Emerald Crab; Atl. - Dromidiopsis edwardsi

The Emerald Crab is a popular reef-safe crustacean known for its vibrant green color and algae-eating abilities. Native to the Caribbean and Gulf of Mexico, these crabs are often introduced to reef tanks to help control nuisance algae, including bubble algae (Valonia spp.). While generally peaceful, they can become opportunistic feeders if underfed.

Care Guide:

• Tank Size: Minimum 10 gallons, though 20+ gallons is recommended for stable water conditions.
• Temperament: Peaceful but opportunistic – usually safe in reef tanks but may occasionally pick at corals or small invertebrates if food is scarce.
• Diet: Omnivorous – primarily feeds on algae (including bubble algae), but also accepts:
  • Nori (dried seaweed)
  • High-quality sinking pellets
  • Mysis shrimp, brine shrimp, or meaty foods (if scavenging)
  • Leftover fish food
• Water Parameters:
  • Temperature: 72-78°F (22-26°C)
  • pH: 8.1-8.4
  • Salinity: 1.023-1.026
  • Ammonia/Nitrite: 0 ppm
  • Nitrate: <10 ppm
  • Calcium: 400-450 ppm (for healthy exoskeleton molting)
• Reef Safe? Mostly – excellent for algae control, but may nip at soft corals, polyps, or small fish if underfed.
• Tank Setup:
  • Requires plenty of live rock for grazing and hiding.
  • Moderate flow preferred to prevent detritus buildup.
  • Secure corals and loose frags, as crabs may knock them over while climbing.
• Compatibility:
  • Safe with most fish and invertebrates, but avoid aggressive tank mates like triggerfish, large wrasses, or predatory crabs.
  • Can be kept with other Emerald Crabs, but multiple crabs should only be housed in larger tanks (30+ gallons) to avoid territorial disputes.

Summary:

The Emerald Crab is a useful algae eater and a great addition to most reef tanks. With plenty of algae, supplemental feeding, and stable water conditions, it will thrive and help keep the tank clean. However, to prevent coral or invertebrate aggression, make sure it has a steady food supply and adequate space.