Common name: Emerald Crab

General Information

The Emerald Crab or Green Clinging Crab (Mithraculus sculptus) is a popular addition to many reef aquariums, valued for its algae-eating capabilities and striking green coloration. This small, hardy crustacean is native to the Caribbean and western Atlantic, where it inhabits coral reefs and rocky substrates. Its compact size and peaceful demeanor make it a favorite among aquarists looking for a functional and visually appealing invertebrate.

Emerald Crabs are known for their bright green carapace, which can sometimes exhibit a metallic sheen under aquarium lighting. Their claws are relatively large compared to their body size, and they use these to scrape algae off rocks and other surfaces. While they are primarily algae eaters, they are opportunistic feeders and may scavenge for other food sources in the tank.

Care

Emerald Crabs are relatively easy to care for and are suitable for aquarists of all experience levels. They thrive in well-established reef tanks with plenty of live rock, which provides both food and shelter. These crabs are nocturnal and tend to be more active during the night, often hiding in crevices or under rocks during the day.

A stable environment with consistent water parameters is essential for their health. They are sensitive to sudden changes in salinity, pH, and temperature, so regular maintenance and monitoring are crucial. Providing a variety of hiding spots will help them feel secure and reduce stress.

Diet and Feeding

Emerald Crabs are primarily herbivores, feeding on various types of algae, including nuisance algae like Valonia. In captivity, they will also accept supplemental foods such as algae wafers, seaweed sheets, and small pieces of meaty foods like shrimp or fish. Feeding them occasionally with these supplements ensures they receive a balanced diet and helps prevent them from nibbling on corals or other tank inhabitants.

Feed them sparingly, as they are efficient scavengers and will find much of their food naturally in a well-stocked reef tank. Overfeeding can lead to water quality issues and may encourage undesirable behavior, such as picking at corals.

Behavior and Compatibility

Emerald Crabs are generally peaceful and reef-safe, making them an excellent choice for community tanks. However, they can become opportunistic if underfed, occasionally nibbling on soft corals or small invertebrates. Keeping them well-fed minimizes this risk.

They are solitary creatures and do not require companions, although multiple individuals can coexist in larger tanks with ample space and resources. Avoid housing them with aggressive tank mates or species that may prey on small crustaceans, such as certain wrasses or triggerfish.

Health and Common Issues

Emerald Crabs are hardy but can be susceptible to poor water quality and sudden changes in tank conditions. Maintaining stable parameters and providing a varied diet will help ensure their longevity. They molt periodically, shedding their exoskeleton as they grow. During this time, they may hide and appear lethargic, which is normal behavior.

When selecting an Emerald Crab, look for individuals with intact legs and claws, as missing appendages can indicate stress or poor health. Avoid crabs that appear discolored or have visible signs of disease.

Habitat

In the wild, Emerald Crabs are found in shallow coral reefs and rocky areas, often hiding in crevices or under rocks. They prefer environments with abundant algae and detritus, which serve as their primary food sources. Replicating this habitat in a home aquarium with live rock and stable water conditions will help them thrive.