Emerald Crab

Identity

Common Name: Emerald Crab

Scientific Name: Mithraculus sculptus

Other Names: Green Clinging Crab; Emerald Mithrax Crab

Family: Mithracidae

Type: Crab (decapod crustacean)

Native Range: Western Atlantic, including Florida, the Gulf of Mexico, the Antilles and Brazil.

Lifespan: Captive lifespan uncertain; no dependable numerical range is available.

Overview

Husbandry Basis: Tank-volume and feeding-frequency values are practical starting points, not species-wide minimums or guarantees. Adjust to actual crab size, usable grazing and shelter, supplemental-food acceptance, and observed livestock interactions.

Natural Habitat

Native Distribution: Western Atlantic, including Florida, the Gulf of Mexico, the Antilles and Brazil.

Natural Habitat: Reef and seagrass habitats

Aquarium Setup

Minimum Tank Size: Hydro Habitats starting recommendation: 20 US gal (76 L); not a universal requirement.

Rockwork: Provide secure rockwork with sheltered crevices and access to grazing surfaces; secure loose frags.

Lighting: Provide lighting appropriate to the whole system; no species-specific irradiance target is asserted.

Water Flow: Keep shelter and feeding areas accessible without a direct jet displacing offered food.

Space Requirements: Allow room for shelter and foraging without crowding; food availability and observed interactions matter as well as tank volume.

Special Setup Requirements: Match transfer water and avoid abrupt changes; protect intakes and reserve coral clearance.

Water Parameters

Temperature: Starting target: 74-80°F (23-27°C)

Salinity: Starting target: 1.023-1.026 specific gravity; use a calibrated seawater instrument and its stated reference temperature.

pH: Starting target: 8.1-8.4; not a species tolerance limit.

Alkalinity: Starting target: 7-11 dKH; not a species tolerance limit.

Calcium: Starting target: 380-450 ppm using the test manufacturer's convention; not a species tolerance limit.

Magnesium: Starting target: 1250-1350 ppm using the test manufacturer's convention; not a species tolerance limit.

Other Relevant Parameters: Ammonia and nitrite should be undetectable with suitable seawater tests. Confirm the units, method and detection limit before comparing results; interpret ammonia with pH, temperature and salinity. Monitor nitrate/phosphate trends and manage feeding/export for the actual system. See Aquarium Ammonia and Aquarium Nitrite for test-unit guidance.

Stability Requirements: Use a biologically established aquarium with a documented history of stable conditions. Tank age alone does not establish readiness.

Husbandry Basis: Hydro Habitats starting targets, not species tolerance limits; use the test manufacturer's reporting convention.

Behavior

General Behavior: Observe shelter use, grazing and actual supplemental-food acceptance. Bubble-algae feeding varies; it is not a reason to stop monitoring the crab's nutrition or tankmates.

Compatibility

Compatibility Precautions: Emerald crabs may damage corals or small tankmates. Monitor feeding and contact, protect vulnerable livestock, and separate animals if injury occurs; compatibility is not guaranteed.

Contact Precautions: Coral and small-livestock damage is reported in aquarium care accounts; monitor the individual.

Diet & Feeding

Natural Diet: Available evidence describes algae and alternative foods, but does not establish a complete wild diet.

Captive Diet: Hydro Habitats starting recommendation: Algae-based and small meaty foods near shelter.

Feeding Frequency: Small supplemental meals 2-3 times weekly; adjust portions to observed food acceptance and grazing and remove excess food.

Feeding Method: Offer algae-based and small meaty foods near shelter, monitor acceptance, remove excess, and do not withhold food to encourage grazing.

Sexing & Breeding

Reproductive Strategy: Laboratory-reared Mithraculus sculptus passed through two zoeal stages and a megalopa before the first crab instar. This guide provides no breeding protocol.

Health & Special Sensitivities

Common Health Problems: Persistent loss of attachment, feeding response or coordination, visible injury or tissue deterioration warrants checking measured water conditions and obtaining appropriate aquatic-health advice. Appearance alone does not diagnose the cause.

Molting/Shell Problems: Crabs have chitinous exoskeletons, not snail shells. Do not pull attached tissue or exoskeleton.

Copper Sensitivity: Do not use copper medication in a display containing these invertebrates. Treat fish separately under appropriate aquatic-health guidance; a reef-safe label alone does not establish safety for the animal or system.

Beginner Suitability

Beginner Friendly: Conditional; assess readiness and care demands.

Why: Provide grazing, supplemental food, shelter and ongoing checks for livestock damage. Bubble-algae control and beginner success are not guaranteed.

Before You Buy

Important Considerations: Confirm Mithraculus sculptus rather than relying only on a green-crab trade label. Ask whether the individual accepts supplemental food and inspect its movement and visible condition.

Compatibility: Protect vulnerable corals and small tankmates; monitor feeding and contact, and separate animals if injury occurs.

Diet: Hydro Habitats starting recommendation: Algae-based and small meaty foods near shelter.

Adult Size: No verified aquarium adult-size range is asserted here; confirm expected size for the identified animal before stocking.

Long-Term Care: Continue checking food acceptance and desirable livestock even after bubble algae decline. Persistent feeding loss, poor coordination or visible injury warrants water checks and aquatic-health advice, not a diagnosis from appearance alone.