Ruby Emerald Crab

Tank Size

• 10 gallons minimum
• Larger tanks provide more stable conditions and food sources

Water Parameters

• Temperature: 76–80°F
• Salinity: 1.024–1.026
• pH: 8.1–8.4
• Stable reef conditions are essential

Habitat & Placement

• Provide plenty of live rock for grazing and hiding
• Likes crevices and shaded areas

Diet

• Algae (including film algae and some nuisance algae)
• Detritus

Supplemental Feeding (important if algae is limited)

• Dried seaweed (nori)
• Algae wafers
• Small meaty foods

While they may help with bubble algae, results can vary—some individuals are more effective than others.

Behavior & Compatibility

• Generally reef-safe with caution
• Peaceful when well-fed
• May become opportunistic if underfed:
  • Can pick at corals
  • May bother slow or weak tank mates
• Best kept with:
  • Other invertebrates with caution

Molting

• Will periodically shed its exoskeleton to grow
• During this time, it may hide for several days
• You may see what looks like a “dead crab”—this is usually just a molt

Growth & Lifespan

• Grows to about 2 inches across
• Lifespan: typically 2–3 years in captivity with proper care

Important Notes 

• Do not overcrowd—can become territorial with other crabs
• Keep well-fed to reduce risk of coral picking
• Secure rockwork—they can move small pieces while climbing
• Handle carefully—pinching is possible, though usually mild