Emerald Crab

The Green Emerald Crab (Mithraculus sculptus) is a popular addition to marine aquariums, valued for its vibrant coloration and algae-eating habits. Native to the Caribbean Sea and the Gulf of Mexico, this species is generally considered reef-safe, though occasional reports suggest they may consume small fish or corals if not adequately fed. 

Essential Information:

• Common Names: Green Emerald Crab, Emerald Crab, Green Clinging Crab
• Scientific Name: Mithraculus sculptus
• Family: Majidae
• Origin/Habitat: Caribbean Sea and Gulf of Mexico, inhabiting coral reefs and rocky substrates
• Maximum Size: Up to 2 inches (5 cm)
• Lifespan: 2–4 years in captivity
• Level of Difficulty: Easy; suitable for beginners
• Reef Safe: Generally considered reef-safe; monitor individual behavior

Appearance & Physical Traits:

• Coloration & Pattern: Bright emerald green exoskeleton; some individuals may exhibit white spots on the carapace and claws
• Body Shape & Structure: Flattened, compact body with hairy legs; front claws are spoon-shaped, aiding in algae consumption

Habitat & Environmental Needs:

• Minimum Tank Size: 20 gallons (75 liters)
• Water Temperature: 70–80°F (21–27°C)
• pH Level: 8.1–8.4
• Specific Gravity: 1.020–1.025
• Aquascape: Provide ample live rock structures and hiding spots; these crabs are nocturnal and prefer crevices to retreat during daylight hours

Diet & Feeding:

• Diet Type: Omnivorous
• Preferred Foods: Primarily feeds on various forms of algae, including bubble algae; will also scavenge for detritus and may accept meaty foods like mysis shrimp if algae is scarce
• Feeding Frequency: Typically sustains itself on available algae; supplemental feeding can be provided a few times a week if necessary

Behavior & Compatibility:

• Temperament: Generally peaceful; may become semi-aggressive if underfed or in cramped conditions
• Social Behavior: Solitary; does not require companions and may exhibit territorial behavior towards other crabs
• Tank Mate Compatibility: Compatible with most reef-safe fish and invertebrates; caution is advised when housing with small, slow-moving fish or delicate invertebrates
• Activity Level: Nocturnal; most active during nighttime hours

Care Considerations & Additional Notes:

• Ease of Care: Hardy and low-maintenance, making them suitable for aquarists of all experience levels
• Special Requirements: Regular monitoring of water parameters is essential; ensure a well-established tank with stable conditions
• Breeding Info: Breeding in captivity is rare and not well-documented
• Additional Notes: While Emerald Crabs are beneficial for algae control, it's important to monitor their behavior, especially in tanks with limited algae, as they may resort to eating other desirable organisms if underfed