This species has not been researched very well because Uca species are often grouped together as a whole. Some researchers have reported that gulf mud fiddler crabs are a subspecies of Uca rapax.
Gulf mud fiddler crabs communicate with each other mainly through visual channels. Males communicate by waving their large chelipeds, which may be stimulated by female pheromones (sensed via their setae), physical touch of either sex, or visual cues (for example, another crab approaching). They also create noise and vibrations, using their larger chelipeds and, as part of their mating rituals, males "dance" for the females, running back and forth between their burrow and a female, also performing a "curtsey." These crabs communicate mainly for reproductive purposes, including creating dominance hierarchies.
Communication Channels: visual ; tactile ; acoustic ; chemical
Other Communication Modes: pheromones ; vibrations
Perception Channels: visual ; tactile ; acoustic ; vibrations ; chemical
This species has not been evaluated by IUCN and is not considered to be endangered or threatened.
US Federal List: no special status
CITES: no special status
State of Michigan List: no special status
Female gulf mud fiddler crabs lay thousands (reports of over 19,000 per clutch) of very small eggs (averaging 25 mm in diameter). Clutches, known as a "sponges," are incubated by females for two weeks, after which eggs are released into the water where they hatch. Fiddler crabs begin their lives as planktonic larvae, completing five zoeal larval stages, increasing in size after each molt. They reach a final larval stage (megalop), at which point young look like very small crabs, but continue to live in the water, on the bottom. Megalops have more mouth parts than previous zoeal stages and do not go through numerous molts, instead finding a shallow area to hide. At this point, they lose their swimming capabilities. Males begin to develop their characteristically large cheliped after their third molt and, if they lose their larger chelipad during combat, their smaller one will develop further to replace it. Juveniles typically reach sexual maturity by August, when they begin to hibernate for colder months. They will begin to reproduce during the following April when warm weather returns.
Development - Life Cycle: metamorphosis
There are no known adverse effects of this species on humans.
Gulf mud fiddler crabs, along with many other species of fiddler crabs, are often found in the pet trade. Additionally, many researchers study fiddler crab burrowing behavior and reproductive habitats.
Positive Impacts: pet trade ; research and education
These fiddler crabs are important to their ecosystems as biodegraders, cleaning coastlines by eating dead matter on beaches. They also aerate the substrate as they feed, providing oxygen to salt marsh plants. Gulf mud crabs also serve as an important food source for many species.
Gulf mud fiddler crabs serve as intermediate hosts to a number of trematode and nematode parasites, some of whose terminal hosts are birds and mammals.
Ecosystem Impact: biodegradation
Species Used as Host:
Mutualist Species:
Commensal/Parasitic Species:
As larvae, gulf mud fiddler crabs filter feed, eating plankton, algae, decaying matter and smaller crab larvae. In their adult stages, they feed most actively as the tide is going out, eating detritus and algae in sand and along the shoreline. Females feed by scooping mud into their mouth with their spoon-like chelipeds, using both alternately, but males feed using only their smaller cheliped. They remove food matter from grains of sand and mud, forming inedible material into balls called pseudo-feces, which are discarded.
Animal Foods: carrion ; aquatic crustaceans; zooplankton
Plant Foods: algae; phytoplankton
Other Foods: detritus ; microbes
Foraging Behavior: filter-feeding
Primary Diet: carnivore (Eats non-insect arthropods, Scavenger ); herbivore (Algivore); omnivore ; planktivore ; detritivore
Gulf mud fiddler crabs live in coastal marsh regions of the northern Gulf of Mexico, from Western Central Florida to Texas. They are the most common fiddler crab species found in salt marshes of Mississippi and Alabama.
Biogeographic Regions: nearctic (Native )
Gulf mud fiddler crabs create cylindrical burrows in marshy areas and sand or mud flats. They burrow more actively when few other species are present. This species is semi-terrestrial and prefers moderately salty marshes (they are tolerant of water salinity of 5-35 ppt, with larger individuals found more often in environments at the lower end of this range) with smaller-grained substrate and lower clay content.
Range elevation: 2 to 15 m.
Average elevation: 10 m.
Range depth: 0 to 1 m.
Average depth: .6 m.
Habitat Regions: temperate ; terrestrial ; saltwater or marine
Aquatic Biomes: coastal ; brackish water
Wetlands: marsh
Other Habitat Features: estuarine ; intertidal or littoral
Although there is little information available regarding life span for this species specifically, fiddler crabs in general are known to have life spans of 1-2 years, dependent largely on predation.
Typical lifespan
Status: wild: 1 to 2 years.
Gulf mud fiddler crabs have four pairs of walking legs and a fifth (most anterior) pair of legs that are modified into chelipeds (clawed limbs). Body color is generally dull gray, becoming more green-blue towards the anterior of the carapace and eyestalks. Their color differs from day to night: during the day, these crabs are darker as their melanophores (dark pigment spots) are open and leucophores (white pigment spots) are closed, while the reverse is true at night, making them lighter in color. Crabs in this genus have carapaces that are narrow anteriorly, but the front of this species is comparatively broad. Their upper orbital margins are typically composed of two sharp edges, creating an eyebrow that is strongly inclined and nearly vertical. These crabs can be distinguished from other species by a pubescence (covering of soft down/short hairs) on the ventral side of their first and second pairs of walking legs and males' extremely large major cheliped. They can be distinguished from crabs in their most closely related genus, g. Ocypode, by their smaller eyes on longer stalks, longer antennae, and shorter legs.
Although sexes are similar in size, these fiddler crabs are sexually dimorphic, with the males having one small cheliped and one very large cheliped, which is used during courtship. Female gulf fiddler crabs have two small chelipeds and a tubercle (projection) at their gonopore. Average carapace length of a female is 12mm and the average width is 16mm; for males the average carapace is 13mm long and 21mm wide.
Range length: 12 to 13 mm.
Other Physical Features: ectothermic ; bilateral symmetry ; polymorphic
Sexual Dimorphism: male larger; ornamentation
These fiddler crabs are prey to amphibians, birds, crustaceans, fishes, jellyfish, small mammals, and reptiles. Adults will hide in their burrows when threatened.
Known Predators:
Gulf mud fiddler crabs live in large social groups consisting of about 20 individuals, making partners easier to find. Males wait near their burrow entrances and wave their larger chelipeds, using a weak jerky movement repeated 8-15 times to signal females. Males fight with each other for partners, creating dominance hierarchies when they "win" females. Unlike many crustaceans, fiddler crab females do not need to have recently molted in order to mate. An interested female will stare at a male, at which point he will move toward her then toward his burrow a number of times until she follows him. A male will then drum on his burrow's edge, lead the female in, then plug the burrow's entrance and return to her to mate. She will remain in his burrow to incubate her sponge (egg clutch) before releasing it into the water. This species is polygynandrous, and females may lay multiple egg clutches during a breeding season.
Mating System: polygynandrous (promiscuous)
Females develop sexually (ovaries increase in size) during the winter and spring seasons after they reach adulthood, with a peak reproductive period during summer months (May to August). During reproductive periods, females follow males into their burrows, where they mate. On average, 19,000-20,000 eggs are laid per clutch, though there are records of clutches as large as 45,000. Eggs vary in color from red to gray. After a two week incubation period, eggs are released into the water, but it is difficult to determine how many embryos grow into viable offspring.
Breeding interval: Gulf mud fiddler crabs reproduce during a yearly breeding season.
Breeding season: Breeding season for this species peaks during summer months.
Range number of offspring: 1500 to 45000.
Average number of offspring: 20000.
Range age at sexual or reproductive maturity (female): 2 to 8 months.
Average age at sexual or reproductive maturity (female): 3 months.
Range age at sexual or reproductive maturity (male): 2 to 8 months.
Average age at sexual or reproductive maturity (male): 3 months.
Key Reproductive Features: iteroparous ; seasonal breeding ; gonochoric/gonochoristic/dioecious (sexes separate); sexual ; fertilization (Internal ); oviparous
Female gulf mud fiddler crabs exhibit parental care by carrying eggs clutches (sponges) on their genital appendages at night and remaining in a burrow with the eggs during the day. They aerates their eggs by standing in the water and jerking their appendages back and forth, a behavior that is continued until the eggs are ready to be released and hatch. Males exhibit no paternal investment following fertilization.
Parental Investment: female parental care ; pre-fertilization (Provisioning, Protecting: Female); pre-hatching/birth (Protecting: Female)
