Description

The Emerald Crab (Mithraculus sculptus) is a hardy, reef-safe crab often added to saltwater aquariums as part of a clean-up crew. It’s particularly valued for its ability to eat bubble algae (Valonia), making it a natural choice for algae control in reef tanks.

🦀 Emerald Crab Description:

• Scientific Name: Mithraculus sculptus

• Common Names: Emerald Crab, Green Mithrax Crab

• Size: Up to 2.5 inches (6.5 cm) across the body

• Coloration: Shiny, metallic green body with flat claws and hairy legs

• Lifespan: 2–4 years in captivity

• Behavior: Mostly nocturnal, peaceful when well-fed but can become opportunistic

🧪 Tank Requirements:

• Minimum Tank Size: 20 gallons

• Water Temperature: 72–78°F (22–26°C)

• pH Level: 8.1–8.4

• Specific Gravity: 1.023–1.025

• Water Hardness: 8–12 dKH

• Aquascape: Plenty of live rock for grazing and hiding

🍽️ Diet:

• Omnivorous, but leans herbivorous:

  • Bubble algae (their specialty)

  • Hair algae and film algae

  • Leftover fish food

  • Dried seaweed (nori), sinking algae pellets

  • Will eat detritus and decaying matter

Feed occasionally if algae is scarce to prevent them from nibbling on soft corals or small inverts.

🤝 Compatibility:

• Reef Safe: Yes, with caution – generally safe, but may pick at corals or inverts if hungry

• Tankmates:

  • Good with peaceful fish and other clean-up crew members

  • Avoid housing with aggressive predators (e.g. large wrasses or triggerfish)

  • Keep only one per small tank unless plenty of space and food is available

💡 Care Tips:

• Very helpful for bubble algae control, but may not always target it

• Provide ample algae or supplemental food to avoid opportunistic behavior

• Will molt regularly—discarded shells may be mistaken for dead crabs

• Sensitive to copper and nitrates – maintain good water quality

• Requires stable salinity and a mature tank with natural algae

📝 Summary: