Emerald Crab (Mithrax sculptus)

The Emerald Crab (Mithrax sculptus) is one of the most useful and popular algae-control invertebrates in the reef hobby, celebrated primarily for its appetite for bubble algae (Valonia sp.) — a notoriously persistent nuisance algae that few other clean-up crew members will eat. Its vivid bright green carapace and dense hairy legs give it a distinctive, rugged appearance, and its constant, busy foraging behavior is highly entertaining. Beyond bubble algae, it consumes film algae, detritus, and uneaten food from rock surfaces and substrate. Naturally found in the Caribbean, it is well suited to reef and FOWLR aquariums of 75 liters and above.

Provide abundant live rock with surface algae to forage on. Supplement diet with algae wafers, dried seaweed, and meaty foods if natural algae is limited — an underfed Emerald Crab may pick at corals, soft-bodied invertebrates, or slow-moving fish. Provide empty shells or rubble for shelter. Generally reef-safe when adequately fed. Avoid copper-based medications.