Breeding the Coral Guard Crab (Trapezia cymodoce)
Trapezia cymodoce is an obligate symbiont of Pocillopora corals that defends its host against predators. It broods eggs and releases planktonic larvae, so home breeding is not achievable.
Overview
Trapezia cymodoce is a coral guard crab of the family Trapeziidae that lives in obligate association with branching corals, especially Pocillopora. It feeds on coral tissue and mucus and grazes lipids from the polyp tentacle tips, and in return defends its host from corallivores, including the crown-of-thorns seastar Acanthaster planci. Removal experiments show that corals lose this protection when guard crabs are absent.
Sexing
A single mating pair of a given Trapezia species typically occupies each coral colony, so a settled male-female pair on one coral head is the practical indicator of sexes. Females are recognized when carrying a brooded egg mass under the abdomen.
Conditioning
A healthy host Pocillopora (or comparable branching coral) supplying mucus and lipids is the natural conditioning environment for a resident pair. No documented protocol reliably induces or completes reproduction in a home reef, because the larvae are planktonic and cannot be reared in a display.
Breeding Setup
No practical home breeding setup exists. Resident pairs may produce broods on the host coral, but the female releases planktonic larvae into the water column that require open-water plankton and stable parameters absent from a closed system.
Spawning & Larvae
As in other brachyuran and trapeziid crabs, fertilized eggs are brooded by the female and hatch into planktonic zoea larvae that develop through successive molts before settling. Newly settled juveniles must locate a suitable host coral. This combination of planktonic development and obligate host dependence makes captive rearing impractical.
Common Challenges
- Planktonic larvae are removed by filtration and skimming.
- Larvae require continuous planktonic food through multiple stages.
- Settling juveniles must find a compatible host coral.
- Only one pair occupies a coral head, limiting stocking.