Atlantic Blue Crab
Callinectes sapidus
Mottled Lightfoot Crab
Grapsus albolineatus
About
The mottled lightfoot crab is a shore crab of the Indo-Pacific. It belongs to the family Grapsidae, the flat-shelled crabs of rocky coasts. It is a plant eater that grazes algae off wave-washed rock. Divers and snorkellers usually meet it at the start or end of a dive rather than underwater, because it spends much of its time out of the water on rock in the splash zone.
How to tell it apart
Body colour will not help you here, since it ranges from red to blue to green. The mottled legs are the mark to check: whatever colour the crab is, its legs carry that same irregular dark brown mottling.
Appearance
The carapace, the upper shell, is flat and almost circular, rough to look at, with gently arched sides. The claws are short, small and flattened, much smaller than you might expect on a crab of this size. The legs are long and taper to a point. Body colour varies: animals may be red, blue or green. The legs match the body colour but carry irregular dark brown mottling. Males have larger claws than females.
Habitat
It lives on rocky shores and reef tops that take the full force of the waves, and on rocky ground and coral reef nearby. It is a shore animal more than a dive animal, found in the splash zone and just below it. Its range runs across the Indo-Pacific, from the East African coast to the coast of Chile, including the Red Sea and the tropical islands of the Pacific. It is treated as a key species of healthy, wave-exposed rocky shores.
Log it in Into the Blue
Describe what you saw and we name it, then keep every species you find in your Oceandex.
