Canoe or kayak through a mangrove-lined creek, or stroll along a mangrove-fringed boardwalk on Tampa Bay, and you are almost guaranteed to see the ubiquitous and industrious mangrove crab.
True to its name, this small crab lives in the mangroves, scurrying along the tree's trunk and branches. They are home bodies and don't travel far. At high tide, the crab conceals itself by hiding upside down on mangrove roots and branches. When startled, it releases its hold and falls to the water below, where it may be snatched by a passing fish or even the larger blue crab. Wading birds such as herons or egrets find them to be tasty treats as well.
Although mangrove crabs are omnivores that eat both plant and animal matter, their diet relies heavily on mangrove leaves. In particular, they seem to prefer the leaves of the red mangrove (Rhizophora mangle). When the crabs do leave the safety of the trees to scavenge in the mud, their burrowing and "mining" activities help to aerate the soil.
Spotted Mangrove Crab
Mangrove crabs are dark green or dark brown, with light spots, wide-set eyes and hairy legs that are sharp at the tips to facilitate their scrabbling along the mangrove branches. They do not have true pincers like fiddler crabs or blue crabs.Mating takes place throughout the year. Within a day or two or mating, the female attaches an average of 11,000 fertilized eggs to her abdomen.
As the larvae develop, the eggs pass through four color stages. The eggs swell and change from khaki to dark brown, light brown and finally gray. The eggs are ready to hatch in about 16 days. Hatching usually takes place at night, during a spring high tide (during a full or new moon). When ready, the female moves down the mangrove roots to the water's edge, and moves her abdomen back and forth as she releases the larvae into the water.
The larvae drift with the current for about 30 days, passing through several forms before they metamorphose into tiny versions of the adult crabs they will eventually become, and setting up shop in a mangrove forest. Adult mangrove crabs are truly survivors, since less than one percent of mangrove crab larvae make it to maturity.