Emerald Crab

The emerald crab, scientifically known as Mithraculus sculptus, is a small marine crustacean native to the warm tropical reefs of the Caribbean and Atlantic Ocean. Reaching an average size of 1.5 to 2 inches (3.8 to 5 centimeters) across its carapace, it is easily identified by its shiny, deep green coloration, flat body structure, and distinctively spoon-tipped claws designed specifically for scraping algae off rocky surfaces. These crabs are famous in the saltwater aquarium hobby as specialized cleanup crew members, valued above all for their ability to eat problematic bubble algae (Valonia ventricosa) alongside hair algae and organic detritus. Using their modified claw tips, they puncture and scrape away tough algal growths from live rock and tight reef crevices that other scavengers cannot reach.

In a home reef environment, emerald crabs are generally peaceful nocturnal scavengers, though they require adequate food sources to stay well-behaved. If a tank lacks sufficient algae or supplemental seaweed offerings, an underfed emerald crab may occasionally pick at polyps, corals, or small invertebrates, making routine supplemental feedings beneficial once a tank's algae supply is cleared.