Emerald Crab

The emerald crab is a small crab found on coral reefs throughout the Caribbean Sea, named for its smooth, bright green shell. It is popular in the reef aquarium trade largely for its willingness to eat bubble algae, a nuisance algae that few other reef animals will consume, making the crab a commonly recommended addition to tanks struggling with an outbreak. It is nocturnal, spending daylight hours hidden within rock crevices and emerging at night to forage across the reef surface. Although it is generally regarded as reef safe because of its algae grazing habit, it is an opportunistic omnivore and will prey on small invertebrates, coral polyps, or other tank inhabitants if its preferred algae becomes scarce. Its flattened, rounded body and relatively small size allow it to squeeze into narrow rock crevices for shelter from larger predators. In the wild it occupies a similar niche among the coral rubble and rockwork of Caribbean reef systems.