03 January 2021

Ghost Crab – Farasan Islands

Ghost crabs are semi-terrestrial crabs of the subfamily Ocypodinae. They are common shore crabs in tropical and subtropical regions throughout the world, inhabiting deep burrows in the intertidal zone. They are generalist scavengers and predators of small animals. The name "ghost crab" derives from their nocturnality and their generally pale coloration. Characteristics of the subfamily include one claw being larger than the other, thick and elongated eyestalks, and a box-like body. The differences in claw sizes, however, are not as marked in male fiddler crabs. The subfamily includes 22 species in two genera. Ocypodinae is one of two subfamilies in the family Ocypodidae, the other being the fiddler crab subfamily, Ucinae. Both subfamilies have members in which one of the claw-bearing legs (the chelipeds) is much larger than the other. Both male and female ghost crabs have unequally sized claws with the carapaces of ghost crabs more or less box-like. The eyes of ghost crabs have large and elongated eyestalks, with the corneas occupying the entire lower part. Most ghost crabs have pale-colored bodies that blend in well with the sand, though they are capable of gradually changing body coloration to match their environments and the time of day with some species being brightly colored. Ghost crabs have elongated and swollen eyestalks with very large corneas on the bottom half. Their carapaces are deep and box-like, squarish when viewed from the top with straight or slightly curving sides. The regions of the carapace are usually not clearly defined. The "whip" of their antennules are small or rudimentary. They fold back into the body diagonally or almost vertically. The plate between them is broad. The third pair of mouth appendages completely cover the mouth opening. A small orifice with edges thickly fringed with hair is found between the bases of the second and third pairs of walking legs. Ghost crabs are generalists, scavenging carrion and debris, as well as preying on small animals, including sea turtle eggs and hatchlings, clams, and other crabs. They are predominantly nocturnal. They remain in their burrows during the hottest part of the day, and throughout the coldest part of the winter. Ghost crabs are swift runners, darting away at the slightest sign of danger. They either head back to their burrows or plunge into the sea to escape intruders. Ghost crabs also have the ability to change colors to match their surroundings by adjusting the concentration and dispersal of pigments within their chromatophores. They can even match the specific colors of the grains of sand in their habitats. However, ghost crabs are only capable of morphological color change, which occurs over a long span of time. Ghost crabs lay their eggs in the sea, which develop into planktonic marine larvae.
Ghost Crab