Diversity of Crab Species in a Transitional Tidal Basin on

Ossabaw Island, GeorgiaRosemary Anne Calvert

University of Tennessee – Knoxville

Summer 2004

While walking along the shoreline of a Transitional Tidal Basin, several different species of invertebrates are observed within the same area.

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HabitatFeeding Breeding Predators

Relationship withOther animals

Animal Trivia

Habitat

Feeding Breeding Predators

Relationship toOther Animals

Animal Trivia

These are five species of crabs found at this habitat.

Atlantic Horseshoe Crab Sand Fiddler Crab

Limulus polyphemus Uca pugilator

Ghost Crab

Oxypode quadrata

Flat-clawed Hermit Crab Mud Fiddler Crab

Pagurus pollicaris Uca pugnax

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Horseshoe Crab Limulus polyphemus

Did you know that the Horseshoe Crab is called a “living fossil” since it is one of the oldest living species of animal?

Did you know that the Horseshoe Crab is not really a crab, nor is it a Crustacean, but is in a separate class of its own, Merostomata?

Horseshoe Crab blood is blue and is used extensively in medical research?

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Horseshoe Crab Habitat

• Horseshoe Crabs are found on mud or sand bottoms, from near the low tide line to 75 feet under the ocean

• Its range is from the Gulf of Maine to the Gulf of Mexico

Next HabitatOther Habitats

Horseshoe Crab Food and Feeding Habits

• Horseshoe Crabs plow slowly through the bottom sand and mud, preying on mollusks, crustaceans, worms, and other small animals such as clams.

• The legs of the Horseshoe Crab not only provide locomotion, but aid in grinding the food eaten by the animal.

• As the animal walks, spines on the upper joint of each leg chew the food much like teeth. The food is then passed backward through the legs into the mouth. In fact, they are unable to eat except when walking.

Other Feeding BehaviorOther Feeding Habits

Horseshoe Crab Breeding Habits

• Horseshoe Crabs crawl on the shore to breed

• A female crawls out of the surf and clinging on to her are one or more males

• The female makes a small hollow in the sand, just below the high-tide line and deposits thousands of eggs

• The male deposits sperm on the eggs, and the eggs are covered with sandOther Breeding Behaviors

Other Breeding Habits

Predators

• Horseshoe Crab eggs are eaten by birds, crabs, and other animals in the surf area.

Other PredatorsOther Predators

Horseshoe Crab - Relationship with Other Animals

• Adult Horseshoe Crabs are home and transportation to other animals.

• Barnacles, tube worms, and slipper shells sometimes make their homes on the Horseshoe Crabs shell.

• Flatworms live on the crab’s book gills.• The blood of the Horseshoe Crab is distinctive in that it is blue when

exposed to air and contains copper, instead of iron like mammals and other vertebrates. Horseshoe Crab blood has a strong reaction when exposed to bacteria, and because of its unique properties, it is used in medical research.

Relationship with other animalsRelationship With Other Animals

Flat-clawed Hermit Crab Pagurus pollicaris

• The Hermit Crab does not live in the shell of its own making, but in a shell “borrowed” from another animal.

• The Hermit Crab needs the shell to protect its soft parts since only its head and front claws are calcified.

• The last two legs of the Hermit Crab are modified to hold the crab in its adopted shell.

• The right pincer claw larger than the left in both males and females, and the larger claw is used to seal the opening of the shell.

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Flat-clawed Hermit Crab Habitat

Flat-clawed Hermit Crabs live in shallow protected waters along open shores and in brackish water estuaries, from low-tide line to 150 feet deep.

Their range is from Cape Cod to Florida and Texas.

Can survive out of water for short periods of time.

Next HabitatOther Habitats

Hermit Crabs Food and Feeding Habits

• Hermit Crabs are scavengers eating dead animals and debris.

• At times they can be carnivorous and will eat small animals.

• Hermit crabs may even eat their own kind if a fellow Hermit Crab is found outside of its shell (at a time the crab changes from one shell to another)Other feeding behaviorsOther Feeding Behaviors

Hermit Crab Breeding Habits

• On the right side of the Hermit Crabs abdomen, the pleopods are reduced or lost, but in the female crabs, the left pleopods are retained to carry eggs

• Fertilization occurs externally

Other Breeding behaviorsOther Breeding Behavior

Hermit Crab Predators

• Hermit Crabs are eaten by many kinds of fish and shorebirds.

• Hermit Crabs are sometimes eaten by other Hermit Crabs when found outside of its shell when a crab is molting.

• Humans eat some types of Hermit Crabs as a delicacy.

Other PredatorsOther Predators

Hermit Crab Relationship with Other Animals

• Sea Anemones, barnacles, and hydroids sometimes live on the shells of Hermit Crabs.

• The symbiotic relationship between the sea anemones and the Hermit Crab allow the anemone to gather scraps of food when the crab eats and in turn the anemone protects the crab from potential predators.

• The Zebra Flatworm often shares the shell as a commensal organism.

Relationship with otherAnimalsRelationship With Other Animals

Ghost Crab Oxypode quadrata

• Unlike its crab relatives, the Ghost Crab does not have a thick protective shell, nor are its pinching claws very powerful.

• The Ghost Crab does possess protective coloration, swift locomotion (it can run sideways, forward, and backward on its spindly legs.

• The Ghost Crab has “periscope eyes” that are mounted on stalks and can rotate to provide 360-degree vision. For protection, the crab can retract its eyes into grooves on the front of its shell.

More TriviaMore Trivia

Ghost Crab Habitat

• Ghost crabs live on the desert-like habitat of the sandy upper beach zone.

• Several times a day the crab must return to the ocean shallows to wet its gills.

• The burrows of the Ghost Crab are located in the dry upper portion of the beach and are as large as three inches in diameter and the tunnel leading to the crab’s burrow may go down four feet in the sand.

• Ghost Crabs remain dormant in their burrows during the winter months.

• Found from Rhode Island to Florida and Texas; West Indies to Brazil.

Next HabitatOther Habitats

Ghost Crab Food and Feeding Habits

• Ghost crabs seek live prey such as Beach Fleas, Mole Crabs, Coquina Clams, sea turtle hatchlings, and other small animals.

• Dead flesh and beach debris are also consumed.

Other feeding behaviorOther Feeding Behavior

Ghost Crab Breeding Habits

• The female Ghost Crab deposits her eggs directly into the ocean.

• Ghost Crab larvae become part of the free-floating zooplankton and undergo several form changes while developing.

• Mature crabs emerge from the ocean to spend its life on land.

Other Breeding HabitsOther Breeding Habits

Ghost Crab Predators

• Ghost Crabs are eaten by animals such as gulls and raccoons.

• Ghost Crabs possess protective coloration to blend into the sandy environment, swift locomotion, and rapid burrowing ability, all of which contribute to its ability to protect itself from predators.

• Ghost Crabs are eaten by humans on some Caribbean Islands.Other PredatorsOther Predators

Ghost Crab Relationship with Other Animals

• Ghost Crabs are found on undisturbed beaches.

• Ghost Crabs are somewhat solitary.

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Sand Fiddler Crab Uca pugilator

• Fiddler Crabs along with Ghost Crabs are in the family Ocypodidae, meaning “swift footed.”

• Fiddler Crabs are named for the appearance and behavior of the male crabs; when the crabs wave their large claws back and forth as if playing a base fiddle.

So, what have you learned about…..So, What Have You Learned About…

Sand Fiddler Crab Habitat

• Sand Fiddler Crabs are found on protected sand and sandy mud beaches, marshes and tidal beaches.

• Range is from Boston Harbor to Florida and Texas, and the West Indies.

• Fiddlers dig burrows that are dime-size openings in the muddy soil.

• Fiddlers burrow by scraping sand and mud into pellets and then carrying the pellets out of the burrow and depositing them on the surface.

• The burrows are one to two feet in depth.

What else can be observed?What Else Can Be Observed?

Fiddler Crab Food and Feeding Habits

• Fiddler Crabs are almost exclusively herbivorous feeding on the abundant algae in their habitat.

• The first pair of legs is modified into spoon like pincers that enable them to scrape algae.

• Female crabs feed by rapidly alternating right and left claws like children stuffing candy into their mouths as fast as they can. Males eat with just one claw since they have one oversized claw used for territorial defense and courtship.

What else can you observe?What Else Can You Observe?

Fiddler Crab Breeding Habits

• The forbidding-looking large pincer of the male Sand Fiddler Crab is used in a courtship display prior to mating.

• The crab rises on tiptoes, extending the pincer, then flexing it and bowing down.

• This courtship dance becomes faster and more exaggerated as a female approaches.

• The female will pop in and out of several burrows until it finally selects a burrow.

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Fiddler Crab Predators

• The Predators of Fiddler Crabs include shorebirds, raccoons, terrapins, fish and larger crabs.

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Fiddler Crabs Relationship with Other Animals

• Where sand and mud run together, populations of Sand Fiddler Crab and Mud Fiddler Crab may be intermixed but they do not interbreed.

• These crabs are used in the study of neuro-secretory hormone control of mechanisms that regulate light adaptation and chromatophore (pigment containing cell)

activity.

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Mud Fiddler Crab Uca pugnax

• The Mud Fiddler Crab prefers a muddy habitat and frequently digs into mud banks along tidal marshes, sharing burrows with the Marsh Crab.

• Its range is from Cape Cod to northeastern Florida, and from northwestern Florida to Texas.

What else can you observe?What Else Can You Explore?