The Atlantic sand fiddler, Uca pugilator, is one of approximately 97 species belonging to the family Ocypodidae (Rosenberg 2001). Members of this family are characterized by a thick, squarish body and herding behavior (Ruppert & Fox 1988). Male crabs also bear one greatly enlarged pincer, either right or left, for combat and mating rituals; whereas, the claws of females are roughly equal in size. Fiddler crabs share many common morphological characteristics and behaviors, but identification of species is usually easily achieved through examination of body color and claw structure. Body color of the Atlantic sand fiddler is mostly white to yellowish white, becoming paler during courtship (Crane 1975). Displaying males have a characteristic pink or purple patch on the middle of the carapace, which is often mottled brown in non-displaying males. The major cheliped (appendage bearing the major claw) of the male is yellowish white, often with pale orange at the base of the claw. The minor claw is white, and the eyestalks are buff to grayish white, never green like some similar species. Many tubercles or bumps cover the outer surfaces of the claw. However, the oblique ridge of tubercles common in several fiddler crab species is absent in U. pugilator.

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)

Biogeographic Regions: nearctic (Native )

Virginian, southside of Cape Cod to Cape Hatteras

Gulf of Mexico, North West Atlantic

United States

Origin: Unknown/Undetermined

Regularity: Regularly occurring

Currently: Present

Confidence: Confident

Type of Residency: Year-round

The Atlantic sand fiddler is located throughout the India River Lagoon, mostly on sandy beaches near mangroves and salt marshes.

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)

The maximum carapace width for U. pugilator is approximately 2.5 cm, but most individuals collected in the field measure up to 1.4 cm and 2.1 cm for carapace length and width, respectively (Crane 1975). The major claw in males is much larger than the body, with a maximum length of 4.1 cm (Gosner 1978) and up to 3.5 cm in most specimens collected in the field (Crane 1975). Little information is reported for the maximum age and average lifespan of U. pugilator. However, the lifespan in a similar species, U. rapax, is only about 1.4 years (Koch et al. 2005).

Several other species of fiddlers occupy the estuarine habitats of the IRL, including: the saltpan fiddler, U. burgersi; the redjointed fiddler, U. minax; the Atlantic marsh fiddler, U. pugnax; the mudflat fiddler and its subspecies, U. rapax and U. rapax rapax; the longfinger fiddler, U. speciosa; and the Atlantic mangrove fiddler, U. thayeri. The palm, or interior surface, of the major claw in all these species is rougher than that of U. pugilator. The saltpan fiddler is small, with a carapace length of about 1.2 cm (Kaplan 1988). The body is dark mottled brown, with red or pink on the carapace and red on the major claw. Walking legs are usually brown or striped with gray, and the palm of the major claw bears large tubercles. Most populations of U. burgersi are found in mud or muddy sand around mangroves or near the mouths of streams from eastern Florida to South America.The redjointed fiddler is large, with a carapace width reaching 2.3 cm (Kaplan 1988). It is aptly named for the red bands present on the joints of the appendages. The large claw bears many tubercles, which diminish to granules toward the bottom, and the upper finger (movable top part of the closable claw) curves down below the tip of the lower (Kaplan 1988). This species prefers muddy sediments around Spartina marshes, from brackish to nearly freshwater, in Massachusetts to northern Florida and Louisiana.The Atlantic marsh fiddler, U. pugnax, has a carapace approximately 1.2 cm long (Kaplan 1988). The body is usually brown or yellowish with a row of tubercles on the palm of the major claw (Ruppert & Fox 1988). This species is most abundant in muddy areas of salt marshes from Massachusetts to eastern Florida (Kaplan 1988).The carapace of the mudflat fiddler, U. rapax, is about 2.1 cm long and light tan in color (Kaplan 1988). The color of the major claw is similar, with a darker lower palm and finger. The center of the palm is almost smooth, but still bears small granules. This species inhabits mud banks near mangroves and mouths of streams from Florida to South America. Crane (1975) defines the Daytona Beach area on the east coast of Florida as the northern limit for U rapax. The subspecies U. rapax rapax is very similar in appearance (see Crane 1975 for diagnostic characteristics). The longfinger fiddler, U. speciosa, has a small carapace length of about 1.1 cm (Kaplan 1988). Its color is seasonally variable, but usually remains darker than the characteristic brilliant white of the major claw. The palm bears a slightly curved row of large tubercles. These crabs inhabit muddy areas, mostly around mangroves from Florida to Cuba.The Atlantic mangrove fiddler, U. thayeri, has a carapace measuring about 1.9 cm in length (Kaplan 1988). The carapace and major claw are both brown to orange-brown (Crane 1975, Kaplan 1988), and both fingers of the claw are bent down (Ruppert & Fox 1988). This species is found on mud banks of estuaries and streams near mangroves, from Florida to South America. Females often build tall mud chimneys at the entrance to their burrows during breeding season (Crane 1975, Kaplan 1988).Regional Occurrence & Habitat Preference: Populations of U. pugilator inhabit the shores from Massachusetts to Florida (Kaplan 1988), the Gulf of Mexico from Florida to Texas, and the Bahamas (Crane 1975). The Atlantic sand fiddler is found on muddy to sandy soils, but is usually more prominent in sandier areas containing scattered shells and stones (Crane 1975). Individuals also occupy areas around mangroves and in salt marshes, among stands of the cordgrass, Spartina alterniflora (Brodie et al. 2005).

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)

Aquatic Biomes: coastal

Depth range based on 15 specimens in 1 taxon.
Water temperature and chemistry ranges based on 2 samples.

Environmental ranges
  Depth range (m): 0 - 1.8
  Temperature range (°C): 23.660 - 23.660
  Nitrate (umol/L): 0.457 - 0.457
  Salinity (PPS): 35.580 - 35.580
  Oxygen (ml/l): 4.845 - 4.845
  Phosphate (umol/l): 0.110 - 0.110
  Silicate (umol/l): 0.868 - 0.868

Graphical representation

Depth range (m): 0 - 1.8
 
Note: this information has not been validated. Check this *note*. Your feedback is most welcome.

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)

Although they are occasionally cannibalistic, the majority of the fiddler crab diet consists of detritus, bacteria and algae on and in the sediments (Gosner 1978). The small claws transfer sediment to the mouthparts, where food is separated from sand and other unwanted particles. Food is swallowed and the mouthparts roll the remaining sand into tiny balls that are placed back on the ground. These balls are much smaller than those created during the excavation of burrows (Ruppert & Fox 1988). Mouthparts in many fiddlers are specialized for a specific size range of sediment particles, and this adaptation is partly responsible for the habitat and distribution of species. Crabs also wander while feeding and some species move as far as 50 m away from their burrows (Ruppert & Fox 1988).Predators: Predators of fiddler crabs include birds, fishes, turtles, and mammals such as otters and raccoons (Colby & Fonseca 1984, Crane 1975, Ruppert & Fox 1988), in addition to being occasionally cannibalized by other fiddlers (Gosner 1978). Crabs reduce predation risk by fleeing into their burrows, and some studies speculate that U. pugilator changes to a sandy color in part to camouflage its carapace from predators (Dawkins 1971). Larvae of Uca spp. are preyed upon by a variety of pelagic and benthic organisms, and are cannibalized by adult fiddler crabs in captive populations (O'Connor 1990).

Many species of fungi are obligate associates of arthropod hosts (Mattson 1988). A fungus belonging to the genus Enterobryus has been discovered in the hindgut of U. pugilator. The fungus is not parasitic (Hibbits 1978, Lichtwardt 1976), and it has been suggested that the species may even provide necessary chemical compounds, such as amino acids, to the crab (Williams & Lichtwardt 1972). In addition to obligate associations, Atlantic fiddler crabs are found alongside several organisms common to mangroves and salt marshes. For extensive lists of other species found throughout the ecosystems in which U. pugilator occurs, please refer to the "Habitats of the IRL" link at the left of this page.

Although fiddler crabs are territorial, the species is quite social and lives in large groups. When U. pugilator was first described by Louis Bosc in 1802, he observed that "thousands or even millions" covered the beaches of the Carolinas (Crane 1975). Today, those numbers have declined as a result of pollution and habitat degradation, but relatively large populations can still be found. Little information exists for abundance estimates of U. pugilator in the IRL, but field densities in South Carolina populations have reached up to 75 m-2 (Pratt & McLain 2006). Studies on fiddlers in North Carolina revealed that females are more abundant than males (Colby & Fonseca 1984), a pattern that likely exists for populations in other locations based on courtship and mating behaviors (see below).Molting & Limb Regeneration: Like other arthropods, fiddler crabs must molt in order to grow larger. This process, known as "ecdysis", occurs most frequently in fast-growing juveniles and slows during adulthood. During ecdysis, the hard exoskeleton is shed in one piece, exposing the new, soft underlying skeleton. Water is pumped into the body to expand the size of the new exoskeleton before it hardens (eg. Guyselman 1953). Molting is not only used for growth, but also to regenerate missing limbs. During combat or to escape from predators, fiddler crabs autotomize or cast off limbs at a predetermined point (Weis 1977), usually at the base of all walking legs (Hopkins 2001). New limbs grow in a folded position within a layer of the cuticle, unfolding and expanding during the molting process. Ecdysis is triggered and accelerated by multiple autonomy and removal of the eyestalks (Abramowitz & Abramowitz 1940, Hopkins 1982). Molting under these circumctances may not result in growth, and the overall size of the crab may even decrease as energy is used to regenerate several missing limbs (Hopkins 1982). A single molt in some individuals is often enough to completely regenerate a missing limb (Hopkins 2001), but other crabs may require several molts before an appendage is restored to its original size. Several factors affect the frequency and success of molting and limb regeneration, including food availability, temperature and pollution. For example, the presence of methylmercury in polluted waters can partially or fully inhibit regeneration of limbs in both temperate and tropical fiddler crabs (Weis 1977).

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)

Fiddler crabs are social organisms that engage in elaborate mating displays before copulation. Males use their large claw to attract mates through a series of waving motions and acoustic drumming, also used to ward off potential competitors. Waving displays are often characteristic of a certain species, but usually occur at the mouth of the burrow in all crabs. In U. pugilator, the large claw makes a loop as it is brought up, pausing slightly before moving to the side and down in front of the crab (Crane 1975). The carapace rises with each wave and the small claw makes a roughly corresponding motion. In high intensity displays, a series of 4 to 5 waves is completed before the claw is lowered to its resting position. Often, acoustic drumming and other sounds are produced by the claws and legs to attract females (Crane 1975). Atlantic fiddler crabs court and mate both during the day and at night. In daylight, waving displays by males are likely most important; whereas, acoustic signals predominate during nocturnal courtship. Once the male has attracted a mate, she usually follows him into the burrow for copulation, and it has been suggested that underground mating in U. pugilator results in more viable eggs (Salmon 1987). The resulting fertilized eggs are carried in a clump, often called a sponge, on the abdomen of the female until hatching. Ovigerous, or egg-bearing, females were seen from May through August in North Carolina populations, most measuring over 1.0 cm in carapace length (Colby & Fonseca 1984).

Females release larvae into the water column once they are fully developed, usually during large nocturnal ebb tides (eg. Christy 1989). The purpose of this behavior is most likely to transport larvae offshore, away from abundant estuarine predators. Planktonic larvae develop through a series of five zoeal stages (Christy 1989), feeding mostly on smaller zooplankton. The final larval stage (postlarva) is the demersal, or bottom-associated, megalopa. As the larvae travel back toward the estuary, they metamorphose into megalopae and look for settlement cues such as the presence of other members of the same species (conspecifics) and the appropriate sediment type, before settling to the bottom and undergoing their final metamorphosis to a juvenile crab (eg. O'Connor 1993). Studies have shown that U. pugilator megalopae have the ability to delay metamorphosis for a limited time until a suitable habitat is found (Christy 1989, O'Connor 1991).

The following is a representative barcode sequence, the centroid of all available sequences for this species. 

 
There are 114 barcode sequences available from BOLD and GenBank.  Below is a sequence of the barcode region Cytochrome oxidase subunit 1 (COI or COX1) from a member of the species.  See the BOLD taxonomy browser for more complete information about this specimen and other sequences.
 

Download FASTA File

Barcode of Life Data Systems (BOLDS) Stats
Public Records: 112
Species: 112
Species With Barcodes: 1

US Federal List: no special status

CITES: no special status

United States

Rounded National Status Rank: NNR - Unranked

Rounded Global Status Rank: GNR - Not Yet Ranked

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

(He Zhong 2001)

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)

Ecological Importance: The digging activity in fiddler crabs exists not only to create territorial burrows, but also to bring organic matter to the surface, stimulating microbial growth. Burrowing activity often increases when food is limited to create a more abundant nutrient source, but also results in the stimulated growth of nearby mangroves and Spartina plants (Genoni 1985, 1991) through increased soil aeration and more nutrient availability.