Emerald Crab care guide
Emerald Crab (Mithraculus sculptus) — minimum tank 60 L, temperature 24-26 °C, pH 8.1-8.4.
Compiled by Aquairi from published sources · Published · Updated
Overview
Emerald Crab (Mithraculus sculptus) is a marine clinging (emerald) crab of the family Mithracidae, listed in the Aquairi knowledge base as a beginner-level species. Bright green Caribbean crab popular for hair-algae and bubble-algae (Valonia) control. Reef-safe when well-fed but old males may sample corals or pick at small fish.
Taxonomy
- Family: Mithracidae
- Genus: Mithraculus
- Scientific name: Mithraculus sculptus
- Common synonyms: Green Clinging Crab, Mithrax Crab
Habitat
Mithraculus clinging crabs (family Mithracidae) are small, flat-bodied majoid crabs of the tropical western Atlantic and Caribbean reefs. They shelter in rockwork by day and graze algae and detritus, and some species associate with anemones. In the Aquairi knowledge base this species is recorded from Caribbean.
Tank requirements
- Minimum tank volume: 60 L (15.9 US gal)
- Adult size: 3-5 cm
- Temperature: 24-26 °C (75-79 °F)
- pH: 8.1-8.4
- GH: 8-12 °dGH
- KH: 8-12 °dKH
- Salinity (specific gravity): 1.024-1.026
- Lifespan: 2-4 years
Diet
The species is an omnivore, grazing algae, biofilm and detritus across the rockwork and substrate; in aquaria its diet is supplemented with dried algae and sinking foods when natural growth is scarce.
Compatibility
The Aquairi knowledge base lists this species as peaceful. Suitable tank mates include Reef fish, Inverts. It should be kept away from Very small fish, Predatory fish.
Breeding
Breeding requires an extended planktonic larval stage in open water before the young settle, which makes captive reproduction very difficult and rarely accomplished in home aquaria. Most specimens in the hobby are wild-collected.
Breeding the Emerald Crab (Mithraculus sculptus)
Overview
Mithraculus sculptus (Lamarck, 1818), the emerald or green clinging crab, is native to the Caribbean Sea and Gulf of Mexico from the Bahamas and southern Florida to northern Brazil, at depths to about 54 m. It grows to around 4 cm, is principally a scavenger that also feeds on algae, and is largely nocturnal, hiding by day. In reef tanks it is valued for grazing bubble algae and hair algae.
Sexing
In brachyuran crabs the sexes are separated by the shape of the abdominal flap on the underside: males have a narrow flap, females a broad rounded one that covers and protects the egg mass. An ovigerous (egg-carrying) female is recognised by the spongy clutch held beneath this abdomen.
Spawning & Larvae
The female carries the fertilized eggs under her abdomen until they hatch. Larval development of M. sculptus comprises two zoeal stages and a megalopa, with a mean larval duration of roughly 9-10 days when fed newly hatched Artemia nauplii; starved larvae fail to develop past the first zoeal stage. The zoeae are planktonic and feed in the water column before metamorphosing.
Common Challenges
- Planktonic zoeae are lost to skimmers, filters and pump intakes in a display tank.
- Larvae must be fed live planktonic food such as newly hatched Artemia; without food they die at zoea 1.
- Successful rearing requires dedicated larval tanks, specialised filtration and precise temperature and salinity control.
- Even in laboratory culture, survival is low, so home propagation is impractical.