Animal Diversity Web

Geographic Range

Red-jointed fiddler crabs, or brackish water fiddlers, are found along the eastern shore of North America, ranging from Cape Cod to Texas (Mienkoth 1995).

• Biogeographic Regions
• nearctic
  • native

Habitat

Uca minax live on muddy or sandy beaches that are uncovered at low tide. Each crab will dig its own burrow in the sand. The burrow will be 2-5 cm in diameter and have various depths. The maximum depth of the burrow is two feet. The entrance to the burrow can be plugged up with mud if the crab feels threatened (Zhong, date unknown). These crabs prefer areas of low salinity and can survive in freshwater for only three weeks (Mienkoth 1995).

• Aquatic Biomes
• coastal

Physical Description

Male red-jointed fiddler crabs have one large claw and one relativly small claw. The female fiddler crab has two normal sized claws. They both are chestnut brown with a gray color in the front. The claws of this crab has red joints. They have eight walking legs that are either olive or grayish brown in color. Near the center of the shell, called the carapace, there is a H-shaped depression. Behind the eye there are horizontal depressions (Zhong, date unknown). The eyes Uca minax have are compound. This means they are attached by eye stalks. The male can either be right or left clawed, meaning the large claw can appear on the right or left side of the crab. (Chesapeake Bay Program 1999).

• Other Physical Features
• ectothermic
• bilateral symmetry

Reproduction

The breeding period of Uca minax is every two weeks in the summer. During this time the male may have two burrows. One they live in and one that is for mating. The male will dig a small round burrow, this will be used for mating. When the females begin to return from eating the males stand at the edge of thier mating burrows. They wave their large claws in the air to attract a mate. If a female is attracted to the way the male is waving his claw she will stop in front of the burrow. When the male sees this he will wave the claw more vigorously. After this the male will run from his burrow to the female and back again. This is to show her the location of the burrow. If she approves of the burrow she will go to the edge of it and wait. The male runs into his burrow and drums both claws against the side and the female will feel the vibrations and enter. The male then leads the female to the back of the burrow and the returns to the entrance to plug it up with mud. Locked in the burrow mating occurs and two weeks later the female returns to the surface and releases her eggs into the ocean to develop (Zhong, date unknown).

Behavior

Red-jointed fiddler crabs dig temporary burrows to protect themselves from predators during feeding. During the mating season the male fiddler will wave his large claw in front of him to attract a mate (Chesapeake Bay Program 1999).

Food Habits

Uca minax sift through sediment and extract any nutrients that may be there. After they have gotten all the nutrients out they leave behind small pellets of unusable sediment. They prefer to eat in puddles of water so they can separate the food from the garbage. The large claw of the male keeps him form eating properly. He has to eat twice as much and twice as fast as the female crab to obtain the same nutrients (Chesapeake Bay Program 1999). The fiddler crab is omnivorous. They eat algae and decaying vegatation and on occasion they will eat other fiddler crabs. The main food source is a plant called cordgrass (Mienkoth 1995).

Economic Importance for Humans: Positive

The fiddler crab has many more positive environmetal assets then they have negative. They maintain the population of cordgrass. They help to stimulate the turnover of nutrients in the soil. These crabs are sensitive to contaminants which makes them good environmental indicators. Because many larger predators eat the crabs that makes them extremely inportant to the food web (Zhong, date unknown).

Economic Importance for Humans: Negative

The digging of the burrows and life stlye of Uca minax can erode the banks of marshes (Zhong, date unknown).

Conservation Status

unknown

• IUCN Red List

  No special status

• US Federal List

  No special status

• CITES

  No special status

Other Comments

When these crabs are threatened by a predator the crabs either quickly dig a burrow or run to the nearest burrow to hide. Once a year adult fiddlers molt their shell. If the male ever loses the large claw, the remaining one grows to the large size and a new smaller claw replaces the lost one. Even though these crabs breathe in oxygen they do, however, have gills. The gills must remain wet to function. In the winter the crabs bury themselves in a burrow to "hibernate". These crabs are the largest of the three bay species of fiddler crabs and are the most common and widespread (Chesapeake Bay Program 1999). Even though the crabs live in water of low salinity they can survive at least three weeks in freshwater (Mienkoth 1995).

Contributors

Bethany Fisher (author), Western Maryland College, Randall L. Morrison (editor), Western Maryland College.

References

Cheasapeake Bay Progroam-Critter of the Month, August 27, 1999. "Fiddler Crab" (On-line). Accessed Feurary 14, 2001 at http://www.chesapeakebay.net/info/fiddler_crab.cfm.

Meinkoth, N. 1995. National Audubon Society Field Guide to North American Seashore Creatures. New York: Alfred A. Knopf, Inc..

Zhong, H. Unknown. "Florida A & M University: Common Florida Fiddler Crabs (Uca spp.)" (On-line). Accessed February 14, 2001 at http://www.pherec.org/entguides/EntGuide10-Fiddlers.html.