Corals crabs provide a symbiotic relationship with some SPS (stony) corals. Just like the symbiotic relationship between a Clownfish and an Anemone, or a Watchman Goby and a Pistol Shrimp, or a Cleaner Shrimp and a Reef Fish, the crab and the coral both benefit greatly from having a relationship with each other.
Coral crabs can be found living solitary within the branches of the coral, as shown in this photo of an Acropora stony coral in one of our Reef Aquariums. If you look closely, you can see one of the crab’s claws towards the top of the photo. The relationship is amazing to witness, as the crab will protect the coral from predators, such as starfish, and in return, the crab feeds off the nutrient rich mucus produced by the coral.