A White-Handed Fiddler Crab Encounter at the Mangroves of Umm Al Quwain

 

A male white-handed fiddler crab on the prowl

As if minding his manners: covering his mouth while foraging

Heading back to its muddy burrow

When male fiddler crabs collide, a joust is expected. En Guarde!!

The male fiddler crab rendering its signature claw waving movement

A female fiddler crab strolling in the mud

A male fiddler exhibiting his "love gesture" to a nearby female

A muddy mangrove version of crab lovers "hide and seek"

On another section of the mangrove, male and female fiddler crab emerging from their burrows 

Fiddler crab burrows on the muddy mangrove bank

The white spots on the mud are fiddler crabs foraging

After a project meeting at Ras Al Khaimah, on my drive back to Dubai, I went for a side trip to explore a stretch of mangrove just a short distance from the main highway of Umm Al Quwain. It was late afternoon, the sun was about to set and low tide was evident. On the moist surface of the mangrove, I noticed a large number of white crabs moving about in the mud. These were white-handed fiddler crabs emerging from their burrows to feed and to find a mate. 

The White-Handed Fiddler Crab, Austruca albimana (DECAPODA: OCYPODIDAE)

As a fiddler crab, the male is characterized as having one claw much larger as compared to its entire body size. This enlarged claw can occupy up to a third of the crab's body mass. The male possesses a second smaller claw while the female does not have enlarged claws. 

The carapace breath of this crab ranges from 2.1-23.6mm. 

Distribution of the White-Handed Fiddler Crab

The white-handed fiddler crab is reported to be present in the muddy mangroves and sandy beaches of countries lining the Red Sea, Gulf of Aden and the Persian Gulf. It is found in Egypt, Sudan, Eritrea, Djibouti, Somalia, Saudi Arabia, Yemen, Oman and the UAE. 

Biodynamics Notes 

Fiddler crabs feed by scooping up sand and mud unto its mouth and thru special filters it separates the organic particles from the sand, dumps it out and it passes the digestible materials unto its gut. As the males have only 1 feeding claw, they need to put extra effort to forage.

The enlarged claw of the male is waved around in a distinct pattern. This pattern is characteristic for each crab species. Whereas in a muddy bank, even when there are other crab species, the females can recognize the males of their species with this movement. 

The enlarged claw is also used by the males to deter male rivals. If the rival crab did not respond by a withdrawal, "a joust battle" will ensue (here the best and able claw fighter wins).

The love display of the male claw is used by the female to determine which among the crowd of male crabs have the strongest and ablest claw to provide her the best burrow for her offspring. Once the female is convinced, she is taken by the male to his burrow where they mate undisturbed (love in the mangrove motel)!

Another amazing ability of fiddler crabs is their ability to regenerate lost limbs. Crab legs have a weak point and a special muscle that allows them to spontaneously snap their own leg when trapped, when they need to escape, and for survival. However, losing legs and claws is a big hazard for crabs, as this takes time and it happens only during the molting of its carapace. 

Fiddler crabs are so awesome to watch in their natural mangrove habitat. Let us protect and conserve the mangroves and our beaches to allow these awesome creatures to thrive! Stop littering and dispose your waste properly when you are out and about in nature!

Awesome creatures! Awesome CREATOR!