Description
The Emerald Crab is a small, hardy marine crab known for its distinctive emerald-green shell and flattened, hairy legs. It is popular in reef aquariums because it feeds on nuisance bubble algae (Valonia and Ventricaria), as well as other algae and leftover food. Although generally peaceful and useful, it is an opportunistic omnivore and may occasionally bother corals or small animals if food becomes scarce.
Lighting
Low to High: Not directly dependent on lighting, as it does not rely on photosynthesis.
Can adapt to most reef aquarium lighting conditions.
Placement (Aquarium Zone)
Rockwork and Crevices: Prefers rocky areas, caves and spaces where it can hide.
Often emerges at night or during feeding.
Temperature
- 24–27°C (75–81°F)
Salinity
- 1.023–1.026 specific gravity
pH
- 8.1–8.4
Alkalinity
- 7–11 dKH
Calcium
- 380–450 ppm
Magnesium
1,250–1,400 ppm
Flow
Moderate: Adaptable to a range of flow conditions.
Provide sheltered areas among the rockwork where it can feed and hide.
Diet
Omnivore: Feeds on bubble algae, hair algae, film algae, detritus and leftover food.
Can be supplemented with seaweed sheets, algae-based pellets and small portions of marine foods.
May consume bubble algae, but should not be considered a guaranteed solution for an outbreak.
If underfed, it may nip at coral tissue or prey on small invertebrates.
Adult Size (up to)
- Approximately 5 cm (2 inches) across the legs.
Growth Rate
Moderate: Grows through periodic moulting. Requires adequate calcium, magnesium and stable water conditions for successful shell development.
Care Level
- Easy: Generally hardy and adaptable to established marine aquariums.
Reef Compatibility
Generally Reef Safe with Caution: Commonly kept in reef aquariums and often helps control bubble algae.
Usually leaves healthy corals alone when adequately fed, but individuals may nip at corals, particularly when food is limited.
May prey on small snails, shrimp or other tiny invertebrates.
Temperament
Generally Peaceful: Usually avoids larger tank inhabitants but can be territorial toward other crabs.
May defend its hiding place and compete with similar-sized crustaceans.
Special Requirements
Provide plenty of live rock, crevices and hiding places.
Maintain stable salinity and good mineral levels to support moulting.
Avoid housing with aggressive crab-eating fish, such as certain triggers and larger wrasses.
Keep an eye on coral tissue and small invertebrates, especially if the crab becomes large or food is scarce.
