalopa. The first zoea has a gibbose dorsal spine, and the following zoeae bear lateral spines on the carapace. Reared in the laboratory at 25 °C, larvae took on average 30 days to reach the first crab at a salinity of 30 ppt and 34.2 days at 35 ppt; at 20 °C they took 45.7 and 47.7 days respectively ^[2].

Survival to the crab stage was 38% to 45% at 20 °C, and only 2% to 10% at 25 °C. At 30 °C all larvae died within the first 2 days after hatching. A salinity between 30 and 35 ppt did not appreciably change the duration of development ^[2].

In 6 populations along 19° of latitude of the Chilean coast, female size, egg number and egg size, and reproductive output differed among localities following a clinal pattern ^[5].

In Antofagasta bay the individuals showed an aggregated distribution in 15 sampling events and a uniform one in 4. No significant density differences were found between the sites of the urban zone and those of the protected zone ^[3].

Because it lives in the supratidal zone, with constant cycles of immersion and emersion, the crab retains CO2, mainly in the branchial cavity. In 6 Chilean populations exposed to air in the laboratory, those from low latitudes, subject to higher air temperatures, showed greater variation in haemolymph pH, more calcium, and less chloride and activity of the enzyme LDH ^[4].

The species breathes oxygen from both air and water, like an amphibious crab. In 5 populations spread over 2000 km, in almost all of them the ratio of aerial to aquatic metabolism was close to 1, and the metabolic rate was higher at low latitudes ^[6].

A 1967 paper places Cyclograpsus cinereus in Peru only as far as Ancón, the northern limit of its range according to the literature it cites; no more recent presence data for the Peruvian coast are given here. According to that paper, the adults' habitat is the upper part of the intertidal zone, under stones on coarse sand ^[2].