Emerald Crab

About

The emerald crab (Mithraculus sculptus) is one of those invertebrates that earns its place in a reef tank by actually doing a job. Native to the Caribbean and Gulf of Mexico, it lives in shallow rocky and reef environments where it grazes almost constantly on algae, detritus, and organic debris. The coloration is a deep, almost uniform green across the carapace and legs, with a slightly flattened body shape and distinctive sculptured ridges that give the species its name. In the aquarium world it has built a strong reputation as a biological control for bubble algae, particularly Valonia and similar species that can quickly overrun a reef if left unchecked. Most keepers find them hardy and relatively straightforward to keep, which makes them a reasonable choice even for those still getting comfortable with saltwater systems. They are generally peaceful toward fish and corals, though like most crabs they are opportunists and should be watched around very small or slow-moving tank mates. Providing plenty of rockwork and hiding places keeps them comfortable and encourages their natural foraging behavior. The emerald crab is one of the more genuinely useful cleanup crew members available to reef hobbyists.