Breeding the Emerald Crab (Mithraculus sculptus)

The emerald crab Mithraculus sculptus is a Caribbean reef crab in which females carry eggs that hatch into planktonic zoea larvae. Larval rearing has been achieved in research labs but is not feasible in home reef tanks.

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.