Mangrove Root Crab Mystery

crab, Oslo Riverfront Conservation Area

Be on the lookout for this fierce looking crab at the Oslo Riverfront Conservation Area (ORCA). The mangrove root crab (Goniopsis cruentata) is a tropical crab of mangrove forests that ranges from south Florida to southern Brazil, throughout the Caribbean and West Indies, and from Senegal to Angola.

Thank you to Dr. George O’Meara for resolving the mystery and identifying this forbidding looking crab. Sebastian Inlet State Park Ranger Ed Perry reports that he has seen this crab on occasion for many years.

This crab is semi-arboreal and is associated with the prop-and-drop roots of red mangroves (Rhizophora mangle) and is usually is found at heights of about 6′ but has been known to climb as high as 12′.

Their color can be quite variable – reddish, purplish or dark brown. Their legs are red (the species name, cruentata, is derived from Latin and means bloody) and adorned with strong hairs. Their eyes are held on short red stalks near to the outsides of the carapace. At maturity, a mangrove root crab can be more than 3″ wide.

Mangrove root crabs are omnivorous and dine on decaying mangrove leaves, mangrove propagules and even the crustacean corpses of brethren. There’s a bit of plant matter in the claws of the crab pictured above. They also hunt smaller crabs including the mangrove tree crab (Aratus pisonii), the sand fiddle crab (Uca pugilator), and the mud fiddler crab (Uca pugnax).

Mangrove root crabs are said to be solitary because they are belligerent and challenge each other for food. They are generally found alone or at least foot away from any other crab. When challenged by a human or larger crab, they will jump in the water or hide in the burrow of a land crab like the blue land crab (Cardisoma guanhumi) that is quite prevalent at the ORCA.