Sunday, December 12, 2010

Ghost Crab! by Sarah Hurtado

I. Introduction

Ghost crabs, also known as sand crabs are of the genus Ocypode. Ghost crabs live on the sandy shores in tropical and subtropical areas. They are most commonly sighted at dusk or during the night. In drier areas of the upper beach, golfball-sized entrance holes indicate the home of these crabs. The burrows extend 3-4 feet. The crabs are able to pick up clawfuls of sand and toss them up to 12 inches away from the burrowing opening! Later using their claws, they smooth out the surface. Sometimes they cover their burrowing holes with a dome of sand to camouflage their home. The tunnel leading to their chamber, is constructed with wet sand so that it won’t collapse. During the winter, Ghost Crabs hibernate in their burrows and use oxygen stored in their gills for up to six weeks. It is important that they have access to water because periodically for respiration and reproduction, they need to wet their gills. The seawater is stored in the bronchial chambers. The crabs cannot swim, but babies begin life in the water and become amphibious temporally.

II. Anatomy

The Ghost Crabs shell is 1 ½ - 2 inches across. They have six strong and hairy legs that enable him to go up to 10 miles per hour, which makes them the fastest crustaceans. They can run sideways, forwards, and backward. They have strong pinchers of unequal size.

III. Form and Function

The large eyestalks are club-shaped and are capable of 360 degree vision. They have such good vision, they are able to spot and grab insects in mid-air. They powerful claw also allows them to grab food and before eating, crushes their prey. They eat beach fleas, coquina clams, mole crabs, lizards, and carrion. Also, when baby sea turtles are hatching, they are also prey for the Ghost Crabs. They mostly feed at night. Reproduction involves competition between male crabs. Males raise both their claws and their bodies in threatening postures until one sinks into a submissive posture or sometimes there will be a “pushing fight”. Mating occurs on the sand or within burrows, and females lay their eggs in the water. Females with egg masses need to frequently enter the water to keep the eggs wet. They may turn upside down in the water to ventilate the egg mass which is carried under her tail. The larvae drift for four to six weeks and then return to the sand as apple-seed- size babies! While they are drifting, they are prey to small fish and other aquatic animals. Other than this, they have few predators, raccoons and birds being the largest threats. They use their large claw as a defense mechanism as well as retreating to their burrows. They blend in very well with the sand and their excellent eye sight helps them protect themselves from predators. Excretory and osmoregulatory organs are paired glands located in the head, with excretory pores opening at the base of either antennae or maxille. Waste products are mostly ammonia with some urea and uric acid. The waste diffuses through the gills as well as through the excretory glands.

IV. Impact on the World/Humanity
Ghost Crabs are widely distributed and very abundant. They are not under threat, and have very little interaction with humans. Although building and beach traffic can displace the crabs and compact the sand which in turn destroys their burrows, forces needed moisture from the sand, crush vegetation and enhance erosion from waves. On some Caribbean Islands, they are a human food source.

V. Journal Article Review
Uptake of Soil Capillary Water by Ghost Crabs
Thomas G. Wocott

This article is about how the Ghost crab can extract water from damp sand. When they are unable to get to water, they can extract water from the sand and even the inside of their burrow. They are unsure of the mechanism that allows them to do this, but some studies have shown that the mechanism may involve a capillary attraction and the production on a substantial vacuum.


Works Cited

1 comment:

  1. I don't know why there are really big spaces! Sorry everyone!