Common name: green clinging crab

General information

The Emerald Crab, scientifically known as Mithraculus sculptus, is a popular marine invertebrate in the reefkeeping hobby. These small crabs are prized for their vibrant green coloration and their beneficial role in the aquarium. They are known for their algae-eating habits, particularly their appetite for bubble algae (Valonia spp.), which can be problematic in reef tanks.

Emerald Crabs are nocturnal and tend to be more active at night. They have a distinctive, flat, triangular body shape and hairy legs that aid in collecting food particles. Their size is relatively small, with adults typically reaching only about 2 to 3 inches in carapace width.

Care

Emerald Crabs are relatively easy to care for, provided they are kept in a well-established aquarium with plenty of live rock for grazing and hiding. They are peaceful towards most tank mates but may become opportunistic if underfed, occasionally preying on small, slow-moving fish or snails. A varied diet that includes meaty foods and algae will help prevent this behavior.

Reproduction

In the home aquarium, reproduction of Mithraculus sculptus is rare but not unheard of. They have a complex life cycle that includes a planktonic larval stage, which is difficult to sustain in captivity without specialized equipment and food.

Symbiosis

While not involved in the classic symbiotic relationships seen with some fish and anemones, Emerald Crabs do play a symbiotic role in the reef tank by controlling algae growth, which benefits the overall health of the aquarium ecosystem.

Habitat

Emerald Crabs are native to the Caribbean Sea and can be found in a range of reef habitats. They typically inhabit areas with plenty of rockwork and crevices, which provide shelter and feeding opportunities.