Spirobranchus giganteus Breeding Guide

How the Christmas tree worm Spirobranchus giganteus reproduces by broadcast spawning with larvae that settle into living coral, and why it cannot be cultured without its host coral.

Overview

Spirobranchus giganteus, the Christmas tree worm, is a small serpulid polychaete that lives embedded in living coral heads, particularly Porites and brain corals, occurring from the Caribbean to the Indo-Pacific. Its body reaches about 3.8 cm, while the calcareous tube it secretes can extend up to 20 cm into the coral. Two spiral, Christmas-tree-shaped crowns of brightly coloured radioles filter microorganisms from the water for feeding and respiration.

Reproductive Mode

There are both male and female Christmas tree worms, and they reproduce as broadcast spawners, casting their eggs and sperm into the water for external fertilisation. No asexual reproduction is documented for this species in the consulted source.

Sexual Reproduction

The fertilised eggs develop into larvae that subsequently settle on coral heads and then burrow into the coral to form their tubes. Settlement onto living coral is therefore an obligatory step in the life cycle, tying recruitment directly to the presence of a suitable host.

Common Challenges

Because the larvae must settle into and bore into a living host coral, Spirobranchus giganteus cannot be cultured without that coral, and there is no practical route to breeding it in a home aquarium. Specimens are collected and sold within a fragment of their host coral, and the worm's survival depends on keeping that host coral alive.