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Uca pugilatorAtlantic sand fiddler

By Chris Patterson

Geographic Range

The Sand fiddler crab is one of three Uca species, which are found from Cape Cod to Texas with the exception of Florida and south of St. Augustine. The locations of the crabs are usually near the coastal marshes or near intertidal zones.

(NOAA Costal Services Center 2001)

Habitat

Fiddler crabs are found in strongly brackish to saltwater salinities all along the eastern seaboard. They live in low marshes, which have sediments that are covered by water on most high tides, characterized primarily by saltmarsh cordgrass. Uca pugilator each live in a hole or burrow that it digs for itself. The burrow can be closed with a mud cap for security. During low tide fiddler crabs abandon its dwelling to search for food, but never strays very far unless it is to court a female or scare away a neighbor.

(Priest 2000)

Physical Description

The Sand fiddler crab is approximately 1.5 inches(38mm) wide and 1.0 inch(25mm) long. All fiddler crabs are similar in shape, having a smooth carapace and a square-shaped body. The eyes are found at the ends of two long and slender, movable eyestalks located in the center of the carapace. Male fiddler crabs are brighter in color, having a purple grey or blue carapace with irregular markings of black or brown. The females have equal-sized claws and generally have a much more subdued coloration on their carapaces. Being that they are crabs they are considered decapods or animals with ten limbs; although both of their claws are not referred to as legs, they are actually chelipeds or claws. Males have a common characteristic of one large pincer. This pincer, which is usually brightly colored, can either be on the right or left side and is at least four times larger than the other. The large cheliped can be as fifty percent as massive as the rest of the male combined. Uca pugilator use the large claw to defend their burrows and attract mates. Fiddler crabs even get their name from the male's large claw.

(He Zhong 2001)

Reproduction

Breeding occurs approximately every two weeks for most of the summer. Reproduction occurs in burrows similar to the ones Uca pugilator live in only larger and better-maintained. The two crabs mate and then two weeks later after the incubating of the eggs for the night will return to the surface and release her eggs into the water where they develop. The female when at the water extrudeds all of her fertilized eggs, which can be as many as a quarter million, onto her abdominal flap in one small spongy cluster. The eggs will hatch after several months and will be released into the nearest tidal creek during high tide where again after several months the young fiddler crabs undergo metamorphosis and change into their final form. These new adult crabs return to the land for the rest of their lives.

(Priest 2000)

Behavior

Fiddler crabs are colonial, often living together in large clusters. Territorial fighting occurs between the males, and they will go to extremes to defend their burrows. Despite their fighting, they travel in herds of thousands when feeding. The process of reproduction begins by males standing at the edge of their burrows, usually lining up with other males only centimeters away. Then, as a female approaches the male crab of her choosing, the male will wave the large cheliped vigorously. If the female is still interested, the male will then run toward her, back to the burrow, back to her, and back to the burrow again to show which burrow is his. The male finally drums his large cheliped against the sides of the burrow until she enters. Upon her entrance the male crab seals the burrow with a mud cap for mating.

(He Zhongn 2001)

Food Habits

Sand Fiddlers ingest particles of sand or mud and they use their mouthparts to scrape food materials from the sediment, and then deposit the sediment back down on the ground as a "feeding pellet." The actual method of consumption occurs when the scooped mud is put in their mouths and the entrapped detritus is filtered out using specialized brush-like mouthparts. Water is pumped from their gills into their mouths to float the detritus free of the mud. The food material consists of decaying organic matter or unicellular plants such as algae. The chelipeds are used for picking up the small amounts of sediment not for crushing things or for a grip. Because of one enlarged claw the males cannot eat as fast as females so they have to eat twice as fast.

(Priest 2000)

Economic Importance for Humans: Positive

Uca pugilator are not only important regulators of cordgrass but also are important to the foodweb. They are eaten by larger predators, such as blue crab, rails, egrets, herons, and raccoons. Fiddler crabs also stimulate the turnover and mineralization of important nutrients. They can even be a good environmental indicator to environmental contaminates especially insecticides.

(He Zhong 2001)

Economic Importance for Humans: Negative

Growth of marsh grasses can be affected by their activity. Uca pugilator can erode or undermine marshbanks by burrowing and feeding.

(He Zhong 2001)

Conservation Status

Other Comments

A very unique quality of Uca pugilator is that they are able to regenerate lost limbs. Regeneration is based on two growth stages, basal and proecdysial. The first stage of growth, basal growth, is due to the increase of cell number by mitotic division of the blastemal cells. The second stage or proecdysial growth is due to the increase in cell size by protein synthesis and water uptake. It usually takes many months to complete full regeneration and the new pincer is normally not as large nor as strong as the original.

( Chung 2001)

Contributors

Chris Patterson (author), Western Maryland College, Louise a. Paquin (editor), Western Maryland College.

Glossary

Nearctic

living in the Nearctic biogeographic province, the northern part of the New World. This includes Greenland, the Canadian Arctic islands, and all of the North American as far south as the highlands of central Mexico.

World Map

bilateral symmetry

having body symmetry such that the animal can be divided in one plane into two mirror-image halves. Animals with bilateral symmetry have dorsal and ventral sides, as well as anterior and posterior ends. Synapomorphy of the Bilateria.

coastal

the nearshore aquatic habitats near a coast, or shoreline.

ectothermic

animals which must use heat acquired from the environment and behavioral adaptations to regulate body temperature

native range

the area in which the animal is naturally found, the region in which it is endemic.

References

Chung, A. "Biological Sciences" (On-line). Accessed April 14, 2001 at http://gradweb.ou.edu/Poster/Biological.html.

Priest III, W. Fall 2000. Wetland Denizens Fiddler Crab. The Virginia Wetlands Report, 15: 3,5.

Zhong, H. 2001. Common Florida Fiddler Crabs (*Uca* spp.). Public Health Entomology Research & Education Center, 10: 4.

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