Fiddler Crab - Ecology

Ecology

Found in mangroves, in salt marshes, and on sandy or muddy beaches of West Africa, the Western Atlantic, the Eastern Pacific and the Indo-Pacific, fiddler crabs are easily recognized by their distinctively asymmetric claws.

Fiddler crabs communicate by a sequence of waves and gestures; males have an oversized claw or cheliped; used in clashes of ritualised combat of courtship over a female and signal their intentions between conspecifics. The movement of the smaller claw from ground to mouth during feeding underlines the crabs' common name; it looks as if the animal were playing the larger claw like a fiddle.

The crab's smaller claw picks up a chunk of sediment from the ground and brings it to the mouth, where its contents are sifted through (making the crab a detritivore). After anything edible is salvaged, be it algae, microbes, fungus, or other decaying detritus, the sediment is replaced in the form of a little ball. The presence of these sediment balls near the entrance to a burrow is a good indication of its occupation. Some experts believe that the feeding habits of fiddler crabs play a vital role in the preservation of wetland environments; by sifting through the sands, they aerate the substrate and prevent anaerobic conditions.