Geographic Range
Neartic:
Uca pugnax
lives predominately along the Mid-Atlantic coast of the United States.
Habitat
Uca pugnax
lives in saltmarshes along the Mid-Atlantic coast. Marsh fiddler crabs construct
burrows that are utilized for mating, rest, and "hibernation" during the winter. The
burrows of
U. pugnax
also serve as refuge from predators, heat, and incoming tides. Burrows are approximately
1.3 cm wide and are between 30.5 cm and 92 cm deep. Commonly located in sandy and
muddy substrates, burrows may end in a small room or be connected with other burrows.
During high tide,
U. pugnax
plug their burrows with mud. Often these burrows are found near hard structural
elements or grass stems in areas of intermediate root mat density.
- Habitat Regions
- temperate
- saltwater or marine
- Aquatic Biomes
- coastal
- brackish water
- Wetlands
- marsh
- Other Habitat Features
- estuarine
- intertidal or littoral
Physical Description
The sexually dimorphic Atlantic marsh fiddlers can be found to be up to 16 mm long
and 26 mm wide. The average male carapace is 15 mm long and 23 mm wide, while the
average female carapace is 13 mm long and 18 mm wide. The males are dark olive to
almost black in color with a royal blue spot on the center of its carpace. Female
U. pugnax
are of similar color as the males, but do not have the blue spot. Either one of
the male's chelea may grow until it is half of the crabs body weight, while the claws
of the female are isomorphic. The chelea are brownish yellow at the base with white
fingertips in both sexes.
Uca pugnax
have slender eyestalks and dark banded walking legs. The dorsal carapace of
U. pugnax
is flattened rather than convex as in other similar species of crabs.
- Other Physical Features
- ectothermic
- heterothermic
- bilateral symmetry
- Sexual Dimorphism
- male larger
Development
After hatching U. pugnax larvae progress through five stages of zoea (lasting anywhere from one week to a month) and one megalops stage (lasting 4 days to a month). Megalops further metamorphose into the first juvenile crab stage (lasting a few days). At this stage in its life U. pugnax attaches to a hard substrate. The second and third stage juvenile crab stages last for a combined total of approximately 10 days. Atlantic marsh fiddlers are mature after one year. Uca pugnax molts one to two times per year.
The enlarged claw of the male Atlantic marsh fiddlers is a result of sexual selection.
This claw, or chelea, enlarges to almost half the male's body weight. The larger chelea
is both an advantage and hindrance. In displays of aggression the male with the larger
chelea is usually the victor, but the male with the larger claw is at a disadvantage
in burrow construction and foraging.
- Development - Life Cycle
- metamorphosis
Reproduction
Uca pugnax
reproduce sexually, forming "lek-like" communal breeding assemblages. These leks
are gatherings where the males of the species display, "fiddling" with their major
cheliped, to attract females to their burrows.
- Mating System
- polygynous
Male U. pugnax produce visual and acoustical displays to attract their mates. Precopulatory male fiddler crabs wave their major cheliped in a circular motion to generate one form of these acoustical signals. The male marsh fiddler crabs also vibrate the bottom sediment by stamping their walking legs. Female U. pugnax then follows the male to the burrow to copulate. Unlike many other crabs, copulation takes place when the exoskeleton of the female is in the hardened state.
After mating, female
U. pugnax
release the fertilized eggs onto their abdominal flap in a spongy cluster. Eggs
hatch and are released after several months. The number of progeny range from 4,500
to 23,700 eggs. Female
U. pugnax
release the hatched larvae on the nocturnal high tide.
- Key Reproductive Features
- seasonal breeding
- sexual
- fertilization
- oviparous
After mating, female
U. pugnax
release the fertilized eggs onto their abdominal flap in a spongy cluster. Eggs
hatch and are released after several months. Female
U. pugnax
release the hatched larvae on the nocturnal high tide.
- Parental Investment
-
pre-fertilization
- provisioning
-
pre-hatching/birth
-
protecting
- female
-
protecting
-
pre-independence
-
protecting
- female
-
protecting
Lifespan/Longevity
Behavior
Adult
U. pugnax
defend their burrows and challenge other smaller crabs in an attempt to take over
the smaller crab's burrow.
Uca pugnax
respond defensively when probed by tilting their bodies upward, extending their legs,
raising their chelea, and moving away. Challenges between
U. pugnax
males rarely result in injury.
- Key Behaviors
- motile
- nomadic
- sedentary
- territorial
Communication and Perception
Uca pugnax
communicate visually and audibly. Male
U. pugnax
produce visual and acoustical displays to attract their mates. Precopulatory male
fiddler crabs wave their major cheliped in a circular motion to generate one form
of these acoustical signals. The male marsh fiddler crabs also vibrate the bottom
sediment by stamping their walking legs.
- Other Communication Modes
- pheromones
- vibrations
- Perception Channels
- visual
- tactile
- acoustic
- vibrations
- chemical
Food Habits
Uca pugnax emerge from their burrows at low tides to feed. Uca pugnax are filter feeders, feeding on detritus. This species feeds by scooping mud into their mouths and filtering out the detritus. The detritus is separated from the mud by water pumped through their gills. The digestible material is separated from the undigestible material within the gut, and the undigestable material is deposited as fecal pellets. Uca pugnax takes in approximately 0.4 g of material in six hours.
Foods eaten have been estimated to be 33% diatoms, 25% fungi, 20% vascular plants,
20% unknown material.
- Primary Diet
-
herbivore
- algivore
- planktivore
- mycophage
- detritivore
- Plant Foods
- algae
- phytoplankton
- Other Foods
- fungus
- detritus
- microbes
- Foraging Behavior
- filter-feeding
Predation
Uca pugnax
retreat to their burrows when threatened.
Ecosystem Roles
Uca pugnax
affects nutrient cycles and energy flow throughout the salt marsh. Atlantic marsh
fiddlers' burrows increase soil drainage, increase the amount of nutrients available
in the soil, and allow plants to penetrate further into the soil. The bioturbation
of the species stimulates algal growth and oxygenates the sediment. The undigestable
fecal pellets released also contribute organic nitrogen to the soil.
- Ecosystem Impact
- creates habitat
- soil aeration
Economic Importance for Humans: Positive
Uca pugnax do not directly benefit humans.
Conservation Status
There is currently no conservation data available for U. pugnax .
Additional Links
Contributors
Renee Sherman Mulcrone (editor).
Carol Vinton (author), Hood College, Maureen Foley (editor), Hood College.
- 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.
- native range
-
the area in which the animal is naturally found, the region in which it is endemic.
- temperate
-
that region of the Earth between 23.5 degrees North and 60 degrees North (between the Tropic of Cancer and the Arctic Circle) and between 23.5 degrees South and 60 degrees South (between the Tropic of Capricorn and the Antarctic Circle).
- saltwater or marine
-
mainly lives in oceans, seas, or other bodies of salt water.
- coastal
-
the nearshore aquatic habitats near a coast, or shoreline.
- brackish water
-
areas with salty water, usually in coastal marshes and estuaries.
- marsh
-
marshes are wetland areas often dominated by grasses and reeds.
- estuarine
-
an area where a freshwater river meets the ocean and tidal influences result in fluctuations in salinity.
- intertidal or littoral
-
the area of shoreline influenced mainly by the tides, between the highest and lowest reaches of the tide. An aquatic habitat.
- ectothermic
-
animals which must use heat acquired from the environment and behavioral adaptations to regulate body temperature
- heterothermic
-
having a body temperature that fluctuates with that of the immediate environment; having no mechanism or a poorly developed mechanism for regulating internal body temperature.
- 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.
- metamorphosis
-
A large change in the shape or structure of an animal that happens as the animal grows. In insects, "incomplete metamorphosis" is when young animals are similar to adults and change gradually into the adult form, and "complete metamorphosis" is when there is a profound change between larval and adult forms. Butterflies have complete metamorphosis, grasshoppers have incomplete metamorphosis.
- polygynous
-
having more than one female as a mate at one time
- seasonal breeding
-
breeding is confined to a particular season
- sexual
-
reproduction that includes combining the genetic contribution of two individuals, a male and a female
- fertilization
-
union of egg and spermatozoan
- internal fertilization
-
fertilization takes place within the female's body
- oviparous
-
reproduction in which eggs are released by the female; development of offspring occurs outside the mother's body.
- motile
-
having the capacity to move from one place to another.
- nomadic
-
generally wanders from place to place, usually within a well-defined range.
- sedentary
-
remains in the same area
- territorial
-
defends an area within the home range, occupied by a single animals or group of animals of the same species and held through overt defense, display, or advertisement
- visual
-
uses sight to communicate
- tactile
-
uses touch to communicate
- acoustic
-
uses sound to communicate
- chemical
-
uses smells or other chemicals to communicate
- pheromones
-
chemicals released into air or water that are detected by and responded to by other animals of the same species
- vibrations
-
movements of a hard surface that are produced by animals as signals to others
- visual
-
uses sight to communicate
- tactile
-
uses touch to communicate
- acoustic
-
uses sound to communicate
- vibrations
-
movements of a hard surface that are produced by animals as signals to others
- chemical
-
uses smells or other chemicals to communicate
- phytoplankton
-
photosynthetic or plant constituent of plankton; mainly unicellular algae. (Compare to zooplankton.)
- detritus
-
particles of organic material from dead and decomposing organisms. Detritus is the result of the activity of decomposers (organisms that decompose organic material).
- filter-feeding
-
a method of feeding where small food particles are filtered from the surrounding water by various mechanisms. Used mainly by aquatic invertebrates, especially plankton, but also by baleen whales.
- soil aeration
-
digs and breaks up soil so air and water can get in
- herbivore
-
An animal that eats mainly plants or parts of plants.
- planktivore
-
an animal that mainly eats plankton
- mycophage
-
an animal that mainly eats fungus
- detritivore
-
an animal that mainly eats decomposed plants and/or animals
References
Bertness, M., T. Miller. 1984. The distribution and dynamics of *Uca pugnax* burrows in a New England salt marsh.. Journal of Experimental Marine Biology and Ecology , 83 (3): 211-237.
Burger, J., M. Gochfield. 1992. Effects of an oil spill on emergence and mortality in fiddler crabs (*Uca pugnax*). Environmental Monitoring and Assessment , 22 (2): 107-115.
Croll, G., J. McClintock. 2000. An evaluation of lekking behavior in the fiddler crab *Uca* sp.. Journal of Experimental Marine Biology and Ecology , 254 (1): 109-121.
Grimes, B., M. Huish, J. Kerby. September 1989. Species profiles: life histories and environmental requirements of coastal fishes and invertebrates (Mid-Atlantic) -- Atlantic marsh fiddler.. U.S. Fish Wildl. Serv. Biol./U.S. Army Corps of Engineers , Rep. 82 (11.114): 1-18.
Hoffman, J., J. Katz, M. Bertness. 1984. Fiddler crab deposit-feeding and meiofaunal abundance in salt marsh habitats. Journal of Experimental Marine Biology and Ecology , 82: 161-174.
Priest III, W. Fall 2000. Wetland denizens, Fiddler crab, *Uca* species. The Virginia Wetlands Report , 15 (No. 3).
Ringold, P. 1979. Burrowing, root mat density, and the distribution of fiddler crabs in the eastern United States. Journal of Experimental Marine Biology and Ecology , 36: 11-21.