Uca pugilator

Uca pugilator - Fiddler Crab

Habitat Atlantic sand fiddler crabs are the most common crabs in the sandy shorelines of protected beaches, impoundments, and salt marshes. 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 leave their hole to search for food or find a mate.

Range The Sand fiddler crabs range along the Atlantic coast from Massachusetts to Florida. The locations of the crabs are usually near the coastal marshes or near intertidal zones.

Description The Sand fiddler crab is approximately 1.5 inches wide and 1.0 inches long. They have a smooth carapace and a square shaped body. They also have two long and slender eyestalks in the center of the carapace. The male fiddler crabs are usually brighter in color with a purple grey or blue markings on their shell. They also have one claw that is larger than the other, it can be either the right or left claw. The claw is at least five to ten times larger than the other. The females have equal sized claws and subdued colors on their carapace.

Ecological Notes The fiddler crabs are colonial and are found living together in clusters. Fighting does occur between the males in defense for their burrow. They are known to travel in herds of thousands when they feed. The fiddler crabs ingest particles of sand and mud and use their mouthparts to scrape the food from the sediment and then put the sediment back in the ground in a little pellet. When they filter the sediment they feed on the detritus, DOM, algae, and other small creatures in the mud or sand. Males cannot eat as fast as females because of their large claw. Their reproductive strategies are very unique. The males will stand at the edge of their burrow and wave their large claw repeatedly in order to attract a female. The male will also run bak in forth from his burrow to show the females which one is his.

Personal Information We found the fiddler crab in many beaches around the coast of North Carolina such as Coquina Beach, The Oregon Inlet, and Pea Island.

References

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. 

Additional Information

J Roy Robertson, K Bancroft, G Vermeer, K Plaisier. Experimental studies on the foraging behavior of the sand fiddler crab Uca pugilator (Bosc, 1802). Journal of Experimental Marine Biology and Ecology. Volume 44, Issue 1, 1980, Pages 67-83. 

This study tested the hypothesis that foraging sand fiddler crabs move through the habitat in response to low substratum food levels even though these movements may take the crabs considerable distances from the safety of the burrow area. They found that the movement of the crab are controlled by reduction in substratum food levels.They can extract over 70 % of their food.

Kathleen A. Reinsel, Dan Rittschof. Environmental regulation of foraging in the sand fiddler crab Uca pugilator (Bosc 1802). Journal of Experimental Marine Biology and Ecology. Volume 187, Issue 2, 28 April 1995, Pages 269–287. 

Sand fiddler crabs are known to forage in response to chemical cues. This study hypothesized that environmental factors play a role in determining where fiddler crabs forage. They looked at the sediment organic content, the salinity of interstitial water, sediment grain size, and sediment water content. Their results showed that the sediment organic content and sediment water content are the most important factors that determine where fiddler crabs forage.

Contributed by Cassie Craig - 2016

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