Crabs

Range/Geographical Distribution: Maine to Florida and the Gulf of Mexico.

Habitat: Juveniles are found on intertidal sand flats but adults can be found to depths of 600 feet.

Description: The body of a horseshoe crab is divided into three parts: the prosoma, opisthosoma and telson, or tail. The prosoma is the front, semicircular part and the opisthosoma, which protects the gills, is attached to the prosoma with a hinge. The top of the shell has ridges and spines.  Seven pairs of leg-like appendages are found under the shell.

Size: Can grow up to 24 inches in length.

Food: Mollusks, annelid worms, and other benthic invertebrates.

Breeding: Mate during the full and new moons of May and June. Males patrol near-shore waters for mates and are attracted to females by pheromones. The males hook their specially modified second set of appendages onto the body of a female.  The female drags the male onto a sandy beach and uses her pusher legs to form a shallow nest between the high- and low-tide lines. Then the female deposits five to seven clumps of 2000-4000 eggs and drags the male over the eggs to fertilize them.  Females can lay more than 90,000 eggs in one year. The larvae hatch and leave their nest during a high tide.  After one molt the larvae enters its first juvenile stage.  Females mature at ten to eleven years and males at eight to nine years.

Predators: Sea turtles, and alligators.

Conservation Status: Listed as near threatened by the IUCN red list; harvesting and habitat destruction have drastically reduced its numbers in some locations.

Interesting Facts:  Horseshoe crabs have contributed to the medical research community. A substance in their blood called Limulus Amebocyte Lysate is used to test for bacterial endotoxins in pharmaceuticals and for several bacterial diseases.  Also, much of what we know about the function of our eyes is the result of studies that began in the 1960s on the large, compound eyes of the horseshoe crab.  Horseshoe crabs have no jaws or teeth but they use the base of their legs to grind up clams and they have a gizzard.

On the Coast:  Live horseshoe crabs can be seen on Georgia’s beaches during mating.  Molts (shed exoskeletons) commonly wash up onto the beach year round.

Range/Geographical Distribution: Along the coast from Massachusetts to Uruguay.

Habitat: Nearshore, including beaches, marshes, bays, and estuaries.

Description: A large swimming crab with a gray/green or gray/blue carapace and large, blue claws, which are tipped with red in the female.  Underside is light tan/blue.

Size: Can reach nine inches in carapace (shell) width.

Food: Bivalves, crustaceans, fish, worms, plants, detritus, and dead fish and plants.

Breeding: Mate in brackish water from February to November. Male holds onto a female until her final molt, after which they mate.  Two to nine months later the female migrates offshore to release her eggs.  One female may carry as many as eight million eggs. The eggs hatch into planktonic larva and migrate back nearshore into estuaries.  Female crabs store sperm and will use it to fertilize multiple spawnings.

Predators: Fish, sharks, rays, and sea turtles.

Conservation Status: No legal status but loss of habitat combined with the blue crab’s popularity as a food for humans may lead to reduced populations.

Interesting Facts: The blue crab’s scientific name, Callinectes sapidus, translates to “savory beautiful swimmer.” Blue crabs almost always walk sideways, clearing a path with their sharp lateral spines, but when they swim they use their paddle-like rear legs for propulsion. Chesapeake Bay, North Carolina, and Louisiana support the largest blue crab fisheries.

On the Coast: Blue crabs are common in Georgia’s coastal waters and brightly-colored, floating crab pot buoys can be seen along most waterways.

Range/Geographical Distribution: Cape Cod to Mexico

Habitat: Sandy bottoms along beaches and offshore.

Description: A walking crab with a nearly round carapace that is covered in red and white splotches.  The claws are broad and shaped so that they can cover the crab’s “face.” 

Size: Can reach three inches in carapace (shell) width.

Food:  Buries itself completely in sand but when food is in range will erupt dramatically to seize it. It scavenges on fish, worms, clams, and other small invertebrates.

Breeding:  Females produce eggs in the summer and larvae are planktonic.

Predators:  Rays, fish, and sea turtles.

Conservation Status: No legal status.

Interesting Facts: Calico box crabs sometimes carry a tricolor anemone on their carapace.  The anemone’s stinging cells help to protect the crab and the crab offers the anemone mobility and meal scraps.

On the Coast: Calico box crabs are common along Georgia’s coast and pieces of their molts (shed exoskeletons) often wash up on the beach.

Range/Geographical Distribution: Along the coast from Nova Scotia to Brazil.

Habitat: All types of benthos including estuaries, beaches, and bays.

Description: A round, spiny, brown/yellow crab with white-tipped claws.  The carapace is covered in Velcro-like hairs which attract algae, bryozoa, and debris that juvenile crabs use for camouflage.

Size: Can reach four inches in carapace (shell) width.  Legs can reach a foot in diameter.

Food: Scavenger.

Breeding: During mating, the male transfers a spermatophore to the female. The fertilized eggs are brooded on the female’s abdomen until they hatch.  Newly hatched larvae go through three planktonic stages, which last about nine days, before settling onto the benthos.

Predators:  Birds, fish, and rays.

Conservation status: No legal status.

Interesting Facts:  The male spider crab grows larger than the female.  They are sluggish and unaggressive scavengers that have poor eyesight but sensitive chemoreceptors on the tips of their legs.

On the Coast:  The molts (shed exoskeletons) of spider crabs often wash up on Georgia’s beaches.  Juvenile crabs might also be found hitching a ride on cannonball jellyfish when the jellyfish wash up onto the shore.

Range/Geographical Distribution: From Cape Cod to Texas.

Habitat: The sand fiddler (U. pugilator) and the mud fiddler (U. pugnax) are found in high salinity brackish and salt water marshes.  The red-jointed fiddler (U. minax) is found in freshwater to low salinity brackish water marshes.

Description: A small, square-shaped crab.  Males have one claw greatly enlarged; females have claws of equal size.

Size: Can reach a carapace length of one and a half inches.

Food: Sift through sediment for algae and decaying vegetation; leave behind “clean” balls of sand after feeding. Males cannot feed with their large claw and therefore must feed faster and more often than females.

Breeding: Males use their enlarged claw to attract a mate.  After mating, females carry the fertilized eggs on their abdomen until they hatch.   The larvae are released into the water after several months during a nocturnal high tide.

Predators: Birds, fish, and raccoons.

Conservation Status: No legal status.

Interesting Facts: Fiddler crabs dig burrows along the flats and banks of coastal marshes.  Each burrow has one opening and can reach two feet in length.  The male’s claw can be up to half of his body weight.

On the Coast: All three of these species can be found along Georgia’s coast.  They live in large groups along the sandy edge of the saltmarsh and may be seen in large swarms among the grasses.

Range/Geographical Distribution: From Delaware through the Caribbean south to Brazil.

Habitat: Above the intertidal zone on sandy beaches.

Description: A pale, sand-colored crab with white claws and a square shell.  Hairy legs and large, stalked eyes.

Size: Can reach two inches in carapace (shell) width.

Food: Predators and scavengers; feed on clams, mole crabs, and sea turtle eggs and hatchlings.

Breeding: Mate throughout the year. Females carry the eggs on their abdomens and then release them into the surf.  Larvae go through several planktonic stages before metamorphosizing into the adult form.

Predators: Birds and raccoons.

Conservation Status: No legal status.

Interesting Facts: Ocypode means swift-footed.  Ghost crabs may go to the surf to wet their gills but will drown if kept submerged.  These crabs burrow along the beach from just above the high tide line to behind the first line of dunes.  Burrows have one opening and can reach four feet in length.  Ghost crabs are most active at night and communicate using sounds made with their legs and claws.

Range/Geographical Distribution: Along the coast from Cape Cod to the Gulf of Mexico.

Habitat: Shallow subtidal sandy bottoms along beaches and bays.

Description: Pale gray body with purple specks.  Last pair of legs paddle-shaped.

Size: Can reach three inches in carapace width.

Food: Dead and live fish, crabs, clams, and other invertebrates.

Breeding: The female carries the eggs under a flap on her abdomen and when the eggs hatch they are planktonic. The larvae molt several times before resembling an adult and settling down into the benthos.

Predators: Fish, crabs, and birds.

Conservation Status: No legal status.

Interesting Facts: Like blue crabs, lady crabs often bury themselves in the sand with only their eye stalks visable.  These crabs are known for their irritable nature and should be handled with care.

On the Coast: Lady crabs are common along the Georgia coast and their molts, especially the claws, often wash up on the beach.

Range/Geographical Distribution: Nova Scotia to Florida and Texas.

Habitat: Estuarine and coastal habitats from the intertidal zone to 150 feet deep.

Description: Gray or green/white body and tan/gray stripe down the middle of each claw.  Claws are cylindrical with the right larger than the left.

Size: Can reach a carapace (shell) length of half an inch.

Food: Scavenger; feeds on algae, detritus, and other organic particles.

Breeding:  Have sexual, internal fertilization and must partially emerge from their protective mollusk shell in order to mate. Females brood the eggs within their shell and then release newly hatched larvae into the water.  Larvae go through several planktonic stages before becoming an adult.

Predators: Birds, fish, snails, octopus, and other crabs.

Conservation Status: No legal status.

Interesting Facts: The female’s mollusk shell size and quality can impact reproductive success. If the long-wristed hermit crab does not have a shell it will not feed and will soon die.

On the Coast:  This small crab is the most common hermit crab on the Georgia coast.  Long-wristed hermits are very bold and may be found inhabiting periwinkle, mud snail, and auger shells.

Range/Geographical Distribution: Cape Cod to Florida and the Gulf of Mexico.

Habitat: Open sandy beaches between high and low-tide lines.

Description: Egg-shaped crab that is pale gray/tan in color.

Size: Can reach one inch in length.

Food: Plankton and organic debris.

Breeding:  Sexual reproduction, the small males become semi-parasitic during mating.  Female carries the bright orange eggs until they hatch into planktonic larvae.

Predators:  Shorebirds, crabs, and fish.

Conservation Status: No legal status.

Interesting Facts:  Mole crabs are completely harmless; they cannot bite, pinch, or sting.  Also called sand fleas, these crustaceans are one of a fisherman’s favorite baits.

On the Coast:  Mole crabs live beneath the crashing waves along Georgia’s beaches and move up and down the sand with the tides.

Range/Geographical Distribution: North Carolina to the Gulf of Mexico.

Habitat: Shallow, subtidal waters along beaches and bays.

Description: A small crab with a round, globular shell that is pale yellow with red/purple irregular markings.

Size: Can reach two inches in carapace (shell) width.

Food:  Dead and live fish, crabs, clams, and other invertebrates.

Breeding: Mate during the summer. The fertilized eggs are brooded on the female’s abdomen until they hatch.  Newly hatched larvae go through free-floating planktonic stages before settling onto the benthos.

Predators: Crabs, birds, and fish.

Conservation Status: No legal status.

Interesting Facts: Female purse crabs carry their eggs in a large pouch on their abdomen, which somewhat resembles a woman’s purse.

On the Coast: Purse crabs sometimes wash up live on Georgia’s beaches but more commonly beachcombers will find pieces of their molts (shed exoskeleton).

Range/Geographical Distribution: Massachusetts to the Gulf of Mexico and Brazil.

Habitat: Shallow waters along sandy beaches.

Description: A small swimming crab with a brown/maroon carapace covered in yellow spots.

Size: Can reach five inches in carapace (shell) width.

Food:  Detritus, crustaceans, fish, mollusks, and hatchling sea turtles.

Breeding:  Mate year round.  Male holds onto a female until she molts, after which they mate.  Females can produce up to 682,000 eggs and they carry the eggs under their abdomen until they hatch.  Larvae go through several planktonic stages before becoming a juvenile crab.

Predators:  Sea turtles, fish, and birds.

Conservation Status: No legal status.

Interesting Facts:  Speckled swimming crabs are nocturnal and can host parasitic barnacles.  They are also commercially fished in Brazil.

On the Coast:  Live speckled crabs are rarely seen but pieces of their molts (exoskeleton) often wash up on Georgia’s beaches.

Range/Geographical Distribution: Virginia to Brazil and the Gulf of Mexico.

Habitat: Beaches, mud flats, and rock jetties.

Description: A large hermit crab with green and white longitudinal stripes on the legs.  Claws are orange and of equal size.

Size: Can reach a carapace (shell) length of over one inch. 

Food:  Scavengers; eat dead and decaying plant or animal material. 

Breeding:  Mate in shallow waters in the spring and larvae take about two months to develop. 

Predators:  Fish, birds, and larger crabs. 

Conservation Status:  No legal status.

Interesting Fact: The hardiest of all hermit crab species in Gulf waters; they can live without water for days.  Commonly use whelk and moon shells as protection.  The fourth and fifth pairs of legs are modified in hermit crabs to help secure the animal in its borrowed mollusk shell.

On the Coast:  Striped hermit crabs are common along the Georgia coast and often occupy the shells that beachcombers find.