Emerald Crab
Emerald Crab (Mithraculus sculptus).
Available for local pickup only
Bring balance and natural algae control to your reef tank with the Emerald Crab — a favorite among reef keepers for tackling nuisance bubble algae.
These bright green, hardy crabs are not only effective cleaners but add a splash of personality and movement to your live rock and reefscape. Known for their spoon-shaped claws, they can reach into tight crevices that other grazers can’t, making them the perfect addition to your clean-up crew!
Key Care Information
✅ Size: Up to 1.5–2 inches wide when mature.
✅ Temperament: Generally peaceful — mostly active at night.
✅ Reef Safe: Yes! 100% reef safe with corals and inverts when well-fed. May nibble on soft corals if hungry, so occasional feeding helps.
✅ Diet: Omnivorous — thrives on bubble algae, hair algae, film algae, leftover food, and meaty bits like mysis or brine shrimp.
✅ Behavior: Loves to hide during the day and emerge at dusk to clean your rocks.
Description
Specifications
Video Links
User Manual
Emerald Crab (Mithraculus sculptus)
Available for local pickup only
📌 Identification
The Emerald Crab, or Green Mithrax Crab, is well-known for its bright green, shiny carapace and hairy, spoon-shaped claws. It’s a hardy, peaceful crab loved by reef keepers for its appetite for nuisance algae.
✅ Appearance:
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Vibrant emerald-green body and legs.
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Small to medium size — usually grows to about 1.5–2 inches wide.
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Slightly hairy claws that help them scrape algae off rocks and crevices.
Why Reef Hobbyists Love Emerald Crabs
Emerald Crabs are best known for being natural bubble algae eaters — they’re one of the few inverts that will reliably eat Valonia (bubble algae), a notorious pest that many reefers struggle with.
They also graze on film algae, leftover food, and detritus, making them a helpful part of your tank’s clean-up crew.
✅ Reef Safety
✔️ Generally reef safe — won’t harm corals or healthy fish.
❗ Occasionally, if underfed, they might pick at soft corals, polyps, or steal food from corals, so it’s good to monitor them and provide supplemental feeding if needed.
✅ Care Level
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Difficulty: Easy — very hardy and adaptable.
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Minimum Tank Size: 10 gallons or larger.
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Diet: Omnivorous scavenger — loves bubble algae, hair algae, film algae, leftover food, and sometimes meaty bits like mysis.
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Behavior: Mostly active at night — hides in rockwork during the day and emerges to graze at dusk or after lights out.
Water Conditions
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Temp: 72–78°F
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Salinity: 1.023–1.025 SG
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pH: 8.1–8.4
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Needs stable reef conditions — copper-based treatments will harm them.
Tank Mates
✅ Compatible with peaceful reef fish, corals, other clean-up crew inverts like snails and hermits.
❌ Avoid keeping them with large, aggressive predatory fish that might eat crabs.
✅ Provide lots of live rock for hiding and grazing.
Fun Fact
The Emerald Crab’s spoon-shaped claws are perfectly adapted for plucking bubble algae and scraping algae from tight rock crevices that other grazers can’t reach.