Atlantic Ghost Crabs (Ocypode quadrata) are small crabs (up to around 50 mm) with squarish sand-colored shells having margins that are finely beaded but toothless; the claws are white. The space between the eyes is much shorter than the eyestalks. These crabs dig burrows above the intertidal zone on ocean beaches from Delaware (U.S.A.) through the Caribbean and Gulf of Mexico to Brazil. They are occasionally found north to eastern Long Island and Rhode Island, but are uncommon north of Virginia. Atlantic Ghost Crabs are very active and can often be seen dashing into the retreating surf to wet their gills or to grab scraps of food ("Ocypode" means "swift-footed"), although they will drown if kept submerged. Young crabs burrow just above the intertidal zone, but adults dig their burrows higher up, sometimes even behind the forward dunes. Burrows have a single opening and descend 0.6 to 1.2 meters at a 45 degree angle. Although these crabs are often out and about during the day, they are most active at night. (Gosner 1978)
The range of Ocypode quadrata extends from Block Island, Rhode Island to Santa Catarina, Brazil. It has also been found in Bermuda, and larvae have been found as far north as Woods Hole, MA, however no adults have been found at this latitude. Their basic range is 40 degrees N to 30 degrees S on the eastern coasts of North and South America.
Biogeographic Regions: atlantic ocean (Native )
Ocypode quadrata is small, having a carapace length of about 5 cm (2 inches) at maturity. They are either straw-colored or grayish-white. They have a quadrate carapace, large club-shaped eyestalks, unequal chelipeds (claws) and long walking legs. Males are generally larger than females.
Average length: 50 mm.
Other Physical Features: ectothermic ; bilateral symmetry
Sexual Dimorphism: male larger
Ghost crabs inhabit tropical and subtropical areas and can be found on both oceanic and more protected estuarine beaches. They are found on the supralittoral zone (the area above the spring high tide line) of sand beaches, from the water line up to the dunes.
Range elevation: 0 to 3.05 m.
Average elevation: 2 m.
Habitat Regions: tropical ; saltwater or marine
Aquatic Biomes: coastal
Other Habitat Features: estuarine ; intertidal or littoral
Water temperature and chemistry ranges based on 1 sample.
Depth range (m): 1 - 86
Temperature range (°C): 11.782 - 11.782
Nitrate (umol/L): 6.526 - 6.526
Salinity (PPS): 34.586 - 34.586
Oxygen (ml/l): 5.374 - 5.374
Phosphate (umol/l): 0.624 - 0.624
Silicate (umol/l): 3.916 - 3.916
Depth range (m): 1 - 86
Note: this information has not been validated. Check this *note*. Your feedback is most welcome.
Ghost crabs are both predators and scavengers, and they feed at night. Their prey can be influenced by the type of beach they live on. Crabs on oceanfront beaches tend to feed on bean clams (Donax spp.) and mole crabs (Emerita talpoida), while crabs on more protected beaches will feed on the eggs and hatchlings of loggerhead turtles (Caretta caretta).
Animal Foods: eggs; carrion ; terrestrial non-insect arthropods; mollusks
Foraging Behavior: stores or caches food
Primary Diet: carnivore (Eats non-insect arthropods)
The main role of Ocypode quadrata in its ecosystem is the role of top predator in the filter-feeding based food chain. The majority of their food is live prey, although they are also facultative scavengers. Ghost crabs can consume the majority of the production of both Donax and Emerita talpoida crabs. They are a crucial part of the food chain, playing an important role in the energy transfer from organic detritus and smaller invertebrates to larger predators.
Ghost crabs have few terrestrial predators. They are largely nocturnal to reduce the risk of being eaten by shorebirds and gulls. When they do leave their burrows during the day, they are able to slightly change their color to match the surrounding sand. Another predator is the raccoon.
- Raccoons, Procyon
- Burrowing Owl, Speotyto cunicularia
- Gulls, multiple genera
Anti-predator Adaptations: cryptic
Life History and Behavior
Ghost crabs communicate using many sounds, including striking the ground with their claws, stridulation (rubbing together) of their legs and making a “bubbling sound”. Males compete in a ritualized matter that avoids the need for physical contact.
Communication Channels: acoustic
After hatching from an egg, Ocypode quadrata has five zoea stages and one megalopa stage. The megalopa stage requires at least 35 days for development. The larvae develop in saline water. The megalopa stage of Ocypode quadrata is one of the largest of the brachyuran crabs. Metamorphosis into the first crab stage takes place at the surf-beach interface.
Development - Life Cycle: metamorphosis
The typical lifespan of Ocypode quadrata is about 3 years.
Mating can occur throughout the year. Unlike other crab species, ghost crabs can mate even when the female’s integument is hard, which means that they can mate anytime after sexual maturation. This is an adaptation to terrestrial life. Mating occurs while both the male and the female have a hard shell. Usually mating will occur somewhere in or near the burrow of the male. Often copulatory plugs are found in ghost crabs; the male will release a seminal fluid along with his sperm that will become hard and prevent rival sperm from reaching the female’s ova.
Mating System: monogamous
In the Carolinas, ghost crabs spawn from April through July. Females will mature and ovulate in April and again in August. Females reach sexual maturity when their carapace is larger than 25 mm. Males reach sexual maturity when their carapace is larger than 24 mm. This usually occurs when they are about a year old.
Breeding season: Mating occurs throughout the year.
Average age at sexual or reproductive maturity (female): 1 years.
Average age at sexual or reproductive maturity (male): 1 years.
Key Reproductive Features: year-round breeding ; sexual
The female will carry the eggs beneath her body, which will be released into the surf. While carrying the eggs, she must keep them wet by frequently entering the water. Some females may turn upside down in the water to ventilate their eggs.
Parental Investment: female parental care ; pre-hatching/birth (Protecting: Female)
Molecular Biology and Genetics
Statistics of barcoding coverage: Ocypode quadrata
Public Records: 0
Specimens with Barcodes: 2
Species With Barcodes: 1
Currently, ghost crabs are not considered threatened or endangered. One of the main threats to ghost crabs is off-road vehicles (ORVs). The ORVs can crush or bury the crabs and interfere with their reproductive cycle. ORVs can greatly affect ghost crabs at night when they are feeding. Another threat is a decline in their habitat; construction in the upper intertidal zone for residential or commercial use can caused increased mortality and a potential decline in the population.
US Federal List: no special status
CITES: no special status
State of Michigan List: no special status
Relevance to Humans and Ecosystems
There are no known adverse effects of Ocypode quadrata on humans.
Ghost crabs have been used as indicators for measuring the impacts of human use on beaches. Their population is relatively easy to monitor; the density of ghost crabs on a beach can be estimated by counting the number of burrows in a certain area. Population densities have declined due to habitat modification and heavy, continuous trampling. Because ghost crabs are apex predators of the habitat, monitoring their population can allow humans to assess the impact of human activity on sandy beach ecosystems.
Positive Impacts: research and education
Atlantic ghost crab
The Atlantic ghost crab, Ocypode quadrata, is a species of ghost crab, once described as an "occult, secretive alien from the ancient depths of the sea". It is a common species along the Atlantic coast of the United States, where it is the only species of ghost crab; its range of distribution extends from its northernmost reach on Rhode Island's beaches south along the coasts of the tropical Western Atlantic Ocean to the beach of Barra do Chui, in Rio Grande do Sul in southern Brazil.
Adults are greyish or the colour of straw, and around 5 cm (2.0 in) wide at maturity. They must return to water periodically to moisten their gills, and when larvae must be released into the sea, but are otherwise terrestrial. Their stalked compound eyes can swivel to give them 360° vision. Young crabs are cryptically coloured to blend in with their sandy habitats.
Atlantic ghost crabs are found from Block Island, Rhode Island, and Nantucket, Massachusetts, to Santa Catarina, Brazil, on Fernando de Noronha, and Bermuda. Its planktonic larvae have been found even further north, at Woods Hole, Massachusetts, although the adults cannot survive there.
The Atlantic ghost crab lives in burrows in sand above the strandline. Older individuals dig their burrows further from the sea, some starting as much as 400 m (0.25 mi) inland. Burrows can be up to 1.3 m (4 ft 3 in) deep, and can be closed off with sand during hot periods.
This crab can produce a variety of sounds by striking the ground with the claw, by stridulation with the legs, and an incompletely explained "bubbling sound". Males compete in a heavily ritualised manner which prevents the need for physical contact.
Sandy beaches, a habitat frequented by ghost crabs, have seen a decrease in the abundance of ghost crabs due to human behavior. Ghost crabs are negatively impacted by human and vehicle trampling, which results in direct crushing of crabs, as well as indirect damage such as compression of sediment which reduces habitat suitability, interference with reproductive behaviors, reduction in food supply, and light pollution. Consequently, it is less common on beaches frequented by people.
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- David Knott. "Atlantic Ghost Crab, Ocypode quadrata" (PDF). South Carolina Department of Natural Resources. Retrieved January 2, 2009.
- Jeffrey S. Pippen (November 12, 2005). "Ghost crab (Ocypode quadrata)". Jeffrey S. Pippen.
- Adilson Fransozo, Maria Lucia Negreiros-Fransozo & Giovana Bertini (2002). "Morphometric studies of the ghost crab Ocypode quadrata (Fabricius, 1787) (Decapoda: Ocypodidae) from Ubatuba, São Paulo, Brazil". In E. Escobar-Briones & F. Álvarez. Modern Approaches to the Study of Crustacea. New York: Kluwer/Plenum. pp. 189–195. ISBN 0-306-47366-6.
- Roger W. Portell, Richard L. Turner & John L. Beerensson (2003). "Occurrence of the Atlantic ghost crab Ocypode quadrata from the Upper Pleistocene to Holocene Anastasia Formation of Florida". Journal of Crustacean Biology 23 (3): 712–722. doi:10.1651/C-2340.
- Jeffrey Shields (1998). "The ghost crab, Ocypode quadrata". Virginia Institute of Marine Science. Retrieved January 2, 2010.
- Thomas A. Schlacher, Luke Thompson & Sam Price (2007). "Vehicle versus conservation of invertebrates on sandy beaches: mortalities inflicted by offroad vehicles on ghost crabs". Marine Ecology 28 (3): 354–367. doi:10.1111/j.1439-0485.2007.00156.x.
- Graziani de Freitas Antunes, Ana Paula Nunes do Amaral, Fabiana Pinto Ribarcki, Elenir de Fátima Wiilland, Denise Maria Zancan, Anapaula Sommer Vinagre (2010). "Seasonal variations in the biochemical composition and reproductive cycle of the ghost crab Ocypode quadrata (Fabricius, 1787) in Southern Brazil". Journal of Experimental Zoology 313A (5): 280–291. doi:10.1002/jez.593. PMID 20127661.
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